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Transactions 


of  THE 


Illuminating  Engineering 
Society 


VOL.  X 

JANUARY-DECEMBER 

1915 


Subject  Index  and  Index  to  Authors 


ILLUMINATING  ENGINEERING  SOCIETY 

29  WEST  THIRTY-NINTH  STREET 

NEW  YORK 


7p 

100 

J 


SUBJECT  INDEX. 


*  Pages   following  the  numbers  given  should  also  be  consulted  in 
referring  to  a  topic  or  subject. 

PAGE 

Accidents  and  poor  illumination 868 

Animals : 

Experiments  on  vision  of 502 

Arc  lamps:    (See  also  Lamps) 

Photometry    1 

Armory  and  gymnasium  lighting 747 

Data  on  various  installations 1186 

Art  and  science  in  home  lighting 55 

Artificial  daylight  units,  some  data  on 219 

Atmospheric  pressure,  effect  on  candlepower  of  various  flames 843 

Automobiles,  headlights 920,  926,  928,  1017,  1022,  1035 

Barometric  pressures  in  various  cities  in  the  United  States 863 

Bibliography   222,  314,  561 

Car  lighting  problems   245 

Mercury-vapor  lighting  902 

Photometry    318 

School  lighting  199 

Vision  in  animals   513 

Books  on  illumination  222 

Brightness : 

Defined    374,  643 

Measurements  773 

Normal,  defined  644 

Specular    359 

Calculation : 

Illumination 555,  587,  593 

Of  daylight  615 

Candlepower : 

Effect  of  atmospheric  pressure  on  various  flames 843 

Mean  spherical,  mean  hemispherical,  mean  horizontal,  mean 

zonal,  defined   646 

Car  lighting: 

Street,  a  practical  study  of 227,  546 

Central  stations : 

How  can  gas  and  electric  companies  under  one  management 

render  the  best  service  ? 793 

Code  of  lighting  for  factories,  mills  and  other  work  places 605 


IV  TRANS.    I.    E.    S.      VOL.    X 

Color :  PAGE 

Edridge-Green  theory  of  vision 578 

Esthetic  value  of  yellow  light 1024 

Preferences    1036 

Vision    576,  577 

Vision  theories  259 

Yellow  light,  its  importance  in  lighting 1015 

Color  music  and  lighting 5°° 

Colored  light  photometry:     (See  also  Photometry) 

Application  of  Crova's  method  of  colored  light  photometry  to 

modern  incandescent  illuminants   716 

Compensated  test-plate  for  illumination  photometers 727 

Crova's  method  of  colored  light  photometry 716 

Daylight : 

Artificial  units,  some  data  on 219 

Calculations  of  615 

Requirements  for  factories,  mills,  etc 609 

Definitions  (see  Nomenclature) 

Diffusion    353 

Efficiency   (defined)    364 

Integrating  instruments  and  methods 368 

Interior  furnishings    397 

Optical  properties  of  diffusing  media 353,  366 

Optical  properties  of  photographic  papers 388 

Papers  and  inks  379 

Pure  and  partial   362 

Selective  instruments  and  methods 371 

Specular   354,  361,  364 

Theory  of   360 

Disease : 

Light  in  the  treatment  of  disease 137 

Edridge-Green  theory  of  color  vision 578 

Efficiency : 

Diffusion    364 

Eye  448 

Luminous   559 

Efficiency  of  the  eye  (see  Eye) 

Electric  and  gas  lighting  companies : 

How  can  best  light  service  be  rendered  under  one  manage- 

ment    793 

Eye: 

After  images   1004 

A  resume  of  the  physical,  physiological,  and  psychic  phases 

of  vision  562 

Colors  of   light  preferred 1036 

Color  vision    576 


SUBJECT    INDEX  V 

Eye  {continued)  pace 

Disorders  of  1007 

Effect  of  glare  on  vision 1000 

Effect  of  motion  pictures  on  efficiency 491 

Efficiency  under   different   conditions   of   lighting;    effect   of 

varying  distribution  factors  and  intensity 407 

Experiments  on  vision  of  animals 502 

Fatigue,  influence  of  lights  of  different  color 1020 

Further  experiments  on  the  efficiency  of  the  eye  under  differ- 

ent conditions  of   lighting 448 

Light  intensity 407 

Purkinj  e  phenomenon   575 

Retinal  phenomena   1002 

Safeguarding  eyesight  of  school  children 181 

Some   experiments   on   the   eye   with   inverted   reflectors   of 

different  densities   1097 

Tests  for  efficiency  under  different  systems  of  illumination..  408 

Ultra-violet  radiation,  effect  of 932 

Vision  and  yellow  glasses 1019 

Vision:     (See  also  heading  Vision) 

mechanical  theory  of  576 

physical,  physiological  and  psychic  phases 562 

Visual   acuity    573 

and  monochromatic  light   1017 

Factory  lighting  (see  Industrial  lighting) 

Fixtures : 

Progress  in  manufacture   548 

Flame  arc  lamps  (see  Lamps) 

Flashlights   530 

Flicker  photometry   (see  Photometry) 
Foundry  lighting  (see  Industrial  lighting) 
Gas  and  electric  lighting  companies : 

How  can  best  light  service  be  rendered  under  one  manage- 

ment ?    793 

Gas  lighting: 
Atmospheric  pressure  effect  on  flames 843 

Automatic  clock  lighting  attachment 1083 

Automatic  lighters 518 

Burners  517 

Heating  value  519 

How  can  a  company  render  best  light  service, 793 

Lamps : 

candlepower  variations  with  barometric  pressure 843 

high  pressure  (see  Street  lighting) 

pilot  flame  ignition  670 

rating  of  556,  647,  649 


VI  TRANS.    I.    E.    S.      VOL.    X 

Gas  lighting  {continued)  PAGE 

Panama-Pacific  Exposition    1083 

Pilot  flame  ignition  670 

Piping  for  works   296 

Streets  (see  Street  lighting) 

Variation  in  candlepower  with  atmospheric  pressure  of  several 

types  of  burners   852 

Glare : 

Brightness   397 

Contrast    397 

Definitions    992 

Diffusing  media,  optical  properties  of 353,  366,  388 

Effect  on  vision  IOOO 

From  automobile  headlights  1017 

From  illuminants  401 

From  typewriter  papers 385 

From  walls  and  wall  coverings 398 

From  writing  papers   384 

Furniture  and  fixtures  400 

General  report  on,  by  I.  E.  S.  committee 987 

Interior  furnishings  397 

Legislation   557 

Papers  and  inks  379 

Photographic  papers  388 

Veiling   398,  1012 

Window  envelopes    394 

Glassware : 

Glass,  manufacture  of  for  lighting 1086 

Recent  developments   548 

Gymnasium  lighting   746 

Headlights : 

Automobile  920,  926,  928,  1022 

Incandescent    271 

Legislation   558 

Locomotive   919 

Parabolic  mirror   914 

Recent  developments  528 

Hering  theory  of  color  vision 577 

Heterochromatic  photometry  (see  Photometry) 

High  pressure  gas  lighting  (see  Street  lighting) 

Home  lighting   55 

Illuminating  engineering: 

As  a  branch  of  technical  instruction 321 

Definitions  and  terminology 642 


SUBJECT    INDEX  Vll 

Illumination:     (See  also  Lighting)  PA°E 

A  flux  method  of  obtaining  average  illumination 593 

And  one  year's  accidents 868 

Books  on   < 222 

Calculations   555,  587,  593,  615 

Daylight    2I9 

Effect  of  good  lighting  on  industrial  production 617 

Lighthouse   2°9 

Measurements  (see  Photometry) 

Principles  and  theory,  books  on 22" 

Problems  special,  and  small  incandescent  lamps 1171 

Progress,  report  of  committee 5X5 

Small  interiors  303 

Use  of  portable  photometers 766 

Incandescent  lamps  (see  Lamps) 

Industrial  lighting: 
Accidents  and  illumination  868 

Clothing  factories   898 

Code  of °°5 

Cotton  mills    894 

Daylight    °°9 

Effect  of  good  lighting  on  production 617 

Glass  factories   899 

Intensities  required  °°° 

Machine  shops   886 

Maintenance   °3° 

Metal  working  plants 885 

Motion  picture  studios  900 

Newspaper  and  printing  plants 896 

Old  and  new  lamps  for 6l9 

Paper  mills   898 

Power  houses  898 

Safety  and  illumination 619 

Silk  mills   • S02 

Skylights    614 

calculation  for   0I° 

Systematic  procedure  for  remodeling  poor  installations 630 

Warehouses    9°° 

Window  glasses  for  daylighting 6l3 

With  mercury-vapor  lamps   883 

Wood  working  plants   892 

Woolen  mills  ^ 

Integrating  sphere:     (See  also  Photometry) 

Notes  on  the  integrating  sphere  and  arc  lamp  photometry...         I 

Interior  lighting  (see  Lighting) 

Lambert,  defined  555,    644 


Vlll  TRANS.    I.    E.    S.      VOL.    X 

Lamps :  PAGE 

Arc : 

photometry    I 

street  lighting 4°5 

use  in  photography  951 

Arc    (flame)    405 

recent  developments   525 

use  in  photography   951.  959 

Arc,  magnetite   4°5 

Characteristic,  performance,  horizontal  distribution  and  ver- 

tical distribution  curves,  defined 645 

Efficiency  of  647 

Elliott  kerosene : 

variation  in  candlepower  with  barometric  pressure...  856 

Hefner : 

variation  of  candlepower  with  barometric  pressure...  844 

Gas  671 

Incandescent:     (See  also  Lamps  by  name) 

life  testing  of  Bureau  of  Standards 814 

Life  tests  of  647 

Mercury-vapor : 

for  industrial  lighting   883 

use  in  photography  951 

Miner's    528 

Oil    520 

Old  and  new  for  industrial  lighting 619 

Pentane : 

variation  of  candlepower  with  barometric  pressure . . .  844 

Photographic  and  visual  efficiencies  of  various  illuminants . . .  963 

Proj  ection   527 

Rating    5*4 

Small  incandescent  and  special  illumination  problems 11 71 

Spherical  reduction  factor  646,    674 

Tungsten: 

application  in  photography    149 

Tungsten,  blue  glass  bulb : 

use  in  photography  95* 

Tungsten  (gas-filled)  : 

physics    522 

recent  developments   520 

Tungsten,  vacuum : 

recent  developments   522 

use  in  photography  951 

Type  C  (see  Tungsten,  gas-filled) 

Lamp-posts  (see  Street  lighting) 


SUBJECT   INDEX  IX 

PAGE 

Legislation   557 

Glare  557 

Lighting  code   °°5 

Safety  lighting  558 

Light:     (See  also  Photometry) 

Artificial  daylight 2I9 

Cold,  theory  of   289 

Colors  preferred   I03° 

Esthetic  value  of  yellow  light 1024 

Physics  of : 

books  on  222 

Projection,  new  developments   38 

Uses  in  the  treatment  of  disease *35 

Yellow,  a  discussion  of  its  importance  in  lighting 1015 

Lighthouse  illumination 2°9 

Lighting:     (See  also  Illumination  and  Industrial  lighting) 
Accidents  and  illumination   868 

Armories   746,  1 186 

Art  and  science  in  home  lighting 55 

Books  on   222 

Calculations  (see  Illumination) 

Car   227>  546 

Clock  tower 547 

Code  for  factories,  mills  and  other  work  places 605 

Color  and  music   500 

Definitions  and  terminology °42 

Diffusion : 

interior  furnishings  397 

papers  and  inks   379 

photographic  papers    388 

optical  properties  of   353.  366 

Efficiency  of  the  eye  under  different  conditions  of  lighting, 

and  effect  of  varying  the  distribution  factors  and 
intensity   407,    448 

Eye: 

efficiency  under  different  conditions  of  lighting. .  .407,    448 

Factory,  code  of  °°5 

Fixtures,  progress  in  manufacture  of 548 

Flood 543 

Gas  (see  Gas  lighting) 

Glass,  manufacture  of   I086 

Gymnasium    740 

Home: 

art  and  science  in 55 

Hospitals   546 


X  TRANS.    I.   E.    S.      VOL,.    X 

Lighting  {continued)  page 

Hotel   545 

How  can  gas  and  electric  companies  under  one  management 

render  the  best  light  service? 793 

Industrial  (see  Industrial  lighting) 

Kerosene  lamp,  light  of 1034 

Knowns  and  unknowns  in  the  lighting  of  small  interiors..    ..  303 

Legislation   557,  605 

Lighthouse   209 

Locker-room    751 

Measurement  of  lighting  (see  Photometry) 

Modern  street  car  82 

Municipal  buildings  546 

Nomenclature  and  standards  642 

Offices  546,  651,  659,  600 

Panama-Pacific  Exposition  534 

Passenger  boats  and  steamers 681 

Photometry  (see  Photometry) 

Railway  cars  82,  227,  546 

Residence  (see  Home  lighting) 

Rifle  ranges  750 

School    181 

Semi-direct,  office   691 

Service  of  companies  to  customers 793 

Small  interiors   303 

Street  281,  405,  537,  1039 

Street  car  82,  227,  546 

Symbols   648 

Tennis  courts    544 

War    530 

Lighting  code   605 

Literature : 

Bibliographies 199,  222,  314,  318,  561,  902 

New  books  561 

Lumen,  defined  643 

Luminous  efficiency  of  various  light  sources 559 

Luminous  flux  defined  642 

Luminous  intensity  defined    642 

Luminous  point-source    126 

Lux,  defined    643 

Machine  shop  lighting  (see  Industrial  lighting) 

Mazda  lamps  (see  Lamps) 
Mercury-vapor  lamps  (see  Lamps) 
Mill  lighting  (see  Industrial  lighting) 

Mirror,  parabolic,  theory  of 905 

Motion  pictures,  effect  on  the  efficiency  of  the  eye 491 


SUBJECT    INDEX  XI 

Newspaper  plant  lighting  (see  Industrial  lighting)  page 

Nomenclature  and  standards 315,   555,  642 

Office  lighting  651 

Downtown  buildings  659 

Semi-direct  in  the  Edison  building  of  Chicago 690 

Specification     for    purchasing    glassware     for    semi-indirect 

fixtures    698 

State,  war,  and  navy  department  building 651,  659 

Panama-Pacific  Exposition : 

Gas  lighting   1083 

Lighting  534 

Parabolic  mirror   005 

Passenger  boat  and  steamer  lighting 680 

Phot,  defined  643 

Photography : 

Application  of  the  new  high  efficiency  tungsten  lamps 149 

Artificial  illuminants,  their  uses  in 947 

Light  sources    556 

Submarine    403 

Visual  efficiency  of  various  illuminants 03 

Photometers:     (See  also  Photometry) 

Brightness    366 

Compensated  test-plate  for  illumination  photometers 726 

Errors  of  test-plates   729,  743 

Maintenance  of    774 

Physical   101 

Portable  photometers  766 

Portable,  hints  on  use  of     776 

Photometry:     (See  also  Illumination) 

Approximate  uniform  point  source 126 

Arc  lamps    I 

Books  on   225 

Colored  light   717 

Colored  lights  (see  Heterochromatic  photometry  below) 

Compensated  test-plate  for  illumination  photometers 727 

Definitions    315 

Flicker    259 

a  method  of  correcting  abnormal  color  vision  and  its 

application  to  the  flicker  photometer 551 

Heterochromatic   551 

application  of  Crova's  to  modern  incandescent  illumi- 

nants     716 

choice  of  a  group  of  observers  for  measurements....  203 

experiments  on  colored  absorbing  solutions 253 

Integrating  sphere   1,  552 

paint    31,  32 


Xll  TRANS.    I.    E.    S.      VOL.    X 

Photometry  {continued)  PAGE 

Methods  3*5.  768 

Of  gas-filled  tungsten  lamps 553 

Pentane,  standard    554 

Photo-electric  cell   554 

Practical  hints  on  the  use  of  portable  photometers 766 

Proposal  as  to  methods  and  standards 315 

bibliography    318 

Purkinje  phenomenon    575 

Secondary  standards 550 

Standards   3*5 

Theory  of  diffusion    373 

Physical  photometry    IOI 

Pilot  flame  ignition  of  incandescent  gas  lamps 670,  675 

Piping: 

Gas  lighting  (see  Gas  lighting) 

Point-source : 

Luminous    126 

Projectors    (see   also   Headlights) 271 

Purkinj  e  phenomenon    575 

Radiation    555 

Specific  luminous,  defined    643 

Ultra-violet  (see  Ultra-violet  radiation) 

Railway  car  lighting   82,  227,  546 

Reflection : 

Coefficients    399,  548 

Diffuse  (defined)   356,  364,  645 

From  inks  and  papers 383 

From  window  envelopes  394 

Interior  furnishings    397 

Parabolic  mirror   905 

Photographic   papers    388 

Regular,  defined  645 

Specular    353,  360 

Total  and  mean   (defined) 364,  370 

Turbidity   364 

Reflectors : 

Functions  and  uses  631 

Glass  and  metal  compared 633 

Maintenance    636 

Recent  developments   549 

Rifle  range  lighting 749 

Safeguarding  the  eyesight  of  school  children 181 

School  lighting: 

Safeguarding  the  eyesight  of  school  children 181 


SUBJECT   INDEX  Xlll 

Searchlights:     (See  also  Headlights)  page 

Recent  developments   527 

Semi-direct  lighting:     (See  also  Lighting) 

Fixtures   : •' 699.  7°°>  703 

Office 6°o.  °°7 

Specification  for  purchase  of  glassware 608 

Shop  lighting  (see  Industrial  lighting) 

Signal  lights   529,  53i 

Spectrometer   300 

Standards,  primary,  representative  and  working,  defined 645 

Steam  lighting   68° 

Street  car  lighting  82-  227>  546 

Street  lighting  405 

Chicago,  111 281.  540 

Classification  of  streets  I04! 

Color  of  light J034,  1057,  1060 

Data  on  installations  of  various  cities 1064 

Data  on  street  illuminants I050 

Effective  illumination  of  streets 1039 


Gas 


1080 


High  pressure  gas  530,  1083 

Influence  of  pavements   I059»  Jo02 

Investigations    54s 

Lamp  posts,  gas  I0°2 

Large  versus  small  illuminants 1051 

Mounting  height  of  illuminants 1055 

New  York   541 

Progress  and  installations  in  various  cities 537 

Silhouette  effect  I043 

Size  of  lighting  units  and  spacing  intervals 1051 

Uniformity  of  design  of  posts 1063 

Swimming-pool  lighting   754 

Testing : 

Lamps    8l4 

Test-plates  (see  Photometry) 

Textile  mill  lighting  (see  Industrial  lighting) 

Tungsten  lamps  (see  Lamps) 

Turbidity  (see  Reflection) 

Type  C  lamps  (see  Lamps) 

Ultra-violet  radiation  and  the  eye 932 

Vision:     (See  also  Eye) 

Acuity  and  yellow  light ioi6 

Acuity  in  reading  under  lights  of  different  color 1036 

Animals   502 

Brightness,  its  influence 985 

Color   576,  577 


XIV  TRANS.   I.    E.    S.      VOL.    X 

Vision  {continued)  page 

Color  theories  259 

Colors  preferred  1036 

Conditions  for  comfortable  vision 988 

Edridge-Green  color  theory 578 

Effect  of  glare  on 1006 

Mechanical  theory  of  576 

Phases  of  (see  Eye) 

Physical,  physiological  and  psychic  phases 562 

Visual  acuity  (see  Vision) 

Window  envelopes: 

Tests  for  reflection,  glare  and  contrast 394 

Young-Helmholtz  theory  of  color  vision 576 


INDEX  TO  AUTHORS. 


The  letter  d  indicates  discussion. 

PAGE 

Alger,  E.  M.    d— Light  in  the  treatment  of  disease 144 

Anderson,  Earl  A.    d— Photometric  measurements 783 

Atkinson,  A.  A.     d — Illuminating  engineering  education 344 

Bailey,  P.  S.     Incandescent  headlights  and  projectors 271 

Baldwin,  Allen  T.     d— Street  lighting 1067 

Bancroft,  Wilder  D.    The  theory  of  cold  light 289 

Barrows,  G.  S.     d— Illumination  and  accident  prevention 879 

d— Office  lighting • 668 

Barrows,  W.  E.     d— Illuminating  engineering  education 346 

Benford,  Frank  A.,  JR.    The  parabolic  mirror 905 

BenFord,  F.  A.,  Jr.,  and  H.  E.  Mahan.    A  flux  method  of  obtaining 

average  illumination   593 

Black,   Nelson   M.     A  resume   of   the  physical,   physiological   and 

psychic  phases  of  vision 5°2 

d— Efficiency  of  the  eye "39 

Bond,  C.  O.    d— Light  in  the  treatment  of  disease 144 

Bostock,  Edgar  H.     Sheet  glass  in  lighting 1086 

Brinckerhoff,  Frank  M.     d— Railway  car  lighting 249,  250 

Burge,  W.  E.    Ultra-violet  radiation  and  the  eye 932 

Burrows,  Robert  P.    Small  incandescent  lamps  and  special  illumina- 
tion problems    ll7l 

Burrows,  S.  B.     d— Selling  illumination 7*5 

Cady,  F.  E.    d— The  integrating  sphere,  accuracy  and  use 33 

Cassidy,  George  W.    Art  and  science  in  home  lighting 55 

Chadbourn,  R  W.,  A.  E.  Kennelly  and  G.  D.  Edwards.    An  ap- 
proximate uniform  photometric  point-source 126 

Chamberlain,  G.  N.    d— Street  lighting 1078 

Chaney,  N.  K.,  and  E.  L.  Clark.    Notes  on  the  integrating  sphere 

and  lamp  photometry  J 

Chapman,  W.  E.    Artificial  lighting  of  typical  offices  in  the  state, 

war  and  navy  department  building 651 

Chillas,  R.  B.    d— The  integrating  sphere 34 

Clark,  E.  L.,  and  N.  K.  Chaney.     Notes  on  the  integrating  sphere 

and  lamp  photometry  * 

CLEWELL,  C.  E.     Illuminating  engineering  as  a  branch  of  technical 

instruction   321 

Cobb,  Percy  W.    d— Light  in  the  treatment  of  disease 143 

d — Test  for  efficiency  of  the  eye "44 

Committees  on  Lighting  Legislation  and  Factory  Lighting 1184 

Committee  on  Glare.    Reports 353,  366,  379,  388,  394,  397,  987,  1000 


xvi  TRANS.    I.   E.    S.      VOL.    X 

PAGE 

Committee  on  Nomenclature  and  Standards  of  the  Illuminating 

Engineering  Society.     (191 5  Report) 642 

Committee  on  Progress.    Report 5*5 

Cravath,  J.   R.     Knowns  and  unknowns   in  the   lighting  of   small 

interiors    303 

d— Brightness  and  glare  in  office  lighting 7*3 

d — Automobile  headlights  921 

d— Efficiency  of  the  eye 1130,  H33,  "39 

Crittenden,  E.  C,  E.  B.  Rosa  and  A.  H.  Taylor.    Effect  of  atmos- 
pheric pressure  on  the  candlepower  of  various  flames. . .  843 
Dicker,  Alfred  O.,  and  James  J.  Kirk.    Lighting  in  downtown  office 

buildings   °59 

Doane,  L.  C.     Modern  street  car  lighting 82 

Durgin,  W.  A.     d— Use  of  portable  photometers 779 

d — Color  preference  I030 

Durgin,  W.  A.,  and  J.  B.  Jackson.    Semi-direct  office  lighting  in  the 

Edison  building  of  Chicago 690 

Edwards,  G.  D.,  A.  E.  Kennelly  and  R.  W.  Chadbourn.    An  ap- 
proximate uniform  photometric  point-source 126 

Ely,  R.  B.    d— Light  in  medical  practise 145 

Evans,  W.  A.  D.    d— The  mercury-vapor  lamp  in  photography 170 

Industrial  lighting  with  mercury-vapor  lamps 883 

FERREE,  C.  E-,  and  Gertrude  Rand.    The  efficiency  of  the  eye  under 

different  conditions  of  lighting 407 

Further  experiments  on  the  efficiency  of  the  eye  under  differ- 
ent conditions  of  lighting 448 

Some  experiments  on  the  eye  with  inverted  reflectors  of  differ- 
ent densities    I097 

Flowers,  Alan  E.    d— Illuminating  engineering  education 347 

Gage,  H.  P.    d— Parabolic  mirror  and  automobile  headlights 926 

d — Infra-red  radiation  944 

Gilpin,  F.  H.    d— Candlepower  of  gas  flames 864 

Gove,  W.  G,  and  L.  C.  Porter.     A  practical  study  of  car  lighting 

problems   227 

Harrison,  Ward,    d— Photometric  reading  errors 742 

Haskell,  Raymond.     Lighthouse  illumination 209 

Haynes,  Pierre  E.    Street  lighting  in  Chicago 281 

Hibben,  S.  G.    d— Street  car  lighting 99 

d— School   lighting    201 

d— Railway  car  lighting   246 

Hoadley,  George  A.    d— Photography,  lenses  and  plates 178 

Hodgson,  M.  B.,  L.  A.  Jones  and  Kenneth  Huse.    Relative  photo- 
graphic and  visual  efficiencies  of  illuminants 963 

Hunter,  G.  H.    d— Home  lighting 76 

Hurley,  W.  P.     Street  lighting  with  modern  arc  lamps 405 


INDEX    TO   AUTHORS  XV11 

PAGE 

Huse,  Kenneth,  M.  B.  Hodgson  and  L.  A.  Jones.    Relative  photo- 
graphic and  visual  efficiencies  of  illuminants 963 

Hutchinson,  F.  R.    Gas  street  lighting 1080 

Hyde,  E.  P.    d— Automobile  headlights 922 

d — Ultra-violet   radiation    943 

HvER,  Z.  M.    d— Selling  lighting  service 806 

d— Combination  gas  and  electric  lighting  systems 809 

Ives,  Herbert  E.    Physical  photometry 101 

Proposals   relative   to   definitions,   standards   and   photometric 

methods    3*5 

Ives,  Herbert  E.,  and  Edwin  F.  Kingsbury.    On  the  choice  of  a 

group  of  observers  for  heterochromatic  measurements . .  203 
Additional  experiments  on  colored  absorbing  solutions  for  use 

in  heterochromatic  photometry  253 

A  method  of  correcting  abnormal  color  vision  and  its  applica- 
tion to  the  flicker  photometer 259 

The  application  of  Crova's  method  of  colored  light  photometry 

to  modern  incandescent  illuminants 716 

Jackson,  Dugald  C.    d— Street  lighting 1060 

Jackson,  J.  B.,  and  W.  A.  Durgin.    Semi-direct  office  lighting  in  the 

Edison  building  of  Chicago 690 

Johnson,  H.  M.     Some  recent  experiments  on  vision  in  animals 502 

Jones,  L.  A.,  M.  B.  Hodgson  and  Kenneth  Huse.    Relative  photo- 
graphic and  visual  efficiencies  of  illuminants 963 

Jordan,  C.  W.    d — Errors  in  integrating  sphere  readings 35 

Pilot  flame  ignition  of  incandescent  gas  lamps 670 

Junkersfeed,  Peter,     d — Street  lighting 1066 

Kenneley,  A.  E.,  R.  W.  Chadbourn  and  G.  D.  Edwards.    An  ap- 
proximate uniform  photometric  point-source 126 

Kingsbury,  Edwin  F.,  and  Herbert  E.  Ives.    On  the  choice  of  a 

group  of  observers  for  heterochromatic  measurements..  203 
Additional  experiments  on  colored  absorbing  solutions  for  use 

in  heterochromatic  photometry  253 

A  method  of  correcting  abnormal  color  vision  and  its  applica- 
tion to  the  flicker  photometer 259 

The  application  of  Crova's  method  of  colored  light  photometry 

to  modern  incandescent  illuminants 716 

Kirk,  James  J.,  and  Aefred  O.  Dicker.    Lighting  in  downtown  office 

buildings   659 

Lacombe,  Charees  F.    d— Street  lighting 1073 

Lancaster,  Walter  B.    d— The  efficiency  of  the  eye 1140 

LEPAGE,  C.  B.    d— Illuminating  engineering  education 350 

LEWinson,  L.  J.    d— Photometry  of  electric  incandescent  lamps 837 

Litle,  T.  J.,  Jr.    d— Gas  pilots 678 

d— Combination  gas  and  electric  lighting  systems 808,  810 


XV111  TRANS.   I.   E.   S.      VOL.   X 

PAGE 

Uttle,  W.  F.    d — Integrating  sphere,  accuracy 28 

Practical  hints  on  the  use  of  portable  photometers 766 

Little,  W.  F.,  and  Clayton  H.  Sharp.    Compensated  test-plate  for 

illumination  photometers    727 

LiTTLEFiELD,  C.  A.     d — Education  of  lighting  solicitors 805 

Luckiesh,  M.    d— Home  lighting 73 

The  application  of  the  new  high-efficiency  tungsten  lamp  to 

photography    149 

Safeguarding  the  eyesight  of  school  children 181 

d — Application  of  the  tungsten  lamp  in  photography 956,  983 

Yellow  light  1015 

McAllister,  A.  S.     Simplification  of  illumination  calculations 587 

Macbeth,  Norman,    d — Illuminating  engineering  education 341 

d — Photometric  readings  and  equipment 785 

d — Selling  lighting  service  807 

d — Automobile  headlights  928 

Magdsick,  H.  H.     d— Street  lighting 1064 

Mahan,  H.  E.,  and  F.  A.  Benford,  Jr.    A  flux  method  of  obtaining 

average  illumination  593 

MEES,  C.  E.  K.    d — Use  of  the  tungsten  lamp  in  photography 173 

d — Testing  electric  incandescent  lamps 841 

d — Automobile  headlights  920 

Artificial  illuminants  for  use  in  practical  photography 947 

Middlekauff,  G.  W.    d — The  integrating  sphere,  screens ;  paint . .  32,  33 

Middlekauff,  G.  W.,  B.  Mulligan  and  J.  F.  Skogland.    Life  test- 
ing of  incandescent  lamps  at  the  Bureau  of  Standards . .  814 

Millar,  Preston  S.     d — Illuminating  engineering  education 342 

d — Errors  of  photometric  test  plates ;  photometric  data 744,  787 

d — Lighting  company  service  802 

d — Testing  electric  incandescent  lamps 839 

The  effective  illumination  of  streets 1039 

Minick,  J.  L.    d — Photometry  of  electric  incandescent  lamps 839 

d — Locomotive  headlights    919 

Mortimer,  J.  D.    d— Street  lighting 1069 

MoTT,  W.  R.    d — Light  in  the  treatment  of  disease 147 

d — Ultra-violet  radiation   939 

d — The  flame  arc  lamp  in  photography 959,  960 

MouLTON,  W.  R.    d — Lighting  of  passenger  boats 688 

d — Lighting  company  service   804 

d— Street  lighting   1061 

Mulligan,  B.,  G.  W.  Middlekauff  and  J.  F.  Skogland.    Life  test- 
ing of  incandescent  lamps  at  the  Bureau  of  Standards..  814 

Nichols,  G.  B.     d — Armory  lighting 760 

d — Combination  gas  and  electric  lighting  systems 810 

Nordstrum,  L.  D.     d — Street  lighting 1068 


INDEX    TO    AUTHORS  XIX 

PAGE 

Oday,  A.  B.  and  A.  L.  Powell.    Present  practise  in  the  lighting  of 

armories  and  gymnasiums  with  tungsten  filament  lamps     746 

Owens,  H.  Thurston,    d— Sale  of  semi-indirect  fixtures 715 

Piatt,  F.  C.    d— Street  lighting 1070 

Pierce,  R.  ff.    d — Design  of  fixtures  and  glassware 713 

Porter,  L.  C.    New  developments  in  the  projection  of  light 38 

d — Home  lighting   75 

d — Passenger  steamer  lighting  688 

d — Gymnasium  lighting  , 762 

d — Photometric  measurements    781 

d — Combination  gas  and  electric  lighting  systems 809 

d — Automobile  headlights  924 

d — Uses  of  miniature  electric  incandescent  lamps.. 1182 

Porter,  L.  C,  and  W.  G.  Gove.  A  practical  study  of  car  lighting 

problems   227 

Potter,  N.  H.,  and  A.  B.  Spaulding.     How  can  gas  and  electric 
companies  under  one  management  render  the  best  light 

service  ?    793 

Powell,  A.  L.    d — Home  lighting 70 

Powell,  A.  L.,  and  A.  B.  Oday.     Present  practise  in  the  lighting  of 

armories  and  gymnasiums  with  tungsten  filament  lamps    746 

Priest,  I.  G.     d — Ultra-violet  radiation 942,    944 

Pratt,  W.  H.    d— Street  lighting 1065 

Rand,  Gertrude,  and  C.  E.  Ferree.    The  efficiency  of  the  eye  under 

different  conditions  of  lighting 407 

Further  experiments  on  the  efficiency  of  the  eye  under  different 

conditions  of  lighting 448 

Some  experiments  on  the  eye  with  inverted  reflectors  of  differ- 
ent densities  1097 

Regar,  G.  Bertram,     d — Lighting  company  service 880 

Richtmyer,  F.  K.    d — Illuminating  engineering  education 349 

Rolph,  T.  W.     d — Railway  car  lighting 245 

d — Illumination  and  the  eye 1 132 

Rosa,  E.  B.    d — Candlepower  of  pentane  lamps 865 

Rosa,  E.  B.,  E.  C.  Crittenden  and  A.  H.  Taylor.    Effect  of  atmos- 
pheric pressure  on  the  candlepower  of  various  flames. . .     843 
Rose,  S.  L.  E.     d — Measuring  light  dispersed  by  jewels;  the  inte- 
grating sphere,   accuracy 31,      32 

d — Recording  photometric  data   783 

Rowland,  Arthur  J.     d — Illuminating  engineering  education 343 

SCHERESCHEWSKY,  J.  W.     d — Ultra-violet  radiation 941,     945 

d — The  eye  and  lights  of  different  colors 1033,  1036 

d — Tests  for  eye  efficiency 1131 

Scott,  Charles  F.    d — Illuminating  engineering  education 338 

Serrill,  William  J.     d — Illuminating  engineering  education 340 


XX  TRANS.    I.    E.    S.       VOL.    X 

PAGE 

Sharp,  Clayton  H.     d — The  integrating  sphere 28,      35 

Some  data  on  artificial  daylight  units 219 

d — Illuminating  engineering  education  348 

Sharp,  Clayton  H.,  and  W.  F.  Little.    Compensated  test-plate  for 

illumination  photometers    727 

Simpson,  R.  E.     d — Illuminating  engineering  education 345 

Illumination  and  one  year's  accidents 868 

Skogland,  J.  F.,  G.  W.  Middlekauff  and  B.  Mulligan.     Life  test- 
ing of  incandescent  lamps  at  the  Bureau  of  Standards..     814 

Spaulding,  H.  T.     The  lighting  of  a  passenger  steamer 680 

Spaulding,  A.  B.,  and  N.  H.  Potter.     How  can  gas  and  electric 
companies  under  one  management  render  the  best  light 

service  ?    793 

Steinmetz,  Charles  P.    d — Effect  of  color  of  light  on  sight 1036 

Stephens,  C.  E.    d— Street  lighting 1078 

Stickney,  G.  H.     d— Home  lighting 79 

d — Railway  car  lighting 248 

d— Office  lighting  668 

d — Photometric  test-plates   744 

d — Photometric  errors  783 

d — Effects  and  application  of  lights  of  different  colors 1034 

d— Street  lighting   1058 

Sterrett,  H.  R.    Piping  houses  for  gas  lighting 296 

Taylor,  A.  H.     d — Photometric  errors 789 

Taylor,  A.  H.,  E.  C.  Crittenden  and  E.  B.  Rosa.    Effect  of  atmos- 
pheric pressure  on  the  candlepower  of  various  flames. . .     843 

Titus,  E.  C.     Some  uses  of  light  in  the  treatment  of  disease 135 

Vaughn,  F.  A.    d — Combination  gas  and  electric  lighting  systems. . .     810 

Whitehead,  John  B.    d — Street  lighting 1065 

Williamson,  J.  E.     Submarine  photography 403 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 


Vol.  X 


NUMBER    1  1915 


NOTES   ON   THE   INTEGRATING   SPHERE  AND   ARC 
LAMP  PHOTOMETRY.* 


BY  N.   K.   CHANEY  AND  E.  L.  CLARK. 


Synopsis:  After  a  brief  historical  introduction,  the  paper  undertakes 
an  exhaustive  analysis  of  the  characteristics  of  the  integrating  sphere, 
with  special  reference  to  the  asymmetry  in  integrating  properties  arising 
from  the  necessary  introduction  of  screens  and  opaque  bodies.  A  mathe- 
matical expression  is  developed  for  the  error  of  integration,  which  con- 
tains factors  depending  upon  the  reflecting  power  of  the  sphere  walls; 
upon  the  relative  size  and  position  of  the  screen  with  respect  to  the  light 
source,  and  to  the  photometric  window ;  and  upon  the  distribution  of  the 
light  flux  from  the  sources  under  comparison.  Experimental  data  veri- 
fying the  general  theoretical  conclusions  are  given.  An  earlier  paper  on 
this  subject  is  criticized,  particularly  the  statements  regarding  the  use 
of  translucent  screens,  and  the  measurement  of  extended  light  sources. 
The  conclusion  reached  is  that  translucent  screens  are  not  desirable  and 
that  extended  light  sources  of  sizes  now  common  among  modern  arc 
lamps  do  not  give  erroneous  values  when  measured  in  a  properly  designed 
sphere.  A  summary  of  the  conditions  which  should  be  maintained  in  a 
sphere' to  secure  accuracy  is  given.  The  method  used  in  the  photometrical 
laboratory  of  a  large  manufacturing  company  for  comparing  various 
carbons  used  in  a  variety  of  lamps  is  described.  A  rational  method  of 
proportioning  the  measurements  made  upon  a  single  trim  to  the  number 
of  trims  measured  is  given. 

The  integrating  sphere  has  received  relatively  less  attention  at 
the  hands  of  American  investigators  than  that  accorded  it  abroad. 
Among  the  more  important  contributions  to  our  knowledge  of  the 
sphere  in  this  country  is  the  paper  read  before  this  society  by 
Sharp  and  Millar  in  1908.1  The  latter  contains  an  excellent  il- 
lustrated description  of  integrating  spheres  and  their  equipment 
together  with  an  account  of  the  special  advantages  offered  by  their 
use.  It  is  unfortunate,  however,  that  in  the  limited  space  at  their 
disposal  the  authors  felt  obliged  to  deal  so  briefly  with  the  theo- 
retical aspects  of  the  subject,  and  that  they  failed  to  indicate  the 
more  exhaustive  treatment  to  be  found  in  the  original  literature. 

*  A  paper  read  at  the  eighth  annual  convention  of  the  Illuminating  Engineering 
Society,  Cleveland,  O.,  September  31-24,  1914.       .  .,,   „ofltc  _, 

The  Illuminating  Engineering  Society  is  not  responsible  or  the  statements  or 
opinions  advanced  by  contributors. 

1  Trans.  I.  E.  S.,  vol.  Ill,  p.  502. 


2  TRANSACTIONS    I.    E.    S. —  I'ART    1 

The  present  paper  suffers  somewhat  from  the  same  defect. 
No  pretense  is  made  of  giving  an  adequate  resume  of  the  vol- 
uminous German  articles  upon  the  subject.  Owing  to  the  long 
delays  experienced  in  securing  the  original  papers,  the  work  here 
reported  took  its  point  of  departure  from  the  above-mentioned 
paper  of  Sharp  and  Millar.  Theoretical  developments  which 
differ  somewhat  in  form  from  the  German  were  followed  inde- 
pendently. 

A  brief  historical  survey  shows  that  the  earliest  forerunner 
of  the  spherical  integrator  was  the  "lumen-meter"  of  Blondel,  in 
1895.  Three  forms  are  mentioned  in  which  the  light  source  was 
placed  in  the  center  of  an  opaque  sphere,  through  which  light 
could  leave  from  one  or  more  openings  and  after  a  certain  num- 
ber of  reflections  be  thrown  upon  a  screen  and  photometered. 
Its  application  was  limited  to  axially  symmetrical  light  sources. 

The  Matthews  integrating  mirrors  designed  in  1901  suffer 
from  the  same  limitation,  unless  the  radially  asymmetrical  light 
sources  can  be  rapidly  rotated. 

The  fundamental  theorem  of  the  modern  spherical  integrator, 
was  first  mathematically  developed  by  an  Englishman,  Sumpner, 
in  the  Philosophical  Magazine  in  1893.  He  stated  that  "any 
bright  patch  on  the  inner  surface  of  a  diffusely  reflecting  sphere 
illuminates  each  part  of  the  sphere  to  the  same  extent".  It  fol- 
lows conversely  that  any  area  upon  the  inner  surface  of  such  a 
sphere  is  illuminated  by  all  of  the  other  bright  patches  pro- 
portionally to  their  brightness  only,  and  irrespective  of  their 
position.  In  other  words  any  given  area  is  illuminated  propor- 
tionally to  the  average  illumination  of  the  rest  of  the  sphere. 
Sumpner,  however,  overlooked  the  practical  application  of  his 
theorem  to  integration  of  asymmetrical  light  sources  until  after 
Ulbricht  in  1900  had  independently  derived  the  same  theorem 
and  applied  it  to  the  determination  of  the  mean  spherical  candle- 
power  of  light  sources  by  a  single  measurement. 

The  Ulbricht  integrator,  as  is  well  known,  consists  of  a  hollow 
sphere  with  a  white  diffusely  reflecting  coating  and  having  in  its 
wall  a  small  opening  or  photometric  window.  The  light  source 
is  placed  in  the  sphere  and  a  small  screen  placed  between  it  and 
the  photometric  window  or  test  plate,  so  that  the  latter  receives 


CHANEY    AND    CXARK  :     ARC    LAMP    PHOTOMETRY  3 

no  light  directly  from  the  source,  but  only  that  reflected  to  it 
from  the  walls  of  the  sphere.  The  average  illumination  upon 
the  walls  is  proportional  to  the  total  light  flux  and  by  Sumpner's 
theorem2  the  illumination  of  the  test  plate  area  would  be  exactly 
proportional  to  the  average  illumination  of  the  sphere  wall,  that 
is,  to  the  total  light  flux,  except  for  one  fact,  viz.,  the  introduc- 
tion of  the  opaque  screen  into  the  sphere. 

It  is  evident  that  the  variable  direct  light  flux  must  be  screened 
from  the  test  plate  windows,  otherwise  the  test  plate  will  re- 
ceive an  amount  of  light  varying  with  the  position  and  distribu- 
tion of  the  source.  It  is  also  evident  that  the  presence  of  the 
necessary  screen  invalidates  the  rigorous  application  of  the 
fundamental  theorem  of  light  integration  which  we  have  just 
been  considering. 

Sumpner's  theorem  is  valid  only  for  an  empty  sphere.  The 
theorem  does  not  state  that  all  parts  of  the  sphere  wall 
are  equally  illuminated,  for  this  is  contrary  to  fact  with  asym- 
metrical light  sources.  Therefore  if  the  test  plate  window  is  to 
receive  an  illumination  exactly  proportional  to  the  total  light 
flux,  it  must  receive  light  from  the  entire  sphere  wall.  This  will 
be  prevented  by  the  presence  of  screens  or  opaque  bodies  of  any 
kind. 

The  effect  of  a  screen  is  not  only  to  prevent  a  certain  portion 
of  the  direct  light  flux  from  reaching  the  sphere  wall,  but  also  to 
screen  an  opposite  part  of  the  sphere  wall  from  the  test  plate. 
The  resulting  situation  is  readily  seen  by  the  screen  and  sphere 
diagram,  as  shown  in  Fig.  I,  A  and  B. 

The  effect  of  the  screen  is  to  divide  the  sphere  into  three  zones 
or  areas  as  shown  in  Fig.  i,  B.  Each  of  these  three  zones 
possesses  different  physical  characteristics.  Zone  I  is  not  visibly 
distinct  from  Zone  II.  It  is  the  part  of  the  sphere  wall  con- 
cealed by  the  screen  when  observation  is  made  through  the  test 
plate  window  at  C.     The  direct  light  flux  falling  upon  Zone  I 

•-  Mathematical  proof  of  Sumpner's  theorem.— Assuming  the  validity  of  Lambert's 
cosine  law  the  illumination,  E,  which  any  infinitesimal  area,  AA,  will  receive  from  any 
other  similar  area  of  brightness,  e,  is  expressed  as  follows  : 

47rr- 
With  a  given  sphere  radius  this  expression  contains  no  variable  except  the  brightness  of 
the  patch  e,  and  hence  is  independent  of  its  distance  or  position. 


4  TRANSACTIONS    I.    K.    S. — PART    I 

cannot  directly  illuminate  the  test  plate  at  C,  but  must  suffer  an 
additional  reflection  before  reaching  the  test  plate. 

Zone  III  is  visible  when  the  sphere  is  in  operation.  It  is  the 
projection  on  the  sphere  wall  of  the  shadow  of  the  screen.  It 
measures  the  solid  angle  of  the  direct  flux  intercepted  by  the 
screen.    The  flux  falling  upon  the  screen  (as  measured  by  Zone 


ZonelZ.  (/nscreenet/ 


Zone! 
Screened  f 


Fig.  i. — Screen  and  sphere  diagram. 

Ill)  must  be  first  reflected  to  the  central  zone  before  it  can 
contribute  to  the  illumination  at  the  test  plate.  Thus  Zones  I 
and  III  comprising  the  "screened  areas"  both  differ  from  the 
"unscreened"  central  area  or  Zone  II,  in  a  like  manner.  That  is, 
the  light  flux  directed  towards  either  of  the  "screened  areas" 
must  suffer  one  additional  reflection,  and  consequent  loss  by  ab- 
sorption, in  comparison  with  the  light  flux  falling  upon  the  "un- 
screened" central  zone.  The  latter  alone  possesses  the  char- 
acteristics required  for  perfect  integration.  All  of  the  flux  upon 
Zone  II  contributes  in  direct  proportion  to  the  illumination  at 
the  test  plate  C. 


CHANEY   AND    CLARK:     ARC   LAMP    PHOTOMETRY  5 

The  spherical  integrator  is  not  therefore  a  theoretically  per- 
fect instrument.  It  cannot  be  so  designed  as  to  integrate  per- 
fectly every  conceivable  type  of  light  flux  regardless  of  the  dis- 
tribution of  the  latter  in  the  sphere.  It  may  be  so  designed, 
however,  as  to  reduce  the  error  to  any  desired  limits.  With  this 
fact  clearly  in  mind  it  evidently  becomes  necessary  to  inquire 
very  exactly  into  the  limitations  and  characteristics  of  the  spheri- 
cal integrator. 

The  mathematical  treatment  here  employed,  although  devel- 
oped independently,  is  in  some  respects  substantially  similar  to 
the  earlier  work  of  Ulbricht  but  is  less  complicated  in  form  and 
leads  to  simpler  generalizations.  The  problem  is  treated  in  part 
graphically  and  in  part  by  a  few  general  considerations  from 
which  may  be  deduced  a  characteristic  mathematical  expression 
for  the  integrating  properties  of  the  sphere. 

As  shown  by  Sumpner  the  walls  of  any  enclosure  possess  an 
illumination  much  greater  than  that  corresponding  to  the  inten- 
sity of  the  original  light  flux.  When  light  falls  upon  a  reflecting 
surface,  part  of  it  is  absorbed  and  part  is  reflected,  the  relative 
amounts  depending  upon  the  absorption  coefficient  a  and  the 
reflection  coefficient  p  whose  sum  is  unity. 

The  total  illumination  on  the  sphere  wall  I,  is  thus  made  up 
of  two  parts : 

(i)  The  direct  illumination  from  the  light  source  ld,  (2)  plus 
an  infinite  number  of  reflections  from  the  walls  or  the  reflected 
illumination  Ir 

I  =  Irf+  I, (1) 

or 

l  =  Id+pld  +  P'ld  +  ...+  P{"-l)^=   ^[^^  ■ 

Hence 

1=-^-  =^  (2) 

I   —  p  a 

or 

I  =  Irf  +  pi (3) 

and 

I  =al  +  Pl (4) 

The  ratio  of  the  direct  illumination  to  the  total  is  thus  given  by 


6  TRANSACTIONS    I.    E.    S. PART    I 

the  absorption  coefficient,  and  the  ratio  of  the  reflected  illumina- 
tion to  the  total  is  given  by  the  reflection  coefficient. 

Now  the  direct  illumination  of  average  value  I,/,  varies  in 
intensity  at  different  parts  of  the  sphere  according  to  the  dis- 
tance and  degree  of  asymmetry  of  the  light  source.  Its  average 
amount  is  20  per  cent,  of  the  total  illumination  I,  for  the  usual 
value  of  the  absorption  coefficient,  a  is  about  0.2. 

The  reflected  illumination  pi,  usually  amounting  to  80  percent, 
the  average  total  illumination,  is  equal  in  all  parts  of  an  empty 
sphere. 

Therefore  the  direct  illumination  from  the  light  source,  Id,  is 
screened  from  the  test  plate  in  order  to  measure  the  reflected 
illumination,  pi. 

The  presence  of  the  screen,  however,  destroys  the  uniformity 
of  the  illumination  pi  so  that  its  true  or  average  value  is  no 
longer  identical  with  the  apparent  value  at  the  test  plate. 

The  source  of  error  in  integration  thus  depends  upon  the  man- 
ner and  extent  to  which  the  reflected  illumination  as  actuall)' 
read  at  the  test  plate,  differs  from  the  theoretical  value  of 
the  reflected  illumination  pi  for  an  empty  sphere.  Any  constant 
difference  between  the  observed  and  the  theoretical  values  of  pi 
will  be  corrected  by  the  substitution  method  of  determining  the 
"sphere  constant"  with  a  standard  lamp,  and  therefore  may  be 
ignored.  But  variable  differences,  dependent  in  an)'  manner 
upon  the  character  or  position  of  the  light  source  can  not  be  so 
corrected  and  constitute  a  source  of  error  the  magnitude  and 
characteristics  of  which  must  be  known. 

II  the  reflected  light  pi  be  separated  into  two  components  it 
will  be  found  that  one  component  depends  upon  the  light  flux  in 
a  constant  manner,  and  the  other  in  a  variable  manner. 

From  equation  (3)  multiplying  through  by  p  gives  an  ex- 
pression for  the  two  components  of  pi 

pi  -  plrf  -f  p2I (5) 

That  is  the  reflected  illumination  consists  of  the  first  reflection, 
pld,  of  the  direct  illumination  ldt  plus  the  sum  of  the  succeeding 
multiple  reflections  p'l. 

Since  all  reflections  after  the  first  are  assumed  to  be  completely 
diffused  by  the  character  of  the  surface  of  the  sphere,  the  com- 
ponent p2I  is  independent  of  the  character  or  degree  of  asymmetry 


CHANEY    AND    CLARK:     ARC    LAMP    PHOTOMETRY  J 

of  the  original  surface  illumination  by  direct  light.  It  will. 
however,  suffer  a  slight  constant  reduction,  due  to  the  absorption 
of  the  diffusely  reflected  light  by  the  surface  of  the  screen.  The 
component  p1!  amounting  to  80  percent,  of  pi  (ifp  =  o.8)  is 
therefore  subject  to  perfect  correction  in  the  "sphere  constant/ 

The  case  is  different,  however,  in  the  first  component  of 
pi  which  consists  of  the  first  reflection  pl^  of  the  direct  illumi- 
nation Id. 

The  position  upon  the  surface  of  the  sphere  on  which  the 
illumination  ld  exists,  determines  whether  any  part  of  its  first 
reflection  p\d  will  reach  the  test  plate  or  whether  the  illumina- 
tion at  the  test  plate  will  consist  only  of  the  subsequent  reflec- 
tions Kp2I    (6) 

A  glance  at  Fig.  1  shows  that  if  the  direct  light  flux  falls 
entirely  upon  the  central  area  (Zone  II)  the  first  reflection 
pld  will  be  represented  at  the  test  plate  C. 

That  is,  the  observed  illumination  at  the  test  plate  is 
V  =pld+  KpJI (7) 

But  if  the  direct  light  flux  falls  entirely  upon  the  screened 
areas  (Zones  I  and  III)4  the  component  due  to  the  first  reflection 
pld  will  be  intercepted  by  the  screen,  and  the  observed  illumina- 
tion at  the  test  plate  is 

T  =  KVI (8) 

The  maximum  difference  in  the  illumination  I'  due  to  asym- 
metry of  light  flux  is  therefore  equal  to  pld,  or  is  the  fraction 

plrf 

—=-  =  a,  of  the  theoretical  reflected  illumination  pi  of  an  empty 

sphere ( 9 ) 

If  8  =  fraction  of  total  direct  light  flux  falling  upon  the  screened 
areas,  then  the  actual  illumination  at  the  test  plate  from  the 
component  plrf  is  (1  —  8)  pld.  Hence  the  fraction  of  pi  read  at 
the  test  plate  is 

T   __  (1—  8)plrf  +  Kp'I 


Pi  Pl 


(1  —  S)a  -  Kp (10) 


5  If  K  =  fraction  of  p2I  uot  absorbed,  the  illumination  at  the  test  plate  is  Kp*I  for  the 

second  component (6) 

K  is  almost  unity  if  the  screens  are  small  compared  with  the  surface  of  the  sphere. 

*  The  light  flux  falling  upon  the  screen  is  measured  by  Zone  III.     Hence  Zones  I  and 
III  may  be  treated  in  the  same  manner. 


8  TRANSACTIONS    I.    K.    S. PART    I 

The  actual  error  of  integration,  E,  not  compensated  by  the 
standard  lamp  method  of  determining  the  "sphere  constant"  is 
equal  to  the  difference  between  the  fraction  of  pi  read  at  the  test 
plate  with  the  unknown  lamp,  and  that  read  with  the  standard 
lamp. 

If  8'  =  fraction  of  direct  light  flux  falling  upon  screened  areas 
with  standard  lamp  and 

8  =  fraction  of  direct  light  falling  upon  screened  areas  with 
unknown  lamp,  then 

E=  [(i— 8)a  +  Kp]-[(i-8>+Kp]=o(8'-8)..(xi) 
As  8'  and  8  are  coefficients  representing  fractions  of  light  flux 
they  may  be  expressed  in  terms  of  illumination  and  area. 

Let 

Sum  of  screen  areas  , 

o-  =  -r : ,  and 

Total  area 

Direct  av.  illumination  on  screened  area 

Direct  av.  illumination  on  total  area 

then 

8'  =  a6'  for  standard  lamp 

and 

8   =  ad  for  unknown  lamp. 
Hence 

E  =  a<r(0'  —  0) (12) 

Equations  (n)  and  (12)  are  the  most  general  forms  of  the 
mathematical  expression  for  the  integrating  error  of  the  sphere. 
Space  does  not  permit  a  detailed  account  of  all  of  the  interesting 
characteristics  of  the  spherical  integrator  as  shown  by  this  ex- 
pression. 

It  is  obvious,  however,  that  the  error  of  integration  increases 
with  the  magnitude  of  the  absorption  coefficient,  with  the  size  of 
the  screened  areas  relatively  to  the  total  area,  and  with  the  dif- 
ference in  the  relative  illumination  of  the  screened  areas  by  the 
standard  lamp  and  the  unknown  lamp,  and  that  the  error  is  zero 
only  when  the  average  distribution  of  light  flux  upon  the  screened 
areas  is  the  same  for  standard  and  unknown  lamps. 


CHANEY    AND    CLARK:     ARC    LAMP    PHOTOMETRY  9 

Since  8,  or  6  (that  is,  the  ratio  of  flux  or  illumination  respec- 
tively) depends  upon  the  distance  of  the  sources  from  the 
screened  areas,  the  relative  positions  of  the  standard  lamp  and 
unknown  lamp  as  well  as  their  distribution  curves  must  be  con- 
sidered before  assuming  that  the  error  is  necessarily  zero  when 
the  standard  and  unknown  lamps  have  the  same  distribution,  or 
is  greater  than  zero  if  two  sources  have  unlike  distribution. 

Our  general  equation  shows  the  error  of  Presser's  suggestion 
that  a  grey  wall  with  an  absorption  coefficient  of  0.5  would  give 
better  results  than  a  lower  value  of  0.2.  The  argument  advanced 
was  that  the  higher  absorption  coefficient  suffered  less  change  by 
reason  of  the  collection  of  dust  and  dirt  upon  the  sphere  walls. 
While  this  is  true,  the  remedy  is  not  to  allow  the  walls  to  become 
dirty,  rather  than  to  attempt  to  match  the  dirt  by  the  initial  color 
of  the  sphere.  The  change  suggested  more  than  doubles  the  in- 
tegrating error. 

Ulbricht  also  states  that  a  large  absorption  coefficient  causes 
greater  deviation  from  the  cosine  law,  and  lessens  the  range  of 
the  sphere  for  lights  of  low  intensity. 

Further,  the  general  equation  shows  that  the  error  of  inte- 
gration may  be  decreased  by  decreasing  the  size  of  the  screened 
areas  or  Zones  I  and  III  shown  in  Fig.  1.  An  inspection  of  the 
diagram  shows  that  if  a  point  source  be  situated  in  the  center  of 
the  sphere  the  screened  area  (afe)  or  Zone  I  will  be  a  maximum 
when  the  screen,  S,  is  nearest  the  test  plate  C,  while  the  screened 
area  (bed)  will  be  a  maximum  when  the  screen  is  nearest  to 
the  light  source  L. 

At  some  intermediate  position,  the  sum  of  these  two  screened 
areas  will  therefore  be  a  minimum. 

This  minimum  position  may  be  graphically  determined  by 
drawing  diagrams  of  the  intermediate  positions  upon  plotting 
paper,  and  noting  at  which  position  of  the  screen  the  sum  of 
the  two  lines  /  hf  and  h  c  are  a  minimum.  Ulbricht  has  devel- 
oped general  mathematical  expressions  for  the  stun  of  these  two 
areas  and  the  conditions  for  which  they  are  a  minimum.  He 
finds  that  the  horizontal  distance  of  the  screen  from  the  center 
of  the  sphere  should  be  0.39  X  R,  if  R  =  radius  of  sphere,  and 


IO  TRANSACTIONS   I.    E.    S. PART    I 

the  light  source  is  at  the  center.5  If  the  light  source  be  above 
the  center  making  an  angle  of  35  °  with  the  test  plate  and  the 
horizontal,  the  value  is  smaller,  about  0.29  X  R,  the  screen 
being  elevated  proportionally.  (This  design  is  advocated  by 
several  German  writers,  especially  for  arc  lamps  with  a  large 
lower  hemispherical  light  flux).  In  general,  however,  a  value 
of  0.4  X  R  may  De  accepted  as  the  best  distance  between  lamp 
and  screen. 

Having  placed  the  screen  in  the  position  for  minimum  area 
of  Zones  I  and  III,  this  area  may  be  further  decreased  only  by 
increasing  the  size  of  the  sphere,  since  the  size  of  the  screen  is 
determined  by  the  area  of  the  largest  light  sources  to  be  meas- 
ured, or  by  the  cross  section  of  the  largest  diffusing  globes  em- 
ployed. The  largest  permissible  ratio  between  the  screen  and 
sphere  diameters  must  be  arbitrarily  determined  by  the  limits  of 
error  within  which  it  is  desired  to  work. 

Ulbricht  estimates  that  the  cross  section  of  the  sphere  must 
be  at  least  twenty  times  the  cross  section  of  the  screen,  or  with 
circular  screens  the  diameter  of  the  sphere  must  be  over  4.5 
times  the  diameter  of  the  screen.  In  this  case  the  sum  of  the 
screened  areas  is  20  per  cent  of  the  sphere  area  for  a  point 
source  in  the  center  of  the  sphere.  Therefore,  with  a  sym- 
metrical light  source  8  =  0.2  and  the  reflected  illumination  at 
the  test  plate  is  diminished  by  the  fraction 


0.2pl 


—  0.2a  =  4  per  cent,  if  a  =  0.2 (10) 


Pi 

The  error,  however,  by  the  general  equation  (10)  is 
E  =  a<r(0'  —  0)  =  4  per  cent.  (0'  —  0) 
in  which  ($'  —  6)  may  have  values  of  from  o  to  5  respectively. 

6  ^z  —  .      If  the  light  flux   from   the  standard   lamp  is 

o-         0.2 

B  Some  latitude  is  possible  since  small  changes  in  the  screen  position  are  partly  com- 
pensating in  their  effect  upon  the  magnitude  of  the  screened  areas. 

Chillas  has  calculated  that  with  a  screen  diameter  one  fifth  of  the  sphere  diameter 
the  position  for  minimum  screened  areas  is  at  the  distance  0.372R  from  the  sphere  center, 
in  which  case  the  magnitude  of  the  screened  areas  is  15.0  percent,  of  the  sphere  area. 
The  ratio  of  the  area  of  Zone  I  to  the  area  of  Zone  III  is  3  to  2  for  minimum  areas. 

For  screened  areas  of  equal  size  the  distance  of  the  screen  from  the  center  is  about 
0.315R  ond  the  sum  of  the  screened  areas  is  15.6  percent,  of  the  sphere  area,  an  increase 
in  the  screened  areas  but  0.6  per  cent,  over  their  minimum  value. 


CHANEY    AND    CLARK:     ARC    LAMP    PHOTOMETRY  II 

approximately  symmetrical,  6'  =  i  and  therefore  6,  the  ratio  of 
the  average  direct  illumination  upon  the  screened  areas  to  the 
average  direct  illumination  on  the  sphere  wall  as  a  whole,  must 
be  not  less  than  0.75  or  greater  than  1.25  if  the  error  of  in- 
tegration is  to  be  not  more  than  1  per  cent.  Since  6  may  quite 
easily  vary  from  0.5  to  2.0  giving  an  error  of  2  to  4  per  cent,  it 
would  seem  that  the  ratio  between  screen  and  sphere  diameters 
selected  by  Ulbricht  is  much  too  large  even  as  a  maximum,  if  the 
error  is  to  be  kept  below  1  per  cent,  for  light  sources  of  very 
different  types  of  distribution.  The  80-inch  sphere  requires  a 
screen  of  but  one  sixth  the  diameter  of  the  sphere  and  the 
screened  areas  are  but  12  per  cent,  of  the  total  area.  This  cuts 
down  the  above  limits  of  error  nearly  one  half. 

In  arc  lamp  photometry  a  further  source  of  complication  is 
that  the  standard  lamp  must  be  read  while  the  unlighted  arc 
lamp  is  in  the  sphere  in  order  to  correct  for  the  absorption  of 
light  by  the  lamp  parts  and  the  screening  effect  which  it  has  as 
an  opaque  body.6 

A  second  screen    (s'  in  Fig.  2)   is  therefore  required  which 


Fig.  2.— Two-screen  diagram. 

screens  another  part  of  the  sphere  wall  (a'  e'  /')  from  the  test 
plate.  This  screen  s'  may  be  quite  small  as  the  standard  lamp 
filaments  need  not  require  a  large  screen.  Fig.  2  shows,  how- 
ever, that  if  the  lamp  be  moved  from  the  position  1/  to  L  the 
relative  amount  of  total  light  flux  falling  upon  the  two  screened 

6  Any  opaque  body  acts  in  two  ways  to  diminish  the  illumination  at  the  test  plate. 
It  absorbs  an  amount  of  light  proportional  to  its  surface  area  and  the  absorption  coeffi- 
cient of  its  surface,  and  it  screens  a  part  of  the  sphere  wall  from  the  test  plate,  depending 
upon  its  shape  and  relative  position  in  the  sphere. 


I J  TRANSACTIONS   I.    E.    S. — PART    1 

areas  (a  c  f)  and  (a'  e'  /')  will  alter  with  the  change  in  the 
relative  distances  from  the  areas.  The  position  and  size  of  the 
screen,  s',  must  be  so  chosen,  therefore,  that  the  relative  screened 
areas  (b  d  c)  and  (b'  d'  c)  at  the  test  plate  will  be  in  compen- 
sating ratio.  As  Ulbricht  has  shown,  if  the  light  sources  have 
a  pronounced  asymmetry  the  relative  flux  in  the  different  direc- 
tions must  be  determined  from  the  distribution  curves  of  the 
lamps  and  corrected  for. 

This  is  obviously  unsatisfactory,  and  the  rational  correction 
is  therefore  to  construct  spheres  of  sufficient  size  to  make  the  in- 
fluence of  the  screened  areas  small  and  the  effect  of  their  rela- 
tive proportions  negligible.  In  other  words  if  <r,  in  the  general 
equation 

E  =  «r(0'  —  0) 
is  not  greater  than  i/io,  the  screen  errors  may  be  neglected  for 
light  sources  of  ordinary  distribution. 

Before  considering  the  case  for  extremely  asymmetrical 
sources,  it  will  be  convenient  to  derive  a  special  form  of  the 
general  equation  applicable  when  the  standard  lamp  has  a  dis- 
tribution sufficiently  symmetrical  to  give  the  same  average  direct 
illumination  upon  the  screened  areas  as  upon  the  unscreened 
area.     In  this  case 

8'  =  o- 
and 

E  =  a(S'  —  8)  =  a(<r  —  8) (13) 

Since  both  a  and  o-  are  known  or  may  be  determined  for  any 
given  sphere,  the  error  becomes  a  constant  multiplied  by  but  one 
variable  factor  depending  upon  the  distribution  of  the  light  flux 
of  the  unknown  lamp. 

For  example  with  the  80-inch  (2.03  m.)   integrating  sphere  in 

this  laboratory 

a  =  0.2  approx. 

a-  =  0.1  approx. 
Hence 

Per  cent.  E  =  0.2  X  (0.1  —  8)  X  100. 
8  may  have  any  value  from  zero  to  unity. 

If  S  =  o.o,  then  E  =  2  per  cent. 
If  8  —  0.1,  then  E  =  o  per  cent. 
If  8  =  0.2,  then  E  =  —2  per  cent. 
If  S  =  1.0,  then  E  =  —18  per  cent. 


CHANEY    AND    CLARK  :     ARC    LAMP    PHOTOMETRY 


13 


While  the  maximum  possible  error  is  very  large  it  should  be 
noted  that  the  conditions  for  its  occurrence  are  very  unlikely  to 
happen  except  by  design. 

The  expression  E  =  a(<r —  8)  has  two  maxima  (-fa)  and  ( — a). 
In  practise,  however,  o-  is  never  greater  than  0.25,  hence  the 
maximum  of  (-fa)  has  no  practical  significance.  The  condition 
that  E,  approach  ( — a)  is  that  o-  be  very  small  and  8  be  unity; 
since  8  =  a9,  however,  8  usually  decreases  with  a  instead  of  be- 
coming a  maximum.  In  order  for  8  to  be  unity  when  o-  is  small 
all  of  the  light  flux  must  be  concentrated  upon  certain  very  small 
portions  of  the  sphere  area.  In  the  numerical  values  quoted  for 
the  80-inch  (2.03  m.)  sphere  <r  =  o.i.  Therefore  if  the  total 
direct  light  flux  should  be  so  asymmetrical  as  to  illuminate  but 
one  tenth  of  the  area  of  the  sphere  and  if  the  direction  of  the 
rays  were  left  to  chance,  the  probabilities  are  10  to  1  that  none 
instead  of  all  of  the  direct  light  would  fall  upon  the  10  per  cent, 
of  screened  areas,  that  is  8  would  be  o  instead  of  unity,  giving 
an  error  of  +2  per  cent,  instead  of — 18  percent. 

Furthermore  it  so  happens  that  the  screened  areas  are  divided 


0/ re  eft  on  of 
l/f/>rf7ux 


PAofo metric 


Fig.  3. — Diagram  for  hemispherical  distribution. 


and  occupy  opposite  sides  of  the  sphere  which  renders  them 
still  less  likely  to  receive  the  entire  flux  of  extremely  asymmetri- 
cal sources.  This  is  well  illustrated  by  Ulbricht's  classic  experi- 
ment of  rotating  a  lamp  in  the  sphere  one  side  of  which  was 
covered  with  black  paint.  Thus  a  light  source  having  an  ap- 
proximately hemispherical  distribution  was  obtained.  In  a 
20  inch  (50.8  cm.)  sphere,  values  were  obtained  as  shown 
in  Fig.  3. 

The  light  flux  is  directed  toward  the  screen  and  then  is  given 


14  TRANSACTIONS    I.    K.    S. —  PART    1 

successive  900  turns.  The  readings  indicate  a  very  high  degree 
of  integrating  capacity  for  so  small  a  sphere. 

If  the  same  experiment  be  performed  in  a  properly  con- 
structed 80-inch  sphere  no  appreciable  difference  in  the  various 
directions  of  a  hemispherical  light  source  can  be  detected.  An 
examination  of  the  diagrams  will  show,  however,  that  the  suc- 
cess of  the  experiment  depends  upon  the  relative  position  of  the 
two  screened  areas  upon  opposite  sides  of  the  sphere.  Assum- 
ing that  the  two  screened  areas  are  approximately  equal  then  for 
each  position  half  of  the  screened  areas  are  in  the  shadow  of 
the  lamp,  and  half  are  illuminated.  Therefore,  6,  the  ratio  of 
direct  illumination  upon  screened  areas  to  the  direct  illumination 
upon  the  sphere  as  a  whole  is  always  equal  to  1  and  the  error  of 
integration  is  zero  [E  -  a<r(i  —  6)1  for  all  positions  of  the 
hemispherically  asymmetrical  source.  The  same  holds  true 
whether  the  lamp  be  rotated  upon  the  horizontal  or  perpendicu- 
lar axis.  This  compensation  by  position,  however,  holds  only 
for  hemispherically  asymmetrical  light  sources. 

If  the  distribution  curve  of  the  lamp  has  two  horizontal 
maxima  such  as  is  caused  by  heavy  side  arms  in  some  types  of 
arc  lamp,  then  both  screened  areas  might  receive  the  maximum 
flux  in  one  position  of  the  lamp  and  both  would  receive  the  min- 
imum for  a  rotation  of  900 .  To  map  out  the  real  character- 
istics of  the  screened  and  unscreened  zones,  a  much  more  asym- 
metrical light  source  is  required  which  will  directly  illuminate 
a  fraction  of  the  sphere  wall  smaller  than  either  of  the  two 
screened  areas. 

An  examination  was  made  in  this  manner  of  the  80-inch 
(2.03  m.)  metal  sphere  and  an  80-inch  wooden,  box  integrator 
having  an  inner  surface  in  the  form  of  an  18-sided  polyhedron. 

A  large  tungsten  lamp  of  about  160  mean  spherical  candle- 
power  was  entirely  covered  with  black  paper  except  for  one 
opening  of  about  2  inches  (5.08  cm.).  When  this  was  directed 
toward  either  of  the  two  screened  areas  no  direct  light  fell  upon 
the  unscreened  area.  Three  positions  on  the  central  area  were 
also  chosen,  so  that  no  direct  light  fell  upon  either  of  the  screened 
areas.  The  photometric  readings  are  placed  in  ratio  with  the 
900  reading  =  100. 

It  is  seen  that  in  the  case  of  the  sphere  very  good  agreement 


CHANEY    AND    CLARK:     ARC    LAMP    PHOTOMETRY 


15 


is  obtained  for  the  three  positions  (450,  900  and  1350)  upon  the 
central  zone,  or  unscreened  area.  The  same  positions  for  the  un- 
screened area  of  the  box  show  greater  asymmetry  due  to  the 
deviation  from  the  spherical  form  but  considering  the  concen- 
tration of  the  light  flux  the  variation  of  2.5  per  cent,  is  sur- 
prisingly low. 

On  the  other  hand  the  values  for  the  positions,  0°  and  1800, 
on  the  two  screened  areas,  or  Zone  III  and  Zone  I  respectively, 
show  a  large  drop  of  approximately  25  per  cent,  for  both  the 
box  and  the  sphere.  These  values  represent  the  maximum  var- 
iations possible  in  the  reflected  illumination  at  the  test  plate  and 
are  of  the  known  order  of  magnitude  of  the  absorption  coef- 
ficient a,  in  agreement  with  the  theoretical  deduction.  (See 
Equation  9.) 


O/recf/on  of '   . 


/•3S' 


/ao' 


Sp/tere 

72 

'OOJ 

/oo 

/oaj 

76S 

Box 

77* 

S7.5 

/OO 

S7.f 

74 

Fig.  4.—  Diagram  for  concentrated  flux. 

In  fact  with  certain  refinements  this  provides  a  simple  method 
for  determining  the  absorption  coefficients  of  the  sphere  wall  or 
of  the  screen. 

It  is  evident  from  the  foregoing  work  that  extremely  asym- 
metrical light  sources  may  be  accurately  integrated  in  a  well 
designed  sphere  if  the  precaution  is  observed  to  direct  the  flux 
entirely  upon  the  central  zone.  The  slight  error  is  easily  cor- 
rected in  two  ways.  First,  if  the  standard  lamp  gives  the  same 
average  illumination  upon  the  screened  area  (a  e  f)  in  Fig  1  as 
upon  the  rest  of  the  sphere  the  error  is  then  E  =  ao-  in  which 
both  a  and  <r  are  known  or  can  be  easily  determined.  Second,  a 
standard  lamp  which  also  throws  its  entire  flux  upon  the  central 
zone  may  be  employed.  Then  E  =  a(S'  —  8)  =  o  since  both  8' 
and  8  are  zero. 

It  has  been  shown  that  the  conditions  for  perfect  integration 


l6  TRANSACTIONS    I.    E.    S. PART    I 

are,  (i)  a  small  absorption  coefficient  of  the  sphere  walls;7  (2) 
the  smallest  possible  percentage  of  the  sphere  wall  screened  from 
the  test  plate  and  from  the  direct  rays  of  the  lamp;  and  (3),  a 
similar  ratio  of  the  light  flux  upon  the  screened  and  unscreened 
portions  of  the  sphere  wall  for  both  the  standard  lamp  and  the 
unknown  lamps. 

It  has  been  shown  from  the  form  of  the  general  equation  for 
integration  error 

H  =  acr(0'  —  0) 
that  the  more  closely  the  first  two  conditions  are  approached, 
the  greater  may  be  the  deviation  from  the  third  condition  with- 
out serious  error,  while  on  the  other  hand  if  the  third  condition 
be  exactly  fulfilled  the  first  two  conditions  may  be  entirely 
ignored. 

Finally  it  has  been  shown  that  with  exceedingly  asymmetrical 
light  sources  the  possible  error  is  small  if  the  most  intense  por- 
tion of  the  flux  is  always  directed  away  from  the  screened  areas, 
and  upon  the  central  zone  of  the  sphere  (i.  e.,  if  6  is  kept  equal 
to  or  less  than  1 ) . 

The  remainder  of  the  paper  will  be  devoted  first  to  a  discus- 
sion of  certain  points  brought  forward  in  the  paper  of  Sharp 
and  Millar  already  referred  to,  and  second  to  certain  practical 
considerations  arising  in  arc  lamp  photometry. 

A  form  of  correction  for  asymmetrical  light  distribution  which 
is  emphasized  by  Sharp  and  Millar  is  the  use  of  a  translucent  or 
diffusing  screen,  instead  of  an  opaque  screen  between  the  light 
source  and  the  test  plate.  This  was  originally  suggested  by 
Ulbricht  in  the  case  of  very  small  spheres  in  which  it  was  noted 
that  with  the  rotation  of  a  hemispherically  asymmetrical  light 
source,  the  readings  were  lowest  when  the  lamp  was  directed 
toward  the  screen.  This  is  the  case  with  the  readings  for  the 
20-inch  (50.4cm.)  sphere  in  Fig.  3,  the  drop  being  about  2  per 
cent.     Sharp  and  Millar  quote  much  higher  values  of   11   per 

7  The  practise  in  this  laboratory  is  to  use  "factory  white"  and  renew  the  coating  every 
two  weeks.  This  is  preferable  to  using  an  oil  paint  and  attempting  to  wash  the  surface, 
as  a  mat  diffusing  surface  is  more  easily  maintained.  The  relative  reflecting  power  of 
white  porcelain,  white  blotting  paper,  and  "  factory  white,"  for  different  wave-lengths  of 
light  was  determined  with  the  spectrophotometer.  "Factory  white"  showed  a  slightly 
lower  selective  absorption  in  the  red  end  of  the  spectrum.  Otherwise  the  surfaces  were 
the  same. 


CHANCY   AND    CLARK:     ARC    LAMP    PHOTOMETRY  IJ 

cent,  for  an  18-inch  (45.7  cm.)  sphere  and  6  per  cent,  for  a 
30-inch  (76.2  cm.)  sphere.  The  proposal  is  to  correct  for  this  by- 
selecting  a  screen  just  translucent  enough  to  transmit  the  proper 
amount  of  direct  light  to  the  test  plate  and  so  equalize  the  read- 
ings, for  the  two  positions.  This  method  of  compensation  is 
open  to  the  following  objections. 

(1)  The  exact  adjustment  of  screens  to  particular  translucen- 
cies  is  neither  simple  nor  convenient  in  practise. 

(2)  The  compensation  is  made  by  the  transmission  of  direct 
light  of  varying  intensity.  Since  the  sole  object  of  the  screen  is 
to  prevent  such  transmission  the  general  integrating  capacity  of 
the  sphere  is  impaired  and  the  adjustment  is  valid  only  for  the 
particular  distribution  of  light  flux  for  which  it  is  made. 

(3)  Large  errors  are  introduced  by  slight  variations  in  the 
distance  of  the  light  source  from  the  screen. 

(4)  The  method  is  unnecessary.  The  desired  correction  can 
be  made  by  proper  screen  position.  If  the  reading  is  low  when 
the  light  is  directed  toward  the  screen,  as  compared  with  the 
reverse  position,  the  relative  proportion  of  the  two  screened 
areas  is  wrong,  and  may  be  remedied  by  moving  the  screen  nearer 
the  test  plate. 

Much  more  objectionable  than  the  use  of  an  exactly  adjusted 
translucent  screen  for  a  particular  type  of  light  distribution  has 
been  the  indiscriminate  use  of  translucent  screens  in  certain 
commercial  integrating  spheres  placed  upon  the  market,  where 
there  was  no  pretense  of  adjustment,  and  where  such  use  was 
ill-advised  and  harmful.  An  80-inch  integrating  sphere  of  this 
type,  with  complete  photometric  equipment  was  purchased  some 
time  ago  from  a  manufacturer.  This  sphere  was  provided  with 
screens  made  of  translucent  diffusing  paper.  Assuming  that  the 
screens  were  properly  designed,  the  sphere  was  placed  in  service 
without  special  tests.  Later  a  box  integrator  of  the  same  diam- 
eter was  built  in  the  laboratory  and  the  arrangement  and  con- 
struction of  the  screens  were  copied  from  the  above-mentioned 
sphere.  As  the  inner  surface  of  the  box  integrator  was  18 
sided  instead  of  spherical,  a  critical  investigation  was  made  of 
its  integrating  capacity  as  compared  with  the  sphere.  It  was 
found  when  a  series  of  standardized  high  power  incandescent 


l8  TRANSACTIONS    I.    K.    S. —  PART    I 

lamps  were  successively  suspended  in  the  box,  in  the  position 
usually  occupied  by  the  arc  lamp  that  discrepancies  of  serious 
magnitude  frequently  occurred.  The  same  experiment  was  re- 
peated in  the  metal  sphere  with  similar  results,  the  discrepancies 
amounting  to  4  and  5  per  cent. 

The  experiment  with  the  hemispherical  light  source  was  then 
tried  with  the  following  results  in  the  box  integrator.  Three 
positions  were  chosen. 

TABLE  I. 

Away 
Toward  screen  from  screen 

Direction  of  light  flux o°  900  1800 

Readings 100  81  74 

Since  the  illumination  at  the  test  plate  increases  36  per  cent. 
as  the  light  is  rotated  around  toward  the  screen  from  the  oppo- 
site side,  it  would  appear  that  the  compensation  for  loss  of  light 
at  the  test  plate  was  somewhat  excessive. 

Opaque  screens  of  blotting  paper  were  then  employed  and  the 
reading  in  the  three  positions  differed  less  than  0.2  per  cent.  In 
the  sphere  a  smaller  difference  of  18  per  cent,  existed  between 
the  two  opposite  sides,  due  to  the  fact  that  the  translucent  screen 
had  become  somewhat  more  opaque  by  reason  of  age  or  dust. 

But  the  source  of  the  serious  discrepancies  with  horizontally 
symmetrical  sources  was  found  to  be  in  the  fact  that  the  propor- 
tion of  transmitted  light  varied  with  the  distance  of  the  lamp 
from  the  screen.  The  translucent  screen  behaves  toward  the 
test  plate  as  a  primary  light  source,  and  the  illumination  of  the 
screen  necessarily  varies  with  the  distance  of  the  lamp. 

TABLE  II.— Translucent  Screens. 

Per  cent,  change 


Distance 
lamp  to  screen 

Test  plate 
illumination 

Observed 

Calc.  inverse 
square  law 

1 

r   9  in.  (23  cm.) 

20.3 

O.O 

O.O 

Clear  globe  < 

11  in.  (28  cm.) 

18.9 

7.0 

8.9 

1 

1  18  in.  (46  cm.) 

17-3 

'4-5 

19.0 

Diffusing 
opal  globe  . 

r  9  in. 

11  in. 

1  18  in. 

.6.3 
15.4 
13-6 

0.0 

5-5 
16.0 

0.0 

8-5 
19.0 

It  is  seen  from  Table  II  that  a  displacement  of  2  inches  gives  a 
change  in  illumination  of  about  6  per  cent.,  and  a  displacement 


CHANEY   AND    CLARK :     ARC   LAMP    PHOTOMETRY  19 

of  9  inches  a  change  of  about  15  per  cent.    The  change  is  some- 
what less  than  is  calculated  from  the  inverse  square  law. 

In  the  following  table  the  results  with  opaque  screens  are 
given  which  show  no  change  at  all  for  a  displacement  of  2  inches 
(5.08  cm.)  and  only  a  slight  effect  when  the  distance  between 
lamp  and  screen  is  doubled. 


TABLE  III.— Opaque  Screens. 

Distance  Test  plate  Per  cent, 

lamp  to  screen  illumination  change 

9  in.  (23  cm.)  14.9  O.O 

Clear  globe-  •  \  11  in.  (28  cm.)  14.9  0.0 

[8  in.  (46  cm.)  14.7  1.3 


III 


9  in.  12.15  0.0 

Diffusing  opal  globe  •  •  -j  11  in.  12.15  0.0 

18  in.  12.10  0.4 

Inasmuch  as  the  incandescent  lamps  were  merely  suspended 
in  the  sphere,  variations  of  over  an  inch  (2.54  cm.)  in  their 
position  was  easily  possible,  which  accounted  for  the  discrepan- 
cies observed  when  the  translucent  screens  were  employed.  In 
the  case  of  arc  lamps  exact  centering  would  be  impracticable. 

Sharp  and  Millar  make  a  second  indictment  of  opaque  screens, 
however.    They  state  that — 

It  has  been  found  that  when  an  opaque  screen  is  used  the  results  are 
dependent  upon  the  size  of  the  light  source  tested.  So  for  example,  in 
the  80-inch  (2.03  m.)  sphere  the  following  differences  have  been  found 
between  results  obtained  with  an  opaque  screen  of  the  size  which  it  is 
desirable  to  use,  and  those  obtained  with  the  smallest  opaque  screen  which 
could  be  used  in  connection  with  the  particular  light  source  investigated. 

Per  cent, 
difference 
between  deter- 
minations with 
large  and  small 
opaque  screens 

100  candlepower  carbon  filament    2.0 

32  candlepower  carbon  filament    3.0 

16  candlepower  carbon  filament    4-° 

8  candlepower  carbon  filament    5-° 

4  candlepower  carbon  filament  (sign  lamp)    10.0 

2  candlepower  carbon  filament  (sign  lamp)    10.0 

These  data  indicate  that  if  an  opaque  screen  were  used,  an  arc  lamp 
with  an  opal  globe  would  receive  an  undue  advantage  in  comparison  with 
the  same  lamp  equipped  with  a  clear  glass  globe. 


20  TRANSACTIONS    I.    E.    S. PART    I 

They  further  state  that — 
Errors  due  both  to  the  opacity  of  the  screen  and  to  variations  in  the 
relation  between  its  size  and  that  of  the  light  source  may  be  eliminated 
by  substituting  for  the  opaque  screen  one  of  a  particular  translucency. 

The  objections  which  may  be  raised  to  the  above  are  two  in 
number:  first,  that  their  experiment  does  not  prove  what  it  is 
intended  to  prove,  and  second,  that  if  what  they  desired  to  show 
is  true,  no  conceivable  translucency  of  screens  will  be  of  any 
avail. 

In  the  experiment  quoted  the  ratio  between  the  large  and  small 
screen  becomes  successively  greater  with  each  succeeding  number 
of  the  series.  Since  the  illumination  at  the  test  plate  depends 
directly  upon  the  size  of  the  screen,  this  adequately  accounts  for 
the  increasing  divergence  with  each  successive  pair  of  readings. 

In  the  following  table  are  given  readings  taken  successively 
with  a  translucent  screen  and  an  opaque  screen,  first  for  an 
incandescent  lamp  with  clear  globe,  and  second,  for  the  same 
lamp  incased  in  a  large  diffusing  arc  lamp  globe.  The  results 
show  that  there  is  the  same  relative  difference,  viz.,  ij  per  cent., 
between  the  clear  globe  and  the  opal  globe  whether  a  translucent 
or  an  opaque  screen  be  used.  Or,  looked  at  in  another  way,  the 
replacing  of  the  translucent  screen  with  an  opaque  screen  has 
cut  down  the  illumination  at  the  test  plate  by  almost  exactly  the 
same  amount,  viz.,  14.4  per  cent.,  whether  the  area  of  the  light 
source  was  large  or  small. 

TABLE  IV. 

Translucent  Opaque  Per  cent. 

screen  screen  difference 

Clearglobe 24.78  21.19  14.49 

Opal  globe 20.56  17-59  J4-44 

Per  cent,  difference i7-°7  l1-°°  °-° 

Sharp  and  Millar's  conclusions,  therefore,  upon  the  value  of 
translucent  screens,  require  revision. 

Their  original  suggestion,  however,  that  the  relative  areas  of 
the  light  sources  might  affect  their  relative  values  as  determined 
in  the  sphere  was  further  investigated.  As  already  shown,  the 
theoretical  value  of  the  reflected  illumination  for  an  empty  sphere 
is  pi,  and  the  actual  value  of  the  reflected  illumination  read  at 
the  test  plate  with  a  screen  is  [(1  —  Bjpld  -f  Kp'i].     The  ratio 


CHANCY   AND    CLARK:     ARC   LAMP    PHOTOMETRY  21 

of  the  reflected  illumination  with  screen,  to  that  without  screen 
is  therefore  f(i  —  8)a  -f-  Kp]  (10)  which  for  the  lack  of  a  better 
term  we  will  call  the  '  screen  ratio'. 

In  the  above  expression  a  and  p  are  the  absorption  and  reflec- 
tion coefficients  of  the  sphere  wall  ;  K  is  a  coefficient  represent- 
ing the  fraction  of  the  diffuse  reflections  p2I  which  escapes  ab- 
sorption by  the  screen,  and  other  foreign  bodies,  and  is  therefore 
nearly  unity,  and  (i  — 8)  is  the  distribution  coefficient  repre- 
senting the  fraction  of  the  total  light  flux  falling  upon  the  un- 
screened area  or  central  zone  of  the  sphere.  There  is  nothing  in 
this  expression  dependent  upon  the  area  of  the  light  source. 
Unless  the  area  of  the  source  changes  the  distribution  of  the  flux 
it  should  be  without  influence.8 

The  use  of  diffusing  globes  upon  asymmetrical  sources  does 
change  the  resulting  distribution  curves  giving  in  general  a 
more  symmetrical  distribution.  This  means  that  the  ratio 
[(i  —  8)a  +  Kp]  for  a  clear  globe  may  be  either  greater  or  less 
than  the  corresponding  ratio  for  the  same  source  with  a  diffusing 
globe. 

If  the  clear  globe  has  a  relatively  large  fraction,  8,  of  the 
total  light  flux  falling  upon  the  screened  areas,  a  diffusing 
globe  may  diminish  this  and  increase  the  value  of  the  ratio 
[(i  —  B)a  +  Kp].  That  is,  the  diffusing  globe  will  have  a  rela- 
tive advantage. 

If  on  the  other  hand  the  fraction  of  the  light  flux,  8,  falling 
upon  the  screened  areas  is  much  below  the  average,  a  diffusing 
globe  may  increase  8,  and  diminish  the  ratio  given  by  the  ex- 
pression [(i  —  8)a  -f  Kp].  That  is,  the  diffusing  globe  will 
have  a  relative  disadvantage. 

A  direct  experimental  method  of  measuring  the  'screen  ratio' 

8  The  proof  that  a  large  light  source  will  undergo  the  same  screen  absorption  as  a 
small  source  of  equal  candlepower  is  simple  when  the  distribution  is  assumed  uniform 
for  both  cases. 

Imagine  equal  spheres  described  about  the  center  of  both  light  sources,  then  since 
both  sources  emit  the  same  total  flux  uniformly  distributed,  equal  portions  of  the  surface 
on  the  two  spheres  are  traversed  by  equal  light  fluxes.  If  the  radius  of  the  imaginary 
sphere  is  so  taken  that  the  edges  of  the  circular  screen  lie  on  the  sphere  surface  it  is  clear 
that  the  screen  marks  off  a  definite  portion  of  the  sphere  surface  and  therefore  receives 
the  same  light  flux  from  either  the  small  or  the  large  light  source  above  assumed.  This 
is  the  necessary  and  sufficient  condition  for  equal  absorbing  effects  on  both  light  fluxes. 

It  is  true  that  the  light  distribution  on  the  portion  of  the  integrating  sphere  around 
the  screen  shadow  is  different  in  the  two  cases,  but  this  difference  has  no  effect  on  the 
illumination  at  the  test  plate  if  the  portion  of  the  sphere  surface  involved  has  a  uniform 
reflecting  surface. 


22  TRANSACTIONS    J.    K.    S. — PART    1 

[(i  —  8)<x  -j-  Kp]  for  any  given  screen  and  light  source  was  de 
vised  as  follows  : 

Measurements  are  made  of  the  illumination  at  the  test  plate 
under  three  conditions. 

Let  A  —  direct  light  flux  only. 

B  =  direct  plus  reflected  light  flux  (without  screen). 
C  =  reflected  light  only  (with  screen). 

A,  the  actual  direct  illumination  upon  the  test  plate  from  the 
unscreened  light  source,  is  measured  by  attaching  the  lamp  in  its 
proper  position  to  the  half  of  the  sphere  containing  the  test 
plate.  The  opposite  half  is  removed  and  a  series  of  black  screens 
are  set  up  between  the  test  plate  and  the  lamp  to  cut  off  all  light 
except  that  directly  from  the  source. 

B  is  measured  with  the  sphere  closed,  in  the  usual  manner, 
but  with  no  screen.  B  —  A  is  therefore  equal  to  the  theoretical 
value  of  the  reflected  illumination,  pi,  for  an  empty  sphere  (ex- 
cept in  so  far  as  the  lamp  and  its  supports  may  act  as  a  screen). 

C  is  the  value  of  the  reflected  illumination  as  usually  measured 
with  screen  and  is  equal  to  (i  —  S)pl</  -\-  p*I. 

Therefore  C/(B  —  A)  =  [(i  —  B)a  +  Kp]  the  "screen  ratio." 

Table  V  gives  a  series  of  measurements  made  in  this  manner 
with  a  light  source  having  a  clear  globe,  and  with  the  same  light 
source  after  being  incased  in  an  opal  globe. 

TABLE  V. 

ABC  C/(B  —  A  ) 

Clear  globe 8.69  36.64  26.38  0.944 

Opal  globe 5.8  28.35  21.61  0.958 

It  is  seen  that  under  the  particular  conditions  of  this  experi- 
ment the  opal  globe  has  a  slight  relative  advantage  over  the  clear 
globe.  The  results  are  not  open  to  complete  explanation  since 
the  relative  differences  in  distribution  are  only  partially  indi- 
cated by  the  values  of  the  direct  illumination  A,  at  the  test  plate, 
as  the  average  intensity  of  the  light  flux  upon  the  rest  of  the 
screened  areas  is  unknown,  and  may  not  be  proportional  to  A. 
The  method  as  outlined,  however,  affords  a  very  direct  and 
simple  means  of  investigating  special  characteristics  of  the 
spherical  integrator  and  further  data  would  be  of  interest. 


CHANEY   AND    CLARK:     ARC   LAMP    PHOTOMETRY  23 

Another  source  of  error  in  practical  arc  lamp  photometry  which 
is  carefully  avoided  in  German  practise  has  apparently  received 
no  attention  from  the  designers  of  American  built  spheres.  The 
error  consists  in  a  faulty  method  of  determining  the  "sphere 
constant." 

In  the  substitution  method  employed  with  the  sphere  the  ratio 
between  the  known  flux  of  a  standard  lamp,  as  separately  deter- 
mined, and  its  illumination  as  photometered  at  the  test  plate  gives 
the  "sphere  constant,"  by  which  any  other  illumination  as  read 
at  the  test  plate  may  be  converted  to  terms  of  the  flux  or  mean 
spherical  candlepower  of  its  source. 

This  constant9  must  contain  in  itself  all  of  the  factors  affecting 
the  relations  between  light  flux  and  test  plate  illumination,  such 
as  size  and  surface  of  sphere,  ratio  of  screened  and  unscreened 
areas,  absorption  of  reflected  light  by  foreign  bodies  such  as  arc 
lamp  mechanism,  screens,  etc. 

Not  only  do  large  lamp  mechanisms  absorb  reflected  light,  but 
they  screen  certain  parts  of  the  sphere  wall  from  the  test  plate, 
thus  changing  the  ratio  of  screened  and  unscreened  area. 

Therefore,  the  standard  lamp  must  be  read  with  the  arc  lamp 
in  position,  in  order  that  the  sphere  constant  may  contain  the 
proper  corrections.  But  since  only  reflected  light  can  reach  the 
arc  lamp  supports  when  the  latter  is  burning,  the  same  condition 
must  be  observed  with  the  standard  lamp.  That  is,  none  of  the 
direct  rays  of  the  latter  must  strike  the  arc  lamp.  The  German 
practise  is  to  place  the  standard  lamp  below  the  arc  lamp  with  a 
small  cap  upon  the  former  to  shield  the  arc  lamp.  The  standard 
lamp  must  be  standardized  with  this  cap  in  place.  In  the  above- 
mentioned  sphere,  however,  the  standard  lamp  is  placed  laterally, 
where  the  most  intense  part  of  the  flux  will  fall  upon  the  arc 
lamp  parts,  and  no  screen  or  shield  is  provided.  The  arc  lamp 
therefore  absorbs  a  considerable  amount  of  direct  light  in  addi- 

Flux  standard  lamp _ 

'  Sphere  constant  =  1]Ulmination  standard  lamp  as  read  at  test  plate 

4irR2qI  4"-R*ag 

(I  -  S')plrf  +  Kp2I  ~  «[(l  —  «')  +  Kop] 
If  R  =  radius  of  sphere. 
a.  =  absorption  coefficient, 
p  =  reflection  coefficient. 
(1  —  8')  =  fraction  of  direct  light  falling  on  central  zone  of  sphere. 
(1  —  K)  =  fraction  of  reflected  light  absorbed  by  screens  and  foreign  bodies  of  all  kinds. 


24  TRANSACTIONS    I.    E.    S. — PART    I 

tion  to  the  usual  amount  of  reflected  light.  This  increases  the 
sphere  constant  and  the  resulting  values  for  the  arc  lamp  are 
high.  An  arc  lamp  which  intercepts  and  absorbs  a  large  propor- 
tion of  direct  light  is  thus  favored  over  a  lamp  with  smaller  or 
more  highly  reflecting  mechanism. 

In  this  laboratory  where  many  types  of  arc  lamps  are  employed 
in  the  testing  of  experimental  and  factory  carbons,  the  correction 
for  the  change  in  sphere  constant  caused  by  introducing  the  arc 
lamp  into  the  sphere  is  determined  by  placing  a  small  screen 
upon  the  standard  lamp  of  sufficient  size  to  screen  the  arc  lamp. 
The  standard  is  read  with  the  sphere  empty  and  then  with  the 
arc  lamp  in  position.  A  factor  is  thus  obtained  for  the  influence 
of  this  particular  arc  lamp  upon  the  sphere  constant.  The  cap  is 
then  removed  from  the  standard  lamp,  and  the  constant  for  the 
empty  sphere  with  known  light  flux  determined.  This  constant 
multiplied  by  the  lamp  factor  previously  obtained,  gives  the  cor- 
rection for  the  lamp  in  question. 

This  method  has  the  great  advantage  that  once  the  specific 
factor  for  each  lamp  has  been  determined  it  is  only  necessary  to 
determine  the  constant  of  the  empty  sphere  thereafter.  The 
latter  need  be  determined  but  once  a  day,  no  matter  how  many 
different  lamps  are  being  photometered. 

Where  the  primary  object  is  the  comparison  of  different  car- 
bons in  the  lamps,  it  becomes  necessary  to  determine  the  trans- 
mission and  absorption  factors  of  the  globes  so  that  the  data 
over  long  periods  of  time  may  be  independent  of  the  particular 
globes  in  use.  Fairly  uniform  opal  globes  are  selected  and  stand- 
ardized separately  by  incandescent  lamps,  and  the  globe  factor, 
together  with  the  corresponding  lamp  factor,  is  applied  to  the 
particular  value  of  the  sphere  constant  as  determined  for  the 
day  upon  which  the  test  is  made.  By  placing  an  incandescent 
lamp  inside  the  arc  lamp  with  globe  complete,  a  combined  lamp 
and  globe  factor  may  be  determined.  Since  the  incandescent 
lamp  has  neither  the  exact  position  or  distribution  of  the  bare 
arc,  the  resulting  candlepower  values  are  not  those  of  the  naked 
arc,  but  are  proportional  to  them,  and  are  independent  of  chang- 
ing globes. 

If  the  actual  illumination  of  the  arc  lamp  is  desired,  then  the 


CHANEY   AND    CLARK:     ARC    LAMP    PHOTOMETRY  2$ 

latter  method  is  inapplicable,  and  no  globe   factors   should  be 
employed. 


A  brief  consideration  will  now  be  given  to  a  source  of  error  in 
the  practical  photometry  of  arc  lamps  which  has  apparently  been 
too  frequently  neglected. 

All  commercial  products  are  subject  to  characteristic  varia- 
tions and  lack  of  uniformity,  the  range  and  extent  of  which 
depends  upon  the  type  of  product,  the  inherent  difficulties  of 
manufacture,  and  the  standard  of  quality  maintained  by  the 
manufacturer.  No  trustworthy  comparison  of  similar  types  of 
competing  illuminants  is  possible  without  a  knowledge  of  the 
characteristic  range  of  variation  of  the  particular  products  under 
test.  The  measure  of  the  uniformity  of  a  product  is  not  only 
essential  in  determining  the  true  arithmetical  value  of  the  prop- 
erty being  measured,  but  also  in  determining  the  commercial 
worth  of  such  value  when  found.  Moreover,  the  testing  labora- 
tory requires  a  knowledge  of  the  precision  measure,  or  average 
deviation  of  the  individual  samples  from  their  general  mean,  in 
order  to  obtain  the  most  economical  and  efficient  distribution  of 
the  time  and  labor  spent  upon  the  test.  For  example,  let  it  be 
assumed  that  the  actual  variation  in  physical  and  illuminating 
properties  of  a  certain  class  of  carbons  is  5  per  cent.  That  is, 
any  single  trim  will  show  upon  the  average  a  difference  of  5  per 
cent,  from  the  mean  value  of  a  large  number  of  such  trims.  It 
is  then  obvious  that  no  matter  how  exhaustively  a  single  trim 
may  be  tested,  the  result  will  still  differ  on  the  average  by  at 
least  5  per  cent,  from  the  normal  value,  and  may  quite  possibly 
differ  by  three  times  the  average  deviation  or  15  per  cent.  The 
only  possible  way  by  which  a  closer  approximation  to  the  general 
average  value  can  be  secured  is  not  by  increasing  the  accuracy 
or  number  of  measurements  upon  a  single  trim,  but  by  increas- 
ing the  number  of  the  trims  tested.  The  average  deviation  of 
the  mean  of  several  independent  trims  decreases  in  proportion  to 
the  square  root  of  their  number.  That  is,  four  trims  are  required 
to  reduce  the  average  deviation  one  half. 

If  the  actual  physical  differences  possess  an  average  deviation 
of  5  per  cent.,  the  average  deviation  of  the  values  as  measured 


26  TRANSACTIONS    I.    E.    S. — PART    I 

will  be  still  greater,  because  superposed  upon  the  variations  due 
to  the  actual  differences  of  the  carbons  from  one  another,  will 
be  the  variations  due  to  errors  of  measurement  upon  the  indi- 
vidual carbons.  Assume  that  the  latter  has  an  average  deviation 
of  i  per  cent.  One  has,  then,  a  i  per  cent,  average  deviation  due 
to  errors  of  measurement  superposed  upon  a  5  per  cent,  average 
deviation  due  to  variations  in  the  product  measured. 

The  resultant  deviation  is  not,  however,  the  sum  of  these  two, 
/.  e.,  6  per  cent.,  but  is  the  square  root  of  the  sum  of  their  squares, 
i.  e.,  5.1  per  cent.  Thus  if  the  two  variations  are  represented  as 
the  sides  of  a  right  angled  triangle,  the  resultant  deviation  is 
equal  to  its  hypotenuse.  From  this  it  follows  that  if  one  devia- 
tion is  very  small  with  respect  to  the  other,  relatively  large 
changes  in  its  value  will  have  a  relatively  slight  effect  upon  the 
resultant  deviation.  Thus  in  the  example  above  the  errors  of 
measurement  may  be  increased  so  that  their  average  deviation 
of  1  per  cent,  is  increased  to  2  per  cent,  and  the  resultant  devia- 
tion will  only  be  increased  from  5.1  per  cent,  to  5.38  per  cent. 
Whether  the  average  deviation  in  measurement  of  a  single  trim 
should  be  1  per  cent,  or  2  per  cent,  depends  upon  the  relative 
number  of  samples  which  can  be  tested  in  each  case  with  the 
same  total  cost  in  labor,  materials  and  overhead  expenditure. 
If  it  costs  no  more  in  a  given  case  to  secure  an  average  deviation 
of  measurement  of  1  per  cent,  than  of  2  per  cent.,  then  the 
smaller  value  should  be  secured,  however  slight  its  effect  upon 
the  final  result  may  be.  Suppose,  however,  that  the  time  of 
testing  and  the  number  of  observations  can  be  cut  in  half  (i.  e., 
from  1 -hour  to  J^-hour)  with  an  increase  in  the  average  devia- 
tion of  measurement  from  1  per  cent,  to  2  per  cent.  Then  if 
two  J/2-hour  trims  can  be  tested  with  the  same  cost  as  i-hour 
trim,  the  average  deviation  for  the  latter  is  5.10  per  cent,  and  of 
the  former  is  5.38/1/2"  per  cent.  =  3.8  per  cent,  for  the  same 
unit  of  cost. 

The  significance  of  this  is  more  clearly  seen  by  the  statement 
that  26  1 -hour  trims  or  29  J/-hour  trims  will  be  required  to 
secure  an  average  deviation  of  1  per  cent,  for  the  final  result, 
which  means  a  saving  of  44  per  cent,  in  the  cost  of  testing  to 
secure  the  same  degree  of  accuracy  in  the  final  result. 


CHANKY    AND    CLARK:     ARC    LAMP    PHOTOMETRY  TJ 

The  criterion  for  maximum  efficiency  of  testing  in  all  cases  is 
that  the  ratio  of  the  resultant  average  deviation  for  a  single 
sample,  from  all  causes  whatsoever,  to  the  square  root  of  the 
number  of  samples  which  it  is  possible  to  test  with  any  given 
unit  of  cost,  shall  be  a  minimum. 

In  practise,  the  evaluation  of  the  various  independent  sources 
of  variation  is  somewhat  more  complicated  than  is  shown  by 
the  hypothetical  example  above  quoted  and  the  particular  details 
must  be  worked  out  for  the  special  conditions  of  each  laboratory. 

However,  it  serves  to  illustrate  the  principles  employed  in  this 
laboratory  in  determining  the  length  of  tests  upon  single  trims, 
the  number  of  photometric  reading's,  and  the  number  of  duplicate 
trims.  Enough  has  been  said  to  indicate  that  in  the  practical 
photometry  of  arc  lamps  something  in  addition  to  the  errors  of 
the  photometric  apparatus  must  be  considered,  and  that  it  is 
quite  possible  to  make  very  accurate  photometric  measure- 
ments and  yet  obtain  very  inaccurate  data  unless  due  regard  is 
had  for  the  relative  magnitude  of  the  errors  of  measurement 
and  the  variation  in  the  thing  measured. 

Acknowledgement  is  hereby  made  to  Mr.  R.  B.  Chillas,  Jr.,  for 
kindly  assisting  in  the  preparation  of  the  manuscript. 

DISCUSSION. 

Dr.  C.  H.  Sharp:  Since  the  authors  of  the  paper  have  been 
kind  enough  to  rake  out  of  oblivion  the  paper  which  Mr.  Millar 
and  I  prepared  on  this  subject,  I  think  I  may,  with  propriety,  be 
permitted  to  discuss  their  present  paper.  Our  paper  back  in  1908 
was  prepared  with  a  certain  end  in  view ;  it  was  to  put  before  the 
members  of  this  Society  what  at  that  time,  in  this  country,  was  a 
practically  unknown  photometric  device  which  we  believed  to  be 
of  very  great  value.  This  paper  says  that  it  was  unfortunate  that 
we  did  not  deal  more  fully  with  the  theoretical  aspects  of  the 
subject.  We  had.  however,  the  idea  that  the  value  of  our  paper 
to  the  members  of  this  Society  would  not  be  in  direct  ratio  to  the 
amount  of  mathematics  that  we  could  put  into  it,  consequently 
we  did  not  involve  our  discussion  in  any  nebulous  haze  of 
Teutonic  theory  (laughter)  ;  but  tried  to  get  down  to  the  engin- 
eering facts  of  the  case  as  we  knew  them.     Well,  a  good  deal  of 


28  TRANSACTIONS    I.    E.    S. — PART    I 

water  has  run  under  the  bridge  since  1908,  and  if  our  opinions 
in  all  respects  at  the  present  time  do  not  agree  with  what  we  held 
at  that  time,  I  am  willing  to  let  it  go  that  we  perhaps  have  prog- 
ressed and  know  more  now  than  we  did  then.  As  to  the  facts  and 
data  presented  at  that  time,  I  have  no  apologies  to  offer,  as  I 
know  they  were  correct  and  all  right  as  far  as  they  went.  I  think 
it  is  most  timely  and  fortunate  that  the  authors  have  taken  up 
more  fully  at  this  time  the  theoretical  consideration  of  the  in- 
tegrating sphere  and  of  the  errors  which  may  enter  into  its  use. 
Any  considerable  discussion  of  these  points  at  that  time  might 
perhaps  have  been  out  of  place.  At  the  present  time  such  a  dis- 
cussion is  needed  and  I  think  that  we  are  fortunate  to  have  so 
lucid  and  able  a  one  as  the  authors  have  presented  to-day. 

I  am  impressed  more  and  more  with  the  possibility  of  the  use 
and  misuse  of  the  integrating  sphere.  In  view  of  the  possibility 
of  misuse,  for  instance,  of  the  translucent  screen  as  shown  by  the 
authors  and  as  borne  out  to  some  extent  in  our  own  experience, 
I  have  been  for  some  time  inclined  to  the  view  that  on  the  whole 
the  opaque  screen  was  the  best  thing  to  use,  certainly  in  a  large 
sphere.  I  think  that  the  paper  shows  in  a  very  remarkable  way 
the  precision  with  which  the  sphere  will  integrate  the  total  flux  of 
light  from  almost  any  source  whatever  when  it  is  used  in  any 
ordinarily  reasonable  manner;  and  as  a  guide  to  the  proper  use 
of  the  sphere,  the  theory  presented  is  most  timely  and  valuable. 

Mr.  W.  F.  Little  :  A  number  of  experiments  have  been  made 
at  the  Electrical  Testing  Laboratories  to  determine  the  accuracy 
as  well  as  the  flexibility  of  the  integrating  sphere  with  translucent 
screens. 

TEST  NO.  1.— Translucent  Screen. 

Lamp  Extensive       Intensive  Focusing 

alone  reflector         reflector  reflector 

Position  in  sphere  per  cent.  per  cent.         per  cent.  per  cent. 

1  ft.   from   top 100.0  IOO  IOO  100 

2  ft.  from  top 100.0      100      100       — 

3  ft.  from  top 99.5       100       —      100 

Test  No.  1  referred  to  above  consisted  of  mean  spherical  can- 
dlepower  readings  of  a  tungsten  lamp,  alone  and  when  equipped 
with  intensive,  extensive  and  focusing  prismatic  reflectors 
mounted  in  various  positions  in  the  sphere. 


ARC    LAMP    PHOTOMETRY  29 

Test  No.  2. — A  porcelain  enamelled  parabolic  reflector  having 
an   asymmetrical    distribution    was    measured    in   two   positions, 
pointing  toward  the  screen  and  at  90  deg.  to  the  screen. 
TEST  NO  2.— Porcelain  Enamel  Double  Parabolic  Reflector. 

Translucent  Opaque 

per  cent.  per  cent. 

Toward  screen 103  90 

900  to  screen 100  100 

Test  No.  3. — A  bare  lamp  with  one  side  covered  with  black 
paper  oriented  in  several  positions. 

TEST  NO.  3.— Lamp  with  Black  Paper  on  one  Side. 

Translucent  Opaque 

per  cent.  per  cent. 

Toward  screen 100  104 

900  to  screen 100  100 

1800  to  screen —  100 

Even  under  the  above  abnormal  and  adverse  test  conditions, 
the  above  figures  show  comparatively  small  photometric  errors, 
and  the  results  are  somewhat  more  consistent  with  the  translucent 
screen.  However,  under  normal  working  conditions  it  is  known 
that  the  errors  introduced  by  either  screen  are  negligible. 

The  authors  of  this  paper  have  stated  that  the  only  absorption 
of  light  by  the  lamp  or  accessory  to  be  corrected  for  is  the  ab- 
sorption of  reflected  light;  no  direct  light  from  the  standard 
lamp  should  fall  upon  the  lamp  or  accessory.  First,  the  amount 
of  direct  light  from  the  standard  falling  on  the  lamp  or  accessory 
in  the  80-inch  sphere  as  used  at  the  Electrical  Testing  Labora- 
tories is  very  small  and  almost  negligible.  Second,  it  is  the  prac- 
tise at  the  Electrical  Testing  Laboratories  to  cover  the  lamp  hous- 
ing with  a  white  diffusing  substance  so  as  to  reduce  the  absorp- 
tion to  a  minimum,  or  so  to  mount  the  lamp  that  the  housing  and 
opaque  portions  are  outside  of  the  sphere;  therefore,  this  crit- 
icism can  be  easily  taken  care  of. 

The  Laboratories  also  find  a  small  40-inch  integrating  sphere  a 
very  valuable  and  convenient  adjunct  to  the  testing  of  arc  lamps. 
It  has  been  successfully  used  by  lowering  the  lamp  in  from  the 
top  and  placing  an  opaque  screen  horizontally  in  the  center  of  the 
sphere  with  a  mirror  set  at  45  deg.  to  the  vertical  placed  im- 
mediately beneath  it.  The  elbow  tube  of  a  portable  photometer 
is  placed  in  a  small  hole  in  the  side  of  the  sphere,  so  located  that 
3 


30  TRANSACTIONS   I.    E.    S. — PART    I 

the  photometer  tube  then  points  at  the  mirror,  which  reflects  the 
surface  of  the  sphere  immediately  beneath  the  screen,  thus  using 
the  surface  of  the  sphere  rather  than  the  translucent  test  plate 
for  its  comparison  surface.  A  small  comparison  lamp  is  placed 
on  top  of  the  screen  tip  upward.  This  is  used  to  measure  the  ab- 
sorption of  light  by  that  portion  of  the  arc  lamp  which  is  allowed 
to  remain  in  the  sphere  at  the  time  of  measurement.  Here  again 
the  amount  of  direct  light  falling  upon  the  arc  lamp  is  very  small, 
as  the  tip  candlepower  of  the  comparison  lamp  is  relatively  low. 
Also  the  opaque  screen  is  advantageously  located  for  the  arc 
lamp,  as  the  end-on  candlepower  of  the  arc  is  comparatively  low. 

The  integrating  sphere  has  been  used  very  advantageously  in 
the  measurement  of  light  loss  with  various  accessories  to  in- 
candescent lamps.  A  sufficient  number  of  tests  have  been  made 
by  the  "point  by  point  method"  on  several  photometers  and 
spheres  to  prove  the  accuracy  of  the  sphere  method  in  securing 
this  value.  Lamps  of  very  different  reduction  factors,  and  even 
metal  and  mirror  reflectors,  have  been  measured  with  very  close 
agreement  between  the  sphere  and  distribution  determinations. 
In  all  of  this  work  the  Laboratories  have  used  opaque  screens 
merely  because  they  are  more  convenient ;  however,  it  is  probable 
that  when  used  with  discretion  a  slightly  higher  degree  of  ac- 
curacy is  obtainable  with  translucent  screens. 

Mr.  S.  L.  E.  Rose  :  This  paper  is  of  a  great  deal  of  interest 
to  photometrists,  and  one  of  the  points  which  I  wish  to  emphasize 
in  the  paper  which  was  not  brought  out  in  the  reading,  is  the 
method  of  test;  that  is,  it  is  better  to  test  a  number  of  elec- 
trodes and  take  fewer  readings  on  each  one  than  to  take  a  lot 
of  readings  on  one  electrode,  if  you  want  an  average  of  what  that 
particular  light  source  will  do.  That  has  been  the  practise  at  the 
laboratory  which  I  represent,  for  some  time,  as  was  brought  out 
in  the  paper1  at  the  Chicago  Convention  of  the  I.  E.  S.  by  Mr. 
Stickney  and  myself. 

I  don't  see  any  mention  in  the  paper  of  what  was  used  for 
painting  the  inner  surface  of  this  sphere.  I  am  interested  in 
that  and  would  like  to  know  if  the  authors  made  any  investiga- 
tions as  to  the  best  paint  or  material  to  use  for  that  purpose? 

1  Stickney,  G.  H.,  and  Rose,  S.  L.  E.,  Photometry  of  Large  Light  Sources;  Trans. 
I.  E.  S.,  vol.  VI,  p.  641. 


ARC   LAMP   PHOTOMETRY  3 1 

While  it  is  a  little  out  of  the  range  of  this  paper,  it  will  prob- 
ably be  interesting  to  give  you  one  special  application  that  we 
made  of  our  sphere  at  the  laboratory  in  connection  with  some 
work  for  the  Panama-Pacific  International  Exposition.  It  was 
necessary  to  know  how  the  light  was  dispersed  from  the  jewels 
which  are  to  be  used  in  connection  with  the  illumination  of  the 
buildings  of  the  exposition;  a  number  of  different  makes  were 
submitted  with  different  cuttings  and  we  wanted  to  know  which 
was  the  best  for  the  purpose.  It  would  have  been  an  almost 
endless  job  to  have  found  out  the  number  of  reflections  which  the 
jewels  gave  back  from  the  front  faces  without  the  use  of  our 
sphere.  We  simply  took  one  half  of  the  sphere,  mounted  the  jewel 
at  the  center  on  the  axis  and  projected  a  beam  of  light  through 
the  photometric  window,  and  by  means  of  a  small  mirror  reflected 
it  on  to  the  jewel  normally  and  then  made  a  photograph  of  that 
half  of  the  sphere,  and  we  had  immediately  the  distribution  of 
reflected  spectra  from  that  jewel;  and  then  we  could  simply 
introduce  the  different  jewels  which  were  submitted  to  us,  take 
a  photograph  and  count  the  number  and  see  which  one  was 
giving  the  most  reflections  and  the  clearest  and  most  intense 
spectra.  By  means  of  radial  and  circular  lines  drawn  on  the 
photographic  print,  we  could  locate  them,  i.  e.,  we  had  longitude 
and  latitude  and  could  tell  exactly  where  they  were.  This  work 
was  very  convenient,  very  simple  and  done  in  the  minimum  of 
time.  Fig.  A  is  print  from  negative  of  a  good  jewel  and  Fig. 
B  is  print  from  negative  of  a  poor  one.  The  circular  lines  are 
drawn  at  intervals  of  10  deg. 

I  am  about  in  the  same  position  as  Mr.  Little ;  our  sphere  is 
not  in  constant  use,  in  this  way — it  might  be  used  for  a  week 
steadily  and  then  perhaps  stand  idle  a  week,  and  in  that  case  it 
gets  a  coat  of  dust  and  we  find  it  is  awfully  hard  to  brush  that 
dust  off.  We  use  white  alabastine  and  when  you  go  to  brush 
that,  it  will  mix  up  with  the  dust  and  the  best  way  out  is  simply 
to  paint  it  over.  If  we  are  using  it  right  along,  it  is  probably 
painted  every  week;  but  we  might  paint  it  and  use  it  three  or 
four  days  and  then  it  might  set  for  a  month.  I  might  say,  though, 
that  practically  it  is  painted  every  time  it  is  used.  I  don't  want 
you  to  understand  from  that  that  we  paint  it  every  day. 


32  TRANSACTIONS    I.    E-    S. — PART    I 

The  Chairman  :  Take  a  piece  of  new,  white,  fresh  blotting 
paper,  etc. 

Mr.  S.  L.  E.  Rose:  Well,  it  is  not  entirely  a  matter  of  dis- 
coloration, it  is  more  a  question  of  collection  of  dust  and  our 
sphere  happens  to  be  in  a  particularly  dusty  place,  and  for  that 
reason  we  have  to  paint  it  oftener  than  would  otherwise  be 
necessary.  We  use  white  blotting  paper  for  the  internal  screens. 
It  seems  to  me  there  is  a  chance  for  the  Committee  on  Nomen- 
clature to  define  the  different  branches  of  photometry.  We  hear 
of  precision  photometry;  this  morning  we  had  a  paper  which 
spoke  of  practical  photometry,  and  we  have  another  branch  that 
is  called  commercial  photometry,  and  the  degree  of  accuracy 
necessary  for  one  may  be  entirely  out  of  the  question  for  the 
others.  Mr.  E.  J.  Edwards  of  Cleveland  a  short  time  ago  in  an 
article  in  the  engineering  department  news  discussed  practical 
accuracy  and  wasteful  accuracy, — there's  the  two  kinds.  Prac- 
tical accuracy  is  all  we  are  after  in  commercial  photometry,  and 
the  degree  of  accuracy  necessary  for  precision  work  would  be 
wasteful  in  this  case. 

The  Chairman  :  Dr.  Middlekauff,  what  do  you  use  at  the 
Bureau  of  Standards? 

Dr.  G.  W.  Middlekauff:  White  alabastine.  However,  our 
experience  with  the  sphere  has  been  limited,  having  been  confined 
almost  entirely  to  the  acceptance  tests.  Although  a  test  of  the 
color  absorption  by  the  coating  then  in  the  sphere  was  made 
incidentally,  we  were,  at  the  time,  more  particularly  concerned  as 
to  the  accuracy  with  which  the  instrument  would  reproduce 
relative  values  as  found  by  other  methods  when  light  sources  of 
the  same  color  were  compared.  The  best  results  were  obtained 
with  an  opaque  screen  reduced  in  size  as  much  as  possible. 

The  Chairman  :     Would  that  vary  for  each  size  of  lamp? 

Dr.  G.  W.  Middlekauff:  For  our  carbon  standards,  which 
consist  of  several  groups,  each  group  having  a  different  type  of 
filament,  but  all  having  the  same  size  of  bulb,  accurate  relative 
values  were  obtained.  But  for  lamps  of  different  sizes  of  bulb, 
the  area  of  the  screen  remaining  the  same,  the  agreement  in  rela- 
tive values  with  other  methods  was  not  so  good. 


Fig.  A— Photograph  of  reflections  from  a  t:ood  jewel. 


Fig.  B.— Photograph  of  reflections  from  a  poor  jewel. 


ARC   LAMP   PHOTOMETRY  33 

The  Chairman  :     What  is  the  size  of  your  sphere? 

Dr.  G.  W.  MiddlEkauff  :  Thirty  inches  in  diameter.  This 
was  considered  large  enough  for  our  purpose  of  comparing  in- 
candescent lamps. 

In  the  color  absorption  test  referred  to,  we  used  two  carbon 
lamps  that  matched  in  color  at  about  no  volts.  When  one  of 
these  lamps  was  placed  inside  the  sphere,  from  which  the  translu- 
cent window  had  been  removed,  the  other  lamp  had  to  be  reduced 
about  10  per  cent,  in  voltage  to  bring  them  again  to  a  color  match. 
There  being  so  great  a  change  in  color  due  to  selective  absorption, 
it  would  not  be  surprising,  when  lights  differing  considerably  in 
color  (as  for  example  a  4-watt  carbon  and  a  ^4-watt  tungsten) 
are  compared  in  the  sphere,  if  we  should  find  their  relative  values 
quite  different  from  what  they  would  be  if  the  comparison  were 
made  outside  the  sphere  by  some  other  method. 

In  preparing  a  later  coating,  it  was  found  by  a  little  experi- 
menting that  a  very  small  quantity  of  Prussian  blue  mixed  with 
the  white  alabastine  before  applying  to  the  sphere  reduced 
selective  absorption  considerably.  With  this  coating,  it  is  believed 
the  sphere  will  give  quite  accurate  results  in  the  comparison  of 
differently   colored    lights. 

This  simple  color  test  is  mentioned  in  order  to  emphasize  the 
fact  that  if  the  sphere  is  to  be  of  value  in  accurate  standardiz- 
ing work  in  which  lamps  having  widely  different  colors  are  to 
be  compared,  the  character  of  the  coating  is  equal  in  importance 
to  the  proper  design  of  the  instrument. 

The  Chairman:     Mr.  Cady  do  you  have  a  sphere? 

Mr.  F.  E.  Cady  :  No,  we  have  no  sphere.  At  the  Bureau  of 
Standards,  when  the  sphere  first  appeared,  we  were  very  much 
interested  in  integrating  photometry,  but  we  were  in  possession 
of  a  Matthews  type  which  had  proved  very  satisfactory,  and 
consequently,  the  sphere  did  not  receive  the  attention  which  it 
would  otherwise  have  had.  The  engineering  department  of  the 
organization  I  am  connected  with,  however,  has  an  integrating 
sphere  of  the  30-inch  type,  I  believe.  What  little  experience  we 
have  had  in  attempting  to  determine  the  candlepower  per  incan- 
descent lamp  of  that  sphere  has  been  similar  to  that  of  Dr.  Mid- 


34  TRANSACTIONS   I.    E.    S. — PART    I 

dlekauff ;  that  is,  once  or  twice  we  have  attempted  to  determine 
spherical  candlepower  of  lamps  with  filament  windings,  different 
from  those  of  a  standard  whose  mean  spherical  candlepower  we 
knew,  and  the  results  seemed  to  have  some  discrepancy.  The 
lamps  were  afterwards  measured  on  a  universal  photometer  and 
the  mean  spherical  candlepower  calibrated,  and  we  found  differ- 
ences amounting  to  2  or  3  per  cent.  The  cause  for  those  discrep- 
ancies we  did  not  have  time  to  investigate,  but  I  should  like  to 
know  whether  the  authors  of  this  paper,  who  seem  to  have  con- 
fined their  work  more  to  arc  lamp  photometry,  have  done  much  in 
the  work  with  the  incandescent  lamp  and  whether  they  have  found 
that  with  suitably  designed  screens,  it  is  possible  to  take,  for 
instance,  an  ordinary  carbon  lamp  as  a  standard,  and  with  that 
determine  the  mean  spherical  candlepower  accurately  of  a  lamp 
having  a  distribution  such,  for  instance,  as  that  of  the  old  carbon 
downward  light  lamp,  or  in  the  modern  tungsten  lamp,  those 
which  have  filament  windings  of  the  spread  umbrella  type. 

Mr.  R.  B.  Chillas,  Jr.  :  There  are  a  few  points  which  may 
be  of  interest  in  connection  with  equations  2  and  4.  In  the  latter, 
it  is  seen  that  the  direct  light  is  equal  to  the  light  absorbed,  and 
so  disappears  as  heat  radiated  from  the  external  sphere  walls. 
Equation  2,  the  total  illumination  is  equal  to  the  direct  light 
divided  by  the  absorption  coefficient,  affords  a  means  for  ob- 
taining a  quantitative  value  of  light  wall  coverings.  The  follow- 
ing table  gives  the  ratio  of  total  illumination  to  that  obtained 
from  the  source  with  different  reflection  coefficients. 


Reflection 
coefficient 

total 

Ratio 
illumination 

P   =  0.80 

5-00 

0.60 

2.50 

0.50 

2.00 

O.4O 

1.66 

0.20 

1.25 

The  calculations  for  minimum  screened  area  were  based  on 
obtaining  a  trigonometric  expression  for  the  heights  (propor- 
tional to  the  areas)  of  the  two  shaded  zones,  substituting  in  this 
the  values  of  the  trigonometric  functions  expressed  in  terms  of 


ARC   LAMP   PHOTOMETRY  35 

sphere  radius,  and  fractions  of  sphere  radius,  differentiating, 
and  equating  the  first  derivative  to  zero. 

The  resulting  expression  is  quite  complicated  and  is  best  solved 
by  successive  approximations. 

Dr.  C.  H.  Sharp:  Regarding  the  interesting  suggestion  of 
using  a  screen  with  a  mirrored  surface  toward  the  lamp,  I  think 
the  trouble  is  that  it  is  pretty  hard  to  get  a  very  much  higher 
coefficient  of  reflection  from  a  mirrored  surface  than  it  is  from 
a  good,  white  diffusing  surface.  It  takes  a  pretty  good  piece  of 
mirror  glass  to  reflect  80  per  cent,  of  the  light  and  a  good  white 
diffusing  surface  will  do  as  well. 

Mr.  C.  W.  Jordan  :  In  the  practical  working  of  an  integrat- 
ing sphere  it  is  assumed  that  the  operator  has  carefully  tested  the 
apparatus  to  eliminate  any  systematic  errors.  For  example., 
errors  of  serious  magnitude  due  to  the  use  of  an  improperly 
placed  translucent  screen  can  easily  be  detected  by  photometering 
the  standard  lamp  placed  in  the  test  lamp  holder,  after  checking 
in  its  normal  position. 

In  my  opinion  the  general  practise  has  been  to  check  integrat- 
ing spheres  in  this  manner  and  the  photometric  readings  of  the 
standard  made  to  agree  when  in  either  position  by  proper  ad- 
justment of  the  position  or  translucency  of  the  screen. 

One  of  the  sources  of  error  when  using  the  sphere  has  been 
due  to  the  relatively  greater  collection  of  dust  in  the  lower  hem- 
isphere than  in  the  upper.  When  the  light  distribution  of  the 
lamp  being  tested  differs  materially  from  that  of  the  standard, 
this  error  may  become  serious.  Constant  repainting  becomes 
necessary  to  eliminate  this  error. 

I  wish  to  ask  what  type  of  photometer  was  used  in  making  the 
photometric  measurements  and  the  order  of  its  sensibility  com- 
pared with  the  sphere  errors  found. 

I  think  the  authors  are  to  be  congratulated  for  their  excellent 
work  of  individually  analyzing  the  sources  of  error  in  the  use  of 
a  sphere  and  for  the  recommendations  for  their  elimination. 

Dr.  N.  K.  Chancy  (In  reply):  In  replying  to  Dr.  Sharp's 
very  kind  comments  upon  the  paper  we  may  frankly  say  that 
Dr.  Sharp's  general  position  with  respect  to  the  intent  of  his 
earlier  paper  is  perfectly  sound  and  beyond  criticism.     We  still 


36  TRANSACTIONS    I.    K.    S. —  PART    I 

venture  to  believe,  however,  that  it  has  proved  somewhat  unfor- 
tunate for  the  development  of  the  use  of  the  sphere  in  this 
country,  that  Dr.  Sharp's  valuable  introductory  paper  was  not 
more  promptly  supplemented  by  further  theoretical  treatment, 
in  which  the  then  existing  "haze  of  Teutonic  theory"  would 
have  been  made  more  accessible,  and  perhaps  more  intelligible  to 
American  workers.  The  present  treatment  is  based  upon  a  more 
unified  physical  conception  of  the  sphere,  and  we  trust  will  prove 
less  "nebulous"  than  its  Teutonic  predecessors. 

Where  issue  was  taken  with  the  earlier  paper,  the  case  must 
rest  upon  the  merits  of  the  respective  arguments. 

Mr.  Little,  however,  has  presented  certain  tables  for  the  ap- 
parent purpose  of  showing  that  translucent  screens  are  as  good 
or  better  than  opaque  screens.  So  they  are,  if  particularly  ad- 
justed for  particular  cases.  The  point  made  in  the  paper  was 
that  this  particular  adjustment  was  not  only  difficult  in  practise, 
but  was  made  at  the  expense  of  general  integrating  power  for 
all-around  work.  That  Mr.  Little  is  not  seriously  impressed 
with  the  showing  made  by  his  own  figures  is  clear  from  his 
frank  admission  that  they  employ  opaque  screens  in  all  of  their 
work,  "merely  because  they  are  more  convenient."  The  reasons 
for  the  "inconvenience"  of  translucent  screens  are  thoroughly 
discussed  in  the  body  of  the  paper. 

The  "slightly  higher  degree  of  accuracy"  obtainable  by  trans- 
lucent screens,  is  we  believe  purely  mythical,  provided  the  same 
amount  of  "discretion"  is  used  with  opaque  screens  and  the 
proper  corrections  are  made.  Where  the  lamp  supports  are  small 
or  are  not  introduced  into  the  sphere  Mr.  Little  is  correct  in 
assuming  that  the  correction  for  direct  flux  from  the  standard 
lamp  falling  upon  the  lamp  supports  is  negligible.  Where  the 
whole  arc  lamp  is  introduced  into  the  sphere,  as  is  the  practise 
in  the  laboratories  of  the  National  Carbon  Co.,  the  correction 
for  direct  flux  absorbed  in  lamps  in  some  cases  may  amount  to 
as  high  as  8  per  cent,  of  the  reading.  In  our  experience  it  is 
simpler  to  make  this  correction  once  for  all  with  each  arc  lamp 
used,  and  then  take  all  regular  standard  lamp  readings  with  the 
sphere  entirely  empty,  to  correct  for  daily  changes  in  the  walls  of 
the  sphere. 


ARC    LAMP    PHOTOMETRY  37 

Dr.  Middlekauft'  and  Mr.  Cady,  both  raised  questions  concern- 
ing the  amount  of  discrepancy  likely  to  occur  between  different 
types  of  incandescent  lamps  with  various  filament  windings.  If 
the  size  of  sphere  and  screen,  and  the  approximate  distribution 
curves  of  the  lamps  are  known  this  error  could  be  figured  out 
directly  by  means  of  a  sphere  diagram  and  the  formulae  in  the 
paper. 

In  a  sphere  of  reasonable  dimensions  with  proper  screens,  the 
variations  from  this  cause  should  be  very  small — less  than  i 
per  cent.  If  the  sources  are  very  unsymmetrical  it  is  always 
important  to  direct  the  most  intense  parts  of  the  flux  upon  the 
central  unscreened  area  of  the  sphere,  if  the  lowest  limits  of 
error  are  to  be  obtained. 

In  reply  to  Mr.  Jordan's  questions,— a  Sharp-Millar  photom- 
eter was  employed.  With  our  standard  incandescent  lamps  upon 
a  line  voltage  hand-regulated  by  a  rheostat,  the  average  deviation 
of  the  mean  of  20  readings  is  slightly  less  than  0.25  per  cent. 
The  data  in  the  paper  was  the  average  of  two  or  more  independ- 
ent readers  in  all  cases. 

In  adjusting  screens  the  test  lamp  screen  should  be  set  up 
according  to  the  proper  formula,  and  then  the  standard  lamp 
screen  may  be  adjusted  by  reading  the  standard  lamp  in  both 
positions  as  Mr.  Jordan  suggests.  It  would  be  possible,  however, 
to  have  both  screens  wrong  and  yet  secure  identical  readings  with 
the  same  lamp.  The  real  test  is  the  agreement  in  the  two  posi- 
tions of  lamps  of  different  distribution. 

In  regard  to  painting  the  sphere,  attention  is  called  to  the 
foot  note  upon  the  sixteenth  page  of  the  paper. 

The  matter  of  precision  in  commercial  work, — obviously  that 
is  to  be  decided  by  the  needs  of  the  work  in  hand.  It  is  always 
proper  to  find  what  degree  of  precision  is  possible  upon  any 
instrument,  and  then  decide  how  much  of  that  precision  is  re- 
quired for  any  particular  purpose. 


3^  TRANSACTIONS   I.    E.    S. — PART    I 

NEW  DEVELOPMENTS  IN  THE  PROJECTION  OF 

LIGHT.* 


BY  E.   C.   PORTER. 


Synopsis:  This  paper  deals  with  the  theory  of  the  projection  of  light. 
It  shows  different  methods  of  concentrating  light  into  a  beam  and  men- 
tions the  different  factors  which  must  be  taken  into  consideration  in  the 
design  of  lenses,  reflectors  and  light  sources  for  light  projection.  The 
theory  is  followed  by  a  short  description  of  the  practical  application  of 
the  new  focus  type  tungsten  lamps  to  headlight  service,  signal  work,  navi- 
gation, stereopticon  lanterns  and  advertising  lighting. 


The  concentration  of  light  into  beams  for  projection  purposes 
has  been  a  field  of  experiment  for  many  years.  Probably  one  of 
the  best  known  early  applications  of  light  projected  to  a  dis- 
tance, and  one  which  to-day  is  playing  an  enormous  part  in  the 
struggle  for  supremacy  raging  in  Europe,  is  that  of  the  naval 
searchlight.  Here  the  light  generated  by  a  powerful  arc  lamp  has 
been  used  largely  for  defence,  i.  e.,  to  show  up  attacking  torpedo 
boats  before  they  can  get  within  striking  distance  and  discharge 
their  deadly  "whitehead." 

Another  old  and  familiar  application  is  in  stereopticon  work, 
largely  for  illustrating  lectures,  etc.  Headlight  service  is  another 
common  use,  the  light  being  projected  to  a  distance  for  a  double 
purpose :  ( i )  to  act  as  a  warning  of  the  approach  of  a  train  to 
trespassers,  yardmen,  etc.,  (2)  to  illuminate  obstructions  on  the 
right  of  way,  or  whistle  posts,  etc.  Until  recently  the  oil  lamp  was 
the  most  widely  used  equipment  for  this  class  of  service. 

That  these  applications  of  projected  light  were  rather  limited 
was  due  largely  to  two  reasons.  Powerful  searchlights,  such  as 
arc  and  calcium,  were  expensive,  complicated  and  required  ex- 
pert attention ;  while  the  oil  lamp  was  not  powerful  enough  for 
various  other  applications. 

When  the  incandescent  lamp  was  developed  it  was  realized  by 
Mr.  G.  H.  Stickney  that  here  was  a  possible  light  source  for 

*  A  paper  read  at  a  meeting  of  the  New  England  Section  of  the  Illuminating  Engi- 
neering Society,  November  10,  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


PORTER :  PROJECTION  OF  LIGHT 


39 


various  other  forms  of  projectors;  not  so  powerful,  simpler  and 
more  economical  than  the  arc,  and  yet  of  greater  capacity  than 
the  oil  light.  Under  Mr.  Stickney's  direction,  a  thorough  study 
of  this  field  is  being  carried  on  at  the  Edison  Lamp  Works  of 
the  General  Electric  Company. 

Before  taking  up  the  applications  of  incandescent  lamps  in 
particular,  to  projection  work,  I  will  review  briefly  some  of  the 
fundamental  principles  pertaining  thereto.  Assume,  for  ex- 
ample, that  each  ray  of  light  emanating  from  a  light  source  is 
of  ioo  candlepower  intensity.     If  one  of  these  ioo  candlepower 


r 

h 

C 

d 

z 

f 

* 

U" 

** 

f<> 

< 

i 

4 

/ 

/ 

t 

<?, 

£ 

f 

£ 

i 

Si 

X. 

r 

6 

c 

4 

r. 

f 

Fig-  i. —Diagram  showing  construction  of  the  parabola. 

rays  be  redirected  so  as  to  coincide  with  another,  the  result  is 
200  candlepower  in  the  latter  direction.  Similarly,  adding 
together  many  rays  from  a  low  candlepower  source,  produces  a 
beam  of  many  times  the  intensity  of  the  original  light. 

There  are  two  general  methods  of  accomplishing  this :  one  is 
by  refracting  the  light  rays  with  transparent  lenses;  the  other 
by  reflecting  the  rays  with  opaque  reflectors.  In  each  case,  to 
obtain  the  best  results,  the  light  must  all  originate  as  nearly  as 
possible  from  one  point.  The  smaller  this  point,  the  more  pow- 
erful will  be  the  beam  obtained.     All  light  rays  which  fall  on  a 


40  TRANSACTIONS   I.    E.    S. — PART    I 

convex  glass  lens  will  be  bent  or  refracted  as  they  enter  the 
glass.  They  will  be  turned  again  as  they  leave  the  lens,  those 
originating  at  the  principal  focus  finally  emerging  in  parallel 
rays.  Rays  of  light  originating  at  the  focus  of  a  parabolic  re- 
flector1 will  be  reflected  in  parallel  lines.  Thus,  either  apparatus 
produces  the  beam  of  the  so-called  "searchlight."  Fig.  2 
illustrates  this,  showing  the  cross  section  of  a  convex  lens  and  a 
parabolic  reflector,  indicating  the  paths  of  the  light  rays. 

As  already  mentioned,  the  smaller  the  dimensions  of  the  actual 
light  source,  the  more  powerful  and  narrower  will  be  the  beam 
obtained.  In  other  words,  the  greater  the  departure  of  the  light 
source  from  a  theoretical  point,  the  more  will  the  rays  be  scat- 
tered.   Consider,  for  example,  a  spherical  light  source,  having  its 


lens  ffe-f/ec/or 


Fig.  2.-  -Diagram  showing  projection  of  light  rays  from  a  point  source  by  a 
convex  lens  and  a  parabolic  reflector. 

center  at  the  focus  of  a  convex  lens,  Fig.  3.  A  light  ray  a  orig- 
inating at  the  focal  point  of  the  lens  will  be  turned  parallel  to  the 
axis;  a  ray  b,  originating  at  the  surface  of  the  sphere  will  be 
similarly  bent  in  passing  through  the  lens.  This  will  bring  it 
below  the  horizontal;  in  other  words  scatter  it.  The  further 
away  from  the  focus  the  light  originates,  the  greater  will  be  the 
divergence.     Thus,  it  becomes  evident  that  the  smaller  the  light 

1  A  parabolic  reflector  is  a  highly  polished  surface  so  formed  that  all  light  rays 
emanating  from  a  certain  point  called  its  focus,  will  be  reflected  in  parallel  lines.  Such 
a  surface  is  formed  by  rotating  a  parabola  aiound  a  horizontal  axis  through  its  focus, 
thus  forming  a  surface  of  revolution. 

A  parabola  is  the  path  of  a  point  moving  in  such  a  manner  as  to  be  always  equidistant 
from  a  fixed  point  (called  the  focus)  and  a  fixed  straight  line  (called  the  directrix)— see 
Fig.  1.  The  mathematical  formula  is  Y!  =  4px,  where  Y  =  half  of  diameter;  jjt  =  depth; 
p  =  focal  length  of  the  parabola.  To  construct  a  parabola,  take  a  piece  of  cross  section 
paper;  assume  a  directrix  YY;  assume  a  focal  length  gfand  let,  ag  =  gj.  To  find  where 
the  parabola  cuts  bb,  take  a  compass  and  using  ag  as  a  radius  and/as  the  centre,  strike 
an  arc  till  it  cuts  bb  at  the  pointy,  which  will  be  on  the  parabola.  Similarly,  using  a/as 
a  radius  and/as  a  centre,  another  point  h  on  the  parabola  may  be  obtained,  etc. 


PORTER  :  PROJECTION  OF  EIGHT 


41 


source,  the  more  nearly  parallel  will  be  the  rays ;  hence  the  more 
powerful  the  resultant  beam.  The  same  thing  holds  true  for 
parabolic  reflectors. 

It  is  not  practical  to  produce  an  absolute  point  source  of  light ; 
hence,    beams    from    even    the    most    highly    concentrated    light 


Fig.  3.— Diagram  showing  projection  of  light  rays  from  a  spherical 
source  by  a  convex  lens. 


I  •  £/y/rf  Jovrce 

f'foCt/3   Of  A* 

1-3-C-  £/£/>/■  Cones 
Fig.  4.— Illustrating  cones  of  light  from  spherical  light  source  in  parabolic  reflector. 

sources — such  as  the  crater  of  a  small  arc — will  have  a  spread,  de- 
pending in  amount  and  direction  upon  the  size  of  the  source  and 
the  focal  length  of  the  lens  or  reflector.  For  example:  assuming 
that  we  have  a  spherical  light  source,  the  projected  beam  will  be 


42 


TRANSACTIONS   I.   E.    S. — PART    I 


round  and  have  a  maximum  spread  limited  in  the  distance  by- 
two  rays  a  and  b  shown  (Fig.  4)  striking  the  center  of  the  re- 
flector and  tangent  to  the  sphere.  The  spread  from  all  other 
points  of  the  lens  or  reflector  will  be  decreasing  towards  its  edge. 
Each  point  of  the  reflector  will  receive  a  set  of  extreme  tangent 
rays;  hence  each  point  emits  a  little  cone  of  light.  The  sum  of 
all  these  cones  make  up  the  whole  beam,  which,  therefore, 
actually  consists,  up  to  a  certain  point,  of  converging  and  diverg- 


Fig.  5. — Diagram  illustrating  actual  beam  from  searchlight. 


Parcr6o//c    ffef/ecfor  farabo/tc  ftef/ecfor  of  /"focus 

of  /"  focus 

L  -  L/fftt    Source 
f'  foe  a/  fo/nt 

Fig.  6. —Diagram  showing  maximum  spread  of  beam  from  large  and  small  light  sources 
in  the  same  focal  length  parabolic  reflector. 

ing  rays,  which  at  some  distance  cross  and  all  become  diverging 
— as  shown  in  Fig.  5.  In  the  same  reflector  the  maximum  spread 
from  a  large  light  source  will,  therefore,  be  greater  than  from  a 
small  light  source,  each  being  located  at  the  focus,  Fig.  6.  If  the 
same  size  light  source  is  used  in  a  long  focus  lens  or  reflector,  the 
spread  will  be  less  than  in  one  of  short  focus  (Fig.  7).  The 
shape  of  the  resultant  beam  depends  upon  the  shape  of  the  light 
source.     For  example,  an  incandescent  lamp  having  its  filament 


porter:  projection  of  eight 


43 


in  the  form  of  a  helix  with  its  major  axis  greater  than  its 
diameter  would  throw  an.  elliptical  beam,  because  the  spread 
along  its  axis  would  be  greater  than  across  its  diameter. 

To  demonstrate  the  enormous  effect  of  the  size  of  the  light 
source  upon  the  intensity  of  the  resultant  beam,  I  had  five  lamps 
made,  all  of  the  same  candlepower  (32)  but  of  varying  filament 
concentrations  (Fig.  18).  Each  of  these  lamps  was  focused  in 
a  parabolic  reflector   11   inches   (27.9  cm.)   in  diameter  and  of 


Pam6o//c  flef/ecfi>r 
of  /"  focus 


/'aro6o//c  /fef/ectoy 
of S" focus 


/"•  foca/  Po/n+ 
/.  '  L  if  /it  Source 


Fig.  7. — Diagram  showing  maximum  spread  of  beam  from  same  light  source  in  short 
and  long  focus  parabolic  reflectors. 


5-in.  (12.7  cm.)  focal  length.    The  maximum  beam  candlepower 
measurements  were  as  follows  : 

Lamp  Beam  cp. 

32  candlepower  240  volt  carbon,  regular 268 

32  candlepower  240  volt  carbon,  stereopticon 555 

32  candlepower  120  volt  carbon,  stereopticon 1,400 

32  candlepower    40  volt,  tungsten  stereopticon    3i335 

(special  lamp) 
32  candlepower      6  volt,  tungsten  stereopticon    3,600 

(special  lamp) 

A  concentrated  light  source  out  of  focus  may  give  poorer  re- 
sults than  a  non-concentrated  light  source.  Consequently,  it  is 
of  extreme  importance  to  focus  the  light  source  exactly.  Practi- 
cally all  projectors  have  some  means  furnished  to  accomplish 
this.  To  illustrate  the  importance  of  accurate  focusing  I 
measured  the  maximum  candlepower  of  the  beam  of  a  head- 
light (consisting  of  a  16-in.  parabolic  reflector  of  3-in.  focus) 
equipped    with    a    6-volt,     36-watt    tungsten    headlight    lamp. 


44 


TRANSACTIONS    1.    K.    S. — PART    1 


This  lamp  has  a  filament  concentrated  into  a  cylinder  1.5  mm. 
in  diameter  by  3  mm.  long.  The  light  source  was  located  34  m- 
(25.  mm.)  back  of  the  focal  point  and  moved  forward  through 
it  to  a  point  34  in-  ahead,  in  1/16  in.  (6.2  mm.)  steps.  The 
resultant  maximum  foot-candle  intensities  100  ft.  from  the 
headlight  are  shown  in  Fig.  8.  Fig.  9  shows  the  maximum 
spread  from  reflectors  of  various  focal  lengths  with  different 
sized  light  sources.  If  the  light  source  is  moved  too  far  ahead 
or  back  of  the  focus,  a  dark  spot  occurs  in  the  center  of  the  beam. 
If  the  light  source  is  above  the  focus  the  beam  is  thrown  down; 
if  below,  the  beam  goes  up;  to  the  right  the  beam  is  thrown  to 


20 

1  \ 

1  \ 
1  \ 
1  \ 

1  \ 
\  \ 
1 

'  T 
1 
I 

v 

1  2 

1 
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1 

\ 
\ 

\c 

6 

k 

fe\ 

\E 

Ka 

% 

h 

\ 

4 

0 

$/if 

12  3  4  5 

Dl  STAMCL  OF  LIGHT  SOURCE.  FROM  FOCUS 
SIXTEENTHS  OF  AN  INCH 

Fig.  8. — Curve  showing  change  in  maximum  intensity  of  beam  from  an  incan- 
descent headlight  (consisting  of  i6-in.  silver-plated  parabolic  reflector  of3-in. 
focus  equipped  with  a  6-volt,  36-watt,  tungsten  headlight  lamp)  with  a  change 
in  the  position  of  the  light  source. 


the  left,  etc.  Fig.  10  shows  the  distribution  curves  of  the  above- 
mentioned  equipment  with  the  light  source  located  at  the  focus. 
34  in.  back  of  it  and  34  m-  to  the  side  of  it. 

It  has  been  shown  that  a  concentrated  light  source  can  be  made 
to  produce  a  powerful  beam,  either  with  a  lens  or  a  reflector.  In 
some  instances  lenses  are  in  use ;  in  others  reflectors.  Naturally, 
the  question  arises  as  to  why  lenses  are  used  in  one  case  and  re- 
flectors in  another ;   what  are  the  advantages  of  one  over  the 


porter:    projection  of  light 


45 


other,  etc.  In  general  it  may  be  said  that  lenses  or  accurately 
ground  glass  reflectors,  such  as  mangin  mirrors,  are  preferable 
where  stray  light  is  objectionable — such  as  for  stereopticon  lan- 
terns: and  where   extreme   accuracy  is   necessary — as   in   large 


Diameter  of  /./fftt  Joi/rce  /n  fixfe  enter     /nchej 


Fig.  9. — Curve  showing  spread  of  beam  from  parabolic  reflectors  of  various  focal 
lengths  equipped  with  various  sized  light  sources. 

searchlights.  Such  work  warrants  the  more  accurate  and  more 
expensive  ground  glass  lenses  and  mirrors.  On  the  other  hand, 
such  applications  as  headlights  do  not  require  very  accurate  dis- 
tribution of  light;  in  fact,  a  little  stray  light  in  the  immediate 

4 


46 


TRANSACTIONS   I.    It.    S. — PART    I 


20 

— 

"I 

-  FCC 

Ab 

2 

A=  LAMP?  AHEAD  0 
B--      "      AT  FOCUS 
C=      "   i"  BEHIND  F0 

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a. 

cus 

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g-~^ 

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9  II 

FEET 


Fig.  io. — Distribution  curves  across  beam  of  a  headlight  (equipped  with  a  i6-in. 
silver-plated  parabolic  reflector  of  3-in.  focus,  and  a  6-volt,  36-watt  single 
vertical  helix  tungsten  headlight  lamp)  with  lamp  in  different  positions. 


/.es?<s 


/fef/ec/or 


Fig.  11.— Diagram  showing  amount  of  light  flux  from  a  point  source  utilized  by 
a  convex  lens  and  a  parabolic  reflector  of  equal  diameters. 


Fig.  12.— Diagram  showing  amount  of  light  utilized  by  a  short  focus  and  a 
long  focus  parabola  of  equal  diameters. 


porter:    projection  of  light  47 

foreground  is  desirable.  Nor  does  this  class  of  work  warrant 
expensive  lenses.  For  this  service  metal  parabolic  reflectors  are 
excellent. 

The  parabolic  reflector  has  the  advantage  of  covering  and 
utilizing  a  greater  percentage  of  the  total  light  flux.  For  ex- 
ample, Fig.  ii  shows  a  reflector  and  a  lens  of  the  same  diameter. 
The  shaded  portion  illustrates  the  total  light  falling  on  and  being 
redirected  by  each,  showing  a  considerably  greater  percentage 
for  the  parabolic  reflector.  It  is  evident  from  the  figures  that  by 
placing  the  focus  deeper  in  the  parabola — or  in  other  words, 
using  a  reflector  of  shorter  focal  length — a  still  greater  per- 
centage of  the  total  light  flux  could  be  utilized. 

A  short  focus  parabola  is  a  deep  curve,  while  a  long  focus  one 
is  shallow.  Fig.  12  shows  two  parabolas  of  equal  diameter,  but 
different  focal  lengths,  A  being  short  and  B  long.  A  reflects  the 
greater  percentage  of  the  total  light  emitted  (Fig.  13).2 

On  the  other  hand,  a  short  focus  reflector  requires  a  lamp  of 
small  diameter,  while  the  long  focus  allows  a  larger  bulb — hence 
a  higher  candlepower  lamp — to  be  used.  Assuming  the  size  of 
a  light  source  to  remain  constant,  an  increase  in  its  candlepower 
will  produce  an  equal  increase  in  the  intensity  of  the  resultant 
beam. 

From  the  figures  shown  the  thought  occurs,  Why  not  combine 
a  parabolic  reflector  and  convex  (or  condensing)  lens,  and  thus 

-  This  curve  sheet  is  made  up  to  indicate  the  various  mechanical  properties  of  the 
parabola  and  can  be  best  illustrated  by  an  example:  a  reflector  for  a  headlight:  16  in.  in 
diameter.  3-in.  focus;  desired  first  to  find  the  total  depth  of  the  parabola  x.  This  is  done 
by  using  the  lower  left  hand  series  of  curves  and  drawing  a  horizontal  line  from  a  inter- 
secting the  16-in.  diameter  curve  at  b\  from  b  the  perpendicular  is  dropped  to  the  line  of 
abscissas.  It  is  then  found  that  the  depth  is  slightly  over  5^  in.  (13.3  cm.).  It  is  now 
desired  to  find  the  angle  alpha  which  is  one  half  of  the  total  angle  from  the  focal  point 
to  the  edge  of  the  parabola.  This  is  done  by  using  the  upper  right  hand  series  of  curves 
and  drawing  a  horizontal  line  from  d.  intersecting  the  16  in.  (40.6  cm.)  diameter  curve  at  e 
and  erecting  a  perpendicular  intersecting  the  top  line  of  abscissas  at/.  The  angle  alpha 
is  then  found  to  be  106^  deg.  In  estimating  the  efficiency  of  the  parabola,  it  is  very  desir 
able  to  know  how  much  of  the  total  light  flux  emitted  by  the  lamp  strikes  the  parabola. 
This  is  done  by  projecting  the  line  </"until  it  intersects  the  cosing  curve  running  diagonally 
across  the  sheet.  Upon  the  point  intersecting  g  a  horizontal  line  is  drawn  intersecting 
the  right  hand  line  of  the  ordinates  at  0.65.  This  means  that  65  per  cent  of  the  total  light 
is  useful.  Not  only  is  the  curve  sheet  useful  for  finding  the  particular  values  mentioned 
above,  but  it  will  also  serve  to  help  estimate  the  dimensions  of  the  parabola  to  perform 
various  functions. 

Provided  the  diameter  and  depth  of  the  parabola  can  be  readily  measured,  the  focal 
length  can  be  easily  obtained,  as  well  as  the  angle  alpha.  (By  courtesy  of  Mr.  K.  W. 
Mackall,  General  Electric  Company,  Schenectady.  New  York.) 


48 


■IKANSACTIONS    I.    E.    S. — PART    I 


direct  into  one  beam  ioo  per  cent,  of  the  light  flux  generated? 
This  could  not  be  done,  for  the  following  reason.  Light  coming 
from  the  focus  of  the  lens  would  be  refracted  in  parallel  rays; 
coming  from  some  other  point,  it  would  be  scattered.  Place  a 
lens  in  front  of  a  parabolic  reflector,  and  the  reflector  becomes 


ANGLE  CC 
120       100         80 


9         II         13        15  .     n 
DEPTH  OF  PARABOLA  IN  IMCHES 


Fig.  13 —Physical  properties  of  the  parabola. 


~R«f/ector         /.ens 

Fig.  14. -Diagram  showing  effect  of  combining  a  convex  lens  and  parabolic 
reflector  on  light  rays  from  a  point  source. 

the  light  source  for  the  lens,  giving  a  result  similar  to  that  shown 
in  Fig.  14.  This  has  been  done  where  a  double  beam  is  desired : 
one  narrow  and  powerful  to  reach  far  ahead,  the  other  wide  to 
pick  up  objects  to  one  side  in  the  foreground— such  as  whistle 
posts,  etc.,  in  railway  service.  Lenses  and  reflectors  are,  however, 
frequently  combined  in  this  manner:  A  convex  lens  is  backed 
by  a  mirror  in  the  form  of  a  sphere,  having  its  center  at  the  light 


porter:    projection  of  light  49 

source.  Such  a  spherical  mirror  will  re-direct  the  light,  throwing 
it  back  through  the  light  source;  thus  increasing  its  apparent 
intensity.  Where  incandescent  lamps  are  the  light  sources,  the 
spherical  mirror  has  an  additional  advantage.  By  throwing  an 
inverted  image  of  the  filament  back  on  the  filament  itself,  the 
apparent  light  source  becomes  more  nearly  solid,  resulting  in  a 
more  uniform  field. 

The  first  incandescent  lamps  to  be  commercially  applied  in 
considerable  use  to  this  work  were  the  old  carbon  stereopticon 
lamps  of  128,  200  and  260  watts  capacity.  These  lamps  had  a 
conical  shaped  spiral  filament  and  operated  at  an  efficiency  of  3.94 
watts  per  candle.  Similar  lamps  of  64  and  128  watts,  at  4  watts 
per  candle,  were  also  put  out  for  street  car  headlights.  The  fila- 
ment was  wound  in  a  conical  spiral,  in  order  to  concentrate  it 
as  much  as  possible  (Fig.  18). 


Fig.  15.— Focusing  headlight  lamp. 

With  the  introduction  of  the  drawn-wire  tungsten  filament 
lamp,  operating  at  a  much  higher  efficiency  than  the  carbon,  and 
obtainable  in  considerably  greater  capacities,  the  scope  of  the 
incandescent  projector  was  enormously  enlarged.  Not  only  were 
these  lamps  available  in  much  higher  wattages  than  carbon,  but 
the  filaments  could  be  concentrated  to  a  much  greater  degree. 
Operating  at  a  remarkable  advance  in  efficiency  over  the  carbon, 
further  increased  their  advantages  for  this  class  of  service.  The 
production  of  lamps  varying  from  very  low  to  very  high  candle- 
powers  offered  light  sources  for  almost  all  forms  of  projection 
apparatus. 

The  first  field  to  apply  these  lamps  was  that  of  automobile 


50  TRANSACTIONS   I.   E.    S. — PART    I 

headlights.  Six-volt  lamps  of  various  candlepowers  were  devel- 
oped. The  filaments  of  these  lamps  took  the  form  of  a  double 
helix,  i.  e.t  screw  shaped,  in  order  to  give  sufficient  spread  to  the 
beam  to  cover  the  road  (Fig.  15).  The  first  large  lamp  made 
was  a  100-watt,  no-volt  stereopticon  lamp.  The  filament  of  this 
lamp  was  wound  into  a  closely  coiled  helix  of  small  diameter  and 
this  helix  in  turn  rewound  in  such  a  manner  as  to  concentrate  all  of 
the  light  source  of  the  lamp  into  a  cylinder  8  mm.  long  by  8  mm. 
in  diameter.  This  lamp  is  made  in  a  round  bulb  2>Ya  in-  (9-52  cm-) 
in  diameter  (Fig.  16).  Lamps  of  this  type  are  commercially 
available  in  100,  250,  500  and  1,000  watts  capacity,  though  the 
latter  lamp  has  not  yet  been  standardized.     Experimental  lamps 


Fig.  16.— Focus  type  tungsten-filament  stereopticon  lamp  for  105-125  volt  service. 

have  been  made  of  considerably  higher  wattage,  and  at  a  very 
high  operating  efficiency. 

The  low-voltage  lamps  can  be  made  with  much  more  highly 
concentrated  filaments,  due  to  the  short  thick  wire  used  and, 
therefore,  require  less  wattage  to  produce  the  same  beam  intensity. 
The  filament  of  a  6-volt,  108-watt  headlight  lamp  occupies  a 
cylinder  2.5  mm.  in  diameter  by  5  mm.  long;  while  that  of  a 
100-watt,  uo-volt  stereopticon  lamp  is  8  x  8  mm. 

The  field  of  application  of  these  concentrated  filament  lamps 
is  very  large,  starting  with  the  low  voltage  lamps  of  which  an 
enormous  number  is  used  for  headlight  service  (headlights  for 
all  sorts  of  purposes,  particularly  automobiles,  motor  boats,  aero- 
planes, fire  fighting  apparatus,  etc.)  ;  and  as  portable  lamps  for 


porter:  projection  of  light 


5i 


small  searchlights,  small  spotlights,  theatres,  etc.  At  first  one 
thinks  of  a  6- volt  battery  lamp  as  of  rather  small  capacity,  yet 
several  thousand  6-volt  lamps  are  now  in  use  by  one  of  the  large 
railroads  for  headlights.  The  lamps  are  108  watts  capacity,  150 
candlepower,  and  have  a  highly  concentrated  filament.  In  a 
20-inch  (50.8  cm.)  silver  plated  parabolic  reflector,  this  type  of 
lamp  produces  a  beam  of  over  900,000  candlepower — sufficiently 
powerful  to  discern  objects  over  2,000  feet  away.1 


Fig.  17.— Tungsten-filament,  focus  type  headlight  lamps. 

Many  locomotives  are  already  equipped  with  30-volt  generator 
sets,  with  which  arc  headlights  were  previously  used.  Thirty-volt 
concentrated  filament  lamps  have  been  developed  of  100,  150  and 
250  watts  capacity,  to  enable  the  operation  of  incandescent  head- 
lights from  these  generators  (Fig.  17).  A  special  lamp  of  1,500 
candlepower  in  this  voltage  is  also  available,  to  meet  the  rather 
extreme  law  in  some  states,  requiring  locomotives  to  carry  head- 
lights of  1,500  unreflected  candlepower. 

3  Schrugham  J.  G.,  Electric  Headlights;  Journal  of  Elechicity,  Power  and  Gas, 
February  7,  1914,  p.  125;  Minick,  J.  X...  The  Locomotive  Headlight:  Trans.  I.  E.  S.,  vol. 
IX    Xo.  9. 


52  TRANSACTIONS    I.    K.    S. PART    I 

The  incandescent  head-lamp  has  many  advantages,  such  as 
ease  of  control,  steadiness  of  beam,  simplicity,  reliability,  etc., 
which  make  it  especially  applicable  to  this  class  of  service.  Vari- 
ous tests  have  shown  that  for  equal  beam  candlepowers  the  in- 
candescent headlight  will  pick  up  objects  at  considerably  greater 
distance  than  the  arc  headlight.  This  is  probably  due  both  to  the 
color  and  steadiness  of  the  light  from  the  incandescent  lamp. 

Another  large  field  of  application  for  the  low  volt  concentrated 
filament  lamp  is  in  signal  work.  The  railroads  are  experimenting 
with  the  so-called  "daylight  position  signal."  The  indications  of 
these  signals  are  given  by  three  rows  of  lenses  at  90,  45  and  o 
deg.  positions.  Each  lens  is  backed  by  a  low  candlepower 
concentrated  filament  lamp  and  either  the  o,  45  or  90  deg.  row 
is  lighted,  depending  upon  whether  the  signal  is  stop,  slow  or 
proceed.  It  is  claimed  that  even  under  the  trying  conditions  of 
looking  at  the  signal  toward  the  setting  sun  it  is  visible  from 
a  greater  distance  than  the  regular  semaphore  blades.  The  day- 
light position  signal  eliminates  moving  semaphore  blades  and  pre- 
vents possible  mistakes  through  color  blindness  of  engineers,  or 
color  changes  due  to  atmospheric  conditions.  If  the  trial  installa- 
tions prove  as  satisfactory  as  expected,  this  method  of  signaling 
should  be  widely  applied. 

Another  field  in  which  the  lamps  have  been  used  is  for  light- 
ships and  range  lamps  having  a  low  candlepower,  highly  con- 
centrated filament,  backed  by  a  silver  plated  parabolic  reflector. 
Lights  from  these  lamps  have  a  distinctive  color  and  sparkle  and 
are  visible  at  great  distances. 

Experiments  are  being  made  with  small  lamps  and  dry  bat- 
teries for  heliograph  signals.  Lamps  of  about  0.5  candlepower, 
2.7  volt,  backed  by  5-in.  (12.7  cm.)  mirrors,  operated  by  small  dry 
batteries  have  successfully  been  read  at  night  without  the  aid  of 
glasses  from  a  distance  of  12  miles  (19.3  km.). 

The  big  commercial  demand  for  focusing  filament  lamps,  how- 
ever, will  probably  be  in  the  105-125  volt  class.  Here  the  number 
of  applications  is  very  large.  I  will  simply  touch  on  some  of 
the  principal  ones.  Chief  of  these  at  present  is  stereopticon 
work.  An  incandescent  lamp  makes  a  stereopticon  lantern  safe, 
simple  and  clean,  so  that  it  can  be  operated  anywhere,  by  any- 


Fig.  iS  (Reading  from  left  to  right).— 1-32-cp.,  240-volt  regular  carbon  lamp;  2-32-cp.,  240- 
volt  carbon  stereopticon  lamp;  3— 32-cp.,  120-volt  carbon  stereopticon  lamp;  4-32-cp 
40-volt  tungsten-filament  stereopticon  lamp;   5-32-cp.,  6-volt  concentric  helix  tung- 
sten-filament lamp. 


Fig.  19.— Building  frout  illumination  with  one  500-watt  tungsten  stereopticon  lamp  in 
16-in.  parabolic  reflector  of  3-in.  focus. 


Fig.  20.— Morgan  memorial  library,  Hartford,  Conn.,  illuminated  by  four  500-watt  tutu 
sten  stereopticon  lamps  in  parabolic  reflectors  located  across  the  street. 


Fig.  21. — Billboard  lighted  by  one  500-watt  tungsten  stereopticon  lamp  in  a 
16-in.  parabolic  reflector  of  3-in.  focus  250  ft.  away. 


porter:    projection  of  light  53 

body.  A  lecturer  is  not  bothered  by  the  operator  forgetting  to 
regulate  the  feed  of  his  lantern,  or  by  the  humming  or  hissing 
noise  inherent  in  most  of  the  powerful  lanterns ;  in  fact,  numer- 
ous advantages  are  gained.  For  the  small  lantern,  sign  pro- 
jector, etc.,  the  100-watt  lamp  is  ample.  For  larger  lanterns, 
such  as  used  in  small  auditoriums  and  lecture  rooms,  the  250-watt 
is  preferable.  As  these  lamps  are  in  the  same  size  bulb,  they  are 
interchangeable.  The  500  and  1.000-watt  stereopticon  lamps 
have  been  developed  to  take  care  of  larger  lanterns.  The  lamps 
should  always  be  used  with  a  spherical  mirror,  thereby  increas- 
ing the  intensity  on  the  screen  at  least  30  per  cent,  and  also  ob- 
taining a  more  uniform  field.  The  500  and  1,000-watt  lamps  are 
also  satisfactory  for  small  moving  picture  machines. 

No  satisfactory  lamp  is  yet  available  for  the  large  commercial 
motion  picture  machine,  but  lamps  of  very  high  candlepower 
are  being  experimented  with,  and  it  is  hoped  these  used  with  the 
proper  mirrors  and  condensing  lenses  will  be  successful.  Their 
adaption  to  moving  picture  machines  would  largely  reduce  the 
fire  risk,  and  eliminate  synchronism  troubles  in  motion  picture 
theatres  supplied  with  alternating  current. 

For  playhouse  lighting,  focusing  filament  lamps  have  been 
successfully  used  as  floodlights  and  for  lighting  drops.  The  ease 
and  steadiness  with  which  they  can  be  dimmed  any  desired 
amount  enables  sunrise  and  sunset  effects  not  practical  with 
other  illuminants. 

A  field  which  is  just  opening  and  promises  to  be  large  is  that 
of  floodlighting  of  building  surfaces  and  painted  signs.  Many 
buildings,  beautiful  pieces  of  architecture,  cease  to  attract  with  the 
approach  of  darkness,  simply  because  they  cannot  be  seen.  Figs. 
18,  19,  20  and  21.  By  the  use  of  500- watt  tungsten  stereopticon 
lamps  and  parabolic  reflectors,  it  is  a  fairly  easy  matter  to  flood 
them  with  light  from  the  roofs  of  neighboring  buildings,  or  any 
convenient  location,  and  make  them  stand  out  in  all  their  beauty 
after  dark ;  causing  them  to  appear  even  more  conspicuous  than 
in  daylight,  by  contrast  with  the  surrounding  darkness.  Fre- 
quently signs  painted  on  water  tanks,  walls  of  buildings,  chim- 
neys, etc.,  or  regular  billboards,  are  so  located  as  not  to  be  easily 
accessible  to  current  supply  or  are  difficult  to  wire.     These  can 


54  TRANSACTIONS    I.    E.    S. PART    I 

be  effectively  lighted  at  night  by  projecting  light  onto  them  from 
distances  of  several  hundred  feet;  thus  greatly  lengthening  their 
advertising  value  at  a  low  cost.  At  night  they  become  more  at- 
tractive than  during  the  day,  and  can  be  read  from  considerable 
distance.  Advertising  banners,  flags,  etc.,  have  been  similarly 
lighted  to  advantage.  This  is  a  most  excellent  field  for  central 
stations.  The  load  is  steady,  the  hours  of  burning  are  long,  and 
the  installation  is  simple.  The  class  of  service  does  not  conflict 
with  the  regular  electric  sign.  Flood  lighting  is  generally  applied 
to  such  signs  as  are  visible  from  other  and  more  distant  portions 
of  a  city  than  the  electric  sign  on  the  main  business  street;  and 
on  account  of  its  low  installation  cost  and  easy  maintenance,  it 
can  often  be  installed  where  it  would  be  impossible  to  sell  a  reg- 
ular electric  sign. 


cassidy:    art  and  science  in  home  lighting  55 

ART  AND  SCIENCE  IN  HOME  LIGHTING.* 


BY  GEORGE   W.   CASSIDY. 


Synopsis:  Some  of  the  factors  and  conditions  which  influence  the 
design  of  lighting  systems  for  moderate  priced  suburban  or  country  homes 
are  discussed  in  the  following  paper.  The  author  suggests  methods  for 
lighting  various  rooms  of  homes  costing  from  $5,000  to  $15,000. 


The  proper  lighting  of  the  home  has  become  a  very  important 
subject  in  recent  years  from  two  standpoints,  namely,  the  esthetic 
and  the  scientific.  A  broad  and  comprehensive  knowledge  of 
both  these  phases  is  required  if  satisfactory  results  are  to  be 
obtained  in  practise. 

As  to  the  different  points  governing  good  lighting  of  the  home, 
almost  as  many  expert  opinions  have  been  expressed  as  there  are 
different  kinds  of  lighting,  each  statement  being  based  on  the 
individual  point  of  view  of  the  lighting  expert. 

The  illuminating  engineer  whose  training  has  been  essentially 
scientific,  although  he  may  have  the  artistic  temperament,  when 
it  is  necessary  to  compromise  between  what  is  scientific  and  what 
is  purely  esthetic  in  a  given  case,  is  almost  sure  to  tip  the  scales 
in  favor  of  the  scientific.  The  same  argument  applies  vice  versa 
to  the  architect  or  designer  whose  training  leads  him  to  give  the 
greater  weight  to  the  esthetic  side. 

I  doubt  whether  in  most  cases  the  best  results  can  be  obtained 
except  by  the  cooperation  of  the  architect  and  the  lighting  engi- 
neer. For  instance,  a  lighting  engineer  asked  me  to  cooperate 
with  him  in  designing  a  table  lamp  which  should  be  essentially 
beautiful  and  at  the  same  time  efficient  both  for  reading  and  as 
medium  for  general  illumination.  It  was  specified  that  the  lamp 
should  be  equipped  with  a  250-watt  distributing,  mirror  reflector 
for  the  indirect  light  and  four  direct  lamps  properly  shielded  by- 
diffusing  glass  for  reading ;  also  the  indirect  equipment  should  be 
outside  the  field  of  vision  of  a  tall  person  coming  into  the  room. 
Our  first  attempt  was  a  flat  failure  from  the  artistic  side,  as  the 
silk  shade  portion  had  to  be  made  on  the  graceful  curves  and  gen- 

*  A  paper  read  at  a  meeting  of   the  New  York  Section,    Illuminating  Engineer 
ing  Society,  December  10,  1914. 

™;Ji?C  I",imina]ing  Engineering  Society   is   not  responsible   for    the    statements  or 
opinions  advanced  by  contributors. 


56  TRANSACTIONS    I.    E.    S. — PART    I 

erous  proportions  of  a  barrel.  A  number  of  compromises  were 
then  made,  the  most  important  being  the  reduction  of  the  size 
of  the  lamps  from  250  watts  to  150  watts.  This  change  so 
reduced  the  dimensions  of  the  shade  that  a  well  designed  lamp 
was  possible  both  from  the  artistic  and  scientific  standpoints. 

To  illuminate  a  home  properly,  the  lighting  must  be  consid- 
ered from  the  esthetic,  physiological,  psychological  and  econom- 
ical standpoints.  From  that  old  saying,  "a  man's  house  is  his 
castle,"  one  knows  that  every  man  desires  to  have  his  home  as 
beautiful  as  his  means  will  afford  and  as  his  taste  dictates. 
Therefore  the  primary  requirements  is  that  the  lighting  should  be 
esthetically  correct ;  the  fixtures  should  be  designed  to  harmonize 
with  the  decoration  of  the  respective  rooms.  Most  homes  to-day 
have  lighting  fixtures  which  are  esthetically  correct. 

In  taking  up  the  second  consideration  one  is  confronted  with 
an  entirely  different  condition.  How  many  homes  even  approach 
being  correctly  lighted  from  the  physiological  standpoint?  The 
change  in  the  type  of  illuminants  in  the  last  few  years  has  placed 
a  much  greater  emphasis  on  the  physiological  side  of  the  ques- 
tion not  only  from  the  increase  in  intensity  of  the  light  but  also 
from  the  decided  change  in  color.  Instead  of  the  soft  yellow 
light  of  the  carbon  lamp,  one  must  now  contend  with  the  hard, 
cold  white  light  of  the  tungsten  lamp. 

This  point  was  particularly  forced  on  my  attention  while  I  was 
walking  through  some  of  the  prominent  streets  of  my  home  town 
when  I  saw  the  large  number  of  houses  which  were  lighted  with 
brilliant  and  glaring  tungsten  lamps.  If  these  lamps  were  not  of 
the  frosted,  ball  type,  they  were  shielded  by  some  form  of  frosted 
shade  which  is  a  good  medium  to  show  just  where  the  filament 
has  its  brightest  point. 

From  an  ocular  hygienic  standpoint,  it  is  very  easy  to  under- 
stand why  a  great  majority  of  the  people  of  to-day  are  com- 
pelled to  wear  glasses  and  why  there  is  so  much  suffering  from 
eyestrain. 

The  third  consideration,  the  psychological,  is  also  of  great 
importance  for  it  has  to  do  with  the  effect  light  has  on  the  mind. 
I  will  not  take  time  to  go  deeply  into  this  phase  of  the  subject. 
However,  there  is  no  question  that  certain  kinds  of  lighting  will. 


cassidy:    art  and  science  in  home  lighting  57 

as  the  saying  goes  "get  on  one's  nerves."  For  illustration,  the 
improper  use  of  semi-indirect  or  indirect  lighting  in  the  home. 
One's  first  impression  on  entering  a  room  lighted  by  either  of 
these  systems  is  the  lack  of  glare;  but  after  sitting  in  the  room 
for  a  while  one  often  wonders  why  the  ceiling  seems  so  low ;  or 
why  a  beautifully  carved  table  or  chair  does  not  seem  to  have 
the  proper  perspective,  for  the  slight  shadows  they  cast  are  from 
an  unnatural  angle ;  there  is  a  spectral  look  to  the  objects  in  the 
room.  In  other  words,  the  whole  room  looks  flat;  it  lacks  the 
correct  balance  of  light.  I  will  later  explain  this  effect  in  a 
specific  case. 

It  is  also  a  known  fact  that  color  is  an  important  factor  from 
the  psychological  standpoint  and  applies  particularly  to  white 
lights.  Just  how  the  nerves  or  mind  are  affected  is  a  question 
that  comes  within  the  province  of  the  psychologist.  Personally, 
I  know  of  a  number  of  cases  where  the  effect  of  white  lights, 
I  mean  white  light  of  the  ordinary  tungsten  lamp,  concealed  in 
ground  glass  shades,  has  caused  the  person  to  be  depressed  or 
have  the  blues. 

In  lighting  a  house  the  problem  should  be  taken  up  first  from 
the  practical  side  and  not  the  artistic  or  esthetic.  Often  the 
outlets  are  placed  without  regard  to  the  purpose  for  which  the 
room  is  to  be  used.  It  is  very  important  to  study  the  specifica- 
tions carefully,  to  learn  the  area  of  the  room,  the  height  of  the 
ceiling,  the  general  decorative  scheme  and  particularly  the  pur- 
pose for  which  the  room  is  to  be  used. 

Knowing  the  use  of  the  room,  one  can  readily  decide  upon  the 
foot-candle  intensity,  place  the  outlets,  and  determine  the  proper 
amount  of  wattage,  etc. 

I  have  tried  to  describe  in  a  general  way  the  most  important 
principles  which  should  be  borne  in  mind  when  a  problem  of 
home  lighting  is  being  considered.  For  a  more  comprehensive 
understanding  of  a  number  of  the  points  already  mentioned,  it 
will  be  better  to  mention  the  actual  conditions  encountered  by 
giving  a  particular  case:  the  proper  lighting  of  a  modern  sub- 
urban or  country  house  costing  from  $5,000  to  $15,000.  Such  a 
house  usually  has  an  entrance  hall,  living  room,  den  or  music 
room,  dining  room,  kitchen  and  pantry  on  the  first  floor  and 
sleeping  and  bath  rooms  above. 


58  TRANSACTIONS   I.    E.    S. — PART    I 

Entrance  Hall. — Frequently  this  room  is  given  little  or  no 
attention  as  far  as  correct  lighting  is  concerned — ''just  a  light," 
many  owners  seem  to  think,  is  sufficient.  And  yet  one's  first 
impressions  of  a  home  are  obtained  from  the  appearance  of  this 
room.  Very  often  the  first  thing  to  be  seen  is  the  typical  hall 
lantern  with  its  glaring  lamp.  I  do  not  think  I  exaggerate  when 
I  say  that  a  very  large  percentage  of  all  houses  to-day  have  halls 
lighted  in  this  manner. 

Suppose  the  following  specifications  for  this  hall :  dimensions 
1 6  ft.  long,  10  ft.  wide  and  9  ft.  6  in.  high,  with  colonial  treat- 
ment. The  stairway  is  situated  at  the  rear  end.  The  wood- 
work is  to  be  white  with  medium  colored  walls  and  light  buff 
ceiling. 

The  first  question  to  determine  is  the  approximate  intensity 
of  the  illumination  required.  There  should  be  an  intensity  of 
at  least  1  to  1.5  foot-candles.  Uniformity  here  is  not  at  all 
necessary ;  however,  there  should  be  no  dark  corners.  The 
amount  of  light  required  will  be  determined  by  the  color  of  walls 
and  ceiling,  and  the  absorption  of  the  glass  employed. 

Having  determined  the  light  intensity,  the  position  of  the  out- 
lets is  the  next  problem.  In  this  particular  case  there  should  be 
one  ceiling  and  two  bracket  or  side-wall  outlets.  The  ceiling 
outlet  should  be  in  the  middle  of  the  room  and  the  side  outlets 
arranged  to  balance  properly.  For  economical  reasons  the  ceil 
ing  outlet  should  be  wired  for  two  circuits ;  one  for  the  night  light 
and  the  other  for  general  illumination.  For  convenience  the 
lamps  should  be  controlled  from  the  second  floor  as  well  as  from 
the  first  floor. 

To  illuminate  this  room  and  stairway  efficiently  from  a  single 
ceiling  outlet,  it  would  be  necessary  to  increase  the  power  of  the 
illuminant  to  a  point  where  the  intrinsic  brightness  would  be  very 
annoying.  By  distributing  the  lighting  units  and  using  smaller 
illuminants  shielded  by  properly  designed  shades,  made  of  tinted 
diffusing  glass,  or  by  amber  colored  lamps,  the  glare  would  be  re- 
duced to  a  minimum.  With  this  foundation,  the  designer  or 
decorator,  can  readily  design  fixtures  which  will  harmonize  with 
the  period  or  decoration  of  the  room. 


cassidy:    art  and  science  in  home  lighting 


59 


When  little  thought  is  given  to  these  scientific  principles,  the 
fixture  designer's  efforts  may  often  be  spoiled  because  the  fix- 
tures lose  their  identity  in  their  environment  simply  because  of 
excessive  glare  from  the  lamps. 

Living  Room. — In  lighting  this  room,  there  are  several  very 
important  points  which  have  a  bearing  upon  the  success  of  the 
lighting  scheme.  The  first  and  most  important  point  is  this  :  here 
the  family  lives  and  in  the  evenings  they  must  live  with  the  light- 
ing provided.  In  a  great  many  cases  this  seems  to  require  an 
effort. 


Fig.  i. — Fixture  for  general  illumination  in  a  living  room. 

Suppose  the  following  specifications  are  those  of  a  typical 
living  room :  dimensions :  24  ft.  long,  18  ft.  wide  and  9  ft.  6  in. 
high;  wood  trim  of  flemish  oak;  walls  a  medium  brown,  and 
ceiling  light  buff. 

I  have  already  placed  emphasis  upon  the  fact  that  the  purpose 
for  which  the  room  is  to  be  used  is  very  important.  The  living 
room  is  used  for  several  purposes ;  therefore  the  lighting  scheme 
must  have  flexibility.     In  addition  to  being  the  library  of  the 


60  TRANSACTIONS    I.    E.    S. PART    I 

home,  it  is  often  used  for  festive  occasions.  There  are  other 
times  when  members  of  the  family  simply  desire  to  sit  around 
and  converse.  To  meet  these  conditions  it  is  necessary  to  supply 
at  least  three  different  lighting  arrangements.  In  placing  the 
outlets  the  decorative  arrangement  must  not  be  lost  sight  of,  even 
though  a  compromise  is  necessary.  In  order  to  keep  the  intrinsic 
brightness  reduced  to  a  minimum  there  should  be  two  ceiling 
outlets,  one  in  the  center  of  each  half  of  the  room.  This  arrange- 
ment will  give  a  more  even  distribution  of  light  and  a  decided 
reduction  of  glare. 

With  a  light  intensity  approximating  three  and  a  half  foot- 
candles,  a  high  general  illumination  is  assured  which  will  suffice 
for  card  playing,  dancing  and  special  occasions.  For  average 
conditions  a  one  and  a  half  foot-candle  intensity  will  be  enough. 
In  order  to  accomplish  this  in  the  best  way,  each  fixture  should 
be  wired  with  two  circuits,  the  higher  candlepower  lamps  on 
one  and  those  for  the  lower  intensity  on  the  other. 

Before  considering  the  type  of  lighting  fixture  to  be  suggested, 
it  will  be  well  to  briefly  define  the  three  forms  of  illumination  in 
common  use  at  the  present  time,  namely,  direct,  semi-direct  and 
indirect. 

A  direct  lighting  fixture  throws  most  of  its  light  directly  to 
the  floor  and  walls ;  only  a  small  percentage  of  the  light  reaches 
the  ceiling.  A  semi-indirect  fixture  reflects  the  greater  per- 
centage of  its  light  to  the  ceiling  from  which  it  is  diffusedly 
reflected  downward ;  a  smaller  percentage  of  the  light  passes 
through  a  glass  or  translucent  bowl.  An  indirect  fixture  reflects 
all  the  light  to  the  ceiling  from  which  it  is  diffusedly  reflected 
over  the  room. 

Consider  first  the  usual  semi-indirect  lighting  unit.  The  height 
of  the  ceiling  being  9  ft.  6  in.,  the  maximum  distance  of  the  top 
of  the  bowl  from  the  ceiling  cannot  exceed  2  ft.  4  in.  because  with 
a  bowl  6  in.  deep  the  fixture  would  hang  6  ft.  8  in.  from  the  floor. 
From  the  esthetic  viewpoint,  this  type  of  fixture  in  this  room 
would  be  bad  practise  because  the  distinctly  bright  spots  over 
the  fixtures  would  be  the  most  conspicuous  points  in  the  room. 
With  a  ceiling  11  or  12  ft.  high  a  semi-indirect  fixture  or  an 
indirect  fixture  with  a  luminous  bowl  can  be  hung  far  enough 


cassidy:   art  and  science  in  home  lighting  61 

below  to  give  a  wider  and  more  even  distribution  to  the  light  and 
thereby  overcome  the  objectionable  effects  of  light  spots.  This 
defect  could  also  be  softened  and  the  light  balance  restored  by 
the  use  of  one  or  more  table  lamps  or  by  incorporating  side 
brackets  in  the  decorative  scheme.  These  same  objections  would 
apply  to  the  indirect  unit. 

Esthetically,  the  use  of  the  indirect  fixture  in  the  home  is  in- 
correct unless  designed  with  a  luminous  bowl;  otherwise,  with 
the  opaque  bowl,  the  body  of  the  fixture  forms  a  very  sharp  con- 
trast with  the  lighted  ceiling. 

The  most  commonly  used  fixture  in  living  rooms  is  a  direct 
lighting  type  of  the  multiple  unit  or  shower  design.  The  glass 
manufacturers  have  put  on  the  market  a  great  variety  of  shades 
to  be  used  on  fixtures  of  this  type.  They  have  recognized  the 
fact  that  by  artistic  etching  and  tinting,  in  the  ivory  tones,  they 
have  been  able  to  produce  an  article  which  is  effective  and  at  the 
same  time  eliminates  an  appreciable  amount  of  the  glare,  and 
there  is  no  question  but  that  the  results  obtained  by  the  use  of 
this  glassware  is  a  step  forward.  These  shades  should  be  long 
enough  to  conceal  the  lamp.  Considerable  caution  must  be  exert 
cised  also  in  the  selection  of  illuminants.  If  the  conditions  are 
such  that  a  high  intensity  of  light  is  required  as  in  the  present 
case,  the  filament  of  the  lamp  will  be  visible  as  a  distinctly  bright 
spot  on  the  shade  owing  to  its  closeness  to  it. 

I  have  now  described  three  different  types  of  fixtures  and  ap- 
parently Avithout  arriving  at  a  satisfactory  result.  Therefore 
a  compromise  suggests  itself :  the  blending  of  the  desirable  fea- 
tures of  direct  and  semi-indirect  lighting.  By  designing  a  fixture 
of  the  glass  bowl  type,  equipped  with  an  opal  cover,  one  may 
obtain  a  unit  which  will  transmit  a  soft  diffused  light  to  the 
ceiling  without  spotting,  while  a  good  percentage  of  the  direct 
rays  will  pass  through  the  bowl.  By  reducing  the  ceiling  illum- 
ination and  utilizing  the  direct  rays,  the  effect  of  flatness  in  the 
room  may  be  avoided  and  the  natural  perspective  and  shadows 
of  objects  retained.  Care  must  be  taken  in  placing  the  lamp 
within  the  bowl  to  have  the  filaments  sufficiently  distant  from 
the  side  to  prevent  the  appearance  of  bright  spots  and  to  permit 
the  light  to  be  properly  diffused  through  the  glass.     Glass  afford- 


62  TRANSACTIONS    I.    E.    S. — PART    I 

ing  a  maximum  diffusion  and  the  minimum  of  absorption  should 
be  used.  This  type  of  fixture  will  overcome  many  of  the  defects 
which  are  objectionable  from  a  physiological  standpoint. 

Artistically  and  psychologically  it  is  still  defective,  in  that  the 
room  lacks  color  and  a  correct  balance  of  light.  By  this  latter 
term  I  mean  a  distribution  from  other  sources  in  the  room  such 
as  softly  lighted  lamps  on  side  brackets  or  portable  lamps  so  ar- 
ranged or  placed  as  to  bring  out  the  important  points  in  the 
scheme  of  decoration. 

Supplemental  lighting  is  of  course  more  or  less  extravagant 
and  where  economy  is  essential  it  can  be  omitted  with  possibly 
the  exception  of  the  table  lamp. 

I  have  mentioned  in  a  general  way,  the  desirability  of  the  use 
of  color  in  the  lighting  of  the  home.  It  is  regrettable  that  more 
emphasis  has  not  been  placed  on  this  part  of  the  problem  by 
those  interested  in  artistic  lighting  and  also  those  who  approach 
lighting  problems  from  the  engineering  side.  I  have  heard  and 
read  statements  made  by  lighting  experts  that  the  ideal  arti- 
ficial light  is  that  which  most  closely  resembled  natural  daylight 
in  color  and  diffusion.  I  consider  this  statement  entirely  too 
broad  and  in  need  of  qualification.  Daylight  is  the  ideal  light 
medium  in  all  manufacturing  pursuits,  office  work,  draughting, 
color  matching  and  many  other  commercial  enterprises.  I  may 
be  making  a  rather  radical  statement  when  I  say  that  daylight 
as  it  comes  from  the  heavens  is  not  the  ideal  light  for  lighting 
the  home.  The  really  artistic  home  should  be  esthetically  lighted 
under  daylight  conditions  as  well  as  under  artificial  light. 

The  interior  decorator  studies  his  problem  from  many  angles, 
two  of  the  principal  ones  being  light  and  color;  and  if  daylight 
is  the  ideal  light,  why  does  he  use  so  much  color  in  the  window 
hangings,  portieres,  etc.,  and  at  times  even  shut  it  out  entirely? 
It  is  to  improve  upon  daylight,  to  obtain  color  and  pleasant  light- 
ing effects  and  shadows. 

Therefore,  if  daylight  lacks  color,  and  artistic  warmth,  why 
should  one  strive  to  imitate  it  for  the  home.  The  present  il- 
luminants  have  already  reached  beyond  the  limit  of  good  light 
for  home  use  and  need  modification  for  the  best  results. 

There  are  available  several  materials   suitable  for  producing 


cassidy:    art  and  science  in  home  lighting  63 

color  effects  in  decorative  lighting  such  as  silk,  gelatine  and  glass. 
I  have  been  informed  that  one  of  the  large  lamp  manufacturers 
has  already  perfected  a  method  by  which  regular  sized  lamps 
can  be  made  of  amber  colored  glass  and  put  on  the  market  as 
standard  lamps. 

I  have  said  that  the  fixture  I  have  described  as  the  most  suit- 
able for  the  requirements  of  the  living  room  lacked  color. 
Ophthalmologists  and  oculists  have  agreed  that  amber  light  is 
preferable  to  other  colors.  By  tinting  the  glass  bowl  a  yellow 
tone,  and  by  the  use  of  light  amber  glass  lamps  or  color  caps  on 
incandescent  lamps  giving  white  light,  it  is  possible  to  produce 
the  soft  warm  and  hospitable  effect  so  necessary  to  bring  out  the 
real  fineness  of  the  decorative  scheme  of  the  room. 

The  practical  engineer  will  in  all  probability  say  that  such  a 
scheme  sacrifices  economy.  This  is  true,  but  economy  is  of  sec- 
ondary importance  when  compared  with  the  artistic  results  and 
ocular  comfort.  Ocular  hygiene  may  well  be  a  primary  factor  in 
the  lighting  of  living  rooms.  It  is  unfortunate  that  there  are  so 
few  table  lamps  on  the  market  to-day  which  combine  the  scien- 
tific and  the  esthetic  requirements.  Many  of  these  lamps  are 
artistic ;  some  few  scientific ;  but  a  combination  of  the  two  is  al- 
most wanting. 

In  order  to  demonstrate  more  clearly  the  important  points 
necessary  to  be  borne  in  mind  when  designing  an  efficient  table 
lamp,  I  will  exhibit  a  lamp  (Fig.  2)  which  I  believe  meets  the  re- 
quirements of  a  living  room.  It  possesses  the  three  essential  fea- 
tures of  good  lighting :  first,  it  is  artistic ;  second,  it  is  efficient  as 
a  reading  lamp;  and,  third,  it  has  flexibility.  By  turning  one 
switch,  one  may  connect  indirect  light  which  evenly  illuminates 
the  whole  ceiling  with  a  soft  amber  glow.  By  the  turn  of  a 
second  switch,  two  more  lamps  illuminate  the  silk  shade  which 
diffuses  a  soft  light  over  a  large  area  of  the  floor.  This  is  neces- 
sary to  give  the  correct  balance  of  light  in  the  room.  Under  day- 
light conditions  most  of  the  light  coming  through  the  windows  is 
distributed  on  the  floor  and  there  is  a  balance  between  the  bright- 
ness of  the  ceiling  with  that  of  the  floor.  This  is  the  natural  con- 
dition of  light  direction  which  mankind  has  been  accustomed  to 
for  generations.     With  a  third  switch  the  two  remaining  lamps 


64 


TRANSACTIONS    I.    E.    S. PART    I 


which  are  utilized  for  reading  purposes  may  be  lighted.  These 
switches  also  conduce  to  economy  in  the  use  of  the  lamp.  In 
selecting  the  mirror  reflector  for  the  indirect  light  equipment,  I 
have  taken  the  concentrating  in  preference  to  the  distributing 
type,  because  the  amber  colored  disk  will  distribute  to  a  certain 
extent.  Care  must  be  taken  to  prevent  the  light  distribution 
from  going  beyond  the  stop  line.  In  most  rooms  this  would  be 
at  the  picture  moulding ;  and,  where  this  is  omitted,  the  proper  line 
would  be  at  the  junction  of  the  wall  and  ceiling.  In  the  arrange- 
ment of  the  direct  lamps  the  filaments  are  so  placed  that  the 


Color  -  correcting 
Firfer 

Reflector 


Diffusing  bovwf 


Fig.  2.— A  table  lamp  for  a  den  or  for  local  lighting  in  a  living  room. 

highest  point  will  form  the  apex  of  a  right  angle  with  a  line 
drawn  from  the  maximum  reading  distance  which  is  approxi- 
mately 3  ft. 

The  diffusing  shade  which  is  made  of  alabaster  acided  glass  is 
so  designed  that  its  general  curvature  is  somewhat  parallel  with 
the  filament  of  the  lamp.  This  is  necessary  to  assure  the  great- 
est efficiency  of  the  diffusion  as  no  reading  lamp  is  efficient  with- 
out such  diffusion. 

If  the  light  rays  are  not  diffused  either  by  the  interposition 
of  the  proper  kind   of  glass   or  by   indirect   reflection   from   a 


cassidy:    art  and  science  in  home  lighting  65 

light  colored  non-glazed  or  mat  surface,  specular  reflection  from 
the  book  or  paper  which  one  may  be  reading  is  bound  to  cause 
eyestrain. 

Den  or  Music  Room.— Suppose  the  specifications  of  a  room 
are  14  ft.  long,  12  ft.  wide  and  9  ft.  6  in.  high;  medium  dark 
walls  and  light  buff  ceiling.  A  room  of  this  type  can  be  correctly 
lighted  by  a  table  lamp  similar  to  the  one  described  in  the  lighting 
of  the  living  room.  Fixtures  or  bracket  lamps  are  not  required 
but  the  use  of  wall  lamps  may  enhance  the  decorative  treatment. 
If  used  they  should  be  equipped  with  lamps  of  very  low  candle- 
power,  not  over  10  watts;  and  in  selecting  the  light  shields, 
whether  of  glass,  silk  or  other  fabrics,  a  low  translucency  is  es- 
sential. If  the  room  is  used  as  a  music  room,  it  is  only  necessary 
to  increase  the  size  of  the  illuminant  of  the  indirect  portion  of 
the  lamp  to  obtain  the  proper  amount  of  illumination.  If  for 
economical  reasons  this  is  not  practical,  the  lighting  scheme  must 
be  supplemented  by  a  properly  designed  local  light  at  the  piano. 

Dining  Room.— I  approach  the  problem  of  what  constitutes 
correct  lighting  of  the  dining  room  with  considerable  reluctance. 
I  presume  that  of  all  the  rooms  in  the  house  the  dining  room  is 
lighted  by  the  most  diversified  methods.  There  is  no  question 
about  the  flexibility  of  the  lighting  arrangements  in  this  room. 

Specifications:  dimensions,  18  ft.  long,  15  ft.  wide  and  9  ft. 
6  in.  high.  Ivory  colored  woodwork,  medium  straw  colored 
walls,  and  light  buff  ceiling.  Architecturally,  such  a  room  may 
be  called  colonial.  I  have  mentioned  the  color  scheme  to  demon- 
strate the  direct  relation  between  the  lighter  or  darker  colored 
walls  and  ceiling  and  the  light  intensity.  Dark  toned  rooms 
absorb  more  light  and  therefore  require  a  higher  candlepower  in 
the  illuminant. 

The  placing  of  the  outlets  depends  upon  the  system  of  light- 
ing to  be  installed. 

Decorators  and  architects  have  used  with  success,  from  the 
artistic  as  well  as  the  good  lighting  standpoint,  side  brackets 
around  the  room,  the  light  source  being  properly  shielded  and 
supplemented  by  a  candelabra  on  the  table.  A  room  of  the 
dimensions  given  would  require  at  least  six  two-lamp  side 
brackets  having  low  candlepower  lamps  of  not  over   10  watts 


66 


TRANSACTION?    I.    E.    S. — PART    I 


each.  This  would  give  a  fair  general  illumination  without  annoy- 
ing glare,  but  it  would  be  necessary  to  have  them  all  lighted  or 
there  would  be  dark  corners  or  spots  upsetting  the  esthetic  effect 
and  also  spoiling  the  correct  lighting  scheme.  This  arrangement 
would  not  be  economical  in  the  moderate  priced  residence  here 
considered. 

Another  method  of  lighting  a  dining  room  which  has  been  very 
extensively  used  is  the  so-called  glass  dome  fixture.     This  is  a 


Fig.  3.— A  fixture  for  a  dining  room. 


fixture  designed  with  a  large  glass  dome  suspended  by  a  chain 
or  stem  over  the  table.  From  the  decorator's  point  of  view  it  is 
particularly  bad.  It  breaks  into  the  symmetry  of  the  room  and 
lacks  proportion  to  its  surroundings.  It  is  the  most  conspicuous 
object;  it  occupies  a  position  which  compels  it  to  dwarf  every- 
thing around  it ;  it  also  prevents  the  artistic  arrangement  of 
floral  decorations.     From  the  physiological  side  the  dome  light- 


CASSIDV  :     ART    AND    SCIENCE    IN    HOME    LIGHTING  67 

ing  fixture  is  far  from  desirable.  The  table  cloth  is  so  brightly 
lighted  that  there  is  a  decided  glare.  A  very  simple  experiment 
will  demonstrate  this  point.  If  the  cloth  is  suddenly  removed 
from  the  table,  the  effect  will  be  as  if  some  of  the  lamps  had  been 
extinguished,  for  the  room  will  seem  almost  dark.  The  table  cloth 
has  acted  as  a  diffusing  medium  for  the  direct  light  under  the 
dome.  If  doilies  are  used  instead  of  the  cloth,  one  is  likely  to 
be  troubled  with  specular  reflection  from  the  polished  surface  of 
the  table.  It  is  possible  to  reduce  the  extreme  brightness  upon 
the  table  by  the  use  of  some  diffusing  medium  such  as  a  silk  disk, 
but  even  with  this  precaution,  the  glare  is  not  entirely  eliminated 
because  the  source  of  illumination  is  so  near  the  surface  of  the 
table. 

Another  objection  to  the  use  of  the  dome  fixture  is  the  fact 
that  those  seated  at  the  table  are  constantly  looking  from  a  light 
to  a  dark  zone  and  vice  versa.  Each  change  of  the  direction  of 
the  gaze  under  such  condition  causes  continual  dilation  and  con- 
traction of  the  pupil  with  its  consequent  visual  fatigue.  This 
defect  can  be  overcome  of  course  by  the  use  of  side  brackets  or 
ceiling  fixtures,  but  the  addition  would  not  be  economical. 

As  the  specifications  of  this  dining  room  do  not  call  for  a 
beamed  ceiling,  one  might  place  the  outlet  in  the  center  of  room 
and  install  a  semi-indirect  or  indirect  fixture  to  suit  the  con- 
ditions. 

As  the  ceiling  is  9  ft.  6  in.  high,  and  because  the  light  source 
is  placed  over  the  table,  it  is  possible  to  hang  the  fixture  only 
5  ft.  6  in.  from  the  floor.  This  would  leave  sufficient  distance 
between  the  ceiling  and  the  top  of  the  bowl  to  permit  of  a  wide 
distribution  of  the  light  and  eliminate  light  spots  on  the  ceiling. 
1  his  overcomes  the  artistic  defects  apparent  under  the  other  con- 
ditions. By  the  use  of  an  amber  colored  disk  over  the  bowl  of 
the  fixture,  the  white  light  from  the  tungsten  lamp  may  be 
changed  to  soft  warm  tones,  which  will  improve  the  beauty  of 
the  artistic  scheme  of  the  room.  To  eliminate  whatever  flat 
effect  of  diffused  lighting  may  exist,  it  is  only  necessary  to  add 
outside  direct  light  units  arranged  around  the  glass  bowl  of  the 
semi-indirect  fixture  or  the  opaque  bowl  of  the  indirect  fixture 
according  to  the  taste  of  the  designer.    This  addition  will  correct 


68  TRANSACTIONS   I.    E.    S. — PART    I 

the  light  balance  by  giving  to  the  surroundings  light  and  shadow. 
In  providing  against  the  physiological  defects  of  such  a  fixture, 
thought  must  be  given  to  the  design  and  color  of  the  glassware 
or  silk.  The  glass  should  be  properly  tinted  with  a  yellow  tone 
and  if  silk  is  used  amber  and  champagne  colors  are  preferable. 
Care  must  be  exercised  in  lamping  the  fixture.  The  outside  direct 
lamp  units  must  not  exceed  10  watts  while  the  inside  lamps  must 
be  larger  but  not  to  exceed  60  watts. 

By  this  arrangement  the  center  lamp  will  give  the  necessary 
general  illumination  and  the  outside  lamps  the  supplementary. 
For  the  sake  of  economy  it  is  a  good  plan  to  have  the  wiring  for 
two  circuits. 

In  clearing  or  setting  the  table  it  is  not  essential  that  all  the 
lamps  be  lighted.  In  the  design  of  the  silk  shade  of  the  lamp 
which  I  have  shown,  considerable  compromise  has  been  made. 
In  the  purely  technical  design,  the  line  representing  the  side  of 
the  shade  should  form  a  somewhat  wider  angle  so  that  the  side 
of  the  shade  would  be  parallel  to  the  line  of  vision  of  the  average 
height  person  sitting  at  the  table,  to  avoid  the  possibility  of  any 
glare.  The  flange  at  the  bottom  leaving  a  4  in.  opening  pre- 
vents a  person  seated  at  the  table  from  seeing  the  lamps  and  the 
glare  from  the  reflecting  surface. 

The  lamps  within  the  silk  shades  are  equipped  with  amber 
colored  disks  and  as  a  result  a  beautiful  soft  warm  light  is  cast 
evenly  over  the  table.  The  opaque  bowl  contains  the  indirect 
lighting  equipment  over  which  is  placed  an  amber  plate.  This 
type  of  fixture  combines  general  illumination  with  the  local  light- 
ing over  the  table  and  at  the  same  time  adheres  to  the  important 
principles  of  good  lighting. 

Where  service  lighting  is  required,  such  as  in  kitchen,  pantry 
and  etc.,  fixtures  placed  as  closely  as  possible  to  the  ceiling,  and 
therefore  above  the  line  of  vision,  are  recommended.  The  shades, 
preferably  opal  glass  frosted  on  the  inside  and  of  the  distributing 
type,  should  be  about  7  or  8  in.  in  diameter  and  with  depth  enough 
to  hide  the  lamp. 

In  some  instances  a  side  wall  lamp  is  required ;  in  that  case 
the  bracket  should  be  equipped  with  a  rather  dense  opal  glass, 
deep  enough  to  cover  the  whole  lamp,  the  lamp,  of  course,  being 
placed  up  or  down  according  to  the  position  of  the  outlet. 


cassidy:    art  and  science  in   home  LIGHTING  6Y) 

Regarding  the  proper  lighting  of  a  bed  room,  efficiency  and 
economy  are  the  essential  features  to  be  considered.  By  placing 
one  outlet  in  the  center  of  the  room  and  one  over  the  dresser, 
it  is  possible  to  obtain  good  results.  A  fixture  placed  close  to 
the  ceiling,  having  a  lamp  housed  in  an  artistically  etched  and 
yellow  tinted  distributing  type  of  shade,  from  7  to  8  in.  in  diam- 
eter with  sufficient  depth  to  cover  the  lamp,  is  often  quite  satis- 
factory. The  interior  of  the  shade  should  have  a  roughed  or 
mat  surface  in  order  to  diffuse  the  light  properly.  As  the  fixture 
is  placed  well  above  the  line  of  vision  and  the  distance  between 
the  filament  of  the  lamp  and  glass  will  be  sufficient  to  eliminate 
spot  glare  from  the  filament,  good  general  illumination  without 
glare  and  at  the  lowest  cost  will  be  obtained.  The  fixture  can 
be  artistically  designed  and  installed  at  a  very  small  cost.  The 
dresser  light  should  be  suspended  over  the  middle  of  the  mirror 
and  10  to  12  in.  in  front.  Five  feet  ten  inches  from  the  floor  is 
the  average  height  for  a  fixture  of  this  type.  This,  however,  is 
more  or  less  optional  according  to  the  conditions.  In  the  main,  the 
specifications  of  the  ceiling  fixture  will  apply  in  this  case,  with 
the  exception  that  the  shade,  if  made  of  glass,  must  be  so  tinted 
as  to  prevent  glare.  This  is  very  important  as  the  shade  is 
directly  within  the  line  of  vision.  A  silk  shade  is  preferable  to 
a  glass  one  for  this  reason,  as  well  as  for  the  better  artistic  effect. 
As  the  light  is  directly  from  above,  a  woman  will  have  no  diffi- 
culty in  arranging  her  hair  according  to  the  latest  vogue.  The 
light  being  well  diffused  within  a  considerable  range,  there  should 
be  no  difficulty  in  seeing  well. 

There  are  one  or  two  points  in  regard  to  bathroom  lighting, 
especially  interesting  to  the  man  of  the  house,  which  it  is  well  to 
mention.  Most  bathrooms  in  moderate  priced  houses  have  medi- 
cine closets  with  mirror  doors.  The  men  members  of  the  family 
use  this  mirror  when  shaving.  A  large  number  of  people  do  not 
know  that  in  order  to  see  well  before  a  mirror  by  artificial  light 
the  mirror  should  be  in  shadow,  so  that  the  face  will  receive  the 
greater  flux  of  light.  By  having  a  bracket  outlet  placed  on  each 
side  of  the  medicine  closet  and  approximately  5  ft.  6  in.  from  the 
floor,  which  is  the  average  height  of  a  man's  face,  the  light  source 
will  be  in  a  line  with  the  face  and  the  best  results  from  the  light 
will  be  obtained.     The  shades  should  be  of  some  good  diffusing 


/O  TRANSACTIONS    I.    E.    S. — PART    I 

glass  about  5  in.  in  diameter,  deep  enough  to  shield  the  light  source, 
and  hemispherical  in  design.  This  type  of  bracket  unit  may  be 
termed  semi-indirect  as  the  larger  percentage  of  the  light  is 
reflected  to  the  wall  and  ceiling  and  serves  for  the  general  light- 
ing of  the  bathroom. 

I  have  tried  in  this  paper  to  add  the  scientific  element  to  that 
of  the  esthetic  in  the  lighting  of  a  moderate  priced  house  and  to 
show  how  one  modifies  the  other.  The  results  illustrate  a  state- 
ment in  the  beginning  of  the  paper  that  good  home  lighting  is 
more  or  less  a  compromise. 

DISCUSSION. 

Mr.  A.  L.  Powell:  The  statement  in  the  paper  that  "the 
illuminating  engineer  is  likely  to  tip  the  scales  to  the  side  of  the 
scientific"  may  be  entirely  correct  from  the  decorator's  position; 
yet  those  of  us  worthy  of  such  a  title  will  do  our  utmost  to  make 
the  home  comfortable  while  at  the  same  time  striving  for  the 
proper  artistic  effect.  So,  from  a  humanitarian  standpoint,  even 
if  we  do  give  more  weight  to  the  serviceability  of  the  lighting,  we 
are  on  the  safe  side.  1  believe  that  the  average  individual  really 
does  not  know  a  great  deal  about  esthetics,  but  he  certainly  can 
tell  when  his  house  is  agreeable  and  healthful.  All  too  often 
are  the  fixtures  artistically  correct  when  viewed  by  daylight ;  but 
at  night  cannot  be  so  designated.  In  a  broad  sense  anything 
artistic  is  comfortable. 

Another  statement  that  I  hardly  believe  justified  is,  "Instead 
of  the  soft  yellow  light  of  the  carbon  one  must  now  contend  with 
the  hard  cold  white  light  of  the  tungsten  lamp."  It  is  true  that 
the  light  from  a  carbon  filament  is  somewhat  more  yellow  than 
that  from  a  tungsten  filament,  but  it  is  safe  to  say  that  there  is 
as  much  glare  from  the  carbon  lamp  as  ordinarily  installed,  as 
from  the  latter,  and  glare  is  the  important  factor.  For  instance, 
there  are  millions  of  carbon  lamps  in  use  on  multiple  arm  fixtures 
only  partly  surrounded  by  some  sort  of  a  non-diffusing  shade, 
throwing  the  light  directly  into  one's  eyes.  In  many  cases  where 
tungsten  lamps  are  substituted  changes  are  made  in  the  glass- 
ware or  fixtures,  or  both  ;  so  on  an  average  the  tungsten  lamp 
installation  is  not  as  much  more  harsh  as  might  be  imagined. 


ART    AND    SCIENCE    IN    HOME    LIGHTING  Jl 

Following  this  line  of  reasoning,  it  is  doubtful  if  a  semi-in- 
direct or  totally  indirect  fixture,  no  matter  how  improperly  ap- 
plied, will  ever  "get  on  one's  nerves,"  as  much  as  the  great 
majority  of  direct  lighting  fixtures.  While  on  this  subject  of 
comparative  value  of  various  illuminants,  it  seems  a  rather  broad 
conclusion  that  the  slight  difference  in  color  between  the  carbon 
and  tungsten  lamps  should  be  sufficient  to  cause  a  person  to  be 
depressed  or  have  the  blues.  One  might  follow  this  train  of 
thought  and  arrive  at  the  conclusion  that  daylight  would  be  much 
more  likely  to  cause  such  an  effect  than  the  yellowish  artificial 
light. 

To  me  a  room  does  not  necessarily  look  flat  if  indirect  systems 
are  properly  employed,  and  I  am  sure  many  of  us  have  all  seen 
very  beautiful  rooms  with  these  types  of  units.  It  may  be  true 
that  an  indirect  fixture  with  the  loose  bowl  is  artistically  incor- 
rect, yet  in  this  connection  I  might  mention  a  little  personal  ex- 
perience. While  even  now  I  am  not  an  exponent  of  indirect 
lighting  applied  everywhere,  sometime  ago  I  was  not  at  all  cer- 
tain as  to  the  relative  merits  of  the  three  types  of  fixtures,  so  I 
installed  in  my  home  all  three  systems,  direct,  semi-indirect  and 
totally  indirect,  and  lived  under  them  for  over  a  year.  The 
living  room  is  lighted  from  a  semi-indirect  bowl  with  an  amber 
dipped  lamp  within.  The  light  is  well  diffused.  The  den  is 
lighted  by  a  totally  indirect  fixture  with  a  tungsten-filament 
lamp.  The  chairs  and  other  surroundings  in  the  two  rooms  are 
equally  comfortable  and  there  is  no  reason  why  we  should  use 
one  room  in  preference  to  the  other,  yet  when  we  sit  down  to 
read  or  stay  around  for  any  length  of  time  we  almost  invariably 
go  under  the  indirect  lighting. 

The  author  at  one  point  in  the  paper  states  that  too  little  at- 
tention has  been  paid  to  the  color  of  the  light.  I  believe  that 
illuminating  engineers  take  full  account  of  this  in  designing  the 
lighting  for  a  residence  and  provide  tinted  lamps  or  tinted  glass- 
ware wherever  it  seems  advisable. 

I  cannot  see  how  ophthalmologists  and  oculists  could  agree 
that  amber  light  is  preferable  to  other  colors.  If  this  is  true, 
certainly  any  of  the  incandescent  artificial  light  sources  would  be 
more  generally  desirable  than  daylight.     Possibly  color  of  light 


72  TRANSACTIONS    I.    K.    S. — PART    I 

and  intrinsic  brightness  have  incorrectly  been  used  synonymously. 
We  will  all  agree  that  a  diffused  light  is  extremely  desirable. 

Throughout  the  paper  the  author  recommends  amber  tinted 
light  for  almost  every  room.  This  is  a  matter  of  personal 
preference,  but  it  seems  to  me  that  it  is  largely  dependent  on  the 
finish  of  the  room.  For  instance,  I  would  question  the  advis- 
ability of  using  amber  tinted  shades  in  bedrooms,  save  those 
decorated  in  color  harmonizing  with  this  tint.  My  experience 
and  observations  have  indicated  that  the  average  bedroom  is 
papered  with  some  sort  of  light  blue  or  light  pink  flowered 
decoration,  with  possibly  a  light  purple  or  green,  or  some  other 
dainty  figure.  There  is  glassware  available  in  commercial  forms 
which  has,  for  instance,  a  light  blue  medallion  on  an  etched 
white  background,  or  pink  flowers  with  delicate  green  leaves  on 
the  white  glass.  One  may  choose  among  these  glassware  to 
match  almost  any  scheme  of  room  decoration.  They  are  attractive 
and  fit  in  so  well  with  the  room  treatment  that  a  most  pleasing 
effect  is  secured. 

I  will  grant  that  the  dome  in  the  dining  room  may  be  incor- 
rect from  a  decorative  standpoint,  yet  a  great  many  persons  with 
whom  I  have  talked  upon  this  subject  favor  such  an  arrange- 
ment of  light.  For  the  reason  that  the  table  is  the  part  of  the 
room  where  one  desires  to  have  attention  concentrated.  The 
hygienic  objections  to  a  dome  are  removed  by  hanging  it  at  the 
proper  height  and  covering  its  base  with  a  slightly  tinted  light 
diffusing  silk  screen.  The  lighting  should  blend  so  well  with  the 
general  purpose  of  the  room  that  one  should  not  notice  of  what 
the  lighting  consisted. 

In  the  kitchen  it  does  not  seem  desirable  to  use  reflectors 
etched  on  the  inner  surface,  as  there  is  likely  to  be  a  certain 
amount  of  grease  and  smoke  from  the  cooking  and  on  such  a 
rough  surface  this  dirt  will  readily  collect,  and  it  is  difficult  to 
keep  it  as  clean  as  necessary.  I  believe  it  is  preferable  to  use  a 
rather  dense,  smooth  opalescent  reflector  or  prismatic  bowl- 
shaped  reflector.  These  are  particularly  efficient  and  in  the 
kitchen  where  the  lighting  is  somewhat  of  a  commercial  proposi- 
tion. A  high  intensity  of  illumination  is  desired  on  the  food  as 
it  is  being  prepared,  and  the  light  must  be  obtained  in  the  most 


ART   AND    SCIENCE;   IN    HOME   LIGHTING  73 

economical  manner.     It  is   the  one  room  in  the  house  where 
economy  is  the  primary  factor. 

Mr.  M.  Luckiesh  :  I  believe  that  if  every  fixture  man  would 
attack  the  problem  of  uniting  science  and  art  or  utility  and 
esthetics  as  Mr.  Cassidy  has  done,  proper  lighting  would  exper- 
ience the  greatest  boom  in  its  history.  The  matter  of  proper 
fixture  design  is  one  of  the  most  serious  problems  the  lighting 
specialist  has  to  deal  with.  I  believe  Mr.  Cassidy  has  handled 
this  subject  well  from  the  standpoint  of  the  fixture  man 
who  has  naturally  been  chiefly  interested  in  the  esthetics  of  de- 
sign. The  paper  is  a  valuable  one  even  though  we  all  do  not 
agree  with  some  of  the  statements.  That  condition  is  not  unusual, 
for  we  do  not  thoroughly  agree  on  some  of  the  fundamentals  of 
lighting.  It  is  often  difficult  to  unite  utility  and  beauty,  but  it 
must  be  done. 

Mr.  Powell  stated  that  the  average  man  knows  when  his  home 
is  agreeably  lighted.  How  he  has  found  this  out  I  am  at  a  loss  to 
imagine.  In  the  first  place  the  "average  man's"  home  is  not 
agreeably  lighted.  Secondly  when  we  consider  that  the  average 
man  does  not  know  when  his  home  is  badly  lighted  (which  is 
unquestionably  the  case  at  the  present  time)  it  is  difficult  to  see 
how  he  would  know  when  his  home  is  agreeably  lighted. 

Regarding  efficiency  we  must  remember  that,  especially  in  the 
home,  the  real  efficiency  is  a  measure  of  how  well  the  lighting  ap- 
paratus fulfils  its  object.  And  we  must  remember  that  its  object 
is  not  pure  utility  unless  we  include  the  utility  of  beauty.  As 
Dr.  E.  P.  Hyde  expressed  in  the  Johns  Hopkins  lecture  course, 
"efficiency  is  the  ratio  of  satisfactoriness  to  cost  and  not  the 
reciprocal  of  cost" 

I  agree  with  Mr.  Cassidy's  statement  that  color  is  the  keynote 
in  illumination  of  the  home.  I  seriously  doubt  that  tungsten 
light  "gives  one  the  blues"  any  more  than  the  carbon  lamp  es- 
pecially in  view  of  the  fact  that  we  work  under  daylight  with 
satisfaction  many  hours  each  day.  However  I  believe  quality 
of  light  should  be  considered  a  matter  of  personal  taste  as  long 
as  extremes  are  not  indulged  in.  Mr.  Cassidy  uses  amber  glass 
very  much.  He  uses  it  over  the  "indirect"  portion  of  some  of 
his  fixtures.     This  light  reaches  the  objects  in  the  room  after 


74  TRANSACTIONS    I.    E.    S. — PART    1 

reflection  from  the  ceiling  and  walls.  The  most  common  trend 
in  the  color  of  walls  and  ceiling  is  toward  cream,  yellow,  brown, 
etc.,  that  is,  toward  the  "warmer"  colors.  I  have  shown  in  a 
previous  paper  (Trans.  I.  E.  S.,  Feb.,  1913)  that  only  an  appar- 
ently slight  tint  in  wall  coverings  is  sufficient  to  convert  the 
tungsten  light  by  reflection  to  a  quality  even  more  yellow  than 
that  of  the  carbon  lamp  light.  Amber  glass  has  not  appeared 
satisfactory  to  me  owing  to  the  greenish  tinge.  I  have  therefore 
been  experimenting  for  some  time  with  the  hope  of  producing  a 
proper  yellow  for  converting  tungsten  light  into  the  quality  of 
the  light  from  a  carbon  lamp  and  yet  enjoying  the  efficiency  of 
the  former. 

I  have  made  many  experiments  with  colored  lights  in  the 
home.  These  have  ranged  from  deep  amber  to  the  lighter  yel- 
lows, rose,  artificial  daylight,  etc.  While  I  believe  the  results 
are  largely  a  matter  of  personal  taste,  I  will  state  as  my  opinion 
that  an  unsaturated  yellow  color  is  the  most  pleasing  to  me  and 
appeared  to  be  a  welcome  change  from  daylight  where  daylight 
color-values  are  not  essential. 

In  the  matter  of  the  den  mentioned  in  the  paper  I  would  state 
that  I  believe  it  is  well  to  avoid  the  use  of  too  dark  walls  so  com- 
monly found  in  dens.  I  have  found  by  experiment  that  in  read- 
ing under  a  well-designed  table  lamp  and  facing  a  dark  wall  that 
I  suffered  very  noticeable  eye-fatigue  in  a  short  time. 

I  agree  with  a  previous  speaker  that  the  dome  is  a  satisfactory 
fixture  when  well  designed.  However,  it  is  possible  to  get  prac- 
tically the  same  lighting  effect  from  showers.  Take  a  shower 
with  deep  narrow  bell-shaped  shades  equipped  with  bowl-frosted 
tungsten  lamps.  Direct  light  is  sent  downward  upon  the  table 
and  light  of  any  color  depending  upon  the  color  of  the  shade  is 
diffused  about  the  room.  By  this  method  the  table  is  the  bright- 
est object  in  the  room.  I  believe  this  should  be  the  case  and 
therefore  do  not  recommend  so-called  semi-indirect  lighting  in 
the  dining  room.  I  believe  there  is  nothing  more  important  in 
promoting  sociability  than  the  semi-darkness  pressing  in  on  a 
group  surrounding  the  table. 

I  am  sure  that  we  agree  that  Mr.  Cassidy's  paper  is  very 
timely.     In  his  last  paragraph  he  sums  up  the  situation  very  well 


ART    AND    SCIENCE    IN    HOME    LIGHTING  75 

in  the  statement  that  he  has  tried  in  his  paper  to  add  the  scienti- 
fic element  to  that  of  the  esthetic  in  the  lighting  of  a  moderate- 
priced  house  and  to  show  how  one  modifies  the  other.  I  think 
this  is  highly  commendable  and  suggest  that  we  all  must  realize 
that  the  fixture  man  can  well  reciprocate  our  efforts  to  enlighten 
him  in  bringing  home  to  us  an  extremely  important  phase  of 
lighting — the  esthetic. 

Mr.  L.  C.  Porter:  A  great  many  of  us  are  living  in  homes 
already  equipped  with  fixtures,  which  are  not  so  attractive  as 
those  shown  here.  Some  very  simple  changes  will  frequently 
make  large  improvements  in  many  of  the  fixtures  found  in  mod- 
erate-priced houses  and  apartments.  In  the  kitchen,  for  example, 
there  is  frequently  a  single  one-light  fixture  in  the  center  of  the 
room.  The  use  of  a  socket  with  a  separable  attaching  plug  will 
allow  a  drop-lamp  to  be  run  over  to  the  table  or  other  place 
where  food  is  prepared ;  this  is  a  great  convenience  and  will  per- 
mit the  use  of  an  electric  flat  iron  and  similar  equipment  at  night. 

Many  dining  rooms  are  equipped  with  domes,  having  bracket 
arm  showers  around  the  center  dome.  It  is  a  very  simple  matter 
to  give  these  brackets  a  half  turn,  pointing  them  towards  the 
ceiling,  and  install  a  io-watt  all-frosted  tungsten  lamp  in  each 
bracket.  This  will  produce  a  low  intensity  semi-indirect  illum- 
ination over  the  entire  dining  room.  If,  in  addition  to  this,  an 
efficient  reflector  equipped  with  a  6o-watt  tungsten  lamp  is  fast- 
ened in  the  dome  itself,  directing  a  strong  intensity  of  light  onto 
the  table  top,  excellent  dining  room  lighting  will  result ;  i.  e.,  low 
general  illumination  throughout  the  entire  room  with  strong  light 
on  the  table,  making  the  table  and  those  sitting  around  it  most 
conspicuous  in  the  room. 

The  question  of  amber  light  is  probably  one  of  individual  taste. 
Personally,  I  do  not  care  for  it  in  a  dining  room,  because  it  causes 
the  linen  on  the  table  to  appear  more  or  less  yellow,  giving  it  a 
somewhat  faded  out  appearance;  whereas  a  strong  white  light 
makes  it  appear  fresh  and  clean. 

In  the  living  room  many  table  lamps  at  present  in  use  can  be 
improved  by  the  use  of  lamps  which  are  amber  dipped  on  the 
upper  half,  thus  giving  a  pleasing  color  to  the  shade  itself,  and 
at  the  same  time  throwing  white  light  downward  for  reading. 


/6  TRANSACTIONS    I.    E.    S. PART    I 

Fixtures  having  a  sort  of  hollow  brass  shell,  from  which  showers 
are  hung,  are  often  found  in  these  rooms.  It  is  a  simple  matter 
to  place  in  the  top  of  this  brass  shell  a  ioo-watt  tungsten  lamp 
in  an  efficient  reflector  pointed  towards  the  ceiling  and  connected 
with  a  drop-cord  to  the  nearest  shower  socket.  If  the  bowl  of 
the  ioo-watt  lamp  is  amber-dipped,  semi-indirect  lighting  will  be 
obtained.  Very  nearly  the  same  results  can  be  obtained  by  paint- 
ing the  inside  of  the  brass  shell  white,  instead  of  placing  the  re- 
flector there. 

It  frequently  happens  that  in  the  bedroom  there  are  candle- 
sticks of  one  type  or  another,  which  it  is  not  difficult  to  wire  and 
connect  by  a  drop-cord  from  the  top  of  the  bureau  to  the  nearest 
lamp  socket.  A  little  15-watt  all-frosted  tungsten  candle  lamp  in 
these  candlesticks,  one  placed  on  each  side  of  the  mirror,  makes 
a  useful  ornament  for  a  dresser. 

The  thought,  therefore,  which  I  wish  to  leave  with  you  is  that 
considerable  improvement  can  be  made  in  the  average  fixture 
at  very  little  expense,  and  that  it  is  good  policy  for  the  electric 
light  representative  to  assist  the  small  purchaser — who  does  not 
feel  that  he  can  afford  the  more  elaborate  fixtures — to  make  such 
changes,  thereby  obtaining  the  confidence  of  one  who  some  day 
may  be  a  large  customer. 

Mr.  G.  L.  Hunter:  During  the  past  few  years,  this  Society 
has  changed  its  point  of  view  greatly.  Several  years  ago  when  I 
read  my  first  paper  here,  on  the  subject  of  "Light  and  Color  in 
Decoration,"  many  of  you  thought  I  wandered  far  afield  because 
I  ventured  to  take  up  problems  that  had  not  previously  been  even 
suggested.  I  ventured  to  say  even  then  that  white  light  for  resi- 
dence lighting  is  not  desirable.  I  ventured  to  say  that  there  are 
many  different  kinds  of  daylight ;  that  as  the  environment 
changes,  the  daylight  changes.  Daylight  reflected  from  the  sands 
of  the  seashore  is  one  thing;  from  the  blue  depths  of  the  ocean, 
another;  from  green  forests  and  green  grass,  another;  from 
brown  loam,  or  gray  sagebrush,  another;  from  red  brick  build- 
ings, or  white  marble  buildings,  another.  As  the  clouds  overhead 
change,  as  the  color  of  the  skies  changes,  the  color  of  the  daylight 
changes.  The  color  of  the  daylight  also  depends  upon  the  hour 
of  the  day.    At  early  dawn  when  the  sun  first  arises,  it  is  glorious 


ART   AND    SCIENCE    IN    HOME    LIGHTING  J  7 

with  red.  As  the  sun  ascends  through  the  sky,  the  color  of  the 
light  changes  from  red  through  golden  yellow  to  pure  white  at 
noon. 

Naturally,  the  constant  discussion  of  color  here  to-night  has 
delighted  me,  for  it  was  precisely  what  I  had  hoped  to  provoke. 
I  felt  that  until  color  was  the  first  subject  discussed  in  residence 
lighting,  and  to  some  extent  in  all  illumination,  you  were  wasting 
most  of  your  effort;  that  your  ideals  as  well  as  your  practise 
were  wrong.  The  discussion  here  to-night  makes  it  clear  that 
color  is  now  foremost  in  the  minds  of  those  of  you  who  are 
attempting  to  improve  the  lighting  of  residences. 

Mr.  Cassidy  has  certainly  presented  a  very  interesting  paper. 
He  has  not  only  made  many  useful  suggestions,  but  has  arrived 
at  a  number  of  valuable  conclusions.  But  I  did  notice  one  sen- 
tence in  his  paper  to  which  I  take  the  strongest  exception.  This 
sentence  is  "So  most  homes  to-day  have  lighting  fixtures  which 
are  esthetically  correct."  That  I  emphatically  deny.  I  should 
say  on  the  contrary  that,  most  homes  to-day  have  lighting 
fixtures  that  from  the  esthetic  point  of  view  are  abominable. 
They  are  ugly  in  proportion ;  and  incorrect  in  detail  from  the 
point  of  view  of  historic  style. 

Personally  I  must  admit  that  I  am  prejudiced  in  favor  of 
amber  light.  I  know  that  amber  light  is  softer  on  the  eyes  than 
white  light,  and  that  most  persons  can  see  better  with  the  light 
that  comes  from  the  middle  of  the  spectrum — I  mean  with  light 
that  is  not  red  and  not  blue.  The  effect  of  amber  light  can  easily 
be  tested  by  everyone  for  himself,  either  under  daylight  or  under 
artificial  light,  by  looking  through  a  sheet  of  amber  gelatin. 
Both  interiors  and  exteriors  will  be  made  softer  and  more  agree- 
able to  the  eye.  Many  clashes  of  color  that  exist  in  rugs  or  drap- 
eries or  wallpapers  will  be  overpowered.  Discords  that  by  white 
light  are  accentuated  will  by  amber  light  be  eliminated.  Even  the 
extreme  whiteness  of  the  gas  arc  light  can  be  agreeably  dom- 
inated by  the  use  of  amber  shades.  Some  years  ago  I  equipped, 
with  amber-and-gold  leaded-glass  shades,  the  wall  brackets  at 
each  end  of  a  room  30  ft.  x  16  ft.  The  shades  were  sufficiently 
large  so  that  there  was  no  danger  of  their  being  melted  apart  by 
the  heat,  and  there  was  little  direct  light  sent  up  or  down.  The 
6 


78  TRANSACTIONS    1.    K..    S. — I'ART    I 

diffusion  was  largely  of  amber  light  in  a  horizontal  direction,  or 
nearly  so,  illuminating  brilliantly  the  walls  of  the  room  from  _» 
to  8  ft.  high.  I  do  not  think  I  ever  saw  any  room  more  agree- 
ably lighted  than  this,  or  less  expensively  either.  There  was 
absolutely  no  glare,  and  all  the  light  that  reached  the  eye  had 
been  so  transformed  by  the  amber  and  gold  opalescent  glass  of 
the  shades  as  to  be  grateful  rather  than  offensive  to  the  eye. 

Of  course  the  decorator  will  always  keep  in  mind,  and  others 
always  should  keep  in  mind,  the  fact  that  light  is  colored  quite 
as  much  by  reflection  as  by  refraction ;  that  it  can  be  colored  not 
only  by  the  glass  bulb  of  the  lamp,  and  by  the  glass  or  paper  or 
silk  shade  that  surrounds  it,  but  also  by  the  walls  or  furniture 
that  reflect  it.  The  decorator  knows  that  when  he  colors  the 
walls  of  a  room,  he  is  at  the  same  time  coloring  the  light.  If  the 
room  is  finished  in  soft  tones  the  reflected  light  will  be  soft  no 
matter  if  it  originates  from  tungsten-filament  lamps.  If  the 
walls  be  a  muddy  white  the  light  will  be  a  muddy  light,  no  matter 
if  it  start  as  a  golden  yellow. 

One  thing  the  decorator  will  be  able  to  tell  the  illuminating 
engineer  with  regard  to  amber  light,  is  that  it  is  safer  to  use. 
decoratively,  than  any  other  light.  White  light  makes  a  room 
hard  and  unsympathetic.  Blue  light  makes  the  blues  of  a  room 
cheerful,  but  makes  the  reds  muddy  looking.  Red  light  brings 
up  the  reds  of  a  room,  but  makes  the  blues  sombre  and  the 
greens  impossible.  Amber  light  alone  is  sympathetic  to  all  the 
other  colors,  eliminating  from  an  interior  just  enough  of  the 
extreme  reds  and  the  extreme  blues  to  produce  harmony. 

Mr.  H.  Thurston  Owens:  It  is  apparent  that  the  ideas 
which  Mr.  Hunter  brought  to  the  attention  of  this  Society  were 
of  great  value  but  the  reason  they  did  not  receive  the  attention 
they  deserved  was  due  to  the  commercial  propaganda  of  con- 
siderable influence  which  was  at  its  height  at  that  time.  The 
commercial  propaganda  of  to-day  instead  of  being  at  variance 
with  the  dictates  of  art  is  in  accord  with  them. 

Mr.  G.  H.  Sticknky:  While  there  are  minor  points  in  which 
my  ideas  differ  from  those  of  the  author,  1  am  in  agreement  with 
his  general  thought. 

It  is  not  surprising  that,  on  account  of  our  different  relations 


ART    AND    SCIENCE    IN    HOME    LIGHTING  79 

to  the  problem  and  our  different  antecedents  we  should  have 
different  ideas  and  should  each  hold  our  individual  ideas  as  super 
ior  to  those  of  others.  So  long  as  there  are  so  many  installations 
which  are  neither  artistic,  comfortable  nor  economical,  there  is 
certainly  much  to  be  accomplished,  and  I  believe  the  discussion 
of  a  paper  such  as  this  helps  toward  the  end  of  bettering  the 
practise. 

The  architect,  decorator  and  fixture  man  handle  the  problem  of 
home  lighting  in  advance.  The  central  station  and  lamp  manu- 
facturer often  attain  their  closest  relation  after  the  installation 
is  in  operation,  and  frequently  encounter  dissatisfaction,  due  to 
appearance,  glare,  and  most  often  cost  of  operation.  In  seeking 
to  secure  the  best  results  we  meet  limitations  due  to  the  location 
of  outlets  and  style  of  fixtures  and  glassware.  We  are  inclined 
at  times  to  blame  the  designers,  though  we  realize  that  in  many 
cases  they  have  been  unable  to  express  their  own  ideas  on  account 
of  the  limitations  of  cost  and  taste  imposed  by  the  client.  We  do 
feel  that  in  many  cases  adherence  to  historical  precedents  has 
prevented  designers  from  adapting  their  practise  to  the  modern 
illuminants  and  other  practical  modern  conditions. 

Sometimes  in  the  past  we  have  undoubtedly  erred  toward  the 
other  extreme  of  placing  too  much  weight  on  economy  of  oper- 
ation or  efficiency,  as  measured  in  candlepower  or  foot-candles. 
On  the  other  hand,  I  believe  that  the  illuminating  engineers, 
including  those  employed  by  the  lighting  companies  and  lamp 
manufacturers,  have  done  more  to  prevent  this  class  of  mistakes 
than  almost  any  other  influence. 

A  progressive  manufacturer  is  anxious  to  insure  the  best  pos- 
sible service  from  his  apparatus,  and  likewise,  the  central  station 
is  desirous  of  securing  the  most  satisfactory  use  of  current. 
They  have,  therefore,  employed  illuminating  engineers  to  make 
a  special  study  of  lighting  problems  to  educate  and  advise  light 
users  and  those  interested  in  the  design  of  lighting  installations. 
I  believe  this  has  done  much  to  prevent  undesirable  extremes. 
Much  that  the  artistic  designer  blames  the  illuminating  engineer 
for  is  really  done  by  untrained  light  users  and  others,  without 
the  advice  of  the  illuminating  engineer,  in  seeking  to  better  un- 
satisfactory conditions.    In  such  a  case  it  frequently  happens  that 


80  TRANSACTIONS   I.    E.    S. — PART    I 

the  light  user  turns  to  the  opposite  extreme,  and  I  have  always 
felt  that  this  result  was  somewhat  the  fault  of  the  artist. 

Perhaps  I  can  illustrate  my  thought  better  by  reference  to  a 
typical  experience  in  connection  with  the  lighting  of  a  fine  hotel 
in  a  western  city.  I  was  called  in  because  the  consumption  of 
energy  required  by  the  architect's  plan  seemed  excessive.  I 
found  that  he  was  using  a  considerable  number  of  beautiful 
fixtures,  employing  numerous  round  bulb,  frosted  carbon  incan- 
descent lamps  of  low  power.  The  effect  and  design  was  un- 
questionably attractive,  although  it  seemed  to  be  unnecessarily 
extravagant.  I  had  the  opportunity  of  calling  the  architect's 
attention  to  a  similar  installation  he  had  designed.  Although 
this  had  been  in  service  less  than  a  year  the  management  had 
substituted  higher  power,  bare  tungsten  filament  lamps  in  pear- 
shaped  bulbs,  for  the  round  bulb  lamps  which  had  been  pre- 
scribed. As  can  be  imagined  the  effect  was  both  inartistic  and 
glaring.  After  the  architect  had  failed  to  persuade  the  manage- 
ment to  return  to  the  original  lighting,  it  was  not  difficult  to 
convince  him  to  abandon  this  type  of  fixture  and  design  one  for 
the  new  installation  which  would  be  both  artistic  and  effective 
with  clear  tungsten  filament  lamps.  Through  his  ingenuity  he 
discovered  that  it  was  possible  to  make  such  fixtures  which  satis- 
fied his  artistic  ideas  even  with  due  regard  to  precedent;  and 
he  himself  was  protected,  as  far  as  his  reputation  was  concerned, 
from  having  his  artistic  work  spoiled  by  those  responsible  for  its 
operation. 

While,  technically,  architects  or  fixture  designers  may  not  be 
responsible  for  the  liberties  which  may  be  taken  with  the  fixtures 
which  they  design,  the  fact  remains  that  the  public  does  blame 
them,  and  it  seems  to  me  there  is  some  justice  in  this  wherever 
it  is  possible  for  them  to  avoid  the  condition  likely  to  produce 
these  results. 

Going  back  to  the  cost  question :  I  agree  that  the  home  is  one 
of  the  last  places  where  cost  of  lighting  should  be  the  deciding 
consideration.  It  does  not  seem,  however,  practicable  to  entirely 
ignore  this  factor ;  in  fact,  it  sometimes  seems  to  me  that  the 
lighting  in  the  fine  mansion  of  the  wealthy  man  is  even  more 
liable  to  be  marred  in  search  of  economy  than  in  the  middle-class 


ART   AND    SCIENCE    IN    HOME   LIGHTING  8l 

home.     I  have  in  mind  a  number  of  specific  instances  of  this  sort 
which  have  come  to  my  personal  attention. 

It  is  for  the  best  interest  of  all  of  us  that  we  should  learn  to 
respect  the  truth  in  each  other's  view  points. 

Mr.  G.  W.  Cassidy  (In  reply)  :  Referring  to  Mr.  Powell's 
discussion  of  my  statement,  "Instead  of  the  soft  yellow  light  of 
the  carbon  lamp,  one  must  now  content  with  the  hard,  cold,  white 
light  of  the  tungsten  lamp,"  I  wish  to  say  that  I  referred  to 
the  color  of  the  light  and  not  to  its  physiological  effects  or  glare. 
Regarding  the  statement,  "Too  little  attention  has  been  paid  to 
the  color  of  the  light,"  Mr.  Powell  adds  that  this  condition  is 
being  remedied  by  the  illuminating  engineer.  No  doubt  this  is 
true  of  the  few  cases  where  the  lighting  expert  is  engaged  to 
design  the  installations  of  moderate-priced  residences. 

I  have  used  an  amber  color  in  fixtures  to  bring  out  the  decor- 
ative effect  of  a  room,  and  because  it  is  a  more  or  less  neutral 
tone. 

Mr.  Hunter  takes  exceptions  to  my  statement,  "Most  homes 
to-day  have  lighting  fixtures  which  are  esthetically  correct."  I 
meant  that  most  of  the  fixtures  for  residences  have  been  designed 
simply  from  the  artistic  side  without  regard  to  the  scientific.  I 
agree  with  him  that  many  of  the  results  in  evidence  to-day  could 
hardly  be  called  esthetic. 


82  TRANSACTIONS    I.    K.    S. —  PART    1 

AN  ANALYSIS  OF  REQUIREMENTS  FOR  MODERN- 
STREET  CAR  LIGHTING.* 


BY  L.  C.  DOANE. 


Synopsis:  In  outlining  the  requirements  of  modern  street  car  light- 
ing, the  author  discusses  elimination  of  eyestrain,  maintenance,  effect  of 
dust  on  efficiency  of  reflectors,  efficiency  of  various  lighting  units,  spacing 
of  outlets,  wiring,  etc.  Tables  giving  cost  and  lighting  data  are  appended 
to  the  paper. 


INTRODUCTION. 

The  first  paragraph  in  the  "Code  of  Principles"  adopted  by 
the  American  Electric  Railway  Association  at  Atlantic  City, 
October  14,  1914,  reads  as  follows : 

The  first  obligation  of  a  public  utilities  engaged  in  transportation  is 
service  to  the  public.  The  first  essential  of  service  is  safety.  Quality  of 
service  must  primarily  depend  upon  the  money  received  in  fares.  For 
this  reason,  it  is  necessary  that  the  rate  of  fare  should  be  sufficient  to 
permit  the  companies  to  meet  the  reasonable  demands  of  patrons  and  to 
yield  a  fair  return  on  a  fair  capitalization. 

This  sums  up  very  concisely  the  attitude  of  the  public  utilities 
towards  service  rendered  the  public.  They  wish  to  give  every 
service  possible,  consistent  with  economical  operation,  but  they 
must  be  sure  that  any  new  demands  of  their  patrons  are  reason- 
able and  that  a  fair  return  on  their  investment  is  forthcoming. 

When  it  is  known  that  224,000,000  passengers  were  carried 
in  Pittsburgh  last  year  in  electric  street  cars;  over  1,500,000,000 
passengers  in  New  York ;  and  over  500,000,000  passengers  in  Phil- 
adelphia; and  more  than  40  per  cent,  of  this  travel  was  during 
hours  of  darkness,  artificial  lighting  stands  out  as  a  basic  service 
that  must  be  rendered  by  the  public  utilities.  The  extent  to 
which  this  artificial  lighting  fulfills  its  duty  is  the  determining 
factor  in  regard  to  the  quality  of  the  service. 

*A  paper  read  at  a  meeting  of  the  Pittsburgh  Section  of  the  Illuminating  Engi- 
neering Society,  November  20,  1914. 

The  Illuminating   Engineering  Society   is   not   responsible   for  the  statements  or 
opinions  advanced  by  contributors. 


DOANE:     MODERN    STREET    CAR    LIGHTING  83 

It  is  the  object  of  this  paper  to  determine  what  constitutes 
good  lighting  and  to  show  that  good  lighting  is  an  asset  to  the 
public  utilities  from  the  standpoint  of  returns  on  the  investment 
and  service  to  the  public. 

GENERAL. 

The  artificial  lighting  of  street  cars,  in  order  to  be  satisfactory, 
must  be  acceptable  both  to  the  public  and  the  public  utilities.  An 
analysis  of  the  requirements  to  be  met,  from  the  standpoint  of 
each  interest,  shows  approximately  the  following  results — as- 
suming that  the  illuminating  engineer  is  the  representative  of  the 
public. 

REQUIREMENTS. 

Public  Utilities:  1.  Economy  of  operation;  2.  Economy  of 
installation;  3.  Safety  for  passengers;  4.  Ease  of  handling 
passengers ;     5.  Advertising  value. 

Public:  1.  Sufficient  light;  2.  Elimination  of  eyestrain;  3. 
Pleasing  appearance. 

Economy  of  Operation :  Economy  of  operation  depends  on 
the  following  items:  (a)  Cost  of  maintenance;  (b)  Cost  of 
power;     (c)   Efficiency  of  lighting  units. 

Each  of  these  items  will  be  discussed  separately  later  in  the 
paper. 

Economy  of  Installation. — The  following  items  determine  the 
economy  of  installation  of  a  lighting  system:  (a)  Wiring;  (b) 
Spacing  of  outlets;  (c)  Cost  of  lighting  units.  Each  of  these 
items  will  be  discussed  separately  later  on. 

Safety  for  passengers;  Ease  of  handling  passengers;  Adver- 
tising value. — Each  of  these  requirements  will  be  met  to  the  full- 
est extent  only  when  the  following  conditions  are  fulfilled:  (a) 
Sufficient  light;  (b)  Elimination  of  eyestrain;  (c)  Pleasing 
appearance. 

Sufficient  Light:  An  illumination  of  1.5  foot-candles  is  the 
minimum  intensity  consistent  with  acceptable  lighting.1     Figuring 

1  Ferree  and  Rand  :  Efficiency  of  the  Eye  Under  Different  Systems  of  Illumination  ; 
Postoffice  Department  Specifications  for  the  Construction  of  Full  Postal  Cars  ;  A.  R.  E.  E. 
Report  on  Day  Coach  Lighting  Tests. 


84  rRANSACTIONS   I.   E.   S. — PART   I 

on  the  basis  that  the  voltage  of  the  lamps  often  drops  to  85  per 
cent,  of  normal,  which  is  equivalent  to  55  per  cent,  of  normal 
light,  and  that  a  drop  in  efficiency  due  to  dust  on  the  lighting  units 
will  easily  amount  to  15  per  cent.,  the  lighting  system  should  be 
designed  to  produce  an  average  illumination  of  at  least  3.75  foot- 
candles  at  normal  voltage  at  the  plane  of  illumination.  The 
plane  of  illumination  is  usually  taken  34  in.  (86.36  cm.)  above 
the  floor,  the  elevation  at  which  the  average  reader  holds  a  paper. 

Elimination  of  Eyestrain:  Eyestrain  may  be  caused  by  in- 
sufficient light,  heavy  shadows,  uneven  illumination,  points  of 
high  intrinsic  brilliancy  in  the  field  of  vision,  or  marked  con- 
trasts in  illumination  to  which  the  eye  must  adapt  itself. 

To  eliminate  eyestrain,  it  is  necessary  to  remove  the  causes  of 
eyestrain.  The  chief  causes  of  strain  are,  bare  lamps  with  fila- 
ments of  high  intrinsic  brilliancy  placed  in  the  field  of  vision, 
insufficient  light,  and  extreme  contrasts. 

No  lamps  should  be  used  except  with  some  form  of  shield 
which  will  cover  the  bright  light  source  to  such  an  extent  as  to 
entirely  cut  off  the  view  of  the  brilliant  filament  from  the  or- 
dinary field  of  vision.  This  shield  may  be  either  in  the  form  of 
a  reflector  or  an  indirect  bowl. 

An  indirect  lighting  system  in  a  street  car  is  so  expensive  to 
operate  that  it  will  not  be  considered  further  in  this  paper.  Ex- 
perience has  proven  it  an  unwise  method  to  adopt  at  the  present 
time  in  spite  of  its  merit  in  reducing  eyestrain  and  eye  fatigue. 

A  reflector,  in  order  to  be  satisfactory  as  a  shield,  must  extend 
well  down  over  the  lamp.  The  approximate  screening  angle  re- 
quired has  been  determined  by  a  series  of  tests  conducted  by 
Air.  A.  J.  Sweet.  These  tests  were  conducted  to  determine  the 
variation  of  eye  efficiency  with  angle  of  light  entering  the  eye, 
and  were  made  by  directing  a  beam  of  light  into  the  eye  and 
making  a  determination  of  what  the  eye  could  see  under  this  con- 
dition. The  first  determination  was  made  with  the  beam  directly 
in  line  with  the  eye  and  then  successive  determinations  were 
made  while  the  angle  at  which  the  light  entered  the  eye  was  grad- 
ually changed.  It  was  found  that  the  eye  reached  its  normal  ef- 
ficiency when  the  beam  of  light  entered  at  angles  greater  than  20 


DOANE:     MODERN    STREET    CAR   LIGHTING 


85 


to  24  deg.  from  the  direct  line  of  sight.     A  graphical  summary 
of  the  test  results  is  shown  in  Fig.  1. 

It  is  interesting  to  know  that  Mr.  Sweet  has  just  completed  an 
exhaustive  test  for  the  Wisconsin  Commission  along  similar  lines 


3       10       II       11       16       18      10      U      iq 
DEGREES  FROM  LlflEOF  VISION 

Fig.  i.-Variation  of  eye  efficiency  with  angle  of  light  in  the  eye. 

to  his  previous  tests  and  that  his  original  results  have  been  cor- 
roborated. 

Two  striking  examples  of  the  importance  attached  to  the  angle 
of  cut-off  of  a  reflector  are  the  specifying  by  the  Post  Office 


kfeMzMzMzMz 


W® 


Fig.  2.-Diagram  showing  angles  at  which  light  from  different  units  enters  th 

passengers.     (Light  at  an  angle  of  less  than  20°  is  that  which  produces  glare  and  eve 
fatigue.) 

Department  of  an  angle  of  cut-off  of  not  less  than  20  deg.  from 
the  horizontal  on  reflectors  used  for  postal  car  lighting;  and  the 
standard   specification   adopted   recently   by   the   Association   of 


86 


TRANSACTIONS    I.    E.    S. PART    I 


Railway  Electrical  Engineers,  calling  for  an  angle  of  cut-oft  not 
less  than  25  deg.  from  the  horizontal  on  all  reflectors  for  car 
lighting. 

Fig.  2  shows  the  angles  at  which  a  passenger  may  receive  light 
from  the  lighting  units  in  a  car.  In  the  case  shown  by  this  figure, 
unit  No.  6  has  the  most  injurious  effect.  Units  Nos.  4  and  5  a 
lesser  effect  and  units  Nos.  2  and  3  practically  no  effect.  With 
bare  lamps  light  enters  the  eye  from  each  of  these  units,  but  by 
the  use  of  proper  reflectors,  it  is  possible  to  cut  off  the  light  from 
all  the  units  which  are  so  located  as  to  have  a  harmful  effect. 


Fig.  3. — Angle  of  cut-off  56-watt  lamp  with  prismatic  reflector,  licavy 
opal  reflector,  and  light  opal  reflector. 

Fig.  3  shows  how  it  is  possible  to  cut  off  the  light  above  certain 
angles.  The  reflectors  designated  as  prismatic  and  heavy  opal 
have  angles  of  cut-off  of  18  deg.  and  20  deg.  respectively.  These 
two  reflectors  cut  off  practically  all  the  harmful  light.  It  might  be 
well  to  have  a  slightly  greater  cut-off,  but  this  could  only  be  ob- 
tained at  a  considerable  sacrifice  in  efficiency.  The  reflector 
designated  as  light  density  opal  does  not  give  a  sufficient  angk- 
of  cut-off  and  should  be  changed  in  this  respect  before  it  will 
fully  perform  its  duty. 

Extremes  of  contrast  in  intensities  may.  to  a  great  extent,  be 
avoided  by  the  proper   distribution   of  light   upon   the  plane   of 


f"  US'  ;15'  nf  ,«o"    rti*  l»S-  ISS"  «**"  '•>*" 


Fig.  S.— Distribution  of  light  ftom  a  5t>-watt  lamp  with  prismatic  reflector,  heavy 
opal  reflector,  light  opal  reflector. 


UUANK:      MODERN    STREET    CAR    LIGHTING  &7 

illumination  and  by  using  a  light  colored  finish  on  the  interior  of 
the  car.  The  interior  finish  should  be  unglazed,  for  a  glazed 
surface  would  give  unpleasant  specular  reflection. 

Appearance :  The  appearance  of  a  lighting  installation  gov- 
erns to  a  considerable  extent  its  success.  An  installation  that  is 
unsightly  or  depressing  is  never  a  good  one,  be  the  engineering 
results  what  they  may.  Opaque  reflectors  produce  a  depressing 
effect  due  to  the  gloomy  appearance  of  the  upper  part  of  the 
car  in  comparison  with  the  lower  part.  This  fact  eliminates  them 
from  consideration. 

The  unsightliness  of  an  installation  depends  to  a  certain  extent, 
on  personal  preference.  Certain  translucent  reflectors  may  be 
very  pleasing  to  some  people  while  to  others  they  may  be  rather 
unpleasant.  This  condition  cannot  be  avoided.  It  is  safe  to 
say  that  any  translucent  reflector — with  the  exception  of  a  few 
which,  by  selective  absorption  of  the  transmitted  light  appear 
unpleasant  in  color — will  be  about  equally  acceptable  to  the  aver- 
age public. 

Figs.  4  and  5  show  two  car  lighting  installations  that  are  in 
service. 

Cost  of  Maintenance. — The  cost  of  maintenance  of  an  installa- 
tion is  a  question  of  great  interest  to  the  public  utilities.  Here 
is  an  expense  that  starts  immediately  upon  placing  a  car  in  ser- 
vice and  continues  during  the  life  of  the  car.  It  is  of  vital  im- 
portance that  this  cost  be  kept  as  low  as  possible,  if  the  greatest 
returns  on  the  investment  are  to  be  obtained. 

Maintenance  of  any  magnitude  comes  down  to  two  items,  these 
being  lamp  replacements  and  reflector  cleaning. 

The  life  of  all  lamps  is  practically  the  same.  The  question 
of  the  proper  lamp  for  economical  maintenance,  therefore,  comes 
down  to  the  question  of  cost  of  lamps  and  number  of  lamps. 

Only  tungsten  lamps  will  be  considered,  as  carbon  and  Gem 
lamps  are  uneconomical  in  other  respects  than  that  of  main- 
tenance.    (See  discussion  under  Efficiency  of  Lighting  Units.) 

The  23-watt  and  36-watt  tungsten  lamps  cost  exactly  the  same, 
say  three  units.  The  56-watt  lamp  costs  four  units  and  the 
94-watt  lamp  costs  7  units.  It  requires  J.3  units  worth  of 
23-watt  lamps,  4.7  units  worth  of  36-watt  lamps  and  4.2  units 


88 


TRANSACTIONS    I.    E.    S. PART    I 


worth  of  94-watt  lamps  for  the  same  amount  of  light  as  is  given 
by  4  units  worth  of  56-watt  lamps.  This  means  that  for  equal 
light,  maintenance  considerations  point  to  the  56-watt  lamp  as  the 
most  economical,  the  23-watt  lamp  being  82  per  cent,  more  ex- 
pensive, the  36-watt  lamp  17  per  cent,  more  expensive  and  the 
94-watt  lamp  5  per  cent,  more  expensive. 

The  cost  of  cleaning  reflectors  depends  upon  the  number  of 
reflectors  and  the  length  of  time  before  the  reflector  requires 
cleaning. 

The  number  of  reflectors  depends  on  the  size  of  lamp  and  the 
efficiency  of  the  reflector.     A  full  discussion  of  these  2  points 


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is  given  under  the  headings  of  Spacing  of  Outlets  and  Efficiency 
of  Lighting  Units. 

The  length  of  time  before  the  reflector  requires  cleaning  de- 
pends on  the  rapidity  with  which  efficiency  drops  off  due  to  ac- 
cumulation of  dust,  and  to  appearance. 

Fig.  9  shows  graphically  the  effect  of  dust  on  the  efficiency 
of  three  types  of  reflectors.  This  test  was  made  by  the  engineering 
department  of  the  National  Lamp  Works  to  determine  the  rela- 
tive merits  of  reflectors  for  factory  service,  but  the  results  are 
equally  applicable  to  car  lighting  if  only  relative  values  are  used. 
From  this  figure,  it  is  seen  that  the  efficiency  of  heavy  density 


D0ANE:     MODERN    STREET    CAR   LIGHTING  89 

opal  reflectors  is  least  affected  by  dust  accumulation.     Prismatic 
reflectors  come  next  and  light  density  opal  reflectors  last. 

Cost  of  Power.— Electric  power  costs  the  public  utilities  money, 
whether  it  be  bought  or  generated  in  their  own  plants.  Every 
additional  kilowatt  of  energy  used  means  an  additional  invest- 
ment in  generating  units,  distribution  and  feeder  lines,  and  in 
sub-station  equipment.  Public  utilities  are  constantly  expanding 
adding  more  cars,  extending  their  lines,  requiring  more  power. 
The  argument  that  an  economy  of  power  is  not  a  real  economy 
seems  hardly  justified  under  these  circumstances.  The  day  of 
the  public  service  commission  and  the  elimination  of  all  needless 
expense  is  here,  and  it  is  such  items  as  economy  of  power  that 
are  going  to  lead  to  the  highest  economic  efficiency.  A  study  of 
the  discussion  on  Costs  will  throw  some  interesting  light  on  this 
subject. 

Efficiency  of  Lighting  Units.— Under  the  heading  Sufficient 
Light  it  has  already  been  stated  that  there  is  a  minimum  intensity 
for  satisfactory  lighting.  It  is  also  true  that  the  most  efficient 
method  of  obtaining  this  intensity  will  require  the  least  amount 
of  energy. 

Table  I  shows  the  average  efficiency  of  various  lighting  units 
as  obtained  by  a  series  of  tests  which  is  described  later  under  the 
heading  Tests. 

TABLE  I.— Efficiency  of  Various  Lighting  Units. 

Wting  unit  Efficiency  ^ 

Bare  carbon  lamp  g  <- 

Bare  tungsten  lamp   22  x  g 

Light  density  opal  reflector 35  , 0 

Medium  density  opal  reflector 40  3>5 

Heavy  density  opal  reflector 45  40 

Clear  prismatic  reflector S4  .  g 

The  reason  for  the  increase  in  efficiency  with  the  use  of  tung- 
sten lamps  and  reflectors  is  first,  that  the  tungsten  lamp  generates 
light  practically  3  times  as  efficiently  as  does  the  carbon  lamp 
and  second,  that  reflectors  will  so  redirect  the  light  of  the  tung- 
sten lamp  as  to  make  much  more  of  it  useful  in  lighting  the  bot- 
tom of  the  car  instead  of  the  top.  Fig.  8  illustrates  very  effectively 
the  way  in  which  the  light  of  the  bare  tungsten  lamp  is  redirected 
down  onto  the  seats  by  various  reflectors. 


90  TRANSACTIONS    I.    K.    S. — PART    1 

Wiring. — There  are  four  methods  of  wiring  which  are  in  gen- 
eral use  for  car  lighting.  These  are  as  follows :  i .  Exposed 
wiring  between  roof  and  headlining;  2.  Conduit  wiring  between 
roof  and  headlining;  3.  Open  conduit  wiring  on  ceiling;  4. 
Open  conduit  wiring  on  roof. 

The  first  two  methods  are  probably  best  for  wiring  new  cars 
or  wiring  old  cars  while  they  are  shopped  for  general  overhaul- 
ing. The  latter  two  methods  are  the  most  economical  for  chang- 
ing over  an  old  car,  and  are  necessary  when  there  is  a  very  small 
clearance  between  the  headlining  and  roof. 

Local  conditions  will  have  to  determine  which  method  of  wir- 
ing is  most  economical,  until  such  time  as  street  car  designs  are 
standardized. 

Spacing  of  Outlets. — Spacing  of  outlets  depends  on  the  ef- 
ficiency of  the  lighting  unit,  the  distribution  of  light  by  the  light- 
ing unit,  and  the  seating  arrangement  of  the  car. 

The  Association  of  Railway  Electrical  Engineers  in  its  report 
on  "Day  Coach  Lighting  Tests"  finds  that  a  spacing  of  6  ft.  to 
7  ft.  6  in.  (1.82  to  2.28  m.)  between  units  should  not  be  ex- 
ceeded, as  greater  spacing  produces  uneven  lighting  and  ob- 
jectionable shadows.  They  also  found  that  there  was  no  ad- 
vantage to  be  gained  by  using  two  rows  of  lighting  units  instead 
of  one,  but  this  may  be  modified  in  street  car  lighting  practise. 
It  is  quite  probable  that  two  rows  of  units  reduce  shadows  in 
street  cars  having  longitudinal  seats,  although  the  increased  cost 
of  installation  and  maintenance  for  such  a  system  is  very  likely 
to  offset  any  gain  in  illumination  that  may  be  made. 

By  calculations  from  the  results  of  the  tests  on  the  efficiency 
of  various  lighting  units,  it  is  possible  to  determine  the  maximum 
allowable  spacing  for  any  units.  The  results  of  these  calculations 
are  given  in  Tables  II  and  III. 

TABLE  II. — Maximum   Ai.i.owaki.k   Spacing  of  Units. 
Half -Deck  System.     Two  Rows  of  Units. 

Size  of  lamp 
Reflector  23-w  36-w  56-w  94-w 

None    2  ft.  6  in.  4  ft.  3  in.        6  ft.  o  in. 

Light  density  opal 4  ft.  9  in.  

Medium  density  opal...  5ft.  gin.  

Heavy  density  opal 6  ft.  6  in.  

Prismatic  clear   7  ft.  o  in.  


DOANE:     MODERN    STREET    CAR    LIGHTING  91 

TABLE  III.— Maximum  Allowable  Spacing  of  Units. 
Center-Deck  System.     One  Row  of  Units. 

Size  of  lamp 

Reflector                                23-w                      36- w  56-w                       94-w 

None     1  ft.  3  in.  2  ft.  o  in.  3  ft.  o  in.         5  ft.  6  in. 

Light  density  opal 2  ft.  6  in.  3  ft.  9  in.  5  ft.  9  in.         7  ft.  6  in. 

Medium  density  opal ...  2  ft.  9  in.  4  ft-  6  in.  6  ft.  6  in. 

Heavy  density  opal 3  ft.  3  in.  5  ft.  0  in.  7  ft.  o  in. 

Prismatic  clear    3  ft.  9  in.  5  ft.  9  in.  7  ft.  6  in. 

Cost  of  Lighting  Units.— The  cost  of  lighting  units  depends 
upon  the  cost  of  holders,  lamps  and  reflectors. 

Holders  for  the  various  sizes  of  lamps  are  all  the  same  and 
therefore  the  fewer  the  units  required,  the  lower  is  the  cost  for 
holders. 

It  has  already  been  shown  that  for  equal  amount  of  light  the 
56-watt  lamp  is  most  economical. 

Reflectors  vary  in  cost  according  to  the  glass  that  goes  into 
them  and  the  cost  of  the  molds  in  which  they  are  made.  It  is  a 
peculiar  fact  that  the  lower  the  efficiency  of  a  reflector  the  lower 
is  its  cost.  An  investigation  of  the  discussion  on  Costs  will,  how- 
ever, show  that  though  the  individual  reflectors  may  vary  in  cost, 
the  increased  efficiency  of  the  more  expensive  ones  permits  the 
use  of  a  fewer  number,  which  brings  them  all  down  to  practically 
the  same  plan. 

The  selection  of  lighting  units,  therefore,  should  be  made  on 
the  basis  of  maintenance  cost  and  economy  of  operation,  rather 
than  on  the  cost  of  the  lighting  unit  itself. 

Tests. — A  majority  of  the  various  comparative  tests  conducted 
to  determine  the  efficiency  of  an  installation,  have  been  made  on 
only  two  or  three  types  of  reflectors  and  these  often  the  wrong 
size  or  type  for  the  sen-ice.  It  has  also  been  the  practise  to  use 
uncalibrated  lamps,  inaccurately  calibrated  instruments  and 
fluctuating  voltage.  Under  such  circumstances  the  probability  of 
rather  serious  errors  is  introduced. 

During  the  last  part  of  May,  1914,  an  illumination  test  embody- 
ing twelve  different  installations  was  made  on  one  of  the  double- 
truck  closed  cars  operated  by  the  Indianapolis  Traction  &  Ter- 
minal Company.     Every  precaution  was  taken  to  make  the  re- 


92  TRANSACTIONS    I.    E.    S. — PART    I 

suits  accurate  and  conclusive.     The  car  in  question  measured 
7  ft.  6  in.  (2.28  m.)  wide  by  32  ft.  6  in.  (9.9  m.)  long  inside. 

Photometric  readings  were  taken  on  a  test  plane  34  in.  (86.3 
cm.)  from  the  floor,  at  twenty  stations  30  in.  (76.2  cm.)  apart, 
each  on  one  of  three  position  lines,  one  intersecting  the  position 


/nsta//atian  A/oi  fastat/ation  Afa  2. 

•  -64  Wo/t  Cardan  lamps,  Sore     •-£3-We/f  Tungsbm  Lamps,  Bare 

-*— — # * % $ %—■ 


Iitstoi/otion  A/o.3 
•  S6  h/att  JunasTtn  L*  m/w>  Jtare. 
®-J&  Mf/^TunjSTtJi  Uoi-mpiw/tn  tieory  density  opa/ rvfiectors. 


/nstat/atibn  A/o  4 

•  -£3'H/attTunottm  kamp*,0<"* 

•  -23-/ro#TunoSTt»  Lamps,  *///>  tiyht density  opa/  ref/ectors. 
%-94-WotfTunatTir\l*inj*l*''M  tight  density  opal rtt/ecibrs 


% 


fnstet/ation  A/o.  5 
•  -23  WottTunytTn,  L<rmpi,Bare. 

<g)-23  Wot/Tun^Sten  LampspitA  c/ear prismatic  rs//ectors. 
Sl-fh  H/ottTutijitin  Lampt,^i/h  e/eor prismatic  re/iectors. 

Kig.  ii.  — Arrangement  of  lighting  units. 

of  passengers  seated  next  to  side  windows,  another  intersecting 
the  position  of  passengers  seated  next  to  the  aisle,  the  third  coin- 
cident with  the  longitudinal  center  line  of  car. 

All  instruments  were  calibrated  in  the  laboratories  of  the  Na- 
tional Lamp  Works  immediately  prior  to  the  tests.     All  lamps 


DOANE:     MODERN    STREET    CAR   LIGHTING 


93 


were  rated — with  the  exception  of  the  64-watt  carbon  lamps  and 
23-watt  tungsten  lamps — and  the  exact  amount  of  light  obtained 
from  each  of  them  was  known.  All  voltages  were  held  constant 
by  means  of  rheostats  and  greatest  accuracy  was  used  in  making 
the  readings.  At  the  end  of  every  third  or  fourth  test,  a  check 
reading  was  made  on  the  bare  lamps  to  see  that  no  changes  had 
occurred  either  in  the  output  of  the  lamps  or  in  the  reading  of 
the  instruments. 

Table  IV  gives  a  summary  of  the  results  of  these  tests,  and 
lists  all  items  of  importance. 

COSTS. 

In  order  to  form  an  idea  of  the  comparative  costs  of  lighting 
with  various  installations,  the  figures  shown  in  Tables  V,  VI 
and  VII  have  been  prepared. 


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Five  typical  installations  have  been  figured. 

Fig.  11  shows  the  arrangement  of  the  five  installations. 

Table  V  shows  the  cost  of  power  and  maintenance. 

Table  VI  shows  the  investment. 

Table  VII  compares  the  various  installations  with  respect  to 
cost  of  power  and  maintenance,  and  amount  of  investment. 

Fig.  12  shows  in  graphical  form  the  length  of  time  required 
for  each  installation  to  pav  for  itself,  both  when  replacing  carbon 
7 


94  TRANSACTIONS    I.    E.    S. — PART    I 

lamps  that  have  already  been  installed   and   when   making  an 
installation  in  new  cars. 

CONCLUSIONS. 
The  intention  of  this  paper  is  to  present  what  data  there  is 
available  on  street  car  lighting  and  allied  subjects  before  you  in 
such  form  that  each  one  may  draw  his  own  conclusions. 


doane:    modern  street  car  lighting 
APPENDIX. 


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DOANE:     MODERN    STREET    CAR    LIGHTING 


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o3 


MODERN    STREET    CAR   LIGHTING  99 

DISCUSSION. 

Mr.  S.  G.  Hibben  :  The  fittings  used  here  were  developed 
specially  for  this  high  voltage  service.  The  voltage  across  the 
base  terminals  of  a  lamp,  in  case  of  a  burn-out  or  an  open  cir- 
cuit, would  be  momentarily  the  full  line  voltage  of  1,200;  there- 
fore, the  space  separating  the  contact  points  was  increased  from 
8/ia  to  about  3/s  in.,  or  in  other  words  a  mogul  base  was  neces- 
sary, instead  of  the  standard  Edison  base,  to  safe-guard  against 
arcing  over.  This  large  base  in  turn  necessitated  a  special  shape 
of  lamp  bulb  and  the  use  of  a  shade  with  a  fitter  larger  than  the 
standard  2>4  in.  size.  A  metal  holder  is  manufactured  to  prop- 
erly cover  the  outlet  box  (all  the  wiring  on  high-voltage  circuits 
should  preferably  be  in  metal  conduit)  and  this  holder  takes  a 
white  glass  shade  with  a  3%  m-  fitter. 

Sometime  ago  it  was  debated  whether,  on  account  of  possible 
breakage  due  to  inertia  of  the  shade  and  sudden  stopping  and 
starting  of  cars,  it  would  not  be  better  to  standardize  a  2^4  m- 
or  a  334  m-  fitter  for  the  usual  installation.  However,  the  results 
so  far  have  indicated  that  no  trouble  is  to  be  found  when  using 
a  shade  with  the  regular  2]/^  in.  fitter.  Of  course,  it  is  assumed 
that  this  refers  to  only  those  properly  made  shades  which  are 
carefully  annealed. 

There  is  on  the  market  a  metal  holder  for  shades  with  2^4  m 
fitters,  for  which  prismatic  or  white  glass  shades  are  available, 
either  with  or  without  a  lip. 

If  any  operating  companies  find  that  they  lose  a  considerable 
number  of  lamps  by  theft,  they  may  prevent  this  through  the 
use  of  a  lamp  receptacle  in  which  the  lamp  screws  into  a  closely 
coiled  spring  wire.  This  wire  acts  as  a  screw  thread,  allowing 
the  lamp  base  to  be  inserted  easily,  but  fastens  it  when  one  at- 
tempts to  unscrew  the  lamp.  Pressing  out  the  coiled  wire  by  a 
screw-driver  blade  or  similar  tool  allows  the  lamp  to  be  removed. 

The  author  presents  exact  data  on  the  angles  at  which  glare  is 
found,  but  shows  results  of  some  experimentations  that  is  diffi- 
cult to  perform,  and  rather  uncertain  to  generalize  upon.  As  to 
angles  of  cut-off  in  shades  of  various  depths,  it  is  a  matter  of 
considerable  difference  of  opinion  as  to  how  deep  a  shade  must 
be.     Other  tests  might  lead  to  different  results. 


10O  TRANSACTIONS   I.    E.    S. — PART   I 

Obviously,  also,  any  shade  through  which  the  light  is  not  soft- 
ened will  not  be  satisfactory,  whatever  its  depth  and  its  large 
angle  of  cut-off. 

Judging  from  observation  of  open-bottom  shades  of  various 
depths,  I  would  always  advocate  using  bowl- frosted  lamps  with 
94- watt  units,  and  in  some  cases  on  other  sizes  as  well. 

Fig.  7  gives  interesting  data,  but  would  be  more  nearly  ap- 
plicable to  car  lighting  if  one  could  know  what  were  the  con- 
ditions of  test.  The  shapes  of  reflectors,  the  surroundings  and 
other  items  all  enter  into  and  influence  such  results. 

The  cleaning  cost  for  any  shade  installation,  I  believe,  will 
usually  be  found  to  be  greater  than  that  given  in  Table  V.  at 
least  in  Pittsburgh. 

Mr.  G.  \Y.  Roosa:  Reflectors  should  be  cleaned  as  often  as 
the  car  windows ;  but  I  imagine  that  in  general  practise  this  is  not 
done  since  dirt  on  shades  and  lamps  is  not  so  apparent.  Many 
operators  do  not  realize  the  amount  of  the  loss  of  light  due  to 
dirt. 


IVES:     PHYSICAL    PHOTOMETRY  IOI 

PHYSICAL  PHOTOMETRY.* 


BY    HERBERT  E.   IVES. 


Synopsis:  This  paper  deals  with  the  question  of  substituting  some 
physical  instrument  for  the  eye  in  photometry.  The  nature  of  light  as  a 
measurable  physical  quantity,  the  defects  of  the  eye  as  a  measuring  instru- 
ment and  the  desirable  qualities  of  a  physical  photometer  are  reviewed. 
Next  the  various  means  which  have  been  suggested  are  examined,  among 
these  selenium,  the  photo-electric  cell  and  the  photographic  plate.  A  new 
thermo-couple  artificial  eye  is  described,  with  an  account  of  its  perform- 
ance as  a  laboratory  normal  eye  for  colored  light  photometry. 

INTRODUCTION. 

It  is  perhaps  not  unsafe  to  say  that  the  great  majority  of  those 
who  have  photometric  observations  to  make  in  the  course  of 
their  daily  work  have  at  one  time  or  another  been  attracted,  or 
even  fascinated,  by  the  idea  of  finding  some  substitute  for  the 
eye,  some  instrument  to  make  light  measurement  more  like  other 
kinds  of  measurement  to  which  we  are  accustomed.  Whether  the 
object  sought  is  greater  sensibility,  simplification  of  apparatus, 
greater  ease  in  reading,  or  the  production  of  an  artificial  normal 
eye  to  help  solve  the  heterochromatic  photometry  difficulty,  the 
panacea  recurrently  brought  forward  is  the  physical  photometer. 

As  is  usually  the  case  when  the  same  idea  arises  spontaneously 
in  many  minds,  there  is  a  real  field— or  rather  fields— for  devices 
to  take  the  place  of  the  eye.  But,  as  is  frequently  the  case  with 
a  popular  idea,  there  have  been  many  premature  and  ill-consid- 
ered attempts  to  use  this  or  that  medium  sensitive  to  light, 
attempts  based  on  insufficient  or  faulty  analysis  of  the  real 
requirements.  Much  misdirected  work  might  have  been  saved  or 
made  useful  had  it  been  preceded  by  a  very  careful  study  of  the 
real  weaknesses  of  visual  photometry. 

The  present  paper  is  an  attempt  at  a  thorough  analysis  of  the 
light  measurement  problem  from  the  standpoint  of  a  possible 
purely  objective  means  of  solution.  This  analysis  must  start  at 
the  basis  of  photometric  science  with  the  query :  What  is  light  ? 
It  must  then  study  the  eye  as  a  measuring  instrument;  it  must 
establish  criteria  to  which  an  artificial  eye  must  conform.     Fol- 

*  A  paper  read  at  a  meeting  of  the   Philadelphia  Section  of  the  Illuminating  Entri 
neering  Society,  November  7.  1914.  g  B,ug 

.  The  Illuminating  Engineering  Society  is   not   responsible  for   the    statements  or 
opinions  advanced  by  contributors. 


102  TRANSACTIONS    I.    K.    S. PART    I 

lowing  this,  a  review  will  be  made  of  the  various  promising 
instruments  and  methods  for  physical  photometry,  noting  how 
closely  they  approach  the  criteria  established.  From  this  study 
it  is  hoped  to  show  what  forms  of  physical  photometers  are  even 
now  available  for  some  kinds  of  work,  and  what  we  may  look 
forward  to  in  the  near  future. 

WHAT   IS  LIGHT? 

Steering  clear  of  what  has  appeared  to  be  a  stumbling  block 
to  some,  let  us  at  once  clearly  distinguish  between  the  sensation 
of  light,  which  is  purely  subjective,  and  the  usual  cause  of  that 
sensation,  namely,  radiant  energy  of  certain  qualities.  It  is  with 
this  latter  alone  that  we  have  to  do  at  the  present  time  in  pho- 
tometry. Starting  then,  without  further  discussion,  with  the  fact 
that  light  is  to  be  identified  with  radiant  energy,  the  most  impor- 
tant question  demanding  answer  is  how  to  differentiate  light 
from  other  forms  of  radiant  energy.  The  physicist  has  usually 
been  content  to  accept  Lord  Kelvin's  dictum  that  "if  you  can  see 
it,  it  is  light."  Such  a  conception  of  the  nature  of  light,  perhaps 
more  than  anything  else,  is  responsible  for  the  encumbering  of 
our  physical  journals  and  texts  with  values  of  so-called  "luminous 
efficiencies,"  which  indicate  only  in  the  crudest  approximation 
the  relative  light-giving  efficiencies  of  illuminants.  Any  useful, 
exact,  quantitative  evaluation  of  radiation  as  light  demands  a 
better  considered  definition  than  this.  Such  a  definition  is  that 
officially  adopted  by  the  Illuminating  Engineering  Society, 
namely,  that  "luminous  flux  is  radiant  power  evaluated  according 
to  its  capacity  to  produce  the  sensation  of  light."  This  defini- 
tion tells  us  at  once  what  weight  is  to  be  attached  not  alone  to 
invisible  radiations,  such  as  those  beyond  the  violet,  but  to  that 
inefficient  radiation  at  the  ends  of  the  visible  spectrum  which  has 
furnished  so  large  a  share  of  the  "visible"  energy  in  the  luminous 
efficiency  determinations  to  which  reference  has  been  made.1  It 
presupposes  the  existence  of  a  definite  determinable  evaluating 
factor,  the  stimulus  coefficient  or  luminous  efficiency,  upon  which 
more  will  be  said  in  discussing  the  eye. 

Enough  has  here  been  said  on  the  nature  of  light  to  make  clear 
the  backbone  of  all  schemes  for  physical  photometry,  namely,  the 

1  Ives,  H.  E..  luminous  Efficiency;  Trans.  I.  E.  S..  vol.  V.,  p.  113. 


IVES:     PHYSICAL    PHOTOMETRY  IO3 

measurement  of  radiation.  We  shall  see,  however,  that  the 
further  refinement  of  making  the  proper  evaluation  as  light  is 
not  necessary  for  all  the  purposes  for  which  the  physical  pho- 
tometer has  been  desired. 

THE  EYE  AS  A  MEASURING  INSTRUMENT. 

There  are  in  general  two  types  of  measuring  instruments,  those 
which  indicate  by  the  actual  magnitude  of  their  response,  and 
those  which  indicate  the  equality  or  lack  of  equality  of  two  com- 
pared stimuli.  The  first  of  these  types  is  well  illustrated  by  the 
common  switchboard  ammeters  and  voltmeters,  from  which  the 
current  or  voltage  is  read  off  directly  by  the  position  of  a  pointer 
on  a  scale.  The  second  type,  sometimes  called  "null"  instru- 
ments, is  illustrated  by  the  potentiometer  with  its  sensitive  gal- 
vanometer used  to  detect  the  condition  of  no  potential.  In  gen- 
eral the  null  type  of  instrument  can  be  made  to  yield  greater 
sensibility,  but  this  must  be  paid  for  by  greater  complexity  of 
apparatus. 

The  eye  belongs  in  the  class  of  null  instruments.  It  is  common 
knowledge  that  one  can  make  only  the  crudest  estimate  of  candle- 
power  by  looking  at  a  light,  no  matter  what  one's  previous  experi- 
ence. Nor  is  it  possible  to  estimate  with  any  degree  of  accuracy 
how  much  brighter  one  light  or  illuminated  surface  is  than 
another  alongside.  What  the  eye  can  do,  and  do  very  well,  is  to 
decide  when  two  adjacent  surfaces  are  equally  bright.  That  is, 
the  eye  can  take  the  place  of  the  galvanometer  in  a  potentiometer. 
Just  as  the  latter  tells  when  there  is  no  difference  of  potential 
applied  to  its  two  sides,  so  the  eye  tells  when  there  is  no  differ- 
ence of  brightness.  Just  as  in  the  potentiometer  we  get  at  our 
measure  of  relative  potentials  by  knowledge  of  the  conditions  of 
resistance  and  the  value  of  the  voltage  standard,  so  in  photom- 
etry we  arrive  at  our  result  by  knowing  the  distances  between 
lamps  and  screens,  the  value  of  the  standard  and  the  transmis- 
sions of  various  auxiliaries. 

When  so  used  the  sensibility  of  the  eye  to  small  differences  is 
quite  high.  Differences  of  the  order  of  magnitude  of  y2  per 
cent,  are  sufficient  to  register  as  inequality.  This  degree  of  sen- 
sibility is  probably  quite  sufficient  for  present  technical  needs. 


io4 


TRANSACTIONS    I.    E.    S. PART    I 


For  scientific  purposes,  cases  might  of  course  arise  where  greater 
sensibility  would  be  advantageous. 

So  far  nothing  has  been  said  about  color,  or  more  properly, 
color  differences.  As  long  as  the  two  lights  under  comparison 
are  of  the  same  color  a  condition  of  equality  can  be  decided  upon. 
But  if  the  lights  are  different  in  color  the  one  condition  under 
which  the  eye  has  a  high  degree  of  precision  is  lost. 

The  relative  apparent  brightness  of  two  adjacent  colored  sur- 
faces is,  with  an  individual  eye,  a  function  of  the  illumination,  of 
the  size  of  the  surface,  of  the  surroundings,  of  the  past  history 
of  the  observer.  It  may  be  determined  with  more  or  less  pre- 
cision and  with  varying  results  by  different  photometric  methods. 


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Fig.  i.— Relative  luminous  efficiencies  of  the  various  spectral  radiations.  (Average  normal 
spectral  luminosity  curve  of  eighteen  observers  for  an  equal  energy  spectrum.) 

I  f  another  eye  is  used  a  different  result  may  be  obtained.  Hence 
it  is  that  the  evaluation  of  radiant  power  "according  to  its 
capacity  to  produce  the  sensation  of  light"  is  not  a  simple  matter. 
It  is  my  belief,  however,  that  as  a  result  of  a  thorough  study  of 
photometric  methods  in  relation  to  color,  evaluation  factors  can 
be  determined  applicable  to  the  great  majority  of  practical  cases. 
Such  a  set  of  evaluating  factors  constitute  a  spectrum  luminosity 
curve  of  the  average  eye.  Such  a  curve  is  shown  in  Fig.  I."  It 
will  be  assumed  in  what  follows,  without  further  discussion,  that 
the  question  of  color  in  physical  photometry  is  completely  cov- 

-  Ives,  H.  E.,  The  Luminosity  Curve  of  the  Average  Eye;  Phil.  Mag.,  Dec,  1912. 


IVES:     PHYSICAL    PHOTOMETRY  105 

ered  by  the  common  adoption  of  a  definite  luminosity  curve  or 
luminous  efficiency  curve  of  the  spectrum. 

WHAT  IS  SOUGHT  IN  AN  ARTIFICIAL  EYE? 

The  various  goals  sought  in  physical  photometry  owe  their 
origin  to  dissatisfaction  with  one  or  another  of  the  limitations  of 
the  eye  just  discussed.  They  should  be  listed  and  discussed 
separately,  as  will  now  be  done,  although  various  combinations 
of  desirability  and  feasibility  will  be  found,  which  will  make  any 
classification  merely  of  temporary  aid.  A  helpful  preliminary 
division  is  into  the  cases  where  there  is  no  color  difference  and 
vice  versa. 

A.  Where  there  is  no  color  difference — (i)  Indication  by  posi- 
tion rather  than  by  quality.  Probably  one  of  the  most  insistent 
demands  for  the  physical  photometer  has  its  root  in  the  desire 
to  avoid  the  consideration  of  quality,  substituting  for  it  the  esti- 
mation of  position.  Thus  while  the  eye  can  detect  a  difference 
of  brightness  of  J/2  per  cent,  it  is  probably  almost  universally 
true  that  observers  practised  and  unpractised  much  prefer  to 
have  this  difference  indicated  by  the  movement  of  a  pointer  over 
a  scale.  There  are  several  reasons  for  this.  For  one  thing  the 
great  majority  of  our  measuring  instruments  are  of  this  type.  I 
know  of  but  one  instrument  where  a  quantity  which  could  be 
measured  by  a  moving  pointer  is  indicated  by  the  intensity  of 
illumination,  and  in  this  case  it  is  done  because  the  other  factor 
in  the  comparison  cannot  readily  be  shown  by  positional  indica- 
tions.3 For  another  thing  most  of  our  measuring  instruments 
have  a  comparatively  enormous  store  of  power  to  draw  upon, 
so  that  the  problem  of  getting  large  deflections  is  the  least  to  be 
faced.  As  we  shall  see  later,  the  condition  is  far  different  with 
light  measurement.  Again,  the  eye  is  probably  working  at  higher 
efnciency  in  estimating  the  position  of  a  pointer  than  in  esti- 
mating equality  of  brightness,  for  quality  discrimination  is  at  its 
best  with  the  black  pointer  and  divisions  on  a  light  background. 
and  binocular  vision  and  the  possibility  of  movement  render  our 
determination  of  position  very  exact.  At  any  rate  this  desire  for 
positional  indication  rules  no  matter  whether  readings  are  to  be 
made  by  null  method  or  by  proportional  indication. 

3  Ives,  H.  E.,  A  New  Form  of  Watts  Per  Candle  Meter;  Electrical  World,  June  8,  1912. 


106  TRANSACTIONS   I.    E.    S. — PART    I 

(2)  Proportional  indication.  A  very  common  demand  made 
of  a  physical  photometer  is  that  it  shall  indicate  luminous  intensity 
by  the  magnitude  of  the  deflections  of  a  pointer.  In  short,  that 
we  may  by  this  means  be  freed  from  the  limitations  of  the  null 
method,  for  which  the  eye  is  alone  capable.  A  great  advantage 
of  this  over  the  null  method  lies  in  the  consequent  simplification 
of  apparatus.  It  enables  us  to  dispense  with  the  comparison 
lamp,  with  the  moving  carriage  and,  in  fact,  with  the  whole  pho- 
tometer track. 

(3)  High  sensibility.  Two  kinds  of  sensibility  must  be  distin- 
guished. First  is  what  may  be  called  total  sensibility  measured 
by  the  amount  of  light  which  may  be  detected.  Thus,  as  we 
know,  the  eye  can  see  under  illuminations  extending  all  the  way 
from  thousands  of  meter-candles  down  to  thousandths.  Our 
chief  interest  in  sensibility  in  a  physical  photometer  at  present 
is  to  obtain  even  that  total  sensibility  necessary  to  measure  ordi- 
nary working  illuminations  of   the  order  of    10  meter-candles. 

The  second  kind  of  sensibility  is  the  capacity  to  detect  small 
differences.  It  has  already  been  stated  that  the  present  attainable 
differential  sensibility  with  visual  photometry  is  high  enough  for 
most  practical  purposes.  This  sensibility  is,  however,  the  limit  we 
may  expect,  unless  some  new  principle  like  the  contrast  principle  of 
the  Lummer-Brodhun  should  be  found.  If  higher  sensibility  is 
ever  necessary  it  must  be  sought  in  the  physical  photometer,  to 
which  there  is  apparently  no  inherent  limitation  to  sensibility, 
whatever  may  be  the  present  practical  limitations.  Such  greater 
sensibility  might,  however,  be  purchased  only  at  the  price  of 
simplicity;  the  null  method  would  probably  be  necessary,  leaving 
as  the  only  advance  over  the  eye  (apart  from  the  greater  sensi- 
bility) indication  by  position. 

(4)  Simple  method  of  response.  Where  there  is  no  question 
of  the  use  of  color  filters  to  alter  the  wave-length  sensibility  of 
the  sensitive  surface  the  advantage  of  some  simple  mode  of 
response,  such  as  response  directly  proportional  to  stimulus,  is 
exactly  on  a  par  with  that  in  any  measuring  device.  Perhaps 
the  most  desirable  scale  would  be  one  giving  the  same  increment 
of  deflection  for  the  same  percentage  change  of  stimulus  in  all 
the  most  used  parts  of  the  scale  (Fechner's  law).  The  most  gen- 
erally useful  scale  is  one  giving  directly  proportional  deflections. 


IVES  :     PHYSICAL    PHOTOMETRY  IO7 

(5)  Constancy.  A  physical  photometer  whose  indications  were 
absolutely  constant  from  time  to  time  would  be  the  acme  of 
desirability.  Especially  is  this  desirable  if  its  indications  are  not 
according  to  some  simple  law.  In  this  case  the  labor  of  recali- 
brating after  change  would  be  very  difficult.  If,  on  the  other 
hand,  some  simple  law  is  followed,  constancy  over  long  periods 
of  time  is  not  absolutely  essential.  Frequent  checking  with  a 
standard  is  too  common  a  procedure  in  exact  measurement  to  be 
a  serious  drawback. 

(6)  Recording  capacity.  In  line  with  the  modern  wide  use  of 
recording  instruments,  we  may  note  that  a  recording  photometer 
would  have  much  the  same  reasons  for  use  in  technical  light 
measurement  as  recording  pyrometers  have  in  heat  or  tempera- 
ture measurements. 

(7)  Integrating  capacity.  A  photometer  which  could  store  up 
its  impressions  would  have  certain  uses.  For  instance  it  would 
simplify  the  measuring  of  fluctuating  light  sources  such  as  cer- 
tain arc  lamps.  It  would  as  well  offer  possibilities  in  measuring 
the  quantity  of  light  delivered,  in  distinction  to  gas  or  electrical 
energy,  for  which  the  public  service  company  now  has  to  charge, 
thereby  shouldering  all  the  cost  of  increased  efficiency  in  lighting 
means. 

(8)  Practicability.  Various  paramount  considerations  with 
respect  to  total  sensibility  and  to  convenience  may  be  grouped 
under  "practicability."  Thus  every  desirable  feature  so  far  men- 
tioned would  be  of  no  immediate  practical  value  if  the  physical 
photometer  could  be  operated  only  in  a  specially  built  laboratory 
and  under  certain  weather  conditions.  All  sensitive  apparatus  is 
necessarily  delicate,  and  it  therefore  becomes  necessary  to  know 
whether  the  physical  photometer  is  to  be  feasible  only  in  the 
standardizing  laboratory,  or  in  the  industrial  laboratory,  or  in  the 
field,  and  what  its  limitations  will  be  in  each  case. 

B.  Where  there  is  color  difference. — To  the  desirable  qualities 
which  have  just  been  enumerated  must  be  added  another  which  is 
indispensable  if  lights  of  different  colors  are  to  be  compared. 
The  sensitive  medium  must  be  affected  by  the  different  wave- 
length radiations  of  the  spectrum  in  exactly  the  same  relative 
amounts  as  the  average  eye.     The  extreme  unlikelihood  of  any 


io8 


TRANSACTIONS    I.    E.    S. PART    I 


sensitive  substance  possessing  this  distribution  of  sensibility  as 
found  lends  emphasis  to  the  necessity  of  a  quality  already  men- 
tioned. The  relation  between  stimulus  and  response  must  be  of 
a  simple  character,  preferably  it  should  be  rectilinear.  Unless 
this  is  the  case  it  is  not  possible  to  alter  the  wave-length  sensi- 
bility curve  by  the  use  of  absorbing  media  or  equivalent  means. 
This  requirement  must  be  met  no  matter  whether  the  indications 
are  to  be  by  a  pointer  over  a  graduated  scale  or  by  the  null 
method. 

INSTRUMENTS  USED  TO  MEASURE  RADIATION. 
A  detailed  description  of  the  instruments  available  for  measur- 
ing radiation  will  not  be  attempted  here,  as  such  descriptions  are 
to  be  found  in  the  standard  physical  text  books  and  journals. 


Fig.  2.— Bolometer.    The  resistance  of  the  thin  platinum  grid,  P,  is  altered  when  it 
receives  radiation,  thus  disturbing  the  balance  of  the  Wheatstone  bridge. 

The  salient  points  of  each  are  exhibited  in  the  Figs.  2  to  7  with 
their  attendant  legends.  Our  chief  interest  here  is  in  classifying 
and  appraising  them  for  photometric  needs. 

These  instruments  can  be  divided  on  two  bases — the  basis  of 
sensitiveness,  i.  e.,  the  quantity  of  radiation  they  can  measure,  and 
the  basis  of  their  behavior  to  various  qualities  of  radiation,  or 
selectivity,  as  it  is  called.  For  instance,  a  black  bulb  thermom- 
eter is  equally  sensitive  to  all  kinds  of  radiation,  visible  or  in- 
visible, but  it  takes  a  very  large  amount  of  radiation  to  produce 
respectable  indications.  On  the  other  hand  the  photographic 
plate  is  chiefly  sensitive  to  blue,  violet  and  ultra-violet  light,  but 
it  is  so  sensitive  that  instantaneous  photography  is  a  common- 


IVES:     PHYSICAL    PHOTOMETRY 


109 


place.  It  may  be  noted  in  passing  that  there  appears  to  be  no 
exception  to  the  general  rule,  of  which  these  cases  are  examples, 
that  great  total  sensitiveness  is  obtainable  only  at  the  cost  of 
limited  spectrum  range  of  sensibility.  The  eye,  with  its  range  of 
only  a  single  octave  of  the  lengthy  scale  from  X-rays  to  wireless, 
is  another  notable  example  of  this  fact. 

The  chief  non-selective  radiometers  are  the  bolometer,  the 
thermopile,  the  radiometer  and  the  radiomicrometer.  The  first 
of  these,  made  famous  by  the  researches  of  Langley,  consists  es- 
sentially of  a  fine  strip  of  blackened  platinum  whose  electrical 
resistance  is  altered  with  any  change  in  its  temperature.  Radia- 
tion falling  on  the  strip  heats  it  and  causes  a  change  of  resistance, 


Fig.  3.— Simple  thermopile.    The  unequal  heating  of  the  hot  and  cold 
junctions  causes  an  electric  current  to  flow. 

which  is  indicated  by  a  sufficiently  sensitive  galvanometer  con- 
nected to  the  Wheatstone  bridge  system,  of  which  the  platinum 
strip  is  one  element. 

The  thermopile  consists  of  one  or  more  junctions  of  dissimilar 
metals  or  alloys  selected  as  having  a  large  thermo-electric  power. 
When  the  junctions  are  heated  by  radiation  the  electromotive 
force  produced  is  sufficient  to  drive  a  small  current  through  a 
galvanometer  connected  in  series  with  them.  Both  of  these  in- 
struments, it  will  be  noted,  necessitate  a  galvanometer  as  auxiliary. 


no 


TRANSACTIONS    I.    E.    S. PART    I 


Their  sensibility  and  practicability  are  to  a  large  degree  condi- 
tioned by  this  limitation.  The  two  remaining  instruments  of  this 
group  are  simpler  in  this  respect,  being  complete  in  themselves. 
The  radiometer,  developed  by  E.  F.  Nichols  from  the  toy  de- 
vised by  Crooks,  consists  of  a  light  double  vane  suspended  in  a 
partial  vacuum.  One  side  of  each  vane  is  blackened  and  when 
radiation  falls  on  one  of  these  blackened  faces  the  vane  is  rotated, 
its  motion  being  shown  by  the  reflection  of  a  spot  of  light  by  a 
small  mirror  carried  on  the  suspending  fiber. 


Pig.  1. — Radiometer.    The  radiation  falls  on  a  light  vane,  blackened  on  one 
side,  in  an  evacuated  enclosure  which  is  rotated  on  its  support. 

The  Boys  radiomicrometer  is  practically  a  thermo-junction  be- 
tween the  poles  of  a  magnet.  When  a  current  flows  through  the 
thermo-junction  circuit,  due  to  its  heating,  the  coil  of  wire  to 
which  the  junction  is  attached  turns  in  the  magnetic  field,  its 
motion  being  indicated  by  a  beam  of  light  from  an  attached 
mirror. 

Coming  now  to  selective  radiometers,  the  chief  of  these  are  the 
selenium  cell,  the  photo-electric  cell  and  the  photographic  plate. 


IVES:     PHYSICAL    PHOTOMETRY 


III 


Of  these,  selenium  has  perhaps  secured  the  greatest  notoriety. 
The  applicability  of  this  remarkable  element  is  due  to  its  property 
of  changing  its  electrical  resistance  under  the  action  of  light. 
Consequently  when  connected  in  series  with  a  source  of  electro- 
motive force  and  a  sensitive  galvanometer,  the  illumination  or 
obscurement  of  the  sensitive  surface  is  detectable. 

The  photo-electric  cell,  in  particular  when  constructed  from  one 


Fig.  5.— Radioniicronieter.  The  radiation  falls  on  a  thermo-junction  which  is  carried  on 
a  small  coil  of  wire.  The  coil  lies  between  the  poles  of  a  magnet,  and  when  radiation 
on  the  thermopile  causes  a  current  to  flow,  the  coil  rotates. 


of  the  alkali  metals,  is  one  of  the  most  interesting  and  lately  most 
studied  possibilities  in  this  line.  In  brief,  an  alkali  metal  surface, 
preferably  in  a  vacuum  or  partial  vacuum,  when  illuminated  gives 
off  negative  electricity.  When  connected  with  an  electrometer 
or  a  sensitive  galvanometer  (there  are  several  different  methods 
of  arranging  the  apparatus)  a  current  flows  upon  the  illumination 
of  the  surface.     The  last  of  these  selective  physical  photometers 


112 


TRANSACTIONS   I.    E.    S. — PART    I 


to  be  mentioned  here  is  the  photographic  plate,  which  is  the  best 
known  example  of  chemical  change  produced  by  light.  From  our 
standpoint  the  photographic  plate  is  a  means  of  recording  the 
amount  of  incident  light  by  the  amount  of  deposited  silver.  It  is 
quite  distinct  from  all  the  preceding  means  considered  in  that  it 
requires  nothing  in  the  way  of  an  auxiliary  galvanometer  or  con- 
ditions of  extreme  freedom  from  vibration. 

These  three  instruments  just  considered  have  been  grouped 


Fig.  6.— Selenium  cell  and  connections.    L,  light  source  ;  S.shutter  ;  C, 
selenium  ;  D,  battery  ;  G,  galvanometer. 


'HHHHF-/ 


Fig.  7.— Connections  for  photo-electric  cell.     B,  battery  ;  C,  cell ; 
G,  galvanometer  ;  E,  earth. 

together  for  the  reason  that  they  are  not,  in  their  natural  condition, 
equally  sensitive  to  all  qualities  of  radiation.  Thus  the  selenium 
cell,  speaking  roughly,  is  sensitive  chiefly  to  radiations  near  the 
visible.  The  photo-electric  cell,  of  sodium,  potassium,  rubidium 
or  caesium,  is  chiefly  sensitive  in  the  ultra-violet,  but  increasing 
toward  the  visible  region  in  the  order  given.  The  photographic 
plate  is  normally  most  sensitive  to  the  blue,  violet  and  ultra- 
violet. By  means  of  sensitizers  however  it  may  be  made  sensi- 
tive as  far  as  the  deep  red. 


IVES:     PHYSICAL    PHOTOMETRY  II3 

DISCUSSION  OF  THESE  INSTRUMENTS  AS  PHYSICAL 
PHOTOMETERS. 

It  will  now  be  our  task  to  discuss  each  of  these  instruments 
with  reference  to  the  desirable  qualities  previously  outlined.  From 
this  discussion  one  may  hope  to  determine  in  what  lines  of  work 
physical  photometry  is  apt  to  be  of  practical  value  now  or  in  the 
near  future. 

At  this  point  it  becomes  necessary  to  study  the  quantity  of 
radiation  involved  in  what  we  have  decided  to  call  light,  in  par- 
ticular reference  to  the  sensibility  of  the  instruments  we  have 
been  considering.  For  some  reasons  it  would  be  preferable  to 
reduce  all  the  quantities  involved  to  absolute  units,  but  we  may 
for  our  present  purpose  save  much  time  by  utilizing  the  fortunate 
fact  that  the  sensibility  of  radiometric  instruments  is  usually  ex- 
pressed in  terms  of  the  effect  produced  by  a  candle  at  a  meter's 
distance — our  own  familiar  meter-candle.  Thus  it  is  found  that, 
using  the  most  sensitive  instrument  yet  constructed  of  the  class 
of  the  bolometer,  radiometer  and  thermopile,  a  deflection  of  50 
centimeters  per  square  millimeter  of  sensitive  area  is  of  the  order 
of  magnitude  obtainable. 

Now  the  most  recent  determination  of  the  luminous  efficiency 
of  the  4-watt  electric  lamp  is  0.45  per  cent.  Consequently  a  16 
candlepower  lamp  at  a  meter  distance,  which  gives  no  inconsid- 
erable illumination,  would,  if  measured  through  a  proper  light- 
evaluating  screen,  give  only  4  millimeters  deflection.  And  this 
is  under  the  most  refined  laboratory  conditions,  with  the  most 
perfect  freedom  from  mechanical  disturbance,  and  from  changes 
in  the  temperature  of  the  surroundings.  Reference  to  Fig.  8, 
where  the  total  radiated  energy,  and  the  energy  evaluated  as  light 
are  shown,  tells  the  same  story.  These  illustrations  bring  us  at 
once  to  the  most  serious  problem  in  physical  photometry.  The 
amount  of  energy  available  as  light  is  of  excessive  smallness. 
This  difficulty  can  be  met  and  is  being  met  in  various  ways.  In 
some  of  the  instruments  the  exposed  area  may  be  made  greater 
than  one  square  millimeter;  means  are  being  studied  to  increase 
the  intrinsic  sensitiveness,  such  as  evacuating  the  surrounding 
space;  greater  freedom  from  the  effects  of  changes  in  the  local 
temperature  is  obtained  by  instruments  of  the  compensated  type; 


1  14  TRANSACTIONS    I.    E.    S. —  PART    I 

and  every  year  brings  improvements  in  the  sensibility  and  rug- 
gedness  of  sensitive  galvanometers  and  other  auxiliaries.  How 
far  we  have  progressed  in  this  direction  is  shown  below,  where 
actual  practical  examples  are  given  wherever  practicable. 

A.  The  Non-Selective  Instruments. — The  bolometer,  radio- 
meter, radiomicrometer  and  thermopile  may  be  treated  in  practi- 
cally the  same  description.  First,  the  case  where  there  is  no 
question  of  color  difference;  for  instance  the  measurement  of 
two  electric  incandescent  lamps  of  identical  color.    These  instru- 


3.5        4.0      45 


Fig.  8. — Ratio  of  luminous  flux  to  radiant  power  in  the  carbon  lamp. 
Small  area,  luminous  flux. 

ments  possess  the  simplest  mode  of  response,  that  is,  their  indi- 
cation is  directly  proportional  to  the  intensity  of  the  incident 
radiation.  They  therefore  lend  themselves  to  the  problem  of 
reducing  our  measurements  to  a  positional  basis  and  in  that  way 
to  simplification  of  apparatus.  Their  practicability  depends 
chiefly  on  the  amount  of  radiant  energy  available.  Since  there 
is  no  question  of  color  difference,  we  frequently  meet  with  the 
possibility  of  utilizing  a  large  amount  of  invisible  energy  to  help 
out.  Thus  with  the  two  incandescent  lamps  we  are  considering 
if  we  measure  the  total  energy  instead  of  simply  the  visible  we 
have  at  least  ioo  times  as  much  at  our  command,  and  this  means 
the  difference  between  delicate  laboratory  conditions  and  the  or- 
dinary photometer  room.  Whether  this  opens  up  a  really  valu- 
able possibility  or  not  depends  on  whether  the  light  and  the  total 
energy  are  always  proportional    in   the  two  supposedly  similar 


IVES:     PHYSICAL    PHOTOMETRY  115 

light  sources.  In  many  cases  this  is  true.  A  practical  example  of 
a  promising  field  for  the  utilization  of  total  energy  measurements 
to  secure  positional  indications  is  the  reading  of  gas  flame  candle- 
powers.  So  much  energy  is  here  available  that  with  a  string 
galvanometer  and  a  large  area  surface  thermopile  it  should  be 
possible  not  only  to  read  but  automatically  to  register  candle- 
powers  by  the  photographic  registration  of  a  moving  spot  of 
light  or  similar  sensitive  method. 

A  considerable  degree  of  constancy  is  to  be  expected  in  the 
readings  of  these  instruments,  sufficient  at  least  so  that  checking 
with  a  standard  at  occasional  intervals  during  a  series  of  meas- 
urements would  be  sufficient.  The  possibility  of  securing  greater 
differential  sensibility  than  with  visual  photometry  is  not  to  be 
anticipated,  particularly  where  one  is  compelled  to  use  the  in- 
visible energy  to  obtain  workable  deflections. 

But  so  few  and  of  so  little  importance  are  the  cases  where  we 
work  with  lights  of  exactly  the  same  quality  that  the  slender 
possibility  we  have  just  considered  is  of  little  more  than  aca- 
demic interest.  This  is  shown  by  the  fact  that  practically  all  the 
recorded  attempts  to  use  these  radiometers  in  photometry  have 
involved  some  scheme  for  approximating  the  luminosity  curve 
of  the  eye. 

Turning,  then,  to  the  case  of  photometry  with  a  color  differ- 
ence, we  find  that  the  first  difficulty  with  the  non-selective  radiom- 
eters is  that  they  are  not  sensitive  to  radiation  as  is  the  eye, 
but  to  the  whole  scale.  This  has  two  consequences,  first,  that 
some  means  must  be  adopted  to  alter  the  wave-length  sensibility 
and,  second,  as  already  pointed  out,  that  when  this  alteration  is 
made,  the  remaining  sensibility  is  extremely  small. 

However,  since  these  instruments  possess  the  simplest  mode 
of  response,  it  is  feasible  to  alter  their  distribution  of  sensibility, 
and  the  fact  is  that  at  the  present  time  the  only  truly  satisfactory 
physical  photometer  is  of  this  type.  Before  describing  this  in- 
strument, recently  developed  in  the  United  Gas  Improvement 
Company's  physical  laboratory,  historical  mention  should  be 
made  of  earlier  instruments  of  the  same  type. 

Fery,4  in  1908,  constructed  and  used  a  radiomicrometer  over 

*  Bull.  Soc.  Frauc  de  Physique,  1908,  p.  148. 


Il6  TRANSACTIONS   I.    E.    S. — PART    I 

which  was  placed  an  absorbing  solution  of  copper  acetate  to  ob- 
struct the  infra-red  radiation  and  to  cut  down  the  "visible" 
roughly  in  proportion  to  its  luminous  efficiency.  This  instru- 
ment though  crude  was  on  the  right  principle  and  proved  the 
feasibility  of  the  scheme.  It  was  used  quite  extensively  by  Fery 
in  his  studies  of  the  power  relations  in  the  incandescent  lamp. 
In  191 1  Houston,5  in  connection  with  his  proposal  for  a  primary 
standard  of  light,  described  a  combination  of  two  solutions — 
copper  sulphate  and  potassium  dichromate — which  give  a  close 
approximation  to  the  best  determination  at  that  time  of  the 
luminosity  curve  of  the  spectrum.  These  solutions  used  with  a 
radiometer  constitute  a  physical  photometer  calculated  for  lights 
of  any  color.    Recently  Dr.  Karrer,  at  my  suggestion,  worked  out 


Fig.  9. — Thermopile  artificial  eye.    L,,  light  source  ;  S,  shutter  ;  E,  luminosity 
curve  solution  ;  T,  thermopile  ;  G,  galvanometer. 

a  combination  of  three  solutions  in  separate  tanks,  whose  total 
transmission  is  very  closely  the  luminosity  curve  of  the  spectrum 
according  to  the  latest  determinations.  This  solution  has  been 
used  to  make  determinations  of  true  luminous  efficiencies,  but  is 
immediately  applicable  to  photometry. 

Benefitting  by  this  previous  work  I  have  recently  been  able  to 
develop  a  visual  luminosity  medium,  complete  in  one  solution, 
approximating  practically  perfectly  to  the  luminosity  curve  as 
previously  determined  by  him.  This  has  been  set  up  in  front  of 
a  sensitive  surface  thermopile,  thereby  making  an  artificial  eye 
exactly  corresponding  to  the  real  normal  eye  under  the  adopted 
standard  photometric  conditions  (Fig.  9)  and  indicating  position- 
ally  by  the  relative  deflections  of  a  pointer. 

Now,  all  attempts  hitherto  made  in  this  direction  have  labored 

6  Proc.  Royal  Society  A,  191 1,  p.  275. 


IVES:     PHYSICAL   PHOTOMETRY  117 

under  the  great  disadvantage  that  there  has  been  no  means  of 
determining  whether  the  instrument's  readings  were  right.  The 
convenience  and  precision  of  the  former  devices  was  generally 
recognized,  but  whether  their  readings  actually  corresponded  to 
the  true  ones  could  not  be  established,  because  no  standard  method 
of  colored  light  photometry  had  been  developed;  nor  were  there 
any  standard  reproducible  colors  that  had  been  measured  by  any 
photometric  method.  Recently  in  a  paper6  before  this  society  a 
colored  absorbing  solution  of  very  useful  qualities  was  described, 
together  with  complete  measurements  by  the  method  of  colored 
light  photometry  developed  by  the  writer.  With  these  various 
means  at  hand  it  has  been  possible  to  bring  this  problem  to  a 
definite  and  successful  conclusion.  We  have  carried  through 
with  our  physical  photometer  the  same  measurements  made  vis- 
ually with  the  result  shown  in  Fig.  10.  The  agreement  is  so  per- 
fect that  we  are  now  using  the  physical  photometer  directly  in 
those  cases  where  the  solutions  had  already  made  possible  enor- 
mous simplification  of  work.  We  now  use  this  device  to  calibrate 
incandescent  lamps  of  any  color  and  for  the  standardizing  of 
colored  glasses  for  use  in  visual  photometery  to  eliminate  color 
differences  in  practical  work.  We  are  by  this  means  enabled  to 
secure  accurate  and  satisfactory  results  in  a  few  minutes  which 
previously  required  the  cooperation  of  a  large  number  of  obser- 
vers and  several  days  work. 

The  limitations  of  this  device  are  those  already  enlarged  upon, 
namely,  it  is  strictly  a  laboratory  instrument.  It  is  operated  in 
a  basement  as  free  as  possible  from  vibration  and  large  tempera- 
ture changes.  It  must  be  used  with  rather  high  candlepower 
sources  as  close  as  possible  to  the  receiving  surface.  But  these 
are  not  serious  limitations  at  all  from  the  standpoint  of  those 
standardizing  laboratories  in  whose  hands  will  rest  the  calibra- 
tion of  color  difference  eliminating  media.  It  is  to  the  solution 
of  this  important  problem  that  we  offer  this  completely  developed 
physical  photometer. 

B.  The  selective  instruments.  Of  the  selective  instruments  the 
first  to  claim  attention  is  the  selenium  cell.  This  has  attracted 
a  great  deal  of  attention  and  justly  so,  for  it  actually  rivals  the 

6  Ives,  H.  E.,  and  E-  F.,  Kingsbury,  Experiments  with  Colored  Absorbing  Solutions 
for  Use  in  Heterochromatic  Photometry;  Trans.  I.  E.  S.,  vol.  IX,  No.  8. 


n8 


TRANSACTIONS    I.    K.    S. PART    I 


eye  in  sensitiveness.  That  is,  it  makes  possible  the  translation  of 
illuminations  within  the  range  to  which  the  eye  is  accustomed, 
into  movements  of  a  pointer  of  a  magnitude  easily  appreciated. 
By  so  doing,  as  already  pointed  out,  not  only  is  photometric 
reading  made  easier  but  half  of  the  photometer  bar  or  its  equiva- 
lent may  be  dispensed  with. 


Fig.  10. 


10  0  10 

CONCENTRATION.  PER  CENT 
-Comparative  results,  visual  and  physical  photometers. 


40 


The  error  of  many  who  have  tried  to  use  the  selenium  cell  is 
in  their  assumption  that  this  is  all  that  is  needed  to  fit  a  physical 
photometer  for  the  attack  of  any  problem.  We  may  quickly 
differentiate  between  the  use  and  abuse  of  the  selenium  cell  by 
reference  to  the   various   qualifications   previously   enumerated. 


IVES:     PHYSICAL    PHOTOMETRY 


119 


On  the  standpoint  of  sensibility  and  practicability  it  ranks  high. 
Thus  it  is  possible  with  a  cell  of  large  area,  using  dry  cells  as 
source  of  e.  m.  f.,  to  obtain  satisfactory  readings,  on  a  portable 
millivoltmeter,  of  ordinary  artificial  illuminations.  These  are 
defects  in  the  way  of  inertia,  changing  sensibility  and  the  like, 
which,  however,  can  be  largely  met  by  a  fixed  procedure  in 
exposing  and  by  mounting  the  selenium  in  an  evacuated  space. 

Going  at  once  to  the  question  of  behavior  toward  light  of 
different  colors,  a  very  peculiar  and  interesting  state  of  affairs  is 
found.    The  wave-length  sensibility  curve  of  selenium  is  not  the 


800 


700 


600 


500 


o400 


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o 


200 


100 


400. 


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500  600 
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600 


Fig.  11.— Wave  length  sensibility  curves  of  selenium  for  various 
intensities  of  light. 


same  as  that  of  the  eye.  This  alone  is  not  fatal,  provided  the 
substance  is  sensitive  to  all  visible  radiations,  as  selenium  is,  for 
a  sensibility  curve  may  be  altered  as  was  shown  in  the  case  of 
the  radiometers.  It  is  questionable  whether  any  two  selenium 
surfaces  will  be  apt  to  have  exactly  the  same  distribution  of  sen- 
sibility through  the  spectrum,  which  is  a  serious  drawback,  as  it 
would  make  each  cell  an  individual  problem  to  manufacture 
properly  screened.  But  more  serious  than  this  is  the  fact  that 
the  method  of  response  is  different  for  different  colors.     For 


I20  TRANSACTIONS    I.   E.    S. — PART    I 

most  of  the  visible  and  ultra-violet  spectrum  the  response  is  as  the 
square  root  of  the  stimulus,  while  for  the  deep  red  it  is  directly 
as  the  stimulus.7  As  a  consequence  any  absorbing  medium  or 
equivalent  means  for  producing  a  desired  distribution  of  sensi- 
bility through  the  spectrum  is  rendered  worthless.  This  is 
clearly  shown  by  the  wave-length  sensibility  curves  for  different 
intensities  of  illumination  exhibited  in  Fig.  n.  While  an  absorb- 
ing medium  could  be  provided  to  take  care  of  either  of  these 
methods  of  response,  nothing  will  take  care  of  both. 

What  then  is  the  field  for  selenium  in  photometry  ?  This  :  the 
measurement  of  radiation  of  definite  fixed  quality  upon  which  the 
apparatus  has  previously  been  calibrated.  As  long  as  the  ap- 
paratus is  used  throughout  on  this  same  radiation  all  is  well,  but 
immediately  lights  of  different  quality  are  to  be  measured  and 
selenium  is  of  no  value  to  us,  no  matter  how  great  its  sensibility  or 
convenience.  Selenium  is  now  being  used  successfully  in  scientific 
investigations  where  monochromatic  light  must  be  evaluated  under 
conditions  where  the  much  less  sensitive  radiometers  would  be 
out  of  the  question.  It  could  be  used  to  measure  artificial  il- 
luminations with  great  advantage  over  visual  photometers.  But 
if  so  used  it  would,  after  being  calibrated  on  a  carbon  lamp, 
measure  only  carbon  lamps  correctly. 

Our  discussion  of  the  next  selective  instrument — the  photo- 
electric cell — may  be  considerably  shortened  by  reason  of  the 
fullness  with  which  the  previous  instruments  have  been  treated. 
The  photo-electric  cell  containing  one  of  the  alkali  metals  lies 
between  the  non-selective  radiometers  and  selenium  in  its  total 
sensibility.  Connected  with  the  proper  sensitive  auxiliaries,  it 
has  been  found  sensitive  enough  to  detect  the  illumination  from 
a  single  match  yards  away.  A  cell  of  large  area  of  the  most 
sensitive  type  will  record  daylight  illuminations  on  a  portable 
galvanometer,  and  with  a  voltage  supply  of  50  to  100,  which  can 
be  made  portable,  artificial  illuminants  can  be  at  least  detected. 
The  photo-electric  cell  has  attracted  much  attention  of  late  because 
it  has  been  thought  that  its  indications  are  directly  as  the  inten- 
sity of  the  incident  illumination.  It  has  been  thought,  too.  that 
since  its  color  sensibility  extends   into  the  visible  spectrum,  it 

7  Pfund,  A.  H..  The  Use  and  Abuse  of  the  Selenium  Cell  in  Photometry;  Lighting 
Journal,  1913. 


IVES  :     PHYSICAL    PHOTOMETRY 


121 


should  be  possible  to  apply  absorbing  media,  as  in  the  case  of  the 
thermopile  artificial  eye  but  with  greatly  increased  sensibility.  In 
fact  Dr.  Voege  has  recently  described  experiments  with  such  an 
apparatus.  All  these  hopes  were  fated  to  be  blasted,  for  the 
present  at  least,  by  recent  work  which  has  shown  that  the  response 
to  light  is  not  directly  as  the  intensity,  but  is  a  complicated  func- 
tion of  several  factors,  and  is  as  yet  quite  uncontrollable.8  The 
illumination-current  relationship  for  a  number  of  cells  is  shown 
in  Fig.  12. 

A  still  further  objection  to  the  photo-electric  cell  is  that  the 


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ILLUMINATION 


Fig.  12. — Illumination-current  relationship  in  various  photo-electric  cells. 


wave-length  sensibility  does  not  appear  to  be  the  same  from  one 
cell  to  another,9  a  point  exhibited  in  Fig.  13.  Another  point 
exhibited  by  the  latter  figure  is  that  the  maximum  sensibility  of 
these  cells  lies  far  out  in  the  violet  of  the  spectrum.  Conse- 
quently the  amount  of  available  energy  after  an  appropriate  ab- 
sorbing medium  has  been  introduced  to  make  them  read  "light" 
is  quite  small.  The  presence  of  these  two  defects  in  the  photo- 
electric cell  must  defer  its  consideration  in  this  connection  until 
its  properties  have  been  much  more  thoroughly  studied. 

8  Ives,  H.   E.,  The  Illumination-current   Relationship  in   Potassium   Photo-electric 
Cells;  Astrophysical Journal,  June,  1914. 

9  Ives,   H.   E.,  Wave-length  Sensibility  Curves  of    Potassium    Photo-electric    Cells: 
Asirophy  steal  Journal,  Sept.,  1914. 


122 


TRANSACTIONS    I.    E.    S. — PART    I 


The  fact  that  neither  the  selenium  cell  nor  the  photo-electric 
cell  lend  themselves  to  any  method  of  copying  the  wave-length 
sensibility  curve  of  the  eye  makes  it  possible  to  subject  them  both 
to  the  sweeping  criticism  that  they  do  not  measure  light,  as  we 
have  defined  it,  at  all.  Under  certain  restricted  conditions  they 
measure  radiations  which  under  those  conditions  are  proportional 
to  light. 

We  now  come  to  the  last  of  the  means  for  physical  photometry 


040   042      04+     046     046    050    051     054    056     058    060    Q6t    064    069   QM 

J* 

Fig.  13.— Wave-length  sensibility  curves  of  various  photo-electric  cells, 
reduced  to  equal  energy  spectrum. 


that  we  shall  consider,  namely,  the  photographic  plate.  Perhaps 
the  most  striking  difference  between  it  and  the  instruments  we 
have  been  considering  is  that  in  its  use  we  definitely  abandon  any 
attempt  to  secure  direct  positional  indication.  The  photographic 
record  when  obtained  must  itself  be  measured,  and  in  this  meas- 
urement either  the  ordinary  photometric  methods  or  some  radio- 
metric scheme  must  be  employed.  It  goes  therefore  almost  with- 
out saying  that  the  photographic  plate  is  not  resorted  to  for  con- 
venience.    In  ordinarv  photometry  it  would  only  introduce  extra 


IVES:     PHYSICAL    PHOTOMETRY 


12} 


work  without  any  gain,  unless  the  plate  could  be  measured  with 
greater  precision  than  could .  the  original  illumination,  which  is 
hardly  likely.  Resort  to  photography  is  then  only  to  be  expected 
if  there  are  some  things  the  plate  can  do  well  enough  to  offset  this 
disadvantage. 

The  photographic  plate  has  extreme  sensibility,  as  alreadv 
pointed  out.  It  can  be  made  sensitive  to  the  visible  spectrum  as 
shown  in  Fig.  14.  Its  response  is,  over  a  considerable  range  of 
intensities,  proportional  to  the  stimulus.10  It  presents  thus  far 
no  great  advantage  over  the  eye.  Its  most  striking  peculiarity  is 
that  it  can  integrate,  not  only  the  effects  of  very  faint  stimuli  but, 
with    some   limitations,    fluctuating   or   changing   stimuli.      This 


ERYTH  ROSIN 


ETHYL  RED 


PINACHROM 


DICYANIN 


Fig.  14.— Sensibility  of  photographic  plates  sensitized  and  unsensitized. 
to  different  regions  of  the  spectrum. 

property  is  chiefly  taken  advantage  of  in  the  measurement  of 
faint  spectra,  such  as  that  of  the  fire-fly  and  in  other  cases  where, 
as  above  pointed  out,  the  measurement  is  not  really  that  of  light 
but  radiation.  Some  use  has  however  been  made  of  photography 
to  measure  as  light  the  irregular  distribution  curves  of  arc  lamps, 
which  because  of  the  unsteady  character  of  their  light  are  dif- 
ficult for  ordinary  photometry. 

The  photographic  process  is  very  sensitive  to  many  disturbing 
influences.  To  avoid  the  errors  these  influences  may  cause,  it  is 
necessary  to  use  careful  substitution  methods,  and  to  adhere  to 

10  Ives,  H.  E.,  The  Application  of  Photography  to  Photometry;  Trans.  I.  E.  S.,  vol 
VII,  p.  90. 


124  TRANSACTIONS    I.    E.    S. — PART   I 

very  carefully  worked  out  procedures  in  exposure  and  develop- 
ment, all  of  which  conspire  to  deprive  the  photographic  methods 
of  photometry  of  precision,  leaving  their  field  restricted  to  cases 
where  photography  will  do  something  nothing  else  will. 

SUMMARY. 

In  this  paper  an  attempt  has  been  made  to  clarify  the  question 
of  physical  photometry,  first  by  determining  what  it  is  we  want 
to  measure ;  second,  by  tabulating  the  qualities  which  would  be 
desirable  in  instruments  to  take  the  place  of  the  eye.  It  has  been 
found  that  the  various  desirable  qualities  are  found  scattered 
among  a  number  of  instruments,  none  of  which  possesses  enough 
to  give  it  a  claim  to  be  a  universal  "light"  measuring  device.  At 
the  present  time  only  one  instrument,  the  non-selective  radio- 
meter with  a  proper  evaluating  absorptive  medium,  does  actu- 
ally perform  as  an  artificial  eye.  Its  limitation  is  its  comparative 
insensitiveness,  which  restricts  its  use  to  the  laboratory,  where 
however  it  has  a  field  of  great  usefulness.  For  the  much  greater 
sensitiveness  of  some  of  the  devices  to  become  available  we  must 
look  to  future  developments. 

WHAT  WE  MAY  EXPECT  IN  THE  FUTURE. 

The  history  of  the  measurement  of  radiant  energy  is  a  record 
of  continually  increasing  sensibility  of  instrumental  means,  fol- 
lowed by  the  transfer  of  these  more  sensitive  means  from  the 
laboratory  to  the  technical  stage.  Thus  within  a  few  years  the 
thermopile  has  been  made  much  more  sensitive  by  the  use  of 
new  substances  for  the  thermo-electric  junctions,  by  study  of 
the  best  dimensions,  by  new  processes  of  evacuation.  More  and 
more  sensitive  galvanometers  have  been  built,  and,  what  is  more 
to  the  point  for  the  present  purpose,  increasing  ruggedness  and 
practicability  have  been  attained,  especially  in  the  string  types  of 
galvanometer.  In  view  of  these  facts  it  is  not  unreasonable  to 
hope  that  before  very  long  the  successful  type  of  physical  pho- 
tometer which  has  been  described  here  may  be  available  for  many 
other  than  standardizing  purposes. 

On  the  side  of  the  selective  means  a  truly  enormous  amount  of 
work   is  being  done.     The  photo-electric  cell   in  particular,  be- 


IVES:     PHYSICAL    PHOTOMETRY  I>5 

cause  of  its  bearing  on  many  important  points  in  physical  theory, 
is  the  object  of  wide  study.  The  relation  between  illumination 
and  current,  and  the  differences  in  wave-length  sensibility  in 
various  cells  of  the  same  composition,  are  subjects  under  study, 
and  with  increased  knowledge  it  is  to  be  expected  that  we  shall 
acquire  control  of  the  disturbing  factors.  That  accomplished,  we 
shall  hope  to  utilize  the  enormous  sensitiveness  of  this  class  of 
instrument  and  at  the  same  time  make  them  measure  light. 


126  TRANSACTIONS    I.    K.    S. — PART    1 

AN  APPROXIMATE  UNIFORM  PH(  >T<  METRIC 

POINT-SOURCE.* 


RY  A.  B.  KENNKLLV,  R.  W.  CHADBOURN  AND  G.  I).  EDWARDS. 


Synopsis:  Experiments  are  described  on  a  modified  form  of  frosted 
tungsten  ioo-watt  spherical  stereopticon  lamp  with  a  view  to  producing 
a  uniform  virtual  point-source.  The  measurements  show  that  exempting 
an  axial  cone,  at  each  pole,  of  45  deg.  semi-angle,  or  29.3  per  cent,  of  the 
total  spherical  area,  the  maximum  deviation  ratio  of  the  lamp  (the  ratio 
of  the  maximum  deviation  of  the  intensity  to  the  mean  spherical  intensity 
over  the  retained  area)  was  4.65  per  cent. 

A  luminous  point-source  may  be  denned  as  a  source  of  light 
condensed  in  so  small  a  volume  as  virtually  to  constitute  a  mere 
point  in  space  for  the  purposes  under  consideration.  Such  a 
point-source  would  be  specially  serviceable  for  placing  at  the 
focus  of  a  parabolic  reflector  in  the  production  of  a  parallel  beam 
of  light.  A  point-source  to  serve  for  a  projector  does  not  need 
to  distribute  light  uniformly  in  all  directions.  It  only  needs  to 
radiate  light  from  a  central  point. 

In  the  theory  of  photometry,  however,  it  is  customary  to  start 
with  the  simple  concept  of  a  uniform  luminous  "point-source," 
or  an  ideal  lamp  which  distributes  light  uniformly  in  all  direc- 
tions, as  though  the  source  were  concentrated  at  a  single  point. 
No  lamp  can  be  produced  to  comply  with  such  a  concept.  There 
must  always  be  an  appreciable  surface-area  in  the  luminous 
source,  and  this  surface  is  seldom  even  approximately  spherical. 
It  is  supported  by  a  more  or  less  opaque  structure,  in  a  chamber 
whose  walls  are  not  uniformly  transparent;  so  that  the  distribu- 
tion of  luminous  flux  is  frequently  very  far  from  being  uniform 
in  different  directions,  even  at  long  radial  distances  from  the 
lamp.  At  short  radial  distances  from  the  lamp,  the  distribution 
of  light  is  apt  to  depart  still  further  from  uniformity.  In  actual 
service,  this  departure  from  the  condition  of  a  simple  uniform 
luminous  point-source  is  not  of  great  consequence,  except  that 

*  A  paper  presented  at  a  meeting  of  the  New  England  Section  of  the  IUumtnatinu 
Engineering  Society,  November  10.  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


KEN NELLV,CIIADBOURN, EDWARDS  \  LUMINOUS  POINT-SOURCE      12J 

whereas  from  a  photometric  standpoint,  a  single  measurement  of 
candlepower  taken  in  any  direction  would  completely  specify  a 
uniform  point-source,  the  ordinary  non-uniform  radiator  requires 
to  have  its  candlepower  measured  in  many  directions,  in  order 
adequately  to  specify  its  photometric  properties.  We  also  know 
that  for  particular  purposes  in  illumination,  a  marked  departure 
from  uniform  distribution  may  be  desirable;  as,  for  instance, 
when  a  lamp  is  needed  to  emit  a  strong  beam  of  light  in  a  selected 
direction. 

Nevertheless,  there  would  be  a  certain  convenience  in  the  pho- 
tometer room,  if  a  virtual  uniform  point-source  were  available; 
i.  e.,  a  source  which,  although  of  appreciable  dimensions,  would 
emit  light  uniformly  in  different  directions  and,  under  its  condi- 
tions of  use,  would  act  substantially  as  though  this  light  emerged 
from  a  point.  Standard  incandescent  lamps  are  ordinarily  cali- 
brated for  mean  horizontal  intensity  when  rotating,  or  for  a  con- 
stant intensity  in  one  geometrically  defined  direction,  when  fixed 
with  this  direction  along  the  axis  of  the  photometer  bar.  A  vir- 
tual uniform  point-source  would  make  rotation  unnecessary  in  the 
first  case,  and  the  marking  of  the  fiducial  direction  unnecessary 
in  the  second  case.  Such  a  lamp  would  be  easy  to  set  up,  and  to 
calibrate  in  a  photometer.  It  could  only  be  expected  to  serve  as 
a  virtual  point-source  at  a  suitable  photometric  distance ;  because 
no  light  source  can  be  produced  at  a  mere  point,  and,  at  very 
short  ranges,  actual  luminous  surfaces  must  be  expected  to  depart 
widely  from  point-source  conditions. 

A  virtual  point-source  photometric  standard  would  also  have 
the  advantage  that  its  mean  spherical  reduction-factor  would  be 
unity,  and  its  total  flux  of  emitted  light  would  be  just  47r  times 
its  intensity  as  measured  in  any  direction.  A  rough  criterion  of 
the  degree  of  approximation  offered  by  any  lamp  to  a  point- 
source,  is  its  spherical  reduction  factor  with  respect  to  1.0.  A 
lamp  with  a  spherical  reduction  factor  differing  materially  from 
1.0  must  differ  materially  from  a  point-source  at  the  photometric 
distance  considered.  On  the  other  hand,  a  lamp  might  have  a 
spherical  reduction  factor  of  1.0,  and  yet  might  differ  greatly 
from  a  point-source.  For  example,  it  might  happen  to  have  a 
mean  horizontal  candlepower  just  equal   to  its  mean   spherical 


128  TRANSACTIONS    I.    E.    S. — PART    I 

candlepower,  and  yet  display  considerable  irregularity  in  candle- 
power  in  different  zones.     A  strict  definition  of  deviation  from 
the  point-source  condition     at  a  given  radius  of  measurement 
might  be  stated  as  the  greatest  difference  between  actual  candle- 
power  in  any  direction  and  the  mean  spherical,  divided  by  tin- 
mean  spherical  candlepower.     This  might  be  called  the  point - 
source  deviation  ratio  of  the  lamp,  for  the  radius  of  photometric 
observation  considered.     If  applied  over  the  entire  sphere,  how- 
ever, perhaps  no  existing  lamp  could  possibly  escape  a  large 
deviation  ratio ;  because  in  the  case,  say  of  an  incandescent  lamp, 
where  the  conducting  wires  entered  the  lamp,  a  shadow  would 
have  to  be  cast,  and  the  deviation  from  mean  spherical  candle- 
power  would  have  to  be  considerable  along  the  direction  of  this 
shadow.    Nevertheless,  the  practical  utility  of  the  definition  might 
be  fairly  well  maintained  by  expressing  some  reservation  for  the 
shadow  cone.    Thus,  if  an  incandescent  lamp  had  a  shadow  near 
its  base  comprised  within  a  right  cone  of,  say,  45  deg.  semi-angle, 
within  the  apex  formed  at  the  optical  center  of  the  lamp,  as  indi- 
cated in  Fig.  3,  the  mean  spherical  candlepower  might  be  reck- 
oned to  the  exclusion  of  this  basal  shadow  zone.     Over  the  rest 
of  the  sphere,  the  deviation  from  the  mean  spherical  candlepower 
thus  delimited  might  conceivably  be  reduced  to  insignificance  at 
distances  beyond  one  meter.     Such  a  lamp  would  be  a  virtual 
uniform  point-source  at  and  beyond  meter^distance,  except  within 
the  45  deg.  conical  zone  comprising  the  lamp-base.     In  general. 
the  ratio  of  point-source  deviation  for  such  lamps  could  be  re- 
duced by  increasing  the  size  of  the  exempted  zone ;  until,  however, 
the  exemption  became  so  large  that  the  utility  of  the  lamp  as  a 
virtual  point-source  became  seriously  restricted.     With  an  axial 
cone  of  semi-angle  45  deg.  as  in  Fig.  3,  the  exempted  area  would 
be  vers  45  deg.  =  0.293  of  the  hemisphere  surrounding  the  cone, 
and  with  45  deg.  axial  cone  at  each  pole  the  exemption  would  be 
0.293  of  the  whole  sphere.     That  is,  the  retained  area  would  be 
0.707  of  the  whole  sphere.     Expressed  in  solid-angle  measure, 
the   retained   angle   would  be  0.707    X    4"   steradians   and   the 
exempted  angle  0.293  X  4^  steradians.    In  general,  with  an  axial 
cone  of  semi-angle  6  exempted  at  each  pole,  the  retained  area 
would  be  cos0,  and  the  exempted  area  vers0  =  1  —  cos0.  taking 
the  whole  area  of  the  sphere  as  unit}-. 


KEN  NELLY,  CHADBOURN,  EDWARDS  :  LUMINOUS  POINT-SOURCE      129 


Several  unsuccessful  attempts  were  made  by  the  writers  to  find 
an  existing  type  of  lamp  which  might  approximate  a  uniform 
virtual  point-source.  The  lamp  department  of  the  General  Elec- 
tric Company  assisted  us,  however,  by  preparing  a  modification 
of  one  of  their  tungsten  ioo-watt  stereopticon  lamps  of  the  spher- 
ical frosted  type  with  a  concentrated  spiral  tungsten  filament. 
This  type  of  lamp  is  illustrated  in  Fig.  i.     Its  external  diameter 


Fig.  i.— Diagram  of  a  ioo-watt  concentrated,  tungsten-filament  stereopticon 
lamp  3%  in.  in  diameter. 

is  3.75  in.  (9.53  cm.).  The  tungsten  wire  filament  is  first  wound 
in  a  spiral  approximately  1  mm.  in  diameter.  This  spiral  is  then 
looped  up  and  down  in  a  crown  of  10  hook-supports  indicated  in 
plan  by  Fig.  2.  Two  lamps  of  this  type  were  tested,  one  with  a 
clear  globe,  and  the  other  with  a  frosted  globe.  As  might  have 
been  expected,  the  clear-globe  lamp  was  decidedly  inferior  to  the 
frosted-globe  lamp  as  a  uniform  point-source;  so  that  we  need 
only  consider,   in  what   follows,   the   results  obtained   with  the 


130 


TRANSACTIONS    I.    E.    S. — PART    I 


Fig.  2.— (Upper  diagram)  Plan  of  supported  filament.  Fig.  3.— (lower  diagram)  Axial 
section  of  a  tungsten-filament  stereopticon  lamp,  indicating  an  exempted  core  at 
each  pole  of  semi-angle  450. 

CANDLE  POWER 
ZO  40         A  60      F    80 


Pig,  1.     Rousseau  diagram. 


KENNELLY.CIIADBOURN, EDWARDS  :  LUMINOUS  POINT-SOURCE      13  I 

frosted  lamp,  the  globe  of  which  was  uniformly  and  completely 
frosted. 

The  lamp  was  set  up  in  the  photometer  rotating  about  its  axis 
about  100  revolutions  per  minute.  There  was  actually  but  little 
candlepower  difference  in  azimuth ;  so  that  the  test  might  have 
been  made  without  rotating  the  lamp,  if  the  mean  of  several  read- 
ings in  fixed  azimuths  at  each  zone  had  been  taken. 

The  zonal  distribution  curve  and  the  corresponding  Rousseau 
diagram  are  given  in  Fig.  4.  It  will  be  seen  that  the  luminous 
intensity  remains  fairly  close  to  75  candles  over  a  considerable 
solid  angular  range.  Above  an  elevation  of  60  deg.,  the  intensity 
falls  off  to  55.8  at  the  tip,  apparently  owing  to  reduced  reflecting 
power  from  the  walls  within  the  socket.  Below  a  depression  of 
45  deg".,  the  intensity  falls  off  rapidly,  apparently  owing  to  ab- 
sorption of  light  by  the  hooks,  and  socket.  Nevertheless,  the 
mean  spherical  candlepower  comes  out  70.5  with  a  mean  hor- 
izontal candlepower  of  74.9,  making  a  spherical  reduction  factor 
of  0.941.  It  is  evident  that  the  curved  line  ABCDE  on  the 
Rousseau  diagram  of  a  true  virtual  point-source  would  be  straight 
and  parallel  to  the  base  O  E. 

The  corresponding  involute  diagram  is  shown  in  Fig.  5.1  Here 
the  successive  arcs  are  drawn  in  zones  of  15  deg.  The  polar 
diagram  is  indicated  by  the  broken  line  90  deg.,  75  deg.,  60  deg.. 
45  deg.,  30  deg.,  15  deg.,  o  deg.,  —15  deg..  —30  deg.,  —45  deg.. 
— 60  deg.,  — 75  deg.  The  corresponding  involute  is  ABCDE 
FGHIJKL  M.  Half  the  total  projected  vertical  distance  be- 
tween A  and  M  measures  70.4  candlepower  to  scale  and  repre- 
sents the  mean  spherical  candlepower  of  the  lamp,  with  a  spher- 
ical reduction-factor  of   '—-+  =  0.940.      It  is  evident  that  for  a 

74-9 

virtual  point-source,  the  involute  M  L  K — C  D  E  F  would  be- 
come a  true  semi-circle,  and  the  evolute,  or  line  of  centers 
PQRSTUVWX  would  shrink  to  a  single  central  point  at  T. 
If  we  consider  the  point-source  deviation  ratio  of  this  lamp 
after  exempting  a  conical  region  of  45  deg.  semi-angle  with  re- 

1  Kennelly,  A.  E.  A  Rectilinear  Graphical  Construction  of  the  Spherical  Reduction 
Factor  of  a  Lamp  ;  Trans.  I.  E.  S.,  February,  190S.  A  New  Graphic  Method  for  Deter- 
mining the  Mean  Spherical  Intensity  of  a  Lamp  by  the  Length  of  a  Straight  Line  when 
the  Curve  of  Meridianal  Intensity  is  Given.  Electrical  World,  March  28.  1908. 


I  32  TRANSACTION'S    1.    K.    S. PART    I 

spect  to  the  axis;  i.e..,  retaining  only  the  region  from  — 45  deg. 
to  -(-45  deg.  of  elevational  angle,  we  find  on  the  Rousseau  dia- 
gram that  the  mean  spherical  cp.  is  represented  by  the  distance 
h  1 1  or  *  I  since  the  area  i  I  H  h  is  found  to  be  equal  to  the  planim- 
etered  area  of  the  curve  over  the  base  ih.  The  mean  spherical 
cp.  over  this  exempted  area  is  74.2.    The  greatest  deviation  from 


Fig.  5.— Kennelly  diagram. 

this  value  over  the  retained  area  is  at  eD  =  70.8  or  3.4  cp.    The 

maximum  deviation  ratio  is  thus  — —  —  0.0458  or  4.58  percent. 

74.2 

As  already  pointed  out,  the  area  retained  is  70.7  per  cent,  of  the 

whole  area  of  the  sphere;  or  the  exempted  region  is  29.3  per 

cent.     Over  the  entire  retained  area,   the  maximum   deviation 

from  the  mean  retained  spherical  cp.  is  thus  only  about  4.5  per 

cent. 


KEN  NELLY,  CHADBOURN,  EDWARDS:  LUMINOUS  POINT-SOURCK      1 33 

Similarly,  in  the  involute  diagram  of  Fig.  5,  retaining  only  the 
involute  curve  D  E  F  G  H  I  J,  the  mean  retained  spherical  candle- 

.  .  di'.. 

power  is  half  of  the  vertical  distance  D  J  or  —    divided     by 

0.707,  or  74.3.  The  maximum  deviation  over  this  retained  area 
is  74.3  —  70.8  =  3.5  cp.  and  the  maximum  deviation  ratio  -^- 

=  0.0471  or  4.71  per  cent.  If  both  the  Rosseau  and  involute 
diagrams  could  be  drawn  without  any  inaccuracies,  their  results 
would,  of  course,  be  in  agreement.  In  this  case,  the  maximum 
deviation  ratio  may  be  taken  at  the  average  value  of  4.65  per 
cent,  over  the  retained  area  between  +45  deg.  and  — 45  deg.  It 
is  evident  from  either  of  the  diagrams  (Figs.  4  and  5)  that  be- 
tween -{-30  deg.  and  — 30  deg.  the  deviation  ratio  would  be  much 
less,  but  this  would  exempt  half  the  area  of  the  sphere. 

If  the  frosted  tungsten  stereopticon  lamp  here  considered  were 
further  modified  in  structure,  the  approximation  to  a  uniform 
virtual  point-source  could  evidently  be  increased.  Thus,  the 
base  of  the  lamp  might  be  removed  and  replaced  by  a  thin  glass 
tube,  or  pair  of  tubes,  carrying  out  the  leading  wires.  Again, 
the  globe  might  be  enlarged,  the  spherical  form  continued  over 
the  area  covered  by  the  present  base,  and  the  filament  supporting 
wires  arranged  for  minimum  shadow.  With  all  of  these  amend- 
ments, the  exempted  area  might  probably  be  considerably  re- 
duced, and  the  maximum  deviation  ratio  also.  Perhaps  the  max- 
imum deviation  ratio  might  be  reduced  to  2  per  cent.  It  is  hoped 
that,  as  a  matter  of  interest,  it  may  be  possible  to  carry  on  further 
experiments  in  this  direction. 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 

Vol.  X  NUMBER    2  1915 

SOME  USES  OF  LIGHT  IN  THE  TREATMENT 
OF  DISEASE.* 


BY  E.   C.   TITUS,   M.  D. 


Synopsis:  The  value  of  light  as  an  efficient  remedy  when  properly 
employed  in  the  treatment  of  many  painful  and  diseased  conditions  is 
discussed  in  the  following  paper.  A  brief  review  of  the  art  of  apply- 
ing the  therapeutic  effect  of  light  is  also  included. 


To  many  the  subject  of  phototherapy  is  invested  with  so  much 
mystery,  and  its  fundamental  principles  are  so  frequently  imper- 
fectly understood,  that  it  is  not  surprising  that  progress  in  this 
field  has  been  so  slow.  Even  now  comparatively  few  are  making 
systematic  use  of  this  important  therapeutic  agent.  It  would 
consume  much  more  time  than  is  at  my  disposal  to  present  more 
than  an  outline  of  this  subject,  and  I  will  therefore  confine 
myself  chiefly  to  its  practical  therapeutic  aspect,  as  based  largely 
upon  my  own  observations. 

From  time  immemorial  the  beneficial  influence  of  sunlight  upon 
animal  and  vegetable  life  has  been  recognized,  but  it  is  only  at 
the  present  time  that  we  are  appreciating  its  full  value  in  the 
treatment  of  disease. 

The  excellent  and  even  wonderful  results  of  heliotherapy  in 
the  treatment  of  bone  tuberculosis,  to  which  attention  has  been 
called  within  a  recent  period,  will  serve  as  an  illustration. 

For  obvious  reasons,  however,  sunlight  is  not  always  avail- 
able, and  it  has  therefore  been  found  advantageous  to  resort 
to  other  sources  of  light.  Thanks  to  the  progress  made  in  elec- 
tricity, we  now  have  at  our  disposal  various  means  of  obtaining 
light  closely  approaching  that  of  the  sun  in  its  remedial  action, 
and  to  these  means,  chiefly,  my  paper  will  be  devoted. 

*  A  paper  read  at  the  eighth  annual  convention  of  the  Illuminating  Engineering 
Society,  Cleveland,  O.,  September  21-24,  i9r4- 

The  Illuminating  Engineering   Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


I36  TRANSACTIONS   I.    E.    S. — PART    I 

Phototherapy  may  be  considered  under  two  heads,  its  thermic 
and  actinic  effects,  although  both  of  these  are  represented  in 
varying  degrees  in  all  light,  irrespective  of  its  source. 

It  must  be  remembered  that  the  thermic  effects  of  light  are 
due  to  the  impingement  of  the  rays  upon  the  translucent  cuta- 
neous tissues.  The  arrest  of  the  light  rays  by  the  skin  and  sub- 
cutaneous structures  produces  radiant  heat  which  has  a  higher 
penetrating  power  than  convection  heat  as  generated  by  a  hot- 
water  bag  or  poultice,  for  instance.  It  has  been  found  that  the 
thermic  effects  of  light  extend  to  a  depth  of  two  inches  or  more, 
while  convection  heat  is  principally  exerted  upon  the  surface. 
In  comparing  the  therapeutic  action  of  both  it  will  be  seen  that 
the  changes  produced  in  the  tissues  by  the  former  are  much 
more  pronounced.  Thus  if  the  body  be  exposed  to  an  intense 
light,  as  in  an  electric  light  cabinet  bath,  the  resulting  hyperemia 
and  elimination  of  waste  products  by  the  skin  and  kidneys  (cel- 
lular nutrition)  are  much  more  pronounced  than  in  a  Turkish 
or  Russian  bath.  The  marked  augmentation  of  the  oxidation 
processes  in  the  tissues  is  shown  by  the  greater  amount  of  carbon 
dioxid  thrown  off  by  the  lungs  and  by  the  increase  of  solids  in 
the  urine.  It  is  also  claimed  that  the  natural  defences  of  the 
body  (phagocytosis)  are  greatly  promoted. 

The  actinic  or  chemical  rays  play  an  important  part  in  photo- 
therapy only  when  the  light  is  concentrated  upon  a  localized  area 
as  in  the  use  of  the  arc  lamp.  Under  these  circumstances  the 
actinic  rays  appear  to  enhance  as  well  as  modify  the  action  of 
the  thermic  and  luminous  rays.  Thus  the  ultra-violet  radiations, 
which  are  actinic,  have  been  shown  to  exert  an  anti-bacterial 
action  as  well  as  to  promote  local  phagocytosis. 

I  am  not  unmindful  of  the  fact  that  much  of  our  knowledge 
is  still  in  the  theoretical  stage,  and  for  that  reason  have  refrained 
from  entering  into  the  many  details.  I  will,  therefore,  proceed 
now  to  the  clinical  aspects  of  this  subject,  dividing  it  into  the 
general  and  local  applications  of  phototherapy. 

The  general  application  of  phototherapy  consists  practically  in 
the  use  of  the  electric  light  bath,  and  since  much  of  the  benefit  to 
be  derived  from  this  agent  will  depend  upon  the  apparatus 
employed,  I  will  first  give  a  description  of  what  has  proven  to 
me  to  be  the  most  satisfactory  type  of  cabinet. 


TITUS:     EIGHT    IN    THE   TREATMENT    OF   DISEASE  13/ 

An  electric  light  cabinet  should  be  constructed  according  to  the 
following  plan.  The  cabinet  should  be  octagonal  in  shape,  4  ft. 
square  by  5  ft.  high;  the  lining  should  be  of  white  blotter  and 
not  mirror  surface;  the  source  of  light  should  come  from  100 
40-watt  tungsten  lamps,  conveniently  arranged,  so  that  they  will 
be  under  control  from  within  by  properly  placed  switches,  one- 
half  or  full  number  of  the  lamps  to  be  employed,  as  desired. 
The  cabinet  should  be  open  at  the  top,  not  entirely,  but  partly 
so  and  it  should  have  an  air  vent  3  inches  in  diameter  in  the 
center  of  the  floor,  over  which  is  placed  a  low  stool  18  inches 
high,  upon  which  the  subject  is  seated.  (It  has  been  found  that 
a  ventilated  room  is  much  more  quickly  and  evenly  heated  arti- 
ficially than  one  that  is  closed  or  sealed.)  The  further  advan- 
tages of  this  construction  are  that  a  large  volume  of  light  with 
a  minimum  amount  of  heat  is  produced  in  the  cabinet,  that  the 
emanations  of  noxious  gases  and  odors  from  the  human  body 
are  quickly  carried  off,  that  the  degree  of  cutaneous  hyperemia 
and  diaphoresis  is  much  more  intense,  and  that  the  usual  de- 
pression and  other  unpleasant  symptoms  are  entirely  obviated, 
as  compared  with  the  older  form  of  closed  cabinet. 

Among  the  conditions  in  which  the  electric  light  bath  has 
proved  to  be  most  serviceable  are  arteriosclerosis  (hardening  of 
the  arteries),  gouty  and  rheumatic  conditions,  Bright's  disease, 
diabetes,  obesity  and  acute  catarrhal  affections  of  the  respiratorv 
tract. 

In  the  majority  of  cases  of  arteriosclerosis  in  the  earlier  stages 
I  have  advised  the  regular  use  of  these  baths  with  beneficial 
results,  and  I  firmly  believe  that  they  have  warded  off  more 
serious  organic  changes  which  otherwise  frequently  ensue. 

The  effects  of  the  baths  are : 

1.  To  induce  intense  hyperemia  or  reddening  of  the  skin  and 
thus  reduce  the  congestion  of  the  deeper  organs,  which  is  fre- 
quently present. 

2.  To  increase  elimination  by  way  of  the  lungs  and  skin.  It 
has  been  found  that  during  and  following  the  bath  the  elimina- 
tion of  carbon  dioxid  is  practically  doubled,  while  the  profuse 
perspiration  produced  carries  away  much  toxic  or  poisonous 
material  and  in  that  way  relieves  the  overtaxed  kidneys.  As  it 
is  generally  accepted  that  toxemia  plays  an  important  part  in  the 


l$S  TRANSACTIONS   I.    E.    S. — PART    I 

causation  of  hardening  of  the  arteries,  the  benefit  to  be  derived 
from  this  method  is  readily  apparent. 

Rheumatic  and  Gottty  Affections. — In  late  years  it  has  been 
frequently  pointed  out  that  many  conditions  commonly  termed 
rheumatic  differ  essentially  from  the  acute  type  of  the  disease 
which  is  very  probably  of  bacterial  origin.  On  the  other  hand, 
there  is  abundant  reason  to  believe  that  these  chronic  forms 
which  have  been  grouped  under  the  names  of  rheumatoid  arthri- 
tis, rheumatic  gout,  osteo-arthritis,  arthritis  deformans,  are  the 
result  of  auto-intoxication  and  disturbances  of  metabolism. 
From  what  has  been  said  above  it  will  be  readily  understood 
that  the  marked  effect  of  the  electric  light  bath  in  increasing 
elimination  will  exert  a  beneficial  influence  upon  the  toxemia  in 
these  cases  and  therefore  prove  of  material  aid  to  other  treatment. 
The  distressing  pains  and  stiffness  in  the  joints  are  also  greatly 
relieved  as  patients  have  frequently  assured  me.  In  chronic 
gout,  which  is  more  frequent  in  this  country  than  is  generally 
thought,  the  action  of  light  baths  is  to  augment  the  cutaneous  or 
peripheral  circulation  and  in  that  way  favor  the  absorption  of 
uratic  or  chalky  deposits. 

It  may  be  asked  why  a  Turkish  or  Russian  bath  will  not  do 
equally  well  in  the  conditions  mentioned.  My  own  experience 
has  shown  that  the  effect  of  the  light  bath  is  much  more  pro- 
nounced and  prolonged. 

Bright's  Disease. — One  of  the  chief  aims  in  the  treatment  of 
Bright's  disease  is  to  lessen  the  work  of  the  kidneys.  The  light 
bath  will  be  found  a  better  auxiliary  measure  for  accomplishing 
this  purpose  than  the  usual  hot  pack  or  steam  bath.  As  pre- 
viously pointed  out,  notwithstanding  the  profuse  sweating 
induced,  the  patient  experiences  no  depression  because  of  the 
stimulating  effect  of  the  light  energy  upon  the  peripheral  nerves. 

Diabetes. — The  light  baths  are  not  adapted  to  every  case  of 
this  disease,  but  particularly  to  patients  who  present  a  dry  skin 
with  various  cutaneous  eruptions,  especially  of  an  eczematous 
character.  The  best  results  are  obtained  where  diabetes  is 
attended  with  high  blood  pressure. 

Obesity. — The  heat  penetration  in  an  electric  light  bath,  which 
as  already  mentioned  extends  to  a  depth  of  over  two  inches,  stimu- 


TITUS:     LIGHT   IN    THE   TREATMENT    OF   DISEASE  1 39 

lates  the  oxidation  processes  in  the  fatty  tissues  and  promotes 
their  disintegration  in  cases  of  obesity.  It  will  thus  prove  an 
excellent  auxiliary  to  the  customary  treatment. 

Acute  Catarrhal  Affections  of  the  Respiratory  Tract. — The 
writer  has  frequently  had  an  opportunity  to  witness  the  beneficial 
effects  of  an  electric  light  bath  at  the  beginning  of  a  cold  in 
aborting  it  or  greatly  ameliorating  its  course.  From  personal 
experiences  there  can  be  no  question  of  its  superiority  over  the 
customary  hot  bath  and  diaphoretic  (perspiration  inducing) 
remedies. 

LOCAL  APPLICATION  OF  LIGHT. 

In  the  local  applications  of  light  the  following  means  are 
available : 

i.  The  arc  light,  which  is  best  employed  by  means  of  an  ordi- 
nary marine  searchlight,  with  its  glass  front  window  removed. 
The  one  I  employ  consumes  25  to  35  amperes  of  direct  current 
at  40  volts,  and  projects  the  light  in  parallel  rays  by  means  of  a 
12-inch  parabolic  reflector,  and  has  a  light  value  of  about  5,000 
candlepower. 

2.  The  high  power  incandescent  lamp  with  a  carbon  or  tungsten 
filament  of  500  candlepower  and  provided  with  a  dome  reflector. 
The  carbon  filament  uses  12  amperes  at  no  volts,  while  the 
tungsten  lamp  consumes  only  3  amperes  at  no  volts.  The 
former  gives  off  more  thermic  rays,  while  the  latter  produces  a 
greater  amount  of  white  light  with  a  minimum  amount  of  heat. 

Without  entering  into  detail  regarding  the  physiological  action 
of  light  when  applied  locally,  it  may  be  of  interest  to  call  atten- 
tion to  some  of  its  main  features. 

As  already  mentioned  in  discussing  the  general  applications  of 
light,  it  constitutes  a  means  of  generating  heat  within  the  tissues 
down  to  a  depth  of  two  inches  or  more,  while  connective  heat  is 
far  less  penetrating.  Moreover,  besides  the  conversion  of  light 
rays  into  heat,  we  have  to  deal  with  the  chemical  actinic  rays 
which  also  play  a  not  unimportant  part  in  phototherapy. 

The  sum  total  of  these  combined  effects  is  as  follows.  There 
is  an  increased  local  activity,  as  manifested  by  a  pronounced 
hyperemia  and  an  augmented  tissue  oxidation  and  elimination. 
The  effects  of  radiant  energy,  however,  are  not  confined  to  the 


I40  TRANSACTIONS    I.    E.    S. PART    I 

site  of  application,  but  are  so  diffused  that  remote  effects  are 
produced  in  distant  organs  and  nerve  centers  as  a  result  of 
peripheral  or  cutaneous  stimulation.  It  is  easy  to  understand 
that  the  increased  circulation,  oxidation  and  elimination  in  the 
affected  part  will  relieve  congestion  and  promote  absorption  of 
exudates  and  deposits  and  the  excretion  of  toxic  materials.  It 
has  likewise  been  shown  by  physiological  investigators  that  the 
heat  production  in  the  tissues  increases  phagocytosis  and  thus 
enhances  the  vital  resistance. 

The  rapid  relief  of  pain  and  local  spasm  experienced  from 
light  therapy  is  due  in  a  great  measure  to  the  reduction  of  con- 
gestion and  to  tissue  relaxation.  In  this  connection  it  may  be 
emphasized  that  these  decided  effects  are  brought  about  without 
the  least  risk  to  the  patient,  a  statement  which  is  not  applicable 
unreservedly  to  other  methods  of  treatment. 

I  shall  now  briefly  discuss  those  conditions  in  which  the  local 
application  of  phototherapy  in  my  experience  has  yielded  the 
most  satisfactory  results.  The  employment  of  the  parallel  rays 
from  a  high  power  marine  searchlight  as  described  above,  applied 
for  30  minutes  to  the  spine  at  a  distance  of  10  feet,  is  one  of 
the  most  effectual  and  lasting  means  of  relieving  many  forms  of 
spinal  congestion. 

In  the  acute  stages  of  bronchitis  or  in  pulmonary  congestion 
from  almost  any  cause,  light  applications  to  the  chest  afford  a 
more  prompt  relief  of  chest  pain  and  respiratory  distress  than 
any  other  measure  with  which  I  am  familiar.  In  cases  of  chronic 
bronchitis  marked  benefit  is  obtained  by  prolonged  daily  applica- 
tions of  light  to  the  front  and  back  of  the  chest,  continued  until 
marked  redness  and  tanning  of  the  skin  is  produced. 

To  promote  more  speedy  absorption  in  pleurisy  I  know  of  no 
better  means  than  the  daily  use  of  phototherapy.  In  lobar  and 
bronchial  pneumonia  its  beneficial  influence  is  manifested  by 
marked  relief  of  pain  and  dyspnea  (shortness  of  breath)  and  an 
improvement  in  the  general  comfort  of  the  patient;  and  in  cases 
where  resolution  was  delayed,  it  seemed  to  hasten  this  process. 

I  have  frequently  had  occasion  to  resort  to  this  treatment, 
using  cither  the  arc  or  500  candlepower  tungsten  lamp,  in  cases 
of   both   acute   and    sub-acute   inflammation   of   the  gallbladder, 


TITUS :     LIGHT    IN    THE   TREATMENT   OF   DISEASE  141 

congestion  of  the  liver  and  other  abdominal  viscera  from  chronic 
malaria,  alcoholism  and  persistent  intestinal  auto-intoxication. 
It  is  no  exaggeration  to  say  that  my  results  have  been  far  better 
than  when  sole  reliance  was  placed  upon  customary  medicinal 
treatment. 

In  the  treatment  of  muscular  rheumatism,  neuritis  and  even 
the  intense  discomfort  associated  with  herpes  zoster  (shingles), 
more  rapid  and  lasting  relief,  due  to  diminished  congestion  and 
nerve  sensibility,  will  be  obtained  by  this  method  than  by  recourse 
to  the  various  analgesics  and  with  no  risk  of  undesirable  after- 
effects. 

The  pain  in  acute  middle  ear  catarrh  (common  earache),  the 
frontal  or  orbital  headache  accompanying  acute  colds,  and  espe- 
cially involvement  of  the  frontal  sinus  and  ethmoid  cells  is 
promptly  alleviated  by  a  thorough  application  at  frequent  inter- 
vals of  light  from  a  50  candlepower  carbon  or  tungsten  lamp  in 
a  suitable  reflector.  To  this  I  can  testify  not  only  from  my  own 
experience,  but  I  could  add  the  testimony  of  many  physicians 
familiar  with  the  use  of  this  potent  therapeutic  agent.  In  chronic 
ear  trouble  and  disease  of  the  frontal  sinus  and  antrum,  it  has 
proved  a  very  valuable  auxiliary  by  relieving  the  congestion  and 
clearing  up  the  discharge. 

It  has  been  my  privilege  to  witness  the  success  of  this  treat- 
ment in  several  cases  of  catarrhal  appendicitis,  and  it  has  seemed 
to  me  that  the  pain  and  other  symptoms  were  more  quickly 
ameliorated  and  the  necessity  of  surgical  intervention  more  often 
avoided  than  had  been  my  previous  experience. 

In  various  types  of  septic  conditions,  such  as  phlebitis,  so-called 
milk-leg,  following  child-birth,  or  intrapelvic  operations,  the 
use  of  light  in  the  manner  indicated  or  by  means  of  the  multiple 
light  dome,  as  employed  in  the  Women's  Hospital  in  New  York, 
has  proved  a  well-nigh  indispensable  agent  in  gynecological 
practise. 

It  will  be  found  equally  useful  in  the  treatment  of  infected 
wounds  of  the  extremities,  cellulitis,  furuncles,  varicose  ulcers, 
and  localized  infective  processes  in  general. 

From  experience  up  to  date  there  seems  to  be  a  brilliant  future 


14-  TRANSACTIONS    I.    K.    S. — PART    I 

for  this  measure  in  hastening  repair  in  cases  of  delayed  union 
of  fractures. 

In  an  article  published  some  time  ago  I  reported  observa- 
tions which  showed  that  it  might  be  possible  to  prevent  the  occa- 
sional deleterious  effects  of  the  X-ray  by  following  its  applica- 
tion with  the  rays  from  a  marine  searchlight.  It  is  very  grati- 
fying to  me  to  state  that  subsequent  experience  has  seemed  to 
confirm  these  results. 

If,  in  this  rather  fragmentary  sketch,  I  have  been  sufficiently 
fortunate  to  impress  upon  you  the  value  of  phototherapy  as  a 
safe  and  efficient  auxiliary  in  the  treatment  of  many  conditions, 
the  object  of  this  paper  will  be  fully  realized. 

DISCUSSION. 

Prof.  F.  C.  Caldwell  :  It  is  certainly  desirable  for  us  as 
illuminating  engineers  to  know  something  about  the  curative  ef- 
fects of  light.  It  seems,  however,  that  our  relation  to  a  paper  of 
this  sort  is  rather  a  peculiar  one,  in  that  it  is  something  that  we 
know  little  about  and  are  in  no  position  to  discuss.  It  would  be 
a  matter  of  interest  to  know  to  what  extent  the  statements  that  are 
here  made  represent  the  consensus  of  opinion  of  the  medical  pro- 
fession and  to  what  extent  they  are  the  observations  and  views  of 
only  the  author.  It  seems  that  if  the  contents  of  this  paper  are  of 
the  former  class  they  are  of  great  interest  to  us  from  an  educative 
standpoint.  If,  however,  the  paper  is  of  a  controversial  nature. 
we  really  are  in  no  position  to  handle  it. 

Mr.  John  B.  Taylor:  The  statements  in  the  paper  of  Dr. 
Titus  are  unaccompanied  by  the  data  usually  required  by  engi- 
neers or  physicists  to  justify  opinions  respecting  the  correctness 
of  the  author's  claims.  The  illuminating  engineer,  unless  he  is 
also  a  doctor  of  medicine,  has  neither  opportunity  nor  right  to 
attempt  to  check  the  results  reported.  The  engineer  should, 
therefore,  keep  an  open  mind  and  request  further  and  more 
specific  facts.  Until  these  are  available  it  seems  proper  to  express 
the  opinion  that  much  is  "not  demonstrated." 

There  is  plenty  of  physical  evidence  that  X-rays  and  ultra- 
violet light  affect  the  body  tissue  and  kill  bacteria.  Is  there 
similar  evidence  for  the  statement  which  appears  three  times,  to 


LIGHT   IN   THE   TREATMENT   OF  DISEASE  143 

the  effect  that  "*  *  *  the  thermic  effects  of  light  extend  to 
a  depth  of  two  inches"?  We  may  recall  that  the  body  tissue  is 
largely  water  and  that  water  cells  are  regularly  used  for  the 
purpose  of  cutting  off  the  infra-red  or  so-called  "thermic  rays." 

Dr.  P.  W.  Cobb:  In  the  paper  Dr.  Titus  lays  stress  on  the 
fact  which  Mr.  Taylor  has  just  mentioned,  viz.,  the  thermic 
effects  of  light  extend  to  a  depth  of  two  inches  or  more.  Now, 
the  use  of  heat  in  the  treatment  of  disease  is,  as  you  all  know, 
a  very  old  matter.  Every  mother  of  a  family  knows  the  value  of 
it.  But  the  means  chiefly  employed  have  been  means  which 
involve  conduction,  as  examples,  the  hot  water  bag  and  the  poul- 
tice. In  more  advanced  therapeutics  a  hot  air  bath  has  been  used, 
where,  for  instance,  a  joint  which  is  suffering  from  some  chronic 
trouble,  may  be  baked,  wrapped  in  cotton  and  placed  in  a  chamber 
which  is  heated  by  a  lamp.  The  results  of  this  treatment  have 
been  very  good  in  certain  cases.  The  point  that  Dr.  Titus  wishes 
to  make  here  is  that  the  light  rays  penetrate  to  a  greater  depth 
than  the  heat  that  we  can  introduce  into  the  tissues  by  any  con- 
duction or  convection  method.  In  using  a  light  source  such  as  a 
tungsten  filament  lamp  for  this  purpose,  there  is  a  certain  limit. 
We  know  that  the  infra-red  radiation  beyond  the  visible — barring 
a  short  interval  just  beyond  the  red — is  rapidly  absorbed  by  water. 
There  would  be  then  a  certain  amount  of  the  energy  which  would 
be  stopped  at  the  very  surface,  or  at  very  shallow  depths  in  the 
skin.  If  the  energy  used  were  increased  superficial  burning 
would  be  the  result.  It  has  occurred  to  me  that  there  is  oppor- 
tunity for  scientific  investigation  which  might  materially  augment 
the  resources  of  the  photo-theapist.  It  would  seem  possible  that 
by  investigation  of  living  tissues  the  elevation  of  temperature  at 
various  depths  might  be  determined  and  that,  further,  it  would 
be  possible  to  find  just  which  wave-lengths  are  superficially 
absorbed  and  which  ones  penetrate  the  tissues  deeply.  Knowing 
these  facts,  it  would  be  possible  to  make  screens  which  would  cut 
out  the  rays  that  are  absorbed  at  the  very  surface  by  means  of 
which  the  superficial  heating  effect  could  be  avoided  and  a  deeper 
heating  effect  obtained.  We  know,  for  instance,  that  in  looking 
at  the  hand  toward  the  sun,  there  is  an  orange  reddish  light  that 
is  transmitted  through  the  thinner  portions  of  the  fingers.     We 


144  TRANSACTIONS    I.    E.    S. — PART    I 

know  that  water  will  not  transmit  the  longer-waved  infra-red 
radiations.  Could  we  so  screen  the  light  that  only  those  rays 
which  have  a  deep,  penetrating  power  in  the  tissues  would  reach 
the  skin  and  by  greatly  increasing  the  energy  get  intense  deep 
effects  without  the  superficial  effect  which  might  be  undesirable? 
I  want  to  put  this  in  the  form  of  a  question  to  Dr.  Titus  and  ask 
whether  any  scientific  work  has  been  done  on  the  actual  penetra- 
tion of  the  rays  into  the  living  tissues,  that  is.  with  exact  ref- 
erence to  their  wave-length. 

Mr.  G.  H.  Stickney  :  Dr.  Titus  points  out  what  suggests  an 
important  application  of  light  for  the  good  of  humanity.  As 
most  of  us  are  untrained  in  medical  practise,  we  are  unable  either 
to  confirm  or  question  his  results.  Even  if  only  part  of  the  bene- 
fits described  could  be  assured  of  realization,  it  would  seem  to  me 
that  the  subject  would  be  well  worthy  of  further  investigation 
to  the  end  that  artificial  light  might  be  better  adapted  to  meet 
such  needs,  and  the  facts  of  the  case  made  more  generally  known. 

Mr.  C.  O.  Bond:  In  one  of  the  weeklies  in  the  East,  there 
appeared  recently  an  editorial  concerning  the  sun  bath  cures  that 
were  effected  at  some  place  in  Switzerland,  where  high  altitude 
and  clear  air  gave  an  excess  of  ultra-violet  light  over  what  is 
obtained  in  lower  altitudes  and  through  different  strata  of  filter- 
ing air.  They  are,  it  seems,  accomplishing  some  quite  remark- 
able results  in  cures  of  all  sorts  of  diseases,  so  much  so,  that 
this  editorial  spoke  with  unbounded  enthusiasm.  If  that  be  true, 
then  it  is  quite  worth  while  undertaking  to  duplicate  these  condi- 
tions by  artificial  light.  But  it  would  seem  a  difficult  thing  to  do 
this  where  there  is  a  glass  bulb  surrounding  the  source  of  light  at 
the  very  beginning,  because  much  of  the  ultra-violet  radiation 
would  be  lost  at  that  point.  With  the  searchlight  scheme  which  the 
author  suggests,  the  glass  face  being  removed,  there  is  not  the 
same  chance  of  losing  the  ultra-violet  rays. 

Dr.  Ellice  M.  Alger  (Communicated)  :  I  am  not  competent 
to  discuss  the  technical  side  of  Dr.  Titus'  paper,  but  there  is  one 
point  I  should  make.  The  careless  listener  or  reader  might  easily 
get  the  erroneous  impression  that  photo-therapeutic  apparatus 
was  about  all  the  equipment  that  the  physician  of  the  future  would 
need.     No   doubt  the  author   intended   to  lay   special   emphasis 


UGHT   IN   THE   TREATMENT   OF   DISEASE  145 

on  the  very  important  qualification  contained  in  the  last  sentence 
of  his  paper,  viz.,  "phototherapy  is  a  safe  and  efficient  auxiliary" 
but  not  a  method  of  treatment  in  itself.  To  use  it  as  the  doctor 
advises  in  appendicitis  or  in  earache  would  be  criminal  for  a  man 
who  was  not  competent  to  exercise  the  nicest  judgment  as  to  the 
point  where  the  case  ceased  to  be  medical  and  became  surgical. 
It  would  be  little  better  for  a  man  to  treat  Bright's  disease  and 
diabetes  knowing  nothing  of  their  nature  or  their  danger  signals 
but  with  the  simple  faith  that  his  therapy  is  good  for  all  diseases. 
Electro-therapeutics  has  been  particularly  handicapped  in  just 
this  way.  Its  special  danger  has  been  that  it  can  be  made  useful 
in  many  different  branches  of  medicine,  of  all  of  which  no  one 
human  brain  could  have  more  than  a  smattering.  It  can  be  used 
safely  only  by  one  who  has  a  sound  fundamental  training  and 
who  knows  not  only  his  own  limitations  but  the  limitations  of  his 
medium.  I  am  glad  Dr.  Titus  so  evidently  had  this  in  mind  in 
his  concluding  sentence. 

Dr.  John  Wieeard  Travell  (Communicated)  :  In  this  paper 
the  many  useful  ways  in  which  light  may  be  utilized  to  alleviate 
painful  and  diseased  conditions  of  the  human  body  have  been  set 
forth  briefly  and  forcibly.  The  limited  subject  has  held  the 
speaker  to  a  description  of  certain  therapeutic  uses  of  light  with- 
out permitting  him  to  describe  other  mehods  of  treatment,  or  to 
make  comparison  with  other  methods  as  to  the  degree  of  efficiency 
in  securing  results.  It  is  like  reading  a  page  in  Materia  Medica 
in  which  the  good  qualities  of  a  drug  like  digitalis  are  enumerated 
and  the  many  conditions  in  which  it  might  be  used  noted.  But 
from  such  a  brief  perusal  one  must  not  conclude  that  it  will  act 
in  all  these  many  ways  better  than  all  other  agencies. 

It  is  my  fortune  to  be  familiar  alike  with  the  therapeutic  uses 
of  light  and  with  Dr.  Titus'  method  of  using  it  in  his  practise, 
and  I  feel  impelled  to  emphasize  the  fact  that  he  uses  light  as 
an  adjunct  to  other  physical  agencies  and  drugs,  and  not  as  a 
cure-all. 

Mr.  R.  B.  Ely:  Physicians  have  come  to  the  office  of  the 
central  station  I  am  connected  with  and  asked  for  information 
about  lamps  of  the  kind  described  in  this  paper.  The  only  lamp 
of  this  sort  that  I  knew  of  was  the  "Lucudescent"  lamp,  which 


1 4O  TRANSACTIONS    I.    K.    S. PART    I 

is  regulated  by  a  rheostat.  Its  rays  I  believe  are  more  toward 
the  infra-red  than  toward  the  ultra-violet.  A  great  many 
physicians  have  come  and  wanted  to  purchase  any  kind  of  a 
lamp,  so  long  as  it  was  a  large  source  that  they  could  use  in  some 
way,  apparently  regardless  of  the  spectrum  of  the  lamp. 

Another  question  about  the  electric  bath.  A  great  many  com- 
plain about  the  cost  of  the  electric  baths  in  residences  and  are 
endeavoring  to  reduce  that  cost,  but  it  has  been  my  experience 
that  they  would  not  install  a  tungsten  lamp  in  place  of  a  gem  lamp 
in  these  baths.  I  would  like  to  know  whether  both  carbon  and 
tungsten  lamps  are  used  for  specific  diseases  or  whether  one  lamp 
in  such  a  cabinet  would  answer  all  purposes. 

Mr.  W.  R.  Mott:  For  the  last  four  years,  the  use  of  flame 
carbons  has  been  coming  forward  in  the  treatment  of  disease. 
For  this  purpose  there  are  used  a  blue  flame  carbon  and  the  snow 
white  flame  carbon  which  is  used  for  general  illumination. 

There  is  a  book  on  the  medical  use  of  light,  entitled,  "Light  and 
Energy"  by  Dr.  Margaret  A.  Cleaves.  I  don't  consider  this  a 
particularly  important  book  at  the  present  moment,  but  it  sum- 
marizes an  enormous  fund  of  information.  One  thing  that  il- 
lustrates its  defects  is  that  it  suggests  the  use  of  calcium  peroxid 
in  a  flame  carbon.  Out  of  curiosity  I  tried  it  and  had  an  inter- 
esting result.  With  about  20  per  cent,  of  calcium  peroxid  the 
carbon  did  not  give  any  important  amount  of  light.  With  about 
40  per  cent.,  the  carbon,  after  burning  nearly  five  minutes,  ex- 
ploded due  to  dissociation  of  the  calcium  peroxid  in  the  entire 
length  of  the  electrode. 

In  regard  to  the  use  of  the  white  flame  arc,  it  is  of  interest  to 
know  that  the  candlepower  increases  nearly  as  the  square  of  the 
current.  The  exponent  is  about  1.8  for  some  direct  current  open 
arc  lamps.  The  white  flame  arc  is  much  more  powerful  than  any 
other  known  agent  for  actinic  effect. 

In  the  treatment  of  disease  by  light,  there  are  two  chief  func- 
tions :  one  the  stimulation  of  healthy  growth,  and  the  other  the 
destruction  of  germs.  In  the  destruction  of  germs  the  ultra- 
violet light  is  very  strong.  The  best  wave-length  for  each  bac- 
teria is  not  known. 

A  physician  in  Cleveland  went  to  the  laboratory  of  the  National 


UGHT   IN    THE   TREATMENT   OF   DISEASE  I47 

Carbon  Company  to  find  out  how  to  reflect  ultra-violet  light. 
That  is  not  a  simple  proposition.  In  a  book  by  Landolt  and 
Bornstein,  some  data  are  given  on  the  reflecting  power  of  several 
materials.  At  a  wave-length  of  305^/i  in  ultra-violet  the  reflecting 
power  is : 

Reflecting  power 
Metal  in  per  cent. 

Alloy  (69  per  cent.  Al,  31  per  cent.  Mg) 72.2 

Nickel  plated 44.2 

Copper 25.3 

Platinum 39.8 

Gold 31.8 

Silver 9. 1 

Silver  in  the  red  has  a  reflecting  power  of  about  90  per  cent. 

One  of  the  problems  in  the  design  of  a  lamp  for  therapeutic 
purposes  is  to  reflect  those  rays  which  are  required.  In  some 
cases  the  ultra-violet  rays  are  wanted  in  others  they  are  not. 

The  open  flame  arc  gives  off  fumes  which  are  objectionable 
and  should  be  removed  by  good  ventilation.  I  have  found 
in  the  use  of  the  white  flame  arc  for  the  photographic  studio,  that 
a  small  piece  of  ammonium  carbonate  placed  in  the  enclosed 
chamber  will  eliminate  the  bad  effects  of  the  nitric  acid  produced 
by  all  open  arcs. 

I  have  tried  an  experiment  with  the  snow  white  flame  carbons 
and  found  that  glass  of  an  ordinary  window  pane  (0.08  in.  thick), 
destroyed  at  least  50  per  cent,  of  the  photographic  power,  and 
with  another  chemical  I  found  that  a  greater  portion,  as  much  as 
two-thirds,  of  the  light  was  destroyed.  The  question  of  specially 
designed  glass  therefore,  is  important.  If  ultra-violet  rays  were 
required  then  quartz  would  be  necessary.  If  stimulation  were 
desired  then  other  glasses  specially  selected  for  each  treatment 
would  be  advisable. 

Dr.  E.  C.  Titus  (In  reply)  :  The  great  majority  of  physicians 
do  not  themselves  employ  light  in  the  treatment  of  disease,  but 
do  refer  patients  frequently  to  institutions  where  it  and  other 
physical  agencies  are  in  use. 

The  researches  of  Finger  of  Vienna  demonstrated  that  by 
applying  on  ointment  consisting  of  4  per  cent,  esculin  in  glycerin, 
(the  active  principle  of  horse  chestnut)  to  the  skin  that  80  per 
2 


I48  TRANSACTIONS    I.    E.    S. PART    I 

cent,  of  the  ultra-violet  rays  penetrate  to  the  deeper  tissues  where 
ordinarily  said  rays  are  arrested  by  the  skin. 

The  researches  of  Finsen  of  Copenhagen  seem  to  prove  that 
both  the  ultra-violet  and  the  luminous  rays  exercise  their  char- 
acteristic influence  not  alone  upon  the  surface  of  the  skin,  but 
also  on  the  deeper  parts  as  evidenced  by  their  inhibitory  action 
upon  both  local  and  deep  tubercular  processes. 

Further,  Kellogg  of  Battle  Creek,  Mich.,  the  originator  of  the 
electric  light  bath  cabinet,  has  shown  that  the  processes  of  elim- 
ination of  deleterious  substances  retained  in  the  tissues  are 
promptly  intensified  through  the  increased  activity  of  the  skin  and 
of  the  kidneys,  with  elimination  of  waste  products,  and  the 
doubling  in  quantity  of  the  carbon  dioxid  eliminated  by  the 
lungs,  as  the  result  of  the  constitutional  effects  of  the  intense 
luminous  rays  upon  the  surface  of  the  body. 

One  fact  which  Dr.  Cobb  seemed  to  lose  sight  of  is  that  the 
body  fluid  is  practically  a  circulating  saline  solution  whose  con- 
ductivity for  light  energy  is  one  of  the  best  known.  Photo- 
graphic plates  have  been  affected  by  light  through  two  or  more 
inches  of  living  tissue.  In  accordance  with  the  law  of  conserva- 
tion of  energy,  the  luminous  rays  which  are  carried  into  the 
tissues  are  there  converted  into  heat,  inducing  a  physiological 
hyperemia  and  tissue  oxidation  or  more  active  metabolism. 

In  connection  with  Mr.  Mott's  remarks  it  would  seem  proper 
to  emphasize  that  the  ultra-violet  rays  are  used  principally  for 
local  effects  on  the  skin  and  superficial  conditions,  as  for  the 
dissipation  of  so-called  port  wine  marks. 

The  writer  had  attempted  to  show  the  therapeutic  applications 
of  the  full  spectrum  or  more  particularly  of  the  luminous  rays  as 
an  efficient  auxiliary  in  the  treatment  of  many  painful  and  other 
disease  conditions. 

Referring  to  Mr.  Ely's  remarks, — it  is  the  diffused  and  intense 
light  energy  employed  in  a  cabinet  bath,  properly  ventilated  as 
pointed  out  in  the  paper,  to  which  we  attribute  its  chief  thera- 
peutic efficiency. 


LUCKIKSIi:     NEW    HIGH-EFFICIENCY   LAMP  149 

THE  APPLICATION  OF  THE  NEW  HIGH-EFFICIENCY 
TUNGSTEN  LAMP  TO  PHOTOGRAPHY* 


BY  M.  EUCKIESH. 


Synopsis:  The  results  of  a  general  study  of  the  photographic  value 
of  the  radiation  from  the  new  gas-filled  tungsten  lamp  are  presented.  A 
comparison  has  been  made  of  this  new  lamp  with  the  mercury-vapor  lamp 
and  the  older  type  of  tungsten  lamps.  The  effect  of  voltage  on  actinicity 
has  been  studied.  A  scheme  which  has  been  developed  for  reducing  glare 
from  this  lamp  when  used  in  portrait  photography  is  described.  Other 
photographic  data  are  given.  The  fundamental  principles  of  the  lighting 
of  studios  are  dwelt  upon  and  the  application  of  the  tungsten  lamp  to 
various  branches  of  photography  are  briefly  described.  Data  on  present 
practise  in  moving  picture  production  studios  are  given  and  desirable 
accessories  are  shown. 


The  recent  great  increase  in  the  efficiency  of  tungsten  lamps 
of  large  size,  brought  about  by  introducing  the  filament  in  an  inert 
gas,  has  made  it  possible  for  the  new  lamps  to  invade  fields  in 
which  the  incandescent  lamp  heretofore  has  not  been  an  impor- 
tant factor.  One  of  the  interesting  new  fields  in  which  the  gas- 
filled  tungsten  lamp  is  meeting  with  considerable  success  is  that 
of  photography.  Owing  to  the  higher  operating  temperature  of 
the  filament  the  luminous  efficiency  is  considerably  increased  and 
the  actinic  value  of  the  light  for  ordinary  plates  even  in  a  greater 
ratio.  The  natural  characteristics  of  the  tungsten  lamp,  such  as 
portability,  steadiness,  ease  of  operation,  unvarying  quality,  con- 
tinuous character  of  spectrum,  and  high  efficiency,  are  valuable 
allies  to  the  most  essential  characteristic,  namely,  radiant  energy 
of  high  actinic  value.  A  study  of  the  actinicity  of  the  light  from 
gas-filled  tungsten  lamps  has  shown  that  this  lamp  is  destined  to 
become  an  important  factor  in  photographic  procedure. 

Sensibility  of  Ordinary  Photographic  Plates. — In  ordinary 
photography  only  the  rays  of  wave-length  from  0.30  p  to  0.50  n 
are  of  appreciable  importance.  In  fact  the  ultra-violet  radiation 
in  daylight  practically  ends  at  0.30  n,  the  rays  of  shorter  wave- 

*  A  paper  read  at  a  meeting  of  the  Nevr  York  Section  of  the  Illuminating  Engi- 
neering- Society,  January  14,  1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


i5o 


TRANSACTIONS    I.    E.    S. — PART    I 


length  being  absorbed  before  reaching  the  earth.  Ordinary  clear 
glass  begins  to  absorb  ultra-violet  rays  at  0.35  /*  and  becomes 
opaque  for  rays  of  shorter  wave-length  than  0.30  fi.  Optical 
systems  used  in  photographic  apparatus  usually  being  made  of 
glass,  the  radiation  of  shorter  wave-length  than  0.30 /1  is  of  no 
interest.  Ordinary  plates  highly  sensitive  only  to  0.50  p  can  be 
made  relatively  more  sensitive  to  rays  of  longer  wave-length,  but 
this  procedure  usually  results  in  greatly  decreasing  the  speed  so 
that  ordinary  plates  are  far  from  orthochromatic.  In  ordinary 
portraiture  there  is  no  urgent  need  for  plates  sensitive  to  all  the 


"■.;...-;! 


0 


4* 


Kig.  i.— Spectral  energy  distribution  in  radiation  from  various  sources. 


visible  rays  because  quite  satisfactory  modeling  of  the  subject 
can  be  done  in  light  and  shade. 

Spectra  of  Common  Light  Sources. — In  Fig.  1  are  shown  the 
spectral  distributions  of  energy  in  the  spectra  of  the  light  from 
tungsten  lamps  as  compared  with  skylight  and  noon  sunlight. 
These  are  plotted  with  equality  at  0.59  \i  which  indicates  the 
relative  values  of  energy  of  various  wave-lengths  for  approxi- 
mately the  same  integral  values  of  luminous  intensity.  No 
spectro-photometric  data  on  the  latest  arc  lamps  are  available. 
The  spectrum  of  the  mercury  arc,  being  a  line  spectrum,  is  not 


luckiesh:    new  high-efficiency  lamp  151 

plotted;  but  its  actinic  value  for  ordinary  plates  is  much  more 
nearly  equal  to  that  of  daylight  than  that  of  the  new  tungsten 
lamp.  In  some  other  respects,  however,  it  is  not  as  desirable 
as  the  latter  for  photographic  purposes.  It  is  seen  that  the  new 
high  efficiency  tungsten  lamps  emit  relatively  much  more  of  the 
so-called  actinic  rays  than  the  vacuum  type. 

Sensibilities  of  the  Eye  and  Ordinary  Photographic  Plate. — In 
Fig.  2  are  shown  diagrammatically  the  spectral  sensibilities  of 
the  eye  and  of  the  ordinary  photographic  plate  for  rays  of  equal 
energy  value.  While  it  is  a  well-known  fact  among  those 
acquainted  with  the  science  of  photography  that  the  sensibilities 
of  the  eye  and  the  ordinary  photographic  plate  are  far  different, 
it  is  not  so  well  known  to  many  interested  in  the  art  of  photog- 


_, , , , 1 _ 


Fig-  2.— Spectral  sensibilities  of  the  eye  and  the  ordinary  photographic  plaife 
for  rays  of  equal  energy  value.  1    *     Qf  ofT 

raphy.  One  of  the  aims  of  the  investigator  in  the  science  of 
photography  is  to  produce  a  high  speed  plate  sensitive  relatively 
to  the  various  spectral  rays  in  the  same  general  manner  as  the 
eye.  This  has  not  yet  been  done.  However,  this  is  no  great 
handicap  in  ordinary  portraiture.  On  the  other  hand,  such  a 
plate  would  be  invaluable  in  landscape  and  much  indoor  pho- 
tography involving  the  reproduction  of  colored  objects  in  true 
values. 

Relative  Actinicities  of  Mercury  Arc  and  Tungsten  Lamps. — 
In  order  to  study  the  actinicity  of  an  illuminant1  it  is  advan- 
tageous to  arrange  an  apparatus  which  will  give  a  number  of 
different  values  of  illumination  on  the  same  plate  simultaneously. 
This  is  easily  done  by  means  of  a  disk  having  openings  of  differ- 

1  Luckiesh,  M.,  New  Tungsten  Lamps  in  Photography;  Electrical  World,  July  19, 1914. 


152  TRANSACTIONS    I.    E.    S. PART     I 

ent  degrees.  The  disk  used  by  the  writer  had  ten  openings  vary- 
ing in  size  from  10  deg.  to  180  deg.  The  plate  and  disk  were 
enclosed  in  a  velvet-lined  box  with  a  small  aperture  in  one  end 
covered  with  ground  opal  glass  which  was  chosen  after  finding 
that  it  transmitted  practically  the  same  rays  that  clear  glass  trans- 
mits and  in  the  same  relative  proportions.  This  ground  glass  was 
necessary  in  order  to  obtain  well-defined  circular  strips  on  the 
photographic  plate,  to  obviate  "pinhole"  effects,  and  to  cut  down 
the  light  so  that  a  reasonably  long  exposure  could  be  given.  Ex- 
posures should  be  sufficiently  long  so  that  they  can  be  accurately 
timed  with  a  stop-watch.  In  a  given  case  both  the  exposure  of 
the  plate  and  the  illumination  on  the  disk  were  kept  constant. 
Several  plates  were  exposed  for  each  illuminant  with  the  usual 
unexposed  "fog-strip"  on  each.  These  were  developed  under  the 
same  conditions  and  finally  measured  for  transparency  by  means 
of  a  Martens  polarization  photometer.  In  order  to  interpret  the 
data  the  following  definitions  are  presented : 

light  transmitted 


Transparency  =  T  = 


light  incident 


Opacity  =  O  =  -~ 

Density  =  D  =  log  O  =  log  =  . 

In  Fig.  3  are  plotted  the  results  obtained  on  a  Seed  26  plate 
with  a  mercury-vapor  tube  and  three  tungsten  lamps.  The  plate 
chosen  is  representative  of  the  sensibility  of  common  photo- 
graphic plates.  The  densities  plotted  against  the  logarithms  of 
the  illuminations  produce  a  curve  which  is  straight  over  a  con- 
siderable region.  This  region  is  the  accepted  working  range  of 
the  plate.  Data  of  this  character  are  so  influenced  by  the  con- 
ditions of  exposure,  development,  kind  of  plate,  etc.,  that  no 
more  than  a  general  idea  of  the  relative  actinicities  can  be  gained 
without  presenting  too  extensive  data  for  a  paper  of  this  char- 
acter. It  is  seen  that  for  an  ordinary  photographic  plate  the 
light  from  a  mercury  arc  is  three  to  four  times  more  actinic  than 
the  light  from  the  gas-filled  tungsten  lamp  operating  at  20  lumens 
per  watt.  Owing  to  the  compactness  of  the  light  source  of  the 
tungsten  lamp,  however,  the  light  is  more  efficiently  controlled  or 


euckiesh:    new  high-eeficiency  lamp 


153 


directed  than  in  the  case  of  an  extended  source.  This  tends  to 
overcome  the  disadvantage  of  the  gas-filled  tungsten  lamp  with 
its  lower  actinic  value  per  lumen. 


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Fig.  3.— Relative  actinicities  of  different  illuminants  for  an  ordinary 
photographic  plate  (Seed  26). 

Effect  of  Voltage  on  Actinicity  of  Tungsten  Light.— -The  influ- 
ence of  voltage  or  filament  temperature  on  the  actinic  value  of 
the  light  from  the  gas-filled  tungsten  lamp  is  shown  in  Fig.  4. 


2      3   4   5  6    8  10  20         40    60  80 100  MO  180 

RELATIVE  ILLUMINATION 
Fig.  4.-Effect  of  voltage  on  the  actinic  intensity  of  a  1,000-watt,  115-volt,  nitrogen- 
filled  tungsten  lamp  for  an  ordinary  photographic  plate  (Seed  30). 

A  1,000-watt  gas-filled  tungsten  lamp  operating  normally  at  115 
volts  and  18  lumens  per  watt  was  operated  at  three  voltages  and 
the  relative  actinicities  of  the  light  determined  for  an  ordinary 


'54 


TRANSACTIONS    I.    K.    S. PART    I 


photographic  plate  (Seed  30).  It  is  seen  that  the  actinic  value 
increases  very  greatly  as  the  voltage  is  increased  above  normal. 
For  instance,  to  produce  a  photographic  density  of  unity  (trans- 
parency 10  per  cent.),  the  relative  amounts  of  radiation  were  68 
and  34  respectively  for  normal  voltage  (115)  and  135  volts. 
Thus  it  is  seen  that  an  increase  of  17  per  cent,  in  voltage  above 
normal  doubles  the  actinicity  of  the  light  from  this  lamp  for  the 
plate  used.  In  this  experiment  the  illumination  was  allowed  to 
increase  with  the  voltage ;  that  is,  the  position  of  the  lamp  was  the 
same  for  the  three  voltages. 

Effect  of  Voltage  on  Actinicity  per  Unit  of  Light  Flux. — In 
order  to  show  the  influence  of  voltage  on  actinic  value  per  lumen 
of  visible  light,  another  experiment  was  performed  in  which  the 


1 

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125 

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10  20      30  40  506070     100     150  200 

RELATIVE  ILLUMINATION 

Kig.  5.— Effect  of  voltage  variation  on  the  actinicity  of  the  radiation  from  a  1,000-watt, 
115-volt,  nitrogen-filled  tungsten  lamp;  luminous  intensity  constant. 


illumination  falling  on  the  multi-sector  disk  was  kept  constant. 
The  results  are  shown  in  Fig.  5.  This  shows  that  the  radiation 
affecting  ordinary  photographic  plates  increases  more  rapidly  with 
voltage  than  does  the  total  luminous  radiation.  The  figures  at 
the  right  represent  different  voltages.  In  this  case  a  Seed  26 
plate  and  the  same  lamp  (1,000-watt,  115-volt  gas-filled)  as  in 
the  foregoing  experiment  were  used.  It  is  well  to  note  that 
actinicity  depends  upon  the  sensibility  of  the  plate  under  con- 
sideration. For  instance  if  a  plate  is  more  sensitive  to  the  violet 
or  blue  rays  the  actinicity  of  the  radiation  from  a  tungsten  lamp 
will  increase  more  rapidly  than  the  luminous  intensity  with  in- 
creasing voltage.     However,  the  actinicity  of  this  radiation  for  a 


luckiesh:    new  high-efficiency  lamp  155 

truly  orthochromatic  plate  will  increase  in  the  same  ratio  as  the 
luminous  intensity.  In  other  words,  an  increase  of  17  per  cent, 
in  voltage  would  not  double  the  actinic  value  for  an  orthochro- 
matic plate,  but  would  increase  it  only  67  per  cent.  It  should  be 
noted  that  the  data  represented  in  a  given  curve  in  Fig.  5  are 
for  constant  illumination  as  measured  with  a  direct  comparison 
photometer.  It  is  thus  seen  in  Figs.  4  and  5  that  a  great  gain  in 
actinic  value  can  be  obtained  by  increasing  the  voltage  above 
normal.  This  led  to  an  early  trial  of  the  scheme  and  there  are 
outfits  on  the  market  employing  this  principle.  An  increase  in 
voltage,  however,  results  in  a  decrease  in  the  life  of  a  tungsten 
lamp ;  so  that  the  writer  was  led  to  another  method  of  producing 
light  of  high  actinic  value  which  could  further  be  used  where 
lamps  were  burned  for  long  periods  such  as  in  taking  moving 
pictures.  The  method  which  also  has  other  advantages  will  be 
discussed  later. 

Orthochromatic  Photography. — There  are  some  kinds  of  pho- 
tographic work  (relatively  few,  however)  that  require  an  accu- 
rate reproduction  of  color  values  in  light  and  shade  such  as  in 
the  photography  of  paintings  and  the  tri-color  printing  process. 
Here  orthochromatic  plates  are  necessary  and  also  a  light  source 
emitting  all  the  visible  rays.  There  are  no  truly  orthochromatic 
plates  on  the  market  and  where  accurate  work  is  desirable  a  very 
accurate  filter  is  necessary  to  alter  the  spectral  character  of  the 
light  which  reaches  the  plate  so  that  the  sensibility  of  the  plate 
approaches  closely  to  that  of  the  eye.  Most  of  the  so-called  ortho- 
chromatic plates  available  are  far  from  being  truly  orthochro- 
matic. Some  are  not  even  sensitive  to  red  rays  to  an  appreciable 
extent.    Many  show  a  relatively  insensitive  region  at  about  0.50  fi. 

The  high-efficiency  gas-filled  tungsten  lamp  is  quite  satisfactory 
for  most  of  the  work  in  orthochromatic  photography.  Its  light 
has  all  the  visible  rays,  which  is  quite  essential.  Owing  to  the 
preponderance  of  yellow,  orange  and  red  rays,  it  is  unnecessary 
to  use  such  a  slow  filter  with  this  light  as  with  daylight  for  most 
so-called  orthochromatic  plates.  This  means  a  somewhat  higher 
speed  for  rough  orthochromatic  work  than  with  daylight.  How- 
ever, for  an  orthochromatic  plate  such  as  the  Cramer  spectrum 
plate  it  will  be  found  that  there  is  too  much  of  the  radiation  in 


If-''  TRANSACTIONS    I.    E.    S. PART    I 

the  long- wave  visible  region  in  the  light  of  a  gas-filled  tungsten 
lamp.  In  other  words  this  plate  has  been  over-sensitized  to  the 
orange  and  red  rays,  which  condition,  however,  is  rare.  As 
already  stated  the  need  for  orthochromatic  plates  in  the  portrait 
studio  is  not  urgent. 

Adapting  the  Tungsten  Lamp  to  Portrait  Photography. — Owing 
to  the  fact  that  light  from  the  gas-filled  tungsten  lamp  is  only 
one  third  to  one  fourth  as  actinic  as  daylight,  it  is  to  be  expected 
that  a  condition  of  glare  is  liable  to  obtain  in  portrait  photog- 
raphy- where  a  reasonably  high  speed  is  desirable.  Such  has 
been  found  to  be  the  case.  It  is  quite  desirable  to  have  sufficient 
actinic  value  per  lumen  of  light  in  order  to  permit  lenses  to  be 
used  at  the  smaller  apertures  and  yet  to  insure  sufficient  speed. 
The  lamp,  of  course,  can  be  burned  above  normal  voltage  for  the 
brief  period  of  exposure  in  portrait  work.  However,  this  pro- 
cedure calls  for  special  apparatus  and  introduces  an  undesirable 
flash-light  effect.  Further,  it  may  have  an  appreciable  effect  upon 
the  life  of  the  lamp,  although  this  is  at  present  an  unknown  quan- 
tity to  the  writer.  Certainly  any  appreciable  amount  of  burning 
at  a  voltage  sufficiently  excessive  to  warrant  the  use  of  special 
apparatus  would  seriously  decrease  the  life  of  the  lamp.  For 
continuous  work  such  as  the  making  of  moving  pictures,  the 
lamps  cannot  be  operated  at  any  great  increase  above  normal 
voltage  without  a  very  considerable  decrease  in  the  life  of  the 
lamp.  The  low  actinic  value  of  the  light  with  a  consequent  con- 
dition of  glare  when  sufficient  illumination  is  used  to  gain  high 
speed  cannot  be  overcome  by  the  use  of  diffusing  screens. 

It  early  occurred  to  the  writer  that  some  selective  method  was 
necessary  to  adapt  the  new  tungsten  lamps  in  the  best  manner  to 
portrait  photography.  Experiments  were  made  to  produce  a 
glass  of  such  transmission  characteristics  that  practically  all  the 
rays  to  which  ordinary  plates  were  sensitive  would  be  transmitted 
while  the  non-photographic  but  highly  luminous  rays  would  be 
reduced.  It  was  also  necessary  that  the  glass  be  quite  trans- 
parent to  infra-red  rays,  because  too  much  energy  absorbed  by 
the  bulb  would  be  liable  to  cause  serious  trouble.  Reference  to 
Fig.  2  shows  that  it  should  be  possible  to  produce  such  a  glass. 

5  L,uckiesh,  M.,  Adapting  the  Tungsteu  Lamp  to  Portrait  Photography;  Eleclncal 
World,  November  14,  1914. 


LUCKIESH  :     NEW    HIGH-EFFICIENCY    LAMP  1 57 

Of  course  a  highly  efficient  glass  must  be  as  transparent  to  the 
ultra-violet  rays  as  the  clear  glass  of  the  camera  optical  system.3 
Such  a  glass  was  made  with  a  transmission  for  the  total  visible 
light  from  the  1,000-watt,  115-volt,  nitrogen- filled  tungsten  lamp 
of  about  30  per  cent,  while  the  actinic  value  was  inappreciably 
affected  for  ordinary  photography.  A  further  aim  was  to  reduce 
the  ordinarily  non-actinic  rays  in  just  the  right  proportions  so 
that  a  pleasing  light,  apparently  white  in  appearance,  was  ob- 
tained. A  glass  satisfactory  in  all  these  respects  was  obtained. 
It  was  found  to  transmit  about  85  per  cent,  as  much  of  the  total 
radiation  as  clear  glass,  thus  no  trouble  was  to  be  expected  from 
excessive  local  temperature.  This  glass  must  not  be  confused 
with  the  'daylight'  glass4  recently  developed  by  the  writer.  The 
two  glasses  are  far  different,  for  the  daylight  glass  was  developed 
for  the  purpose  of  altering  only  the  visible  rays  of  tungsten  light 
to  a  spectral  equality  with  daylight,  whereas  the  glass  here 
referred  to  has  for  its  purpose  the  transmission  of  the  ordinary 
photographic  rays  and  the  reduction  of  the  remaining  visible 
rays  to  such  a  degree  that  an  apparent  match  with  daylight  is 
obtained. 

The  result  of  this  development  is  a  light  that  appears  to  be  of 
the  same  color  as  daylight  and  a  light  of  approximately  the  same 
actinic  value  per  lumen.  This  means  a  great  deal  to  the  pho- 
tographer. No  accessory  apparatus  is  necessary ;  merely  a  socket, 
lamp  and  reflecting  apparatus.  The  light  being  practically  of  the 
same  apparent  color  and  actinicity  as  daylight  it  can  be  used  to 
reinforce  daylight.  This  has  been  done  in  many  instances.  When 
daylight  fails  it  can  be  used  satisfactorily  alone  with  the  same 
speed  as  daylight,  thus  the  photographer  does  not  need  two 
different  instincts  for  making  exposures.  Burning  at  normal 
efficiency,  there  is  no  danger  from  burn-outs,  such  as  is  present 
with  excessive  over-voltage  apparatus,  and  the  lamp  can  be  used 
for  such  purposes  as  the  production  of  moving  picture  films  where 
long  periods  of  continuous  burning  are  necessary.  It  has  proved 
successful  in  the  latter  field.    The  lamps  have  also  been  used  suc- 

*  Luckiesh,  M.,  Ultra-violet  Radiation;  Electiical  World,  June  15,  1915.  Luckiesh,  M., 
Glasses  for  Protecting  the  Eyes  ;  Trans.  I.  E.  S.,  No.  5.,  1914. 

4  lyUCkiesh,  M.,  Artificial  Daylight ;  Electrical  World,  September  19,  1914.  Luckiesh 
and  Cady,  Artificial  Daylight;  Trans.  I.  E-  S.,  No.  8,  1914. 


158 


TRANSACTIONS   I.    E.    S. — PART    I 


cessfully  for  home  portraiture,  and  photographers  have  found 
them  readily  portable  for  indoor  work  outside  of  the  studio. 

Difference  in  Transparency  of  Blue  Glasses  for  Ordinary  Pho- 
tographic Rays. — As  will  be  seen  from  Fig.  2,  the  glass  will  be  a 
bluish  color;  but  in  order  to  show  that  any  ordinary  blue  glass 
will  not  be  satisfactory  the  data  in  Fig.  6  are  given.  Out  of  a 
number  of  samples  of  glass  the  writer  asked  an  assistant  to 
choose  two  blue  glasses.  The  assistant  is  somewhat  trained  in 
color-work  and  therefore  understood  clearly  what  'blue'  means. 
The  two  samples  were  exposed  to  the  total  light  from  the  gas- 
filled  lamp  under  the  conditions  previously  described  in  the  use 
of  the  multi-sector  disk.     The  results  show  the  great  difference 


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Fig.  6.— Relative  actinicities  of  the  radiation  from  a  1,000-watt,  115-volt,  gas-filled, 
tungsten  lamp  after  passing  through  two  different  specimens  of  blue  glass. 
This  illustrates  that  there  is  a  great  difference  in  the  transparency  of  blue 
glasses  for  actinic  rays.    Ordinary  plate  used. 

in  the  transparencies  of  the  two  samples  for  the  so-called  actinic 
rays.  At  a  density  of  unity  the  radiation  passing  through  one 
sample  was  about  one  third  as  actinic  as  the  radiation  which 
passed  through  the  other.  Experiments  with  other  media  also 
showed  great  differences  in  their  transparencies  to  ordinary 
actinic  rays.  Many  blue  dyes  were  unsatisfactory  owing  to  lack 
of  permanency. 

In  order  to  show  that  the  glass  finally  chosen  for  use  in  the 
bulbs  of  the  gas-filled  tungsten  lamp  for  photographic  purposes 
is  highly  transparent  to  the  rays  affecting  ordinary  plates,  the 
spectra  of  the  light  from  this  lamp  through  two  samples  of  the 


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Fig.  7--Effect  of  proposed  glass  on  various  Seed  plates.  C-clear  glass.  A  and  B-Samples 
of  proposed  glass  transmitting  50  per  cent,  and  35  per  cent,  of  total  light  from  a  tung- 
sten-filament lamp  operating  at  18  lumens  per  watt. 


Fig.  8.— A  method  of  using  the  new  high-efficiency  special  blue-bulb  tungsten-filament 
lamp  in  a  portrait  studio. 


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pig.  9._An  example  of  photostat  lighting.     Four  i,ooo-\vatt,  115-volt,  tungsten-filatnent 
lamps  in  white-enamelled,  angle,  steel  reflectors. 


luckiesh:    new  high-efficiency  lamp  159 

proposed  glass  of  different  densities,  as  compared  with  the  spec- 
trum of  the  light  through  clear  glass,  are  shown  for  six  ordinary 
plates.  It  is  seen  in  Fig.  7  that  there  is  no  visible  reduction  in 
the  actinic  rays  for  these  first  six  plates  on  the  left.  To  illustrate 
how  insensitive  ordinary  plates  are  to  the  green  and  yellow  rays 
attention  is  directed  to  the  mercury-vapor  comparison  spectrum. 
The  green  (0.546  fi)  and  yellow  lines  (0.577  /*  and  0.579  f0>  t0 
which  95  per  cent,  of  the  visible  light  must  be  credited,  do  not 
show  on  the  reproductions  which  are  made  from  ordinary  plates. 
In  some  cases  the  green  line  shows  very  faintly  on  the  plate. 
Here  it  is  well  to  note  that  these  spectograms  were  made  with  a 
prism  spectrograph  and  owing  to  the  much  greater  dispersion  of 
the  prism  for  the  rays  of  short  wave-length  the  plates  seem  to 
be  more  sensitive  to  rays  at  about  0.46  fi.  This  is  not  the  case, 
for  they  are  most  sensitive  to  rays  close  to  the  short-wave  end 
of  the  visible  spectrum. 

It  may  occur  to  some  that  in  the  rare  cases  of  orthochromatic 
photography  a  lamp  equipped  with  a  bulb  or  screen  of  this  glass 
would  be  unsatisfactory.  There  is  some  reduction  in  speed  in 
this  case,  but  not  an  excessive  amount  as  is  shown  for  three 
so-called  orthochromatic  plates  in  Fig.  7.  All  the  rays  are  yet 
present  in  this  light  after  passing  through  the  blue  glass.  There 
is  really  some  advantage  in  many  cases  of  orthochromatic  pho- 
tography in  using  the  glass  developed  because  the  light  after 
being  altered  by  the  blue  glass  screen  is  a  rough  approximation 
to  daylight  and  therefore  the  same  filters  that  have  been  used 
with  daylight  can  be  used  with  this  light  which  would  not  be  true 
with  the  unaltered  light.  Further  it  should  be  noted  that  the 
light  from  the  gas-filled  lamp  after  passing  through  the  blue  glass 
is  just  as  actinic  as  daylight  for  any  orthochromatic  plate.  In 
other  words,  there  is  produced  a  'photographic  daylight.' 

Spectro-photography. — A  note  on  the  study  of  spectral  sensi- 
bilities of  plates  may  not  be  out  of  place.  Owing  to  the  variable 
dispersion  of  a  prism,  the  rays  of  short  wave-length  are  greatly 
weakened  by  the  greater  dispersion  in  this  region  than  the  rays 
of  longer  wave-length.  The  spectra  of  most  artificial  light  sources 
are  weakest  in  the  ultra-violet  region,  which,  combined  with  the 
weakening  due  to  excessive  dispersion,  causes  difficulty  in  obtain- 


l6o  TRANSACTIONS    1.    K.    S. — PART    I 

ing  the  spectral  sensibilities  of  plates.  A  grating  spectrograph  is 
more  desirable  than  one  of  the  prism  type,  owing  to  the  normal 
spectrum  obtained.  However,  for  some  work  the  prism  spectro- 
graph can  be  made  more  satisfactory  by  allowing  for  the  weaken- 
ing due  to  dispersion  by  means  of  a  screen  or  revolving  disk.  If 
the  spectrum  of  a  continuous  light  source  of  known  spectral 
energy  distribution  be  photographed  on  a  plate  and  a  positive  be 
carefully  made  from  this  negative,  the  resulting  positive  can  be 
placed  in  a  proper  position  in  front  of  the  plates  to  be  used  and 
thereafter  (provided  they  are  the  same  plates)  more  satisfactory 
results  will  be  obtained,  owing  to  the  elimination  of  the  weaken- 
ing due  to  excessive  dispersion  in  the  short-wave  region.  Another 
method  of  overcoming  both  the  non-uniform  spectral  energy  dis- 
tribution and  dispersion  is  found  in  making  a  templet  in  a  revolv- 
ing disk  compensating  for  both  of  the  foregoing  with  the  result 
that  the  photographic  effect  for  energy  of  each  wave-length  would 
be  immediately  that  for  equal  amounts  of  energy  throughout  the 
whole  spectrum.  A  screen  which  will  compensate  for  either  the 
variable  dispersion  or  the  non-uniform  spectral  energy  distribu- 
tion of  the  light  source  (or  both)  can  be  made  by  producing  a 
cam  of  the  proper  character  which  when  uniformly  revolved 
would  move  a  photographic  plate  across  an  image  of  a  straight 
tungsten  filament.  The  cam  would  cause  the  plate  to  move 
at  just  the  proper  non-uniform  rate  to  cause  a  varying  photo- 
graphic effect  on  the  plate  of  just  the  right  amount  at  positions 
corresponding  to  the  various  wave-lengths  so  that  the  negative  or 
positive,  as  the  case  may  be,  could  be  used  as  a  screen  for  com- 
pensating the  effects  of  non-uniform  spectral  energy  distribution 
or  variable  dispersion  or  both.  Possibly  these  schemes  have 
already  been  applied.  At  any  rate  they  are  desirable  aids  where 
considerable  spectro-photographic  work  is  being  done. 

THE  LIGHTING  OF  PORTRAIT  STUDIOS. 

It  certainly  would  be  presumptious  for  the  lighting  specialist 
to  attempt  to  teach  the  portrait  photographer  how  to  light  his 
subjects,  for  lighting  is  the  basis  of  the  photographer's  art.  The 
writer  has  often  recommended  that  the  lighting  specialist  consult 
the  photographer  and  his  product,  for  there  is  much  to  be  gained 
from  such  a  procedure.     However,  the  lighting  specialist  can  be 


LUCKIESH  :     NEW    HIGH-EFFICIENCY    LAMP  l6l 

of  assistance  in  the  portrait  studio  because  he  has  an  acquaintance 
with  the  laws  and  methods  for  obtaining  results  desired  by  the 
photographer.  In  other  words,  the  photographer  knows  the 
effects  he  desires,  but  the  lighting  specialist  is  perhaps  better 
acquainted  with  the  optical  laws  which  govern  the  results. 

The  lighting  of  subjects  in  the  portrait  studio  is  practically 
entirely  a  matter  of  light  and  shade.5  The  character  of  shadows 
depends  upon  the  position  of  the  light  source,  the  solid  angle 
subtended  by  the  source  at  the  shadow-forming  object,  and  the 
amount  of  scattered  light  reaching  the  object.  The  position  of 
the  light  source  determines  the  direction  of  the  shadows,  the 
area  of  the  light  source  or  more  correctly  the  solid  angle  sub- 
tended by  the  light  source  at  the  point  of  interest,  determines  the 
character  of  the  edge  of  the  shadows,  and  the  amount  of  scattered 
light  determines  the  density  of  the  shadows. 


Pig.  io.— a— shadow  produced  by  a  point  source  of  light  amid  non-reflecting  sur- 
roundings; b— shadow  produced  by  a  point  source  of  light  and  io  per  cent, 
scattered  light;  c— shadow  produced  by  source  of  varying  area  and  io  per  cent, 
scattered  light. 

Obviously  a  point  source  of  light  in  a  perfectly  black  room 
would  produce  black  and  sharp  shadows  on  a  diffusely  reflecting 
surface.  If  the  walls  and  surroundings  were  of  such  a  reflecting 
power  that  io  per  cent,  of  the  total  light  reaching  the  object  is 
scattered  light,  a  shadow  on  a  diffusely  reflecting  surface  would 
be  one  tenth  as  bright  as  the  surface  receiving  the  total  light, 
but  would  yet  remain  sharp  in  outline.  By  varying  the  area  of 
the  light  source  the  shadows  would  become  less  defined,  but  the 
io  per  cent,  of  scattered  light  is  still  effective.  Some  combination 
of  these  possible  conditions  is  desired  by  the  photographer. 

The  foregoing  conditions  are  roughly  represented  in  Fig.  io. 
The  receiving  surface  is  here  assumed  to  be  a  perfect  diffusely 
reflecting  substance.    The  third  case,  c,  is  not  an  exact  represen- 

5  Luckiesh,  M.,  Light  and  Art :  Lighting  Jour..  March,  1913.  Luckiesh,  M.,  Light 
and  Art  ;  American  Gas  Inst.,  October.  1913. 


1 62 


TRANSACTIONS   I.    E.    S. — PART    I 


tation,  for  the  sloping  line  would  be  more  or  less  curved  owing 
to  the  different  distances  of  the  elements  of  the  surface  of  the 
light  source  from  the  shadow-producing  point. 

The  lighting  of  a  studio  by  means  of  a  diffusely  transmitting 
skylight  is  illustrated  in  Fig.  II.  The  skylight,  ef,  is  for  sim- 
plicity assumed  to  be  vertical  as  is  the  case  in  many  studios.  Its 
shadow-producing  qualities  are  dependent  upon  the  solid  angle, 
epf,  (the  dimension  perpendicular  to  the  plane  of  the  paper  can 
be  assumed  equal  to  the  dimension  shown  for  simplicity).  Scat- 
tered light  of  course  is  controlled  by  screens  and  the  direction  of 
the  shadows  by  curtains  and  the  orientation  of  the  subject.  Often 
the  amount  of  light  passing  through  the  skylight  (the  flux  den- 
sity) is  insufficient  to  insure  reasonably  short  exposures,  so  the 


Fig.  ii.— Illustrating  the  dependence  of  shadow-producing  effect  of  extended 
sources  upon  the  solid  angle  subtended  at  the  subject  by  the  source;  that 
is,  upon  the  size  of  the  source  and  its  distance  from  the  subject. 

subject  must  be  moved  closer  to  the  skylight.  This  means  that 
the  solid  angle  is  greatly  increased  with  a  result  of  apparent 
flattening  in  the  photograph.  In  order  to  produce  satisfactory 
modeling,  a  source  too  large  in  area  is  undesirable.  This  necessi- 
tates greatly  reducing  the  skylight  area  by  screens  or  moving  the 
subject  further  from  the  skylight,  both  cases  often  resulting  in 
an  undesirable  decrease  in  the  illumination  of  the  subject.  Re- 
ferring again  to  Fig.  1 1  it  is  seen  that  the  light  source  can  be 
decreased  in  area  as  the  subject  approaches  it.  Thus  the  shadow- 
producing  qualities  of  the  three  sources  ab,  cd,  and  ef  are  the 
same,  if  the  dimension  perpendicular  to  the  paper  is  assumed  to 
vary  in  the  same  manner  and  the  sources  are  uniformly  bright. 
A  great  advantage  experienced  in  the  use  of  artificial  lighting 


LUCKIESH  :     NEW    HIGH-EFFICIENCY   LAMP 


163 


is  that  studios  can  be  reduced  very  much  in  size  owing  to  the 
greater  amount  of  light  obtainable  per  unit  area  of  the  source 
than  in  the  case  of  the  average  skylight  in  cities  and  that  the  sky- 
light can  be  dispensed  with.  Thus  the  skylight,  ef,  in  Fig.  11  can 
be  replaced  by  an  artificial  lighting  outfit  covered  by  a  diffusing 
medium  of  much  smaller  actual  size,  ab,  without  altering  the  solid 
angle,  fpe,  and  therefore  without  changing  the  shadow-producing 
effect. 

Accessories  for  Tungsten  Lamps. — The  only  essential  acces- 
sories for  tungsten  lamps  are  a  socket,  a  reflector,  and  a  diffusing 
screen.  In  general  angle  reflectors  such  as  those  shown  in  Fig.  12 
are  found  the  most  convenient.  There  are  many  standards  al- 
ready available  of  the  same  general  character  as  shown  in  Fig.  13. 
These  should  be  readily  adjustable  for  height  and  portable.     As 


Fig.  12.— White  enamelled  steel  reflectors  suitable  for  photographic  purposes. 

would  be  expected,  many  photographers  desire  to  carry  out  their 
own  ideas  as  to  apparatus  for  containing  the  lamps.  This  was 
one  of  the  reasons  for  deciding  to  adapt  the  scheme  of  using  the 
selectively  transmitting  colored  glass,  proposed  and  developed  by 
the  writer,  to  the  lamp  bulbs.  Doubtless  there  are  many  cases 
where  the  glass  could  be  used  as  a  screen  in  front  of  the  reflector, 
but  the  colored  bulb  presents  a  complete  unit.  This  has  been  used 
behind  various  kinds  of  artificial  "skylights"  or  windows.  A 
satisfactory  arrangement  was  found  where  a  photographer  had 
placed  three  of  the  special  photographic  lamps  in  an  asbestos 
lined  vertical  box  covered  on  one  side  with  tracing  paper.  The 
middle  lamp  was  hung  somewhat  lower  than  the  others  and  the 
tracing  cloth  immediately  in  front  of  it  was  replaced  by  thin  silk 
of  less  diffusing  property  with  a  result  that  a  more  directed  effect 
3 


164 


TRANSACTIONS   I.    E.    S. — PART    I 


was  obtained.  Translucent  and  opaque  screens  were  placed  in 
various  positions  over  the  diffusing  front  depending  upon  the 
desired  result.  Some  photographers  have  combined  their  special 
lamps  with  a  mercury  arc  equipment  already  in  their  possession. 
Needless  to  say  the  ghastly  appearance  of  the  persons  in  the 
studio  can  thus  be  largely  eliminated. 


Fig.  13.— A  standard  for  use  with  the  gas-filled,  1,000-watt  tungsten- 
filament  lamp  in  portrait  photography. 


Here  it  might  be  well  to  bring  to  the  attention  of  the  photog- 
rapher the  practise  of  using  the  fluorescent  reflectors  with  mer- 
cury arc  lamps.  This  reflector  is  an  excellent  development,  but 
the  red  and  orange  rays  emitted  by  it,  due  to  fluorescence,  are 
obtained  very  largely  at  the  expense  of  the  ordinary  actinic  rays. 


luckiesh:    new  high-efficiency  lamp  165 

A  more  efficient  scheme  photographically  would  be  to  use  the 
mercury  arcs  with  white  reflectors  and  eliminate  the  ghastly 
appearance  of  the  persons  in  the  room  by  the  addition  of  tungsten 
lamps  which  would  also  contribute  toward  the  actinic  value  of 
the  total  light.  However,  in  general  the  writer  would  not  recom- 
mend the  use  of  a  combination  of  two  different  kinds  of  illumi- 
nants  where  both  are  appreciably  different  in  actinicity  and  color, 
owing  to  confusion  which  would  result  unless  the  light  were  well 
mixed  by  means  of  a  diffusing  screen. 

In  Fig.  8  is  shown  a  photograph  of  a  studio  where  two  of 
the  special  photographic  lamps  are  used  in  separate  portable 
standards.  Here  it  will  be  noted  one  unit  is  placed  on  each  side 
of  the  front  of  the  subject,  but  at  quite  different  distances.  Many 
photographers  prefer  to  use  the  primary  sources  on  one  side  of 
the  subject,  depending  upon  reflecting  screens  for  lighting  the 
opposite  side  sufficiently.  The  writer  believes  that  in  either  case 
two  units  are  desirable  for  satisfactory  modeling  and  the  majority 
of  photographers  with  whom  he  has  discussed  the  matter  are  of 
the  same  opinion.  Of  course  the  units  can  be  placed  behind  the 
same  diffusing  screen,  but  the  two  sources  seem  to  be  necessary. 

Regarding  the  speed  at  which  portraits  can  be  made  with  the 
special  photographic  lamp,  it  is  sufficient  to  state  that  the  expos- 
ures are  the  same  as  for  daylight.  This  is  not  true  with  the  clear 
lamp  because  it  is  impossible  to  obtain  sufficient  actinic  value  to 
insure  success  with  short  exposures  without  producing  a  condi- 
tion of  glare  which  is  not  conducive  to  the  production  of  satis- 
factory pictures,  unless  excessive  over-voltage  is  applied. 

Printing  and  Enlarging. — The  tungsten  lamp  has  already 
played  an  important  part  in  printing.  The  problem  presents  no 
difficulties  and  it  is  very  easy  to  experiment  with  the  lamps  for 
this  purpose.  Here  there  is  no  need  for  the  special  blue-bulb 
photographic  lamp,  the  purpose  of  which  is  to  eliminate  glare 
where  human  subjects  are  being  photographed.  The  writer  has 
seen  many  successful  printing  outfits  employing  various  sizes  of 
gas-filled  tungsten  lamps. 

In  enlarging,  the  new  lamps  find  a  newer  field.  Here  there  are 
two  general  forms  of  apparatus  available;  these  are  shown  in 
Fig.   14.     The  upper  illustration  shows  a  satisfactory  arrange- 


i06 


TRANSACTIONS    I.    E.    S. PART    I 


merit  for  high  speed.  Where  a  condenser  is  used  the  light  source 
should  be  compact.  Concentrated-filament,  gas-filled  tungsten 
lamps  have  proven  satisfactory  for  this  purpose;  the  exposures 
being  only  a  few  seconds  in  duration.  A  cheap  outfit  is  repre- 
sented in  the  lower  illustration.  Here  the  lamp  only  is  contained 
in  a  white  enamelled  reflector.  Over  the  aperture  a  ground  glass 
is  placed  and  the  negative  is  viewed  against  it.  Owing  to  the 
greater  loss  of  light  due  to  the  absence  of  a  light-gathering  con- 
denser the  exposures  are  many  times  greater  than  in  the  other 
case.  However,  satisfactory  enlargements  can  be  made  in  a 
reasonable  length  of  time. 

Of    course   the   variations   in   the    schemes    for   printing   and 


Fig.  14. — A— concentrated  tungsten-filament  lamp;    B— negative:   C— condensers; 
D— ground  glass;  E— lens;  F— enlargement. 


enlarging  are  manifold,  so  that  it  seems  hardly  worth  while  to 
do  more  than  present  the  chief  principles.  However,  a  special 
field  of  interest  is  the  lighting  for  photostats.  This  is  best 
described  by  the  illustration,  Fig.  9.  Here  as  many  as  four 
1,000-watt,  gas-filled  tungsten  lamps  are  used  depending  upon 
the  size  of  the  subject.  Exposures  of  only  a  few  seconds  are 
necessary  for  satisfactory  results. 

Moving  Picture  Production  Studios. — The  lighting  for  mov- 
ing picture  production  studios  is  a  far  different  problem  from 
that  for  ordinary  portrait  and  commercial  photography.  In  this 
field  artificial  light  sources  are  excessively  taxed  in  order  to  fur- 
nish sufficient  actinic  rays  so  that  fully  timed  pictures  can  be 


luckiesh:    new  high-efficiency  lamp  167 

made  in  one  sixty-fourth  of  a  second.  Pictures  are  made  at  the 
rate  of  sixteen  per  second,  but  considering  the  time  during  which 
the  film  is  moving  when  the  shutter  is  closed,  and  further  allow- 
ing for  the  period  during  which  the  lens  is  not  working  at  full 
aperture,  the  actual  exposure  is  perhaps  only  one  fourth  as  long 
as  would  be  indicated  by  the  rate  of  sixteen  per  second. 

There  appear  to  be  two  general  classes  of  production  studios. 
In  one  class  the  lighting  is  permanently  installed  in  position  and 
relatively  large  areas  (approximately  18  ft.  (5.48  m.)  by  32  ft. 
(9-75  m0  are  lighted.  In  the  other  general  class  the  lighting 
apparatus  is  portable  and  relatively  smaller  scenes  are  usually 
lighted.  Both  classes  are  found  combined  in  other  studios. 
Doubtless  both  general  schemes  have  their  own  advantages,  but 
it  appears  to  the  writer  after  visiting  a  number  of  studios  that 
the  scheme  of  using  portable  lighting  apparatus  makes  possible 
better  effects  in  general  and  is  the  more  economical  in  space, 
electrical  energy,  and  equipment.  Certainly  better  lighting  effects 
can  be  obtained  in  many  cases  for  the  scenes  are  continually 
changing  which  demands  a  flexible  lighting  system  in  order  to 
obtain  the  best  possible  effects.  Possibly  some  producers  find 
these  advantages  offset  by  the  desirability  of  order. 

In  order  to  give  an  idea  of  the  lighting  requirements  in  mov- 
ing picture  production  studios  the  following  data  on  lighting 
equipment  required  in  certain  observed  sets  are  presented. 

I.     Set  about  16  ft.  by  30  ft.  (4.9  by  9.1  m.). 

124  mercury-vapor  tubes,  d.  c,  112  volts,  3.5  amperes. 

Energy  used,  about  50  kw. 

Lamps  arranged  in  banks  of  8  each. 

Placed  48  overhead  inclined  at  about  30  deg.  from  horizontal  and 

12  ft.  (3.65  m.)  from  floor. 
64  on  one  side  in  banks  two  tiers  high. 
12  at  front  7  ft.  (2.1  m.)  above  floor. 
Actors  worked  to  within  10  ft.  (3  m.)   from  front  lights. 


II. 


Set  about  16  ft.  by  25  ft.  (4.9  by  7.6  m.). 

24  carbon  arcs,  a.  c,  220  volts,  14  amperes. 

Energy  used,  approximately  50  kw. 

Placed  16  overhead  and  8  in  front  about  8  ft.  (2.4  m.)  from  floor. 

Actors  worked  to  within  10  ft.  (3m.)  from  front  lights. 


1 68  TRANSACTIONS   I.    E.    S. — PART    I 

III.  Set  about  14  ft.  by  20  ft.  (4.3  by  6  m.). 

18  carbon  arcs,  d.  c,  no  volts,  20  amperes. 

2  30-ampere  carbon  arcs  in  series  for  flood  light  through  a  window. 

Energy  used,  approximately  43  kw. 

Placed  12  in  front  and  6  on  side  near  front  from  4  to  7  ft.  (1.2  to 

2.1  m.)  from  floor. 
Actors  worked  to  within  5  ft.  (1.5  m.)  of  front  lights. 

IV.  Set  about  15  ft.  by  15  ft.  (4.5  m.). 

12  carbon  arcs,  d.  c,  no  volts,  20  amperes. 

Energy  consumed,  approximately  27  kw. 

Placed  in  front  overhead  in  two  rows  about  8  ft.  and  9  ft.  (2.4  and 

2.7  m.)   from  floor. 
Actors  worked  to  within  7  ft.  (2.1  m.)  of  front  line  of  lamps. 

V.     Set  about  12  ft.  by  24  ft.  (3.6  by  7.3  m.). 

48  mercury  arcs,  d.  c,  no  volts,  3.5  amperes. 
2  carbon  arcs,  d.  c,  no  volts,  28  amperes. 

2  carbon  arcs,  d.  c,  no  volts,  30  amperes. 

3  quarts  mercury  arcs,  d.  c,  no  volts,  3.5  amperes. 

The  3  quartz  mercury  arcs  and  2  carbon  arcs  were  in  front  and  the 
48  mercury  arcs  were  distributed  on  one  side  with  the  excep- 
tion of  two  banks  of  8  each  which  were  near  the  front  on  the 
other  side.  None  overhead.  The  2  30-ampere  carbon  arcs 
were  on  the  side  near  the  front  and  about  10  ft.  (3  m.)  from 
the  floor.  These  gave  a  marked  effect  in  the  picture.  This 
appeared  to  be  an  exceptionally  intelligent  attempt  to  obtain 
good  lighting  effects. 

Energy  consumed,  about  33  kw. 

Actors  worked  to  within  7  ft.  (2.1  m.)  of  front  line  of  lamps. 

IV.     Set  about  10  ft.  by  10  ft.  (3  m.). 

11  1,000-watt  gas-filled  tungsten  lamps,  no  volts. 

Placed  in   front  corners   about  8   ft.    (2.4  m.)    from   floor.     More 

lamps  on  one  side  than  the  other. 
Energy  consumed,  11  kw. 
Light  well  controlled  by  angle  reflectors. 
Actors  worked  to  within  5  ft.  (1.5  m.)  of  front  line  connecting  the 

lamps. 

VII.     Set  about  10  ft.  by  15  ft.  (3  by  4.5  m.). 

16  1,000-watt  special  blue-bulb,  gas-filled  tungsten  lamps,  no  volts. 

Placed  8  in  front,  6  on  side  near  front,  2  overhead. 

Energy  consumed,  16  kw. 

Actors  worked  to  within  7  ft.  (2.1  m.)  of  front. 

Of  course  the  wattage  necessary  depends  upon  the  actinic  value 
of  the  illuminant  used  and  especially  upon  the  area  of  the  scene. 


IvUCKIESH  :     NEW    HIGH-EFFICIENCY   LAMP 


169 


The  preceding  data  will  be  useful  in  estimating  the  magnitude  of 
an  installation,  the  area  and  character  of  the  scene  being  known. 
There  appears  no  field  where  the  lighting  expert  is  more  needed. 
Notwithstanding  the  fact  that  a  large  number  of  units  are  neces- 
sary in  order  to  obtain  sufficient  illumination  of  high  actinicity 
for  making  moving  pictures  a  great  deal  of  light  was  observed 
to  be  lost  by  lack  of  attention  to  light-controlling  accessories. 
The  tungsten  lamp  can  successfully  be  used  in  moving  picture 
production  studios,  but  care  should  be  exercised  in  conserving 
the  light  for  use  on  the  scene.    This  lamp,  owing  to  its  compact- 


Fig.  15.— A  method  of  supporting  tungsten-filament  lamps  in  moving 
picture  production  studios. 

ness,  readily  lends  itself  to  a  high  utilization  efficiency  which 
must  be  realized  in  order  to  insure  success  owing  to  the  lower 
actinicity  of  this  light.  The  necessity  of  the  use  of  such  a  selec- 
tive method  of  reducing  the  glare  from  these  lamps  by  absorbing 
a  portion  of  the  non-actinic  rays  is  emphasized  in  the  moving 
picture  production  studio.  The  illumination  necessary  is  enor- 
mous and  if  multiplied  several  times  (as  is  the  case  when  the 
clear  tungsten  lamp  is  used)  becomes  very  annoying  especially 
in  the  large  sets. 
As  already  mentioned  portability  of  the  lighting  apparatus  is 


I/O  TRANSACTIONS   I.    E.    S. — PART    I 

quite  desirable.  The  mercury  arcs  are  usually  arranged  in  ver- 
tical banks  of  eight  each  in  a  frame  supported  on  wheels.  The 
carbon  arc  lamps  are  usually  non-portable  with  the  exception  of 
the  bare  high-amperage  arcs  which  are  placed  on  tripods.  A 
form  of  portable  standard  developed  in  one  of  the  studios  using 
the  special  blue-bulb  gas-filled  tungsten  lamps  is  shown  in  Fig.  15. 
The  stand  is  made  to  be  adjustable  for  height  and  the  lamps  may 
be  tilted  about  their  supporting  arms.  One  of  the  white- 
enamelled  angle  steel  reflectors  shown  in  Fig.  12  was  adopted 
and  found  satisfactory.  It  has  also  been  recommended  in  one 
studio  using  the  scheme  of  permanent  installation  that  the  blue- 
bulb  gas-filled  tungsten  lamps  be  used  in  series  with  a  rheostat 
which  would  reduce  the  voltage  of  the  lamps  below  normal.  Only 
while  the  camera  is  being  operated  would  the  rheostat  be  cut  out. 
thus  subjecting  the  lamps  to  about  10  per  cent,  over- voltage. 
This  would  reduce  the  number  of  lamps  necessary  and  if  care 
were  exercised  the  decrease  in  life  of  the  lamp  would  not  be 
serious. 

To  summarize  the  requirements  in  artificial  lighting  of  moving 
picture  production  studios,  the  characteristics  of  the  light  sources 
placed  in  their  order  of  importance  are  as  follows :  high  actinic 
value  of  the  radiation,  portability,  control  of  the  light,  color- value 
of  the  light,  energy  consumption.  In  most  cases  energy  consump- 
tion was  found  to  be  a  minor  consideration. 

The  author  desires  to  acknowledge  his  indebtedness  to  Mr. 
H.  McMullan  for  his  assistance  in  the  experimental  work  and 
for  the  preparation  of  the  illustrations. 

DISCUSSION. 

Mr.  Wm.  A.  D.  Evans  (Communicated)  :  There  are  one  or 
two  points  brought  out  in  Mr.  Luckiesh's  article  which  are  not 
entirely  clear  to  me,  and  there  are  also  two  or  three  items,  re- 
garding which  I  am  not  in  entire  accord  with  his  views. 

On  the  second  page  Mr.  Luckiesh  makes  the  following  state- 
ment : 

The  spectrum  of  the  mercury  arc,  being  a  line  spectrum,  is  not 
plotted,  but  its  actinic  value  for  ordinary  plates  is  much  more  nearly  that 
of  daylight  than  that  of  the  new  tungsten  lamp.  In  some  respects,  it  is 
not  as  desirable  as  the  latter  for  photographic  purposes. 


NEW    HIGH-EFFICIENCY   LAMP  I/I 

I  cannot  conceive  in  any  respect  whatsoever  that  the  mercury- 
vapor  lamp  is  not  as  desirable  as  the  nitrogen-filled  lamps  for 
photographic  purposes.  A  lamp  to  be  desirable  for  photographic 
purposes  should  be  rich  in  the  so-called  "actinic  rays."  And  as 
Mr.  Luckiesh  has  stated  that  the  actinic  value  of  the  spectrum 
of  the  mercury-vapor  lamp  is  nearly  equal  to  that  of  daylight,  it 
would  seem  that  its  desirability  for  photographic  purposes  could 
not  be  added  to. 

On  page  4,  it  is  stated : 
It  is  seen  that  for  an  ordinary  photographic  plate  the  light  from  a 
mercury  arc  is  three  or  four  times  more  actinic  than  the  light  from  the 
gas-filled  tungsten  lamp  operating  at  20  lumens  per  watt.  Owing  to  the 
compactness  of  the  light  source  of  the  tungsten  lamp,  however,  the  light 
is  more  efficiently  controlled  or  directed  than  in  the  case  of  an  extended 
source.  This  tends  to  overcome  the  disadvantage  of  the  gas-filled  tungsten 
lamp  with  its  lower  actinic  value  per  lumen. 

In  relation  to  this,  I  note  further  on  that  Mr.  Luckiesh  states,  on 
the  fifth  page,  that  "a  1,000-watt,  gas  filled  tungsten  lamp  oper- 
ating normally  at  115  volts  and  18  lumens  per  watt."  Under 
ordinary  operating  conditions,  is  the  nitrogen-lamp  operated  at 
18  lumens  per  watt;  whereas,  in  comparative  tests  against  mer- 
cury arcs,  is  the  lamp  operated  at  20  lumens  per  watt? 

Regarding  the  "extended  light  source"  I  desire  to  say  that  the 
average  photographer  is  accustomed  to  natural  light  coming  from 
a  skylight  for  his  work,  which  is  nothing  more  or  less  than  an 
extended  light  source  and  the  question  of  diffusion  is  most  im- 
portant for  proper  photography.  As  far  as  possible,  photo- 
graphers desire  to  get  away  altogether  from  the  so-called  "spot- 
lighting" effects.  It  might  be  advisable  in  some  cases  to  use  a 
spot-light  to  bring  out  certain  high  lights,  etc.,  but  the  main 
lighting  is  always  desired  from  an  extended  source.  I  fail  to 
see  how  in  this  case  the  gas-filled  lamps  by  being  more  efficiently 
controlled  can  overcome  the  disadvantage  of  its  lower  actinic 
value  per  lumen. 

On  page  13  the  statement  is  made  that: 

The  green  line  (0.546  mu)  and  the  yellow  lines  (0.577  and  0.579  mu) 
to  which  95  per  cent,  of  the  visible  light  must  be  credited  do  not  show 
on  the  reproductions  which  are  made  from  ordinary  plates. 

From  investigations  made  by  Messrs.  Fabry,  Lardenburg,  Von 


1/2  TRANSACTIONS   I.   E.    S. — PART    I 

Recklinghausen,  Henri,  Coblenz,  and  others  showing  the  relative 
intensity  of  the  four  visible  lines  in  the  mercury  spectrum,  oper- 
ating in  a  low  pressure  lamp  or  glass  tube  lamp,  the  green  and 
yellow  lines  (0.546  mu  and  0.577-9  mu)  are  responsible  for 
practically  75  per  cent,  of  the  light  in  place  of  95  per  cent.,  as 
stated  by  Mr.  Luckiesh. 

In  this  connection,  it  might  be  stated  that  a  very  curious  co- 
incidence occurs  in  the  mercury  lamp.  Of  the  four  lines  which 
are  prominent  in  the  visible  spectrum,  the  line  546,  which  is 
present,  is  located  at  the  point  of  maximum  sensibility  of  the 
eye;  while  the  line  404  is  located  approximately  at  the  point  of 
maximum  sensibility  for  the  photographic  plate. 

On  page  12  Mr.  Luckiesh  shows  a  photograph  of  a  photo- 
reproducing  machine  lighted  by  four  1,000-watt  nitrogen  lamps. 
In  ordinary  practise,  throughout  the  country,  this  work  has  been 
accomplished  by  two  385-watt  mercury-vapor  lamps,  which 
shows  a  ratio  of  approximately  one  to  five  in  the  amount  of  energy 
consumption  for  the  same  class  of  work. 

On  page  19  it  is  stated: 

Regarding  the  speed  at  which  portraits  can  be  made  with  the  special 
photographic  lamp,  it  is  sufficient  to  state  that  the  exposures  are  the 
same  for  daylight.  This  is  not  true  with  the  clear  lamp  because  it  is 
impossible  to  obtain  sufficient  actinic  value  to  insure  success  with  short 
exposures  without  producing  a  condition  of  glare  which  is  not  conducive 
to  the  production  of  satisfactory  pictures,  unless  excessive  over-voltage 
is  applied. 

From  reading  this,  it  would  see  as  if  the  author  meant  that  with 
the  blue  glass  lamp  added  actinic  value  was  secured,  that  is,  an 
ordinary  clear  lamp  could  have  its  actinic  value  increased  simply 
by  putting  on  the  blue  glass.  I  do  not  think  he  meant  to  convey 
this  idea,  but  this  is  the  impression  which  would  be  gathered. 

In  relation  to  the  lighting  of  motion  picture  studios  I  desire  to 
state  that  most  of  the  data  submitted  by  Mr.  Luckiesh  is  for 
small  work.  For  one  of  the  largest  indoor  stages  in  the  country 
the  lighting  installation  consists  of  17  banks  of  eight  mercury 
lamps  each,  hung  overhead  and  about  8  ft.  from  the  floor  at  the 
front  line  and  gradually  rising  at  about  on  angle  of  30  degrees, 
so  that  the  back  lamps  are  about  20  ft.  from  the  floor.  Two 
banks  are  placed  in   front,  and  the  number  gradually  widening 


NEW    HIGH-EFFICIENCY   LAMP  1J$ 

out  going  towards  the  back.  Along  one  side  are  also  hung  five 
banks  at  an  angle  of  about  45  degrees  to  throw  the  light  in  on 
the  side.  These  lamps  are  all  mounted  overhead  on  trolleys,  and 
can  be  moved  lengthwise  of  the  studio,  so  that  the  scene  can  be 
set  up  on  any  one  of  three  stages.  In  addition,  there  are  pro- 
vided six  floor  stands  of  eight  lamps  each,  which  are  used  on  one 
side  of  the  stage  and  down  towards  the  front,  practically  all  the 
light  coming  from  overhead  and  one  side,  there  being,  as  might 
be  said,  a  complete  curtain  of  light  across  the  ceiling  and  down 
on  the  side.  This  stage  allows  the  setting  up  of  scenes  32  ft.  deep, 
with  a  back  line  of  24  ft.,  and  a  front  line  of  8  ft.,  and  approxi- 
mately with  an  average  intensity  of  about  300  to  350  foot- 
candles. 

Furthermore,  with  this  mass  of  lamps  lighted,  there  is  practi- 
cally no  glare  to  bother  the  actors  and  the  heat  is  in  no  way 
excessive  and  hardly  noticeable. 

In  summarizing  the  requirements  of  the  artificial  lighting  of 
motion  picture  studios,  the  author  places  the  characteristics  of 
light  sources  in  the  following  order :  the  high  actinic  value  of  the 
illuminant,  the  portability  and  control  of  the  light,  the  color  value 
and  the  energy  consumption.  He  states  in  most  cases  the  energy 
consumption  was  found  to  be  a  minor  consideration.  This  has 
not  always  been  the  writer's  experience,  as  energy  consumption 
is  quite  a  vital  fact  in  a  large  studio,  which  is  being  operated  all 
day  and  is  a  point  which  has  to  be  taken  into  consideration. 

Moreover,  another  point  which  the  author  neglected  to  men- 
tion, and  which  is  very  important — that  is  the  maintenance.  This 
is  a  feature  which  I  believe  is  as  important  in  motion  picture 
studio  work,  as  in  any  other  commercial  industry. 

Dr.  C.  E.  K.  Mees  (Communicated)  :  The  advent  of  the  new 
high-efficiency  tungsten  lamp  was  naturally  of  the  very  greatest 
importance  to  those  interested  in  the  development  of  photography, 
inasmuch  as  it  not  only  placed  at  their  disposal  with  artificial 
light  a  high-intensity  source,  but  that  source  differed  from  the 
former  high-intensity  sources  in  the  fact  that  it  was  especially 
rich  in  red  and  green  rays. 

The  importance  of  this  is  derived  from  the  fact  that  the 
tendency  of  photography  is  towards  the  effect  of  color  correct 


1^4  TRANSACTIONS   I.    E.    S. — PART    I 

methods,  and  eventually  of  color  photography.  Whereas  the 
older  photographic  materials  were  sensitive  only  to  the  shorter 
wave-lengths,  within  the  last  few  years  there  have  been  intro- 
duced materials  sensitive  to  the  whole  visible  spectrum  and 
radically  different  from  the  earlier  orthochromatic  plates,  which 
were  sensitive  only  to  the  blue  and  violet  and  to  a  small  region 
of  the  yellow-green  of  the  spectrum.  These  panchromatic  plates 
are  of  comparatively  recent  introduction,  and  while  they  are 
largely  used  for  special  work  requiring  sensitiveness  to  red  and 
green,  such  as  color  photography  or  commercial  work  involving 
the  photography  of  red  and  yellow  objects,  their  use  in  por- 
traiture is  rapidly  increasing,  though  it  is,  at  present,  very  lim- 
ited, the  professional  photographer  preferring  to  use  the  more 
easily  manipulated  and  cheaper  materials  to  which  he  has  hitherto 
been  accustomed.  The  advantages  of  panchromatic  plates  for 
portraiture,  however,  are  manifest.  The  human  skin  is  covered 
with  small  capillaries  of  a  red  color,  producing  streaks  and 
blotches  of  light  red,  which,  while  nearly  invisible  to  the  eye, 
have  a  very  strong  absorption  for  violet  light,  so  much  so  that 
under  a  light  source  which  transmits  no  red  the  skin  is  seen  to  be 
of  a  very  uneven  texture,  and  this  uneven  texture  is  reproduced 
in  photographs  taken  on  materials  sensitive  only  to  the  shorter 
wave-lengths,  so  that  portrait  negatives  exaggerate  skin  defects, 
and  invariably  are  worked  up  by  hand  in  the  retouching  process. 

Retouching  is  used  partly  to  correct  defects  in  lighting,  and 
partly  to  enhance  the  beauty  of  the  sitter,  but  the  greater  portion 
of  the  work  done  is  to  improve  the  surface  of  the  skin,  and  it 
is  this  work  which  has  caused  retouching  to  be  reproached  with 
the  spoiling  of  the  likeness. 

From  this  it  will  be  seen  that  the  use  of  panchromatic  plates 
is  by  no  means  likely  to  be  confined  to  the  few  kinds  of  photo- 
graphic work  where  they  have  hitherto  been  considered  essential, 
because  there  is,  in  fact,  little  photographic  work  where  correct 
color  rendering  is  not  an  advantage,  and  in  portraiture,  which 
represents  the  widest  field  of  all,  the  advantage  is  so  great  that 
red  sensitive  plates  would  probably  have  been  used  long  ago  but 
for  the  difficulties  which  attend  their  use.  Of  these  difficulties 
the  greatest  has  been  the  greater  exposure  which  has  been  neces- 


NEW    HIGH-EFFICIENCY   LAMP  175 

sary  in  order  to  get  correct  color  rendering.  Even  with  the  best 
color  sensitizers,  the  sensitiveness  to  red  and  green  which  can  be 
obtained  is  much  less  than  its  sensitiveness  to  blue  light  when 
tested  on  a  daylight  spectrum,  and  consequently  in  order  to  get 
satisfactory  color  rendering,  yellow  niters  have  to  be  used  with 
the  plate,  which  considerably  increases  the  exposure. 

It  is  not  true  that  orthochromatic  or  panchromatic  plates  are 
much  slower  in  their  total  sensitiveness  than  non-color  sensitive 
plates,  but  even  with  the  best  panchromatic  plates  an  increase  of 
exposure  of  about  three  and  a  half  times  is  necessary  for  day- 
light with  the  lightest  filter  which  will  give  correct  rendering,  and 
this  increasing  exposure  has  greatly  militated  against  the  applica- 
tion of  the  plate  to  portraiture. 

When  we  turn  to  the  employment  of  artificial  light  sources, 
however,  we  are  faced  with  quite  different  conditions.  Artificial 
light  sources  are  so  rich  in  red  and  green  rays  that  only  a  very 
light  filter — if,  indeed,  a  filter  at  all — is  required  for  the  use  of 
panchromatic  plates,  while  the  multiplying  factor  of  this  filter  is 
reduced  by  the  excess  of  red  and  green  in  the  light  source,  so  that 
a  panchromatic  plate,  with  such  a  source  of  light  as  the  nitrogen 
tungsten  lamp,  requires  less  exposure  than  the  corresponding 
plate  unsensitized,  while,  of  course,  the  color  rendering  is  quite 
satisfactory.  The  introduction  of  the  nitrogen  tungsten  lamp, 
therefore,  marks  an  era  in  artificial  lighting  for  studio  work  as 
it  does  in  almost  all  other  branches  of  the  lighting  art. 

With  the  introduction  of  this  lamp  photographers  all  over  the 
world  commenced  experiments  which  were  marked  with  great 
success,  and  there  is  no  doubt  that  the  nitrogen  tungsten  lamp  is 
destined  to  be  one  of  the  chief  illuminants  for  studio  portraiture 
in  the  future,  and  indeed  I,  personally,  am  inclined  to  think  that 
studios  lighted  in  this  manner  will  to  some  extent  displace  day- 
light studios.  With  the  introduction  of  this  illuminant  the  possi- 
bility of  obtaining  correct  color  rendering  in  color  portraiture  is 
very  greatly  increased,  and  although  at  first  the  tungsten  lamps 
would  be  used  with  ordinary  plates,  the  use  of  panchromatic 
plates  will  undoubtedly  grow,  and  we  may  expect  consequently 
that  indirectly  the  tungsten  lamp  will  aid  in  the  production  of 


176  TRANSACTIONS   I.    E.    S. — PART    I 

more  correct  portraiture,  giving  a  more  faithful  rendering  of  the 
skin  texture  than  has  been  possible  in  the  past. 

Turning  to  the  new  lamp  of  blue  glass,  this  lamp,  while 
undoubtedly  of  a  pleasing  color  to  the  eye,  abandons  the  very 
advantages  of  excess  of  red  and  green  which  are  such  valuable 
factors  in  the  tungsten  lamp  when  used  with  color  sensitive 
materials,  and  it  will,  therefore,  clearly  not  be  of  use  for  this 
purpose.  At  the  same  time,  most  studios  do  not  and  will  not  for 
some  time  use  such  color  sensitive  materials,  and,  therefore,  the 
loss  of  the  red  and  green  in  the  blue  glass  lamp  is  of  no  impor- 
tance photographically,  and  the  loss  of  the  blue  light  being  small 
(though  it  is  by  no  means  negligible)  the  diminution  of  glare 
and  the  more  pleasing  color  would  entirely  justify  the  adoption 
of  the  screen  lamp. 

The  great  advantage  of  this  lamp  is  that  it  can  be  used  to  rein- 
force lighting  either  by  daylight  or  by  the  enclosed  arc  where  the 
unscreened  lamp  on  account  of  its  color  would  be  objectionable 
as  introducing  two  different  colors  in  the  lighting,  and  for  this 
purpose  the  new  lamp  will  undoubtedly  be  in  considerable  de- 
mand. Thus,  it  seems  to  me  that  both  the  unscreened  and 
screened  lamps  represent  an  advance  in  photographic  portraiture 
— a  screened  lamp  as  a  reinforcing  lamp  for  daylight,  and  an 
unscreened  lamp  as  assisting  the  introduction  of  materials  giving 
correct  color  reproduction — which  must  tend  to  the  general 
improvement  of  the  status  of  photography. 

When  we  turn  to  cinematographic  work,  however,  it  seems  a 
little  doubtful  whether  tungsten  lamps  will  be  employed  to  the 
same  extent  for  black  and  white  cinematographic  work,  though 
they  represent  an  invaluable  aid  in  the  experimental  work  on 
color  cinematography,  on  which  so  much  is  being  done.  An 
investigation  of  the  gradation  of  non-color  sensitive  materials 
such  as  those  used  for  the  negative  film  in  moving  picture  work- 
shows  that  the  gradation  improves  as  we  pass  towards  the  more 
infrangible  end  of  the  spectrum,  so  that  a  film  which  gives  very 
excellent  gradation  at  400/i/i,  will  give  by  no  means  as  good  results 
for  a  light  with  a  mean  wave-length  of  480/x/*,  and  if  comparative 
photographs  are  taken  by  these  two  wave-lengths,  it  will  be  found 
that  in  the  photograph  taken  by  the  longer  wave-length  the  high- 


NEW    HIGH-EFFICIENCY   EAMP  \yy 

lights  are  clogged  up  and  deficient  in  detail  and  very  easily  show 
strong  halation,  while  in  the  photograph  taken  by  shorter  wave- 
lengths the  highlights  will  retain  all  their  quality,  and  owing  to 
the  opacity  of  the  film  for  light  of  this  wave-length  halation  will 
be  nearly  absent.  For  this  reason  it  is  improbable  that  in  cine- 
matographic work  the  nitrogen  tungsten  lamp  will  displace  the 
illuminants  at  present  used ;  namely,  the  mercury- vapor  lamp  and 
the  enclosed  arc  lamp. 

If  cinematographic  pictures  be  taken  by  mercury- vapor  lamps 
and  also  by  nitrogen  tungsten  lamps,  the  difference  in  the  quality 
of  the  pictures  will  be  most  marked,  the  highlight  gradation  being 
well  retained  in  those  taken  by  the  mercury  lamp  and  the  absence 
of  halation  being  noticeable,  while  in  those  taken  by  the  nitrogen 
tungsten  lamp  the  highlights  are  clogged  up  and  halation  appears 
wherever  any  portion  of  the  picture  has  been  over-exposed.  This 
effect  is  undoubtedly  due  to  the  difference  in  the  color  of  the  two 
light  sources.  If  the  spectra  of  the  two  light  sources  be  pho- 
tographed by  non-color  sensitive  materials,  it  will  be  seen  that 
the  center  of  action  of  the  nitrogen  tungsten  lamp  is  at  480^, 
while  a  fair  average  of  the  lines  of  the  mercury-vapor  lamp 
would  place  its  center  of  action  at  about  400,  the  lines  at  365,  404 
and  436  being  all  of  nearly  equal  density. 

A  small  practical  advantage  of  the  mercury- vapor  lamp  is  that 
it  is  a  light  source  of  considerable  area  and  of  low  visual  intensity, 
so  that  the  lamps  can  be  used  without  any  diffusing  screen,  and 
if  long  tubes  are  used  widely  spaced,  a  set  of  mercury-vapor 
lamps  makes  an  effective  substitute  for  a  window. 

When  we  turn  to  the  question  of  efficiency,  we  also  find  that 
although  the  nitrogen  tungsten  lamp  is  of  high  efficiency  for  the 
visible  spectrum,  it  is  much  surpassed  by  the  mercury-vapor  lamp 
and  the  enclosed  arc  lamp  in  the  violet  and  ultra-violet  regions  of 
the  spectrum,  and  this  is  an  additional  reason  for  the  use  of  these 
latter  lamps  in  moving  picture  studios,  where  efficiency  is  of 
high  importance. 

Summarizing  the  views  expressed  in  this  paper,  therefore,  we 
may  say  that  in  ideal  photography  materials  should  be  used  which 
will  render  color  values  as  they  are  seen  by  the  eye,  and  that 
the  introduction  of  the  nitrogen  tungsten  lamp  renders  the  use 


1/8  TRANSACTIONS   I.    E.    S. — PART    I 

of  such  materials  for  studio  work  easy  and  is  to  be  welcomed 
for  this  reason.  For  studio  work  where  non-color  sensitive 
materials  are  to  be  used,  and  especially  where  a  light  acts  as  a 
supplement  to  daylight,  or  the  enclosed  arc  lamp  is  required,  the 
blue  glass  nitrogen  tungsten  lamp  will  be  of  great  use.  For 
moving  picture  work,  however,  both  conditions  of  efficiency  and 
of  the  quality  of  the  resulting  negatives  are  likely  to  tend  towards 
the  continuance  of  the  light  sources  at  present  in  use,  and  to  pre- 
vent their  replacement  to  any  appreciable  extent  by  the  nitrogen 
tungsten  lamp. 

Prof.  George  A.  Hoadley  :  Mr.  Luckiesh  has  shown  us  in 
the  curves  on  the  third  page  (Fig.  2)  the  difference  in  sen- 
sitiveness, between  the  eye  and  the  photographic  plate.  Now 
take  a  point  source  of  light,  and  let  a  ray  from  it  strike  upon 
a  lens,  of  which  we  may  consider  this  a  half  cross-section.  We 
know  that  when  the  ray  strikes  the  lens,  we  have  a  bending  of 
the  rav.    We  also  know  that  if  it  is  white  light  when  it  strikes  the 


lens,  the  ray  will  not  only  bend,  but  will  be  dispersed,  and  we 
shall  probably  have  it  coming  down  in  this  direction — we  have 
the  red  at  R  (Fig.  A)  and  the  violet  nearer  the  lens  at  V,  and 
consequently  we  have  a  horizontal  spectrum  from  the  red  to  the 
violet — between  those  two  points.  Now  this  becomes  of  value 
when  you  consider  that  we  shall  have  a  red  focus  at  R  and  a 
violet  focus  at  V.  The  eye  will  focus  better  in  the  position 
marked  Y;  the  photographic  plate  in  position  V.  We  have 
pretty  nearly  that  condition  in  astronomical  photography.  We 
are  looking  at  point  sources  in  the  location  of  thousands  of 
stars,  and  if  we  focus  our  apparatus  and  put  the  plate  at  Y,  we 
shall  find  that  the  time  of  exposure  will  have  to  be  very  much 
longer  than  if  we  should  put  the  plate  near  V  at  the  actinic 
focus.  Consequently  in  a  larger  lens  it  is  necessary  to  make 
that  distinction,  or  that  difference  in  the  position  of  the  plate, 
in  order  to  take  the  picture  more  quickly,  and  in  order  to  get  a 


NEW    HIGH-EFFICIENCY   LAMP  1 79 

better  focus.  With  the  ordinary  camera  lens  that  is  not  necessary 
at  all  perhaps  on  account  of  the  fact  that  we  get  rid  of  the  dif- 
ference in  focus  by  many  different  kinds  of  glass  and  a  com- 
bination of  lenses. 

Mr.  M.  LuckiESh  (Reply  to  Mr.  Evans)  :  In  regard  to  Mr. 
Evans'  first  quotation  from  the  second  page  of  my  paper  will 
state  that  the  actinic  value  of  the  mercury  arc,  while  nearer  to 
that  of  daylight  for  ordinary  plate,  need  not  be  sufficient  to  stamp 
the  mercury  arc  as  good  as  tungsten  light  for  all  photographic 
work.  Mr.  Evans  cannot  conceive  this  so  I  will  refer  him  to 
the  proper  rendering  of  color  values  as  one  instance  where  the 
mercury  arc  fails. 

Mr.  Evans  next  quotes  from  the  fourth  page  of  my  paper  re- 
garding the  operating  efficiency  of  the  tungsten  lamps  used.  I 
designated  in  each  experiment  the  efficiency  at  which  the  lamp 
was  operating.  I  am  merely  interested  in  presenting  facts. 
Further  the  efficiency  of  operation  is  subject  to  change  from 
month  to  month  as  there  is  always  the  tendency  toward  higher 
luminous  efficiency  in  the  electric  incandescent  lamp  industry. 
There  is  no  point  in  the  least  to  Mr.  Evans  remarks  on  that 
score.  I  used  different  lamps  at  different  times  and  for  the  sake 
of  exactness  expressed  the  conditions  exactly. 

He  further  takes  issue  with  my  statement  that  the  light  from 
the  small  source  (the  incandescent  filament)  is  more  efficiently 
controlled  than  from  an  extended  source.  I  believe  Mr.  Evans 
at  any  other  time  will  agree  to  this.  He  misconstrues  my  mean- 
ing for  I  do  not  recommend  spot  light  effects  in  the  studio.  His 
conception  will  be  clearer  when  I  remind  him  that  in  the  moving 
picture  studios  is  this  exemplified.  In  a  mercury  arc  installation 
much  of  the  light  is  not  directed  upon  the  objects  to  be  photo- 
graphed but  wanders  away  never  to  return. 

He  further  quotes  from  the  thirteenth  page  and  takes  issue 
with  my  statement  that  95  per  cent,  of  the  light  from  the  or- 
dinary mercury  arc  which  I  used  must  be  credited  to  green  and 
yellow  lines.  He  quotes  others  as  obtaining  different  results. 
I  must  remind  Mr.  Evans  that  the  problem  of  color  photometry 
has  not  yet  been  solved,  so  various  persons  will  obtain  different 
results  depending  upon   the  method  used.      I   quoted   data   ob- 

4 


l8o  TRANSACTIONS   I.    E.    S. — PART    I 

tained  by  myself  by  the  direct  comparison  method  of  photometry 
after  considerable  investigation  of  methods  of  color  photometry. 

I  used  as  an  illustration  a  photostat  equipped  with  four  1,000- 
watt  tungsten  lamps  and  Mr.  Evans  states  that  the  same  work 
is  done  with  two  385-watt  mercury-vapor  lamps.  His  citation 
lacks  value,  however,  inasmuch  as  he  neglects  to  give  compara- 
tive speed.  Various  wattages  are  being  used  for  such  equipment, 
but  I  took  this  photograph  merely  as  an  illustration  for  high 
speed  work.  Mr.  Evans  appreciates  that  the  necessary  factor — 
exposure — has  been  omitted  by  him  in  his  comparison. 

Mr.  Evans  quotes  from  the  nineteenth  page  and  thinks  that 
the  impression  gained  is  that  the  blue  lamp  adds  actinic  value. 
The  portion  of  the  paper  devoted  to  the  modified  bulb  is  devoted 
practically  entirely  to  data  showing  that  I  have  eliminated  rays 
of  practically  no  photographic  value  for  ordinary  plates. 

In  regard  to  the  lighting  of  moving  picture  studios  by  means 
of  tungsten  lamps  I  submitted  only  the  data  available  at  that 
time.  I  am  sorry  that  I  was  only  able  to  cite  smaller  studios, 
but  the  work  has  just  begun.  The  outlook  is  promising  and  I 
will  try  to  present  much  more  data  regarding  this  field  at  some 
future  time. 

Mr.  M.  Luckiesh  (Reply  to  Dr.  Mees)  :  Regarding  the  future 
of  the  tungsten  lamp  in  cinematographic  work  we  can  only  con- 
jecture. It  is  being  used  to-day  in  some  of  the  smaller  studios 
with  entire  satisfaction.  Certainly  it  will  find  a  place  of  more 
or  less  importance  in  such  work.  I  quite  agree  with  Dr.  Mees 
that  we  should  photograph  with  an  object  of  rendering  true 
color-values  as  they  are  seen  by  the  eye.  But  at  present  this  is 
being  done  only  to  a  relatively  small  extent  in  the  portrait  studios. 
It  was  for  this  reason  (and  others)  that  I  have  recommended 
and  developed  the  blue  bulb  lamp  giving  a  rough  "photographic 
daylight."  Dr.  Mees,  however,  shows  that  there  are  exceptions 
when  he  claims  that  the  illuminants  at  present  used  in  cine- 
matographic work  have  an  advantage  over  the  clear  tungsten 
lamp  because  the  light  of  longer  zvave-lengths  is  present  in  lesser 
amounts  in  the  former  light  sources. 


luckiesh:    safeguarding  the  eyesight  181 

SAFEGUARDING  THE  EYESIGHT  OF  SCHOOL 
CHILDREN* 


BY    M.    LUCKIESH. 


Synopsis:  The  object  of  this  paper  is  to  present  to  school  authorities 
the  importance  of  proper  lighting  in  safeguarding  the  eyesight  of  school 
children.  Data  are  presented  showing  the  increasing  prevalence  of  near- 
sightedness with  advancing  school  grades  and  other  data  showing  the 
decrease  in  the  percentage  of  shortsightedness  accounted  for  in  part  at 
least  to  the  improvement  in  lighting  conditions.  Opinions  of  authorities 
are  quoted  which  show  the  importance  of  good  lighting  in  preserving 
eyesight  and  the  economic  gain  in  such  conservation.  Factors  which 
influence  vision  are  discussed;  namely,  illumination,  uniformity,  direction 
of  light,  glare,  character  of  reflecting  surfaces,  etc.  Legislation  on  school 
lighting  is  discussed.  Extracts  from  enacted  laws  pertaining  to  the 
subject  and  general  recommendations  for  school  lighting  legislation  are 
presented.  Satisfactory  and  unsatisfactory  conditions  found  in  modern 
schools  are  illustrated  and  the  co-operation  of  school  authorities  in 
improving  lighting  conditions  is  urged.  A  partial  bibliography  of  the 
literature  pertaining  to  school  lighting  is  appended. 


INTRODUCTION. 
There  are  twenty  million  school  children  in  the  United  States 
who  are  devoting  several  hours  each  day  to  study  or  perform- 
ance of  other  work  equally  trying  on  the  eyes.  According  to 
the  available  statistics  about  10  per  cent,  of  the  number  of  school 
children  examined  are  found  to  have  defective  vision.  In  many 
cases  the  percentage  of  defectives  has  been  found  to  increase 
with  increasing  age.  This  increase  can  be  attributed  largely  to 
the  manner  in  which  the  eyes  are  used.  Light  being  essential  to 
vision,  it  is  natural  to  turn  to  lighting  for  a  possible  cause  of  the 
increase  in  the  number  of  children  with  defective  vision.  Con- 
sidering those  that  are  already  defective  it  is  certain  that  proper 
lighting  and  proper  use  of  the  eyes  will  result  in  a  large  number 
being  permanently  cured.  Further,  this  is  an  age  of  prevention 
as  well  as  cure.  Prevention  of  defective  eyesight  means  proper 
lighting  and  proper  use  of  the  eyes.  It  should  be  remembered 
that  the  child's  eyes  are  immature  in  growth  and  function  and 
therefore  quite  susceptible  to  misuse.  Insufficient  illumination 
whether  due  to  shadows  owing  to  improper  direction  of  light  or 

*  A  paper  read  at  a  meeting  of  the   Pittsburgh  Section   of  the  Illuminating  Engi- 
neering Society,  Cleveland,  Ohio,  January  29,  1915. 

The  Illuminating  Engineering  Society  is  not   responsible   for  the  statements  or 
opinions  advanced  by  contributors. 


182 


TRANSACTIONS   I.    E.    S. — PART    I 


to  an  actual  deficiency  in  the  amount  of  light  at  a  particular 
desk  results  in  the  tendency  of  the  child  to  hold  the  reading 
matter  too  close  to  his  eyes.  Practising  this  continually,  results 
in  a  malformation  of  the  eye  muscles  and  consequent  near-sight- 
edness. The  tendency  once  begun  requires  more  effort  to  correct 
than  to  prevent  beforehand. 

Glare  from  windows,  blackboards,  glazed  paper  or  artificial 
light  sources  causes  eye-fatigue  with  resulting  disorders  too  com- 
plicated to  discuss  in  a  paper  of  this  nature.  A  lack  of  training 
in  avoiding  such  conditions  also  aids  in  increasing  the  number  of 
children  having:  defective  vision. 


Fig.  i. — Prevalence  of  short-sightedness  in  three  secondary  schools 
in  Stockholm,  1894-1903. 

Prof.  Johan  Widmark  of  Sweden  in  a  paper  on  "The  Decrease 
of  Short-sightedness  in  Secondary  Schools  for  Boys  in  Sweden," 
presented  at  the  Fourth  International  Congress  on  School  Hy- 
giene held  in  Buffalo  in  191 3,  publishes  some  interesting  statistics 
Some  of  these  have  been  plotted  and  are  shown  in  Figs.  1  and  2. 
In  Fig.  1  are  shown  the  data  gathered  in  three  kinds  of  schools. 
These  illustrate  the  increase  in  near-sightedness  with  increasing 
grade  of  class.  The  classes  are  named  first,  second,  third, 
fourth,  fifth,  lower  sixth,  upper  sixth,  lower  seventh,  and  upper 


LUCKIESH  :     SAFEGUARDING   THE   EYESIGHT 


183 


seventh.  The  corresponding  percentage  of  near-sighted  pupils  is 
shown  for  each  class.  The  most  striking  feature  is  the  unques- 
tionable increase  of  near-sightedness  from  class  to  class.  A 
further  point  of  interest  being  the  greater  prevalence  of  near- 
sightedness in  the  "classical"  school  than  in  the  "modern"  school. 
Another  school  which  has  both  the  classical  and  modern  side  has 
in  general  a  slightly  less  percentage  of  near-sighted  pupils  than 
found  in  the  classical  school. 


Tv'T'.v-'i-vy^.-r.rr 


Md-W^\H::tm:n^^ 


f     /9oo    / 
Year- 

Fig.  2. — Percentage  of  short-sightedness  in  the  highest  class  of  all 
the  state  secondary  schools  for  boys  in  Sweden. 

In  Fig.  2  is  shown  the  steady  decrease  in  the  percentage  of 
short-sightedness  in  the  highest  classes  of  all  the  state  secondary 
schools  for  boys  in  Sweden  from  1895  to  1906.  Data  obtained 
in  1883  but  perhaps  not  directly  comparable  with  the  foregoing 
data  showed  a  percentage  of  near-sightedness  as  high  as  65  per 
cent,  in  some  schools.  Prof.  Widmark  accounts  for  the  decrease 
in  short-sightedness  in  recent  years  as  illustrated  in  Fig.  2  as 
follows : 

Among  the  hygienic  improvements  which  have  been  effected  during 
recent  years  in  our  schools  and  in  all  the  conditions  relating  thereto  I 
should  be  disposed  to  mention  first  the  improvements  in  the  lighting  of 
rooms  and  in  the  printing  of  the  books  used  by  pupils,  and  that  for  this 
reason  among  others,  that  the  influence  of  these  changes  is  of  effect  in 


184  TRANSACTIONS   I.    E.    S. — PART    I 

the  homes  too,  the  strain  on  the  eyes  when  the  pupils  are  busy  with  the 
preparation  of  lessons  being  thereby  much  reduced.  If  the  comparison  is 
made  between  the  methods  of  lighting  rooms  now  and  those  of  ten  years 
ago,  the  difference  is  very  striking,  both  at  school  and  at  home. 

He  further  comments  upon  the  significance  of  the  decreased 
use  of  the  old  Gothic  types. 

Opinions  of  Other  Authorities. — At  the  Buffalo  meeting  on 
School  Hygiene  conservation  of  vision  received  marked  atten- 
tion as  is  illustrated  by  the  following  abstracts : 

D.  P.  MacMillan,  director  of  child  study  in  the  public  schools 
of  Chicago,  states : 

Defects  of  the  senses  of  sight  and  hearing,  to  which  appeal  is  largely 
made  in  school  room  activities,  are  considered  by  some  to  be  the  primary 
causes  of  delay  or  derangement  of  normal  development,  and  they  lead  to 
the  formation  of  injurious  habits,  etc. 

W.  H.  Brainerd,  an  architect  of  Boston,  states  in  discussing 
"The  Ideal  School  Site": 

The  first  purpose  of  the  school  is  instruction.  The  first  need  of 
instruction  rooms  is  light  for  the  use  of  the  eyes  and  apparatus.  Light 
must  be  in  abundance  and  without  glare.  Sunlight  should  reach  all 
instruction  rooms,  and  others  as  far  as  possible.  Long  continued  hot  sun- 
light is  not  desirable  in  class-rooms.  The  desirability  of  exposure  for 
class-rooms  is  in  the  following  order :  easterly,  southerly,  westerly.  For 
large  buildings  a  site  permitting  of  the  major  axis  running  northeast  and 
southwest  is  most  desirable.  Class-rooms  should  have  the  easterly  and 
southerly  exposures ;  assembly  halls  and  accessories  westerly  and  northerly 
exposures. 

Dr.  F.  Park  Lewis  of  Buffalo  in  a  paper  on  "Sight  Saving  and 
Brain  Saving,"  states : 

It  is  an  accepted  fact,  recognized  by  ophthalmologists  everywhere, 
that  changes  occur  in  the  eyes  of  children  during  the  period  of  their 
school  life,  of  which  the  most  prominent  symptom  is  a  steadily  progressive 
development  of  near-sightedness.  As  definitely  formulated  by  the  late 
Prof.  Dufour:  (1)  In  all  schools  the  number  of  short-sighted  pupils 
increases  from  class  to  class.  (2)  The  average  degree  of  short-sighted- 
ness increases  from  class  to  class.  (3)  The  number  of  short-sighted 
pupils  increases  with  the  increase  in  school  demands. 

Dr.  James  Kerr  of  London,  states : 
Ocular  experience  is  the  only  final  test  of  illumination.  Eyestrain  is 
due  to  fatigue  due  to  overwork  or  glare.  The  eye  adapts  itself  to  bright- 
ness by  varying  its  sensitiveness.  Primary  glare  is  due  to  physical  effects 
on  the  retina,  secondary  glare  to  difficulty  in  adaptation.  One  third  of 
our  school  children  have  such  defective  visual  acuity  that  better  illumina- 
tion is  necessary  than  for  normal  eyes. 


LUCKIESH  :     SAFEGUARDING   THE   EYESIGHT  185 

He  further  states  that 

Artificial  lighting  for  each  school  place  should  not  be  less  than  2 
foot-candles.  Blackboards  require  60  per  cent.  more.  Glare  must  be 
guarded  against. 

Dr.  Lewis  C.  Wessels  of  the  Bureau  of  Health,  Philadelphia, 
in  speaking  of  defective  vision  from  the  economic  standpoint 
states : 

In  Philadelphia  each  pupil  costs  about  $35  per  year  to  teach.  Under 
normal  conditions  a  pupil  14  years  of  age  should  reach  the  eighth  grade 
at  a  cost  to  the  state  of  $280.  If  on  account  of  defective  vision  the  child 
only  reaches  the  fourth  grade  in  that  time  it  has  still  cost  the  state  $280, 
but  with  only  $140  worth  of  result,  a  loss  to  the  State  of  $140.  The  loss 
to  the  child  is  considerably  more  because  at  the  age  of  14  it  is  likely  to  be 
put  to  work,  poorly  equipped,  its  earning  power  curtailed  for  want  of  a 
proper  education  so  that  it  can  contribute  but  little  toward  its  own  support 
or  that  of  the  state.     So  again  the  state  loses. 

He  further  explains  how  the  Department  of  Public  Health 
through  a  division  of  ophthalmology  furnishes  glasses  free  to 
poor  children  and  adds 

We  are  now  refracting  nearly  2,500  cases  a  year.  If  we  save  each 
one  of  these  children  but  one  year  during  its  entire  school  life  there  will 
be  an  annual  saving  of  over  $87,000  not  counting  the  child's  time  and 
increased  efficiency. 

This  is  certainly  an  interesting  phase  of  the  subject.  A  further 
discussion  of  the  economics  of  the  relative  costs  of  prevention 
and  cure  would  also  be  of  interest. 

These  are  opinions  and  statistics  from  only  a  few  authorities 
but  probably  sufficient  to  rout  any  lurking  suspicion  that  the 
safeguarding  of  eyesight  is  not  a  vital  problem.  Further  it  is 
seen  that  the  light  expert  has  a  great  deal  in  common  with  school 
authorities,  medical  examiners,  and  architects  in  safeguarding 
the  most  important  and  educative  sense — vision. 

FACTORS  INFLUENCING  VISION. 
Illumination.— The  eye  is  a  very  flexible  organ  and  can  adapt 
itself  to  a  tremendous  range  of  brightness.  Visual  acuity  or  the 
ability  to  distinguish  fine  detail  depends  upon  the  illumination, 
although  above  a  certain  minimum  value  of  illumination  acuity 
increases  very  slowly  with  increasing  illumination.  One  sees  by 
distinguishing  differences  in  brightness  and  color.  In  ordinary 
reading  brightness  contrast  makes  it  possible  to  distinguish  the 


1 86  TRANSACTIONS   I.    E.    S. — PART    I 

black  letters  or  words  on  the  lighter  background.  After  a  cer- 
tain minimum  value  of  illumination  is  reached  the  process  of 
distinguishing  ordinary  type  becomes  increasingly  difficult  with 
decreasing  illumination.  The  amount  of  illumination  necessary 
for  reading  with  comfort  depends  upon  a  number  of  conditions, 
but  under  fairly  satisfactory  conditions  the  illumination  at  the 
top  of  any  desk  should  not  be  less  than  2.5  foot-candles.  This 
minimum  value  should  be  greater  for  daylight  than  for  artificial 
lighting  because  of  the  greater  non-uniformity  of  the  illumina- 
tion under  average  natural  lighting  conditions  indoors. 

Uniformity.- — A  fair  degree  of  uniformity  of  illumination  on 
the  plane  of  the  desk  tops  is  quite  desirable  owing  to  the  strain 
on  the  eyes  resulting  from  the  necessity  of  adapting  the  eyes  for 
considerable  variations  in  brightness  where  there  is  too  great 
non-uniformity.  Owing  to  architectural  difficulties  it  is  quite 
impossible  to  obtain  uniform  illumination  with  natural  light. 
The  diversity,  however,  can  be  reduced  even  in  this  case  to  a 
satisfactory  value.  Satisfactory  uniformity  is  easily  attainable 
in  artificial  lighting. 

Direction  of  Light. — One  of  the  fundamental  principles  of 
proper  lighting  is  to  have  light  come  from  the  left.  This  of 
course  assumes  that  all  persons  are  right-handed.  In  natural 
lighting  three  systems  are  in  vogue,  unilateral,  bilateral  and  sky- 
lighting. The  predominant  opinion  favors  unilateral  lighting 
with  the  windows  on  the  left  of  the  pupils  when  seated. 

In  artificial  lighting  there  are  three  general  systems  of  lighting. 
the  so-called  direct,  semi-indirect,  and  indirect  lighting.  These 
divisions  are  not  clearly  defined.  The  first  system  in  which  most 
of  the  light  is  directed  downward  by  shades  and  reflectors  is  per- 
haps used  more  than  the  others  although  the  semi-indirect 
method  is  growing  in  popularity  in  many  places  and  is  perhaps 
more  generally  satisfactory  in  the  problems  of  lighting  class 
rooms,  reading  rooms,  etc.  In  this  system  the  light  source  is 
contained  in  a  translucent  glass  bowl  open  at  the  top.  Some 
light  passes  through  the  bowl  to  the  working  plane,  the  remainder 
reaching  the  working  plane  indirectly  by  reflection,  chiefly  from 
the  ceiling. 

Glare. — In    natural    lighting   the    sky   is   the    source   of    light 


LUCKIESH  :     SAFEGUARDING   THE   EYESIGHT 


l87 


chiefly  depended  upon.  Very  elaborate  studies  of  the  amount  of 
visible  sky  necessary  at  any  point  of  the  room  have  been  made  by 
reflection  chiefly  from  the  ceiling.  Various  authorities  agree  in 
general,  notwithstanding  the  fact  that  the  data  have  been  gathered 
by  different  methods.  The  brightness  of  the  light  source  whether 
natural  or  artificial,  should  be  low,  say  not  more  than  three 
candlepower  per  square  inch.  The  brightest  sky  measured  by 
the  writer  has  shown  2.5  candlepower  per  square  inch.  One  of 
the  important  effects  of  high  brightness  is  the  production  of 
annoying  after-images.     In  Fig.  3  are  shown  some  results  on  the 


£zz^>a34/r&  /rr  CSe-casrt/j 


Fig.  3.— Effects  of  brightness  of  source  and  exposure  on  the  duration 
of  the  after-image. 


duration  of  after-images.  The  brightness  of  a  tungsten  filament 
operating  at  7.9  lumens  per  watt  (1.25  w.  p.  m.  h.  c.)  was  found 
to  be  1,080  candlepower  per  square  inch.  In  the  same  units  the 
approximate  brightnesses  of  a  Welsbach  mantle  and  a  frosted 
tungsten  lamp  of  the  older  type  are  respectively  30  and  5.  These 
figures  are  given  to  aid  in  comprehending  the  data.  The  after- 
images actually  lasted  longer  than  shown  in  Fig.  3,  but  at  the 
end  of  the  intervals  of  times  indicated  they  ceased  to  be  annoy- 
ing and  changed  color  which  latter  served  as  a  criterion  in 
making  the  observations.     It  is  seen  that  the  after-images  from 


1 88  TRANSACTIONS   I.    E.    S. — PART    I 

bare  artificial  light  sources  besides  fatiguing  and  being  harmful  to 
the  eye  can  be  annoying  owing  to  loss  of  time  occasioned  and  dan- 
gerous when  the  person  is  working  near  machinery  owing  to  the 
temporary  blinding  effect.  Nevertheless  inspection  shows  that 
bare  lamps  directly  in  the  field  of  view  are  often  found  in  the 
shops  in  technical  schools  where  there  is  an  ever-present  danger 
from  machinery  in  operation. 

Intrinsic  brightness  is  not  alone  the  cause  of  glare.  An  area 
of  sky  when  viewed  through  a  window  surrounded  by  relatively 
dark  walls  causes  a  very  annoying  glare  yet  the  sky  is  perhaps  no 
brighter  than  i  candlepower  per  square  inch.  Thus  excessive 
brightness  contrasts  are  found  to  be  responsible  for  the  annoying, 
and  sometimes  very  discomforting  and  harmful  conditions  of 
glare.  This  is  shown  by  an  easy  experiment.  Hold  a  lighted 
electric  incandescent  lamp  before  your  eyes  in  an  ordinary  room 
and  under  most  conditions  you  will  experience  uncomfortable 
glare.  However,  if  you  take  the  lighted  lamp  to  the  window 
and  view  it  against  the  sky  the  glare  is  hardly  noticeable.  There 
is  another  factor  which  complicates  the  situation  namely  total 
light  flux.  More  light  is  entering  the  eye  in  the  latter  case  which 
possibly  by  the  process  of  adaptation  reduces  the  annoyance 
somewhat.  It  has  become  recognized,  however,  that  brightness 
contrast  plays  a  large  part  in  eye- fatigue.  A  blackboard  viewed 
in  juxtaposition  to  a  white  wall  often  results  in  annoying  glare. 

Light  surroundings  such  as  walls  and  ceiling  have  a  general 
tendency  in  reducing  the  conditions  of  glare.  For  instance  a 
bright  ceiling  reduces  the  annoyance  of  an  artificial  light  source 
viewed  against  it.  Light  walls  reflect  light  back  to  the  side  of  the 
room  containing  windows  thus  lessening  the  contrast  between  the 
bright  sky  and  the  adjacent  walls.  The  colors  of  walls  and 
ceilings  usually  found  satisfactory  are  light  tints  of  buff,  yellow, 
or  grey. 

Artificial  light  sources  should  be  hung  high  in  order  to  be  out- 
side the  normal  visual  field  if  possible.  They  should  be 
screened  with  shades  or  reduced  in  brightness  by  enclosing  glass- 
ware. Likewise  windows  should  be  equipped  with  approved 
shades  in  order  to  control  the  daylight  as  much  as  possible  and, 
when  necessary,  to  screen  out  the  direct  sunlight. 


LUCKIKSH  :     SAFEGUARDING   THE   EYESIGHT 


189 


Polished  surfaces  are  recognized  as  sources  of  annoying  glare 
and  in  many  cases  defeat  well  laid  plans  of  the  lighting  special- 
ist. In  Fig.  4  the  various  kinds  of  reflecting  surfaces  are  il- 
lustrated; a  shows  mirror  reflection,  and  b  the  reflection  from  a 
perfectly  mat  surface;  c  shows  a  combination  of  these  which 
results  from  a  highly  glazed  white  surface,  for  example  varnished 
white  walls  and  glossy  paper.  A  piece  of  polished  window  glass 
placed  over  white  blotting  paper  is  a  simple  illustration  of  this 
kind  of  reflection ;  d  and  e  illustrate  two  other  types  of  reflection 
encountered. 

Obviously  a  child  holding  a  mirror  flat  upon  the  printed  page 
of  a  book  can  see  the  image  of  a  light  source  which  is  well  above 


6 


6 


<?>        6 


<§> 


Fig.  4. — Various  types  of  reflection. 

his  head  out  of  the  normal  visual  field.  The  result  of  glazed 
paper  too  often  used  in  books  is  somewhat  analogous.  Owing  to 
the  fact  that  the  image  of  the  light  source  is  regularly  reflected  by 
the  black  letters  and  white  background  with  practically  equal 
facility,  there  is  a  decrease  in  contrast  between  the  printed 
matter  and  the  background  causing  difficulty  in  reading  and  also 
a  distracting  and  harmful  effect  of  the  "glare  spot."  For  these 
reasons  glazed  surfaces  have  been  condemned  by  the  light  spec- 
ialist. Glare  owing  to  regular  reflection  from  blackboards  is  a 
common  annoyance  in  school  rooms.  This  can  be  overcome  in 
various  ways  including  tilting,  the  judicious  use  of  window 
shades,  and  by  lighting  them  artificially.  The  proper  placing  of 
blackboards  can  be  determined  beforehand  as  illustrated  in 
Fig.  5 ;  a  shows  a  plan  of  a  class  room  lighted  from  one  side. 


190  TRANSACTIONS    I.    E.    S. — PART    I 

In  this  case  the  lighting  is  from  the  wrong  side,  but  this  was 
chosen  because  it  represents  an  actual  case.  The  paths  of  the 
rays  of  light  can  be  followed  in  their  course  with  the  result  that 
the  condition  shown  is  just  what  was  observed  in  the  room  in 
question.  In  b  is  shown  the  elevation.  In  this  case  the  window 
area  was  too  small  and  a  further  mistake  was  made  in  placing  a 
blackboard  between  the  windows.  These  are  conditions  that  can 
not  be  too  severely  condemned.  In  c  is  shown  a  remedy  for  badly 
lighted  blackboards.  Walls  and  desk  tops  should  also  be  as  free 
from  glaze  as  practicable. 

Considerable  data  have  been  obtained  on  the  effect  of  glare  in 
reducing  visual  acuity,  much  of  which  will  be  found  in  references 
cited  in  the  bibliography.  However,  an  interesting  case  is  shown 
in  Fig.  6  because  it  brings  out  various  points  of  interest  and  also 
incriminates  the  sky  in  glare  production.  An  acuity  object  was 
set  up  in  the  shade  of  a  building  as  far  from  the  building  as  pos- 
sible. The  day  was  clear  and  light  reached  the  object  from  more 
than  one  half  of  the  sky.  No  light  from  the  sun  reached  the  eye 
or  test  object  or  immediate  surroundings  directly  or  by  regular 
reflection.  The  writer  who  made  the  observations  wore  no  visor 
to  shield  the  eyes.  Only  a  slight  sensation  of  glare  was  apparent 
before  beginning  the  test.  However,  as  soon  as  acuity  observa- 
tions were  begun  the  glare  became  very  evident  and  rapidly  grew 
painful.  Five  readings  were  made  first  through  clear  correcting 
glasses  (represented  by  the  black  dots).  As  quickly  as  possible 
the  clear  glasses  were  replaced  by  yellow-green  glasses  of  about 
50  per  cent,  transmission  for  the  total  light  and  five  acuity  read- 
ings were  taken  (represented  by  crosses).  A  decided  decrease 
in  discomfort  was  experienced  when  wearing  the  yellow-green 
glasses  and  as  will  be  noted  acuity  is  higher  in  this  case  notwith- 
standing the  decrease  in  illumination  was  fully  50  per  cent. 
These  glasses  were  again  replaced  by  clear  glasses  and  five  acuity 
readings  were  made.  This  procedure  was  continued  as  indicated 
in  Fig.  6.  The  interval  of  time  required  to  make  five  readings 
including  the  change  of  glasses  was  the  same  in  each  case  (being 
three  minutes),  but  the  actual  time  of  taking  the  individual  read- 
ings was  not  noted.  Here  they  are  plotted  at  equal  intervals. 
While  the  above  procedure  is  rather  complex  and  bears  upon 


EUCKIESH  :     SAFEGUARDING   THE    EYESIGHT 


I9I 


A, 


y 


c 


^ 


X 


\3' 


PLAN 


a 


Fig.  5. — Showing  law  of  regular  reflection  applied  to  blackboards. 


192 


TRANSACTIONS   I.    E.    S. — PART    I 


problems  worthy  of  much  careful  investigation,  the  experiment 
answered  the  intended  purpose  in  bringing  forth  several  points: 
(1)  Glare  conditions  are  not  always  apparent  when  the  eyes  are 
not  engaged  in  serious  work  such  as  reading  or  distinguishing 
fine  detail.  However,  bad  lighting  conditions  are  readily  recog- 
nized when  the  eyes  are  called  upon  to  do  such  work.  (2)  There 
is  a  rapid  falling  off  of  visual  acuity  when  the  conditions  of  glare 
are  severe.  (3)  Such  a  harmless  appearing  light  source  as  a  wide 
expanse  of  sky  can  produce  a  very  severe  condition  of  glare.  The 
intrinsic  brightness  is  very  low  as  compared  with  artificial  sources, 
but  the  quantity  of  light  is  high  and  the  image  of  the  sky  is  spread 
over  a  large  portion  of  the  retina.  (4)  There  was  an  apparent 
recuperation  of  the  eye  during  the  periods  that  the  yellow-green 


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X 

L  m     - 

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«  W.a'.n^  <rllwjr«n    5U1 

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•  WtaK-.n^  clear  jl>ISM. 

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1 

6  9  /*. 

Fig.  6. — Showing  rapid  reduction  in  visual  acuity  under  the  glare 
from  the  unobstructed  blue  sky. 

glasses  were  worn.  (5)  Notwithstanding  the  effect  of  glare, 
when  clear  glasses  were  worn,  in  reducing  visual  acuity  the  values 
of  the  latter  when  the  colored  glasses  were  worn  remained  con- 
siderably higher.  (6)  This  experiment  emphasizes  the  necessity 
of  prolonging  acuity  readings  over  a  considerable  period  if 
acuity  is  to  be  a  criterion  of  the  satisfactoriness  of  illumination 
conditions. 

Some  of  the  increase  in  visual  acuity  when  the  yellow-green 
glasses  were  being  worn  can  be  accounted  for  by  the  nearer 
approach  to  monochromatism  of  the  light  that  passed  through 
them.  However,  conditions  indicated  that  the  advantage  was  due 
very  largely  to  a  reduction  in  the  glare.  Other  interesting  con- 
clusions can  be  drawn,  but  the  illustration  has  already  fulfilled  its 


luckiesh:    safeguarding  the  eyesight  193 

object  in  bringing  forth  the  facts  that  glare  conditions  are  very 
complex  and  that  cognizance  of  glare  often  depends  upon  the 
character  of  the  activities  in  which  the  eyes  are  engaged. 

LEGISLATION  ON  SCHOOL  LIGHTING. 
The  legislation  on  this  subject  which  has  come  under  the  obser- 
vation of  the  author  has  been  chiefly  with  reference  to  natural 
lighting.  This  is  quite  the  expected  course,  but  needless  to  say 
attention  must  be  given  to  artificial  lighting.  The  latter  problem 
will  be  found  much  easier  and  no  doubt  will  be  officially  taken 
care  of  eventually.  It  is  the  duty  of  this  society  and  school 
authorities  to  urge  proper  legislation  to  cover  lighting  conditions 
completely.  It  may  be  interesting  to  quote  extracts  from  codes 
already  in  existence. 

Extracts  from  the  Indiana  "Sanitary  School  House  Law"  are 
as  follows : 

Interior  walls  and  the  ceiling  shall  be  painted  or  tinted  some  neutral 
color,  as  grey,  slate,  buff  or  green. 

All  school  rooms  where  pupils  are  seated  for  study  shall  be  lighted 
from  one  side  only,  and  the  glass  area  shall  be  not  less  than  one-sixth  of 
the  floor  area,  and  the  windows  shall  extend  from  not  less  than  4  feet 
from  the  floor  to  at  least  1  foot  from  the  ceiling,  all  windows  to  be  pro- 
vided with  roller  or  adjustable  shades  of  neutral  color,  as  blue,  gray,  slate, 
buff,  or  green. 

For  left-handed  pupils  desks  and  seats  may  be  placed  so  as  to  permit 
the  light  to  fall  over  the  right  shoulder. 

Blackboards  shall  be  preferably  of  slate,  but  of  whatever  material, 
the  color  shall  be  dead  black. 

Abstract  from  the  Rules  and  Regulations  of  the  Indiana  State 
Board  of  Health  are  as  follows : 

No  class-room  shall  exceed  24  feet  in  width,  with  the  ceiling  not  less 
than  12  feet  nor  more  than  14  feet  in  height. 

No  window  sash  shall  have  more  than  four  lights,  and  the  tops  of  all 
windows  shall  be  square.  When  the  proximity  of  other  buildings  or  a 
portion  of  the  same  building  interferes  with  the  proper  lighting  of  a 
class-room,  the  light  shall  be  properly  projected  and  diffused  by  the  use 
of  prism  glass. 

When  artificial  lighting  by  means  of  electricity  or  gas  is  used  the 
lights  shall  be  placed  near  the  ceiling  and  the  lights  deflected  by  proper 
shades  toward  the  ceiling,  either  indirect  or  semi-indirect  lighting  being 
used. 

Where  the  light  in  any  class-room  is  from  the  north,  the  proportion 
of  glass  area  to  floor  area  should  not  be  less  than  1  to  5. 


194  TRANSACTIONS    I.    E-    S. — PART    I 

Architects,  etc.,  shall  certify  hy  affidavit  indorsed  on  all  plans  and 
specifications  submitted  that  such  plans  and  specifications  comply  with  the 
Indiana  Sanitary  Schoolhouse  Law  and  with  the  rules  of  the  Indiana  State 
Board  of  Health. 

Abstracts   from  the   Ohio   State   Building   Code   referring  to 
school  buildings  are  as  follows : 

The  height  of  all  rooms,  except  toilet,  play,  and  recreation  rooms, 
shall  be  not  less  than  one  half  of  the  average  width  of  the  room,  and  in 
no  case  less  than  10  feet  high. 

The  proportion  of  glass  surface  in  each  class,  study  "recitation  high 
school  room,  and  laboratory  shall  be  not  less  than  i  square  foot  of  glass 
to  each  5  square  feet  of  floor  area. 

Windows  shall  be  placed  at  the  rear  or  the  left  and  rear  of  the  pupils 
when  seated. 

Tops  of  windows,  except  in  libraries,  museums,  and  art  galleries,  shall 
not  be  placed  more  than  8  inches  below  the  minimum  ceiling  height. 

The  unit  of  measurement  for  the  width  of  properly  lighted  rooms, 
when  lighted  from  one  side  only,  shall  be  the  height  of  the  window  head 
above  the  floor. 

The  width  of  all  class  and  recitation  rooms,  when  lighted  from  one 
side  only,  shall  never  exceed  two  and  one  half  times  this  unit,  measured 
at  right  angles  to  the  source  of  light. 

The  candlepower  of  electric  lamps  shall  not  be  less  than  the  follow- 
ing, viz. : 

Auditorium  1  candlepower  to  2Y2  sq.  ft.  of  floor  area 

Gymnasium    1  candlepower  to  2^  sq.  ft.  of  floor  area 

Stairways   and   hall 1  candlepower  to  4      sq.  ft.  of  floor  area 

Class  and  recitation  rooms 1  candlepower  to  2      sq.  ft.  of  floor  area 

Enclosed  fireproof  stairways,  service  stairways,  corridors,  passage- 
ways, and  toilet  rooms  shall  be  lighted  by  artificial  light  and  said  lights 
shall  be  kept  burning  when  the  building  is  occupied  after  dark. 

The  Illuminating  Engineering  Society  is  taking  up  the  matter 
of  the  lighting  of  schools  chiefly  through  a  recently  appointed 
Committee  on  School  Lighting.  Observations  have  been  made 
and  data  have  been  collected  for  several  years  previous  to  the 
appointment  so  that  fairly  definite  activities  were  begun  at  once. 
The  following  brief  resume  of  requirements  in  school  lighting 
was  presented  to  the  Committee  on  Lighting  Legislation  for  use 
as  a  basis  in  formulating  a  code  on  school  lighting.  This  is  not 
in  complete  form,  but  is  expected  to  serve  as  a  starting-point. 
GENERAL  CONSIDERATION. 

The  lighting  of  a  school  building  should  be  referred  to  a  com- 
petent expert  before  the  plans  for  the  building  are  drawn.     The 


LUCKIESH  :     SAFEGUARDING  THE   EYESIGHT  195 

importance  of  doing  this  early  is  evidenced  by  the  fact  that  the 
orientation  of  the  building  plays  an  important  part  in  the  design 
of  those  features  which  depend  for  their  satisfactoriness  upon 
proper  lighting. 

Minimum  intensity  of  illumination,  2.5  to  3.0  foot-candles  on 
the  plane  of  the  desk  top. 

Polished  surfaces  such  as  blackboards,  glossy  paper,  polished 
desk  tops,  and  glazed  walls  should  be  avoided. 

Light  sources  (sky  or  artificial)  should  be  well  out  of  the  ordi- 
nary visual  field. 

Glare  from  blackboards  should  be  avoided.  This  can  be  done 
by  carefully  placing  them,  by  lighting  artificially,  by  tilting  them, 
and  by  keeping  their  surfaces  mat.  They  should  never  be  placed 
between  windows. 

Excessive  brightness  contrasts  should  be  avoided.  A  bright 
source  should  not  be  viewed  against  a  dark  background.  The 
walls  adjacent  to  a  blackboard  should  not  be  too  light  in  color. 

Surroundings  such  as  walls  and  ceilings  should  in  general  be 
light  in  color.  Ceilings  and  frieze  should  be  practically  white 
(high  reflecting  power).  Walls  should  be  reasonably  light. 
Colors  used  should  be  white,  grey,  or  tints  of  buff,  cream  or  olive 
green. 

Children  should  be  taught  how  to  safeguard  their  vision;  that 
is,  how  to  hold  their  books,  to  assume  a  correct  position  relative 
to  the  light  source,  to  complain  of  glare  from  blackboards,  etc. 

Teachers  should  be  instructed  to  teach  these  fundamentals  to 
the  children. 

Good  lighting  should  be  incorporated  in  every  course  where 
practicable  and  especially  in  the  "home-making"  course. 

MORE  SPECIFIC  RECOMMENDATIONS. 

Natural  Lighting. — Window  area  should  be  ample — that  is,  an 
appreciable  percentage  (say  at  least  20  per  cent.)  of  the  floor 
area. 

The  windows  should  preferably  be  located  on  one  side  of  the 
room  to  the  left  of  the  students. 

A  portion  of  the  sky  should  be  visible  from  every  desk  top,  at 
least  5  degrees  vertically. 

5 


196  TRANSACTIONS   I.    E.    S. — PART    I 

The  width  of  the  room  should  not  be  more  than  twice  the 
window  height. 

The  windows  should  be  equipped  with  approved  window  shades 
for  controlling  the  light  and  excluding  direct  sunlight. 

Prism  glass  should  be  used  in  extreme  conditions  at  least. 

Lighting  and  ventilating  courts  should  be  painted  white. 

Minimum  illumination  on  desk  top,  3  foot-candles. 

Diversity  of  illumination  not  greater  than  100  to  I. 

Artificial  Lighting. — Ample  general  lighting  is  recommended. 
Local  units  subject  to  control  of  pupils  are  condemned. 

Minimum  illumination  on  desk  top,  2.5  foot-candles. 

Light  sources  should  be  out  of  normal  visual  field  if  possible. 
They  should  be  equipped  with  diffusing  glassware  to  reduce  their 
brightness  and  screen  the  source  from  the  pupils'  eyes. 

Highest  permissible  brightness,  3  candlepower  per  square  inch 
when  viewed  against  a  light  background. 

Blackboards  should  be  lighted  by  properly  screened  and  judi- 
ciously placed  local  units. 

The  system  of  lighting  will  depend  upon  many  conditions.  Any 
well-designed  system  is  satisfactory  in  its  proper  place.  There 
appears  to  be  a  growing  tendency  for  the  semi-indirect  system. 
It  appears  more  generally  satisfactory  for  class  rooms,  reading 
rooms,  etc.    In  the  shops  a  direct  system  is  advisable. 

No  local  units  should  be  used  unless  absolutely  necessary. 

CONDITIONS  FOUND  IN  MODERN  SCHOOLS. 

There  is  a  large  amount  of  authoritative  data  available  per- 
taining to  the  best  practise  in  natural  and  artificial  lighting.  Ref- 
erences to  many  sources  of  valuable  information  are  given  in  the 
bibliography.  The  practises  which  the  writer  considers  best  are 
already  presented  in  a  general  manner  throughout  the  paper. 
Specific  recommendations  apply  only  to  specific  conditions,  so  it 
is  quite  outside  the  scope  of  this  paper  to  go  into  detail.  It  will 
be  enlightening,  however,  to  consider  some  actual  conditions — 
good  and  bad — found  in  modern  schools.  It  is  gratifying  to  be 
able  to  state  that  some  of  the  cases  of  faulty  lighting  shown  here 
are  being  corrected.  In  general  natural  lighting  conditions  do 
not  appear  as  bad  in  the  modern  schools  which  the  writer  has 


LUCKIESH  :     SAFEGUARDING   THE   EYESIGHT  197 

had  an  opportunity  to  visit  as  the  artificial  lighting  conditions 
although  there  are  opportunities  for  improving  the  former. 

In  Figs.  7  to  12  inclusive  are  found  some  very  faulty  artificial 
lighting  installations.  The  first  general  criticism  is  found  in  the 
use  of  the  local  unit  subject  to  the  control  of  the  pupil.  The 
average  pupil  knows  practically  nothing  regarding  the  proper  use 
of  light.  In  the  drafting  rooms  pupils  were  found  working  in 
the  shadow  of  the  hand  or  T-square  when  a  slight  adjustment 
of  the  lamp  in  front  of  him  would  have  given  him  satisfactory 
lighting  were  it  not  for  his  neighbors'  lamps  which  glared  at  him 
from  all  sides.  In  Fig.  7  the  units  are  fastened  to  the  drawing 
table.  In  this  one  respect  this  condition  was  more  favorable 
than  the  case  shown  in  Fig.  8  where  the  units  were  practically 
uncontrollable  for  they  hung  on  drop-cords  from  a  ceiling  perhaps 
12  feet  in  height  with  angle  reflectors  which  could  not  protect 
the  eyes  of  the  individual  without  causing  a  bad  condition  of 
glare  for  many  of  his  neighbors.  The  conditions  were  photo- 
graphed as  found  on  entering  the  rooms.  Much  more  could  be 
said  against  such  practise,  but  the  photographs  speak  for  them- 
selves. 

In  Fig.  9  is  found  the  condition  in  a  machine  shop  in  a  tech- 
nical high  school.  The  complexity  of  shafting  and  belts  make  it 
difficult  to  light  this  room  by  a  system  of  general  lighting.  An 
attempt  has  been  made  and  yet  it  could  be  done  more  successfully. 
If  sufficient  light  cannot  be  directed  to  the  lathes  from  overhead 
units,  local  units  could  be  used  as  a  last  resort.  But  these  should 
be  shielded  from  all  eyes  by  narrow  concentrating  reflectors 
instead  of  being  left  bare  as  shown  in  Fig.  10. 

In  Fig.  11  is  seen  a  condition  not  unusual  in  the  shops  of  the 
technical  school.  The  photograph  was  taken  in  the  position  of 
the  eyes  of  a  worker  at  one  of  the  benches.  Could  one  devise  a 
more  discomforting  condition  of  glare  under  which  to  work? 

Equally  bad  conditions  have  been  found  in  sewing  rooms  and 
domestic  science  laboratories.  A  very  faulty  system  used  in  a 
sewing  room  is  shown  in  Fig.  12.  Glaring  lights  greeted  the 
worker  from  nearly  every  position  in  the  room.  The  same  criti- 
cism applies  here  as  in  Fig.  8.  An  especially  striking  instance  was 
found  in  a  "model"  dining  room  where  the  young  ladies  were 


I98  TRANSACTIONS    I.    E.    S. PART    I 

being  taught  the  principles  of  home-making.  The  furnishings 
were  satisfactory  and  were  arranged  in  a  manner  which  would 
no  doubt  meet  the  approval  of  the  seasoned  house-wife,  but  above 
the  dining  table  was  a  fixture  containing  four  bare  carbon  lamps 
extending  at  an  angle  long  ago  condemned  in  lighting  practise. 
Brackets  too  low  on  the  side  wall  contained  bare  carbon  lamps. 
The  lighting  system  was  wholly  congruous  but  equally  bad.  This 
was  one  of  the  most  discouraging  conditions  encountered  for  it 
showed  that  the  director  of  the  home-making  course  had  no  idea 
that  good  lighting  is  one  of  the  most  essential  features  in  making 
a  home  attractive  and  comfortable.  And  further,  these  young 
ladies  were  graduated  without  a  knowledge  of  the  possibilities  of 
lighting.  The  writer  firmly  believes  that  lighting  has  a  socio- 
logical importance  of  an  unrealized  magnitude.  These  are  just 
a  few  instances  of  bad  lighting  encountered  in  modern  schools. 

That  rooms  can  be  lighted  well  and  inexpensively  is  shown  in 
Fig.  13.  illustrating  a  foundry  lighted  by  the  direct  method  using 
glass  reflectors.  The  use  of  glass  reflectors  is  commendable,  for 
the  ceiling  is  not  left  in  complete  darkness  as  is  the  case  with  the 
opaque  reflector.  Of  course,  this  will  be  considered  wasteful  of 
light  by  some,  but  a  foundry  is  a  dingy  place  at  best,  so  the  waste 
is  justified  if  it  adds  to  the  scanty  cheerfulness. 

In  Fig.  14  is  shown  a  large  class  room  lighted  inexpensively 
by  the  direct  method.  This  lighting  is  fairly  satisfactory.  It 
would  be  excellent  if  the  clear  incandescent  lamps  were  replaced 
by  bowl-frosted  lamps.  The  latter  should  be  used  very  generally 
in  lighting  systems  similar  to  that  illustrated  in  Fig.  14.  The 
daylighting  in  this  case  is  from  two  sides  and  the  rear  which  is 
not  satisfactory. 

In  Fig.  15  is  illustrated  an  approved  method  of  direct  lighting. 
The  lamps  are  hung  high  and  screened  by  large,  deep  diffusing 
reflectors.     The  natural  lighting  is  likewise  satisfactory. 

In  Fig.  16  is  shown  a  large  assembly  room  lighted  with  direct 
units  hung  too  low.  This  is  a  serious  defect  in  this  system.  A 
high  hanging-height  would  convert  this  very  unsatisfactory  con- 
dition into  a  fairly  good  example  of  so-called  direct  lighting. 
Note  the  glare  from  the  glazed  desks  and  doors. 

In  Fig.  17  is  shown  a  highly  approved  method  of  lighting  for 


t* 


Figs.  7  and  8.— Examples  of  faulty  drafting  room  lighting. 


Figs.  9  and  10. — Examples  of  faulty  shop  lighting. 


Fig.  ii.— Faulty  shop  lighting. 


Fig.  12.— Faulty  lighting  in  a  sewing  room. 


Fig.  13. — Satisfactory  foundry  lighting. 


Fi£.  14— Satisfactory  class  room  lighting. 


Fig.  15. — An  example  of  satisfactory  direct  lighting. 


Fig.  16. — Unsatisfactory  lighting  in  an  assembly  room.     Units  are  hung  too  low. 


Fig.  17. — An  example  of  excellent  semi-indiiect  lighting. 


Pig    1-      An  excellent  example  of  indirect  lighting. 


EUCKIESH  :     SAFEGUARDING   THE   EYESIGHT  199 

class-rooms — the  so-called  semi-indirect  system.  The  light  is 
well  diffused  and  the  room  has  a  cheerful  appearance.  The  day- 
lighting  is  from  the  left  and  the  window  area  ample.  Note  the 
glare  from  the  desk  top  and  image  of  the  light  source  reflected 
from  the  window.  This  latter  illustrates  that  in  a  broad  sense 
proper  lighting  involves  surroundings  as  well  as  the  lighting 
units.  In  Fig.  18  is  shown  an  excellent  example  of  indirect 
lighting  which  is  a  very  satisfactory  system  in  the  proper  place. 
Many  auditoriums  and  class  rooms  are  well  lighted  by  this 
method. 

CO-OPERATION  WITH  SCHOOL  AUTHORITIES. 

The  Illuminating  Engineering  Society  through  various  com- 
mittees and  the  individual  efforts  of  members  can  be  of  consid- 
erable assistance  to  school  authorities  in  improving  lighting  con- 
ditions, bringing  about  desirable  legislation,  and  in  promoting 
the  instruction  of  pupils  in  the  correct  use  of  the  eyes  and  of  light 
sources. 

The  need  for  improvements  in  lighting  has  been  shown  from 
several  viewpoints.  Certain  conditions  commonly  found  produce 
glare  from  which  discomfort  arises  and  eye  trouble  may  result. 
Bad  lighting  promotes  near-sightedness  which  in  turn  handicaps 
the  individual  throughout  life.  Teach  the  pupil  the  fundamental 
principles  of  conserving  vision  and  a  life-long  benefit  has  been 
bestowed  upon  him.  But  besides  this,  confront  him  with  good 
examples  of  proper  lighting  and  the  combination  will  be  so  far- 
reaching  in  its  effect  that  the  benefit  derived  can  not  be  estimated 
in  terms  of  the  cost.  It  might  also  be  well  to  note  here  that  in 
school  lighting  as  in  all  other  branches  of  illumination  the  ef- 
ficiency of  the  system  is  the  ratio  of  satisfactoriness  to  cost  and 
not  the  reciprocal  of  cost.  The  Illuminating  Engineering  Society 
is  prepared  to  co-operate  with  school  authorities  and  it  is  to  be 
hoped  that  the  latter  will  recognize  that  their  position  is  a  key- 
stone to  the  promotion  of  the  conservation  of  our  most  important 
and  educative  sense-vision. 

BIBLIOGRAPHY. 

Ueber  die  neue  Wengen'sche  Methode  das  Tageslicht  in  Schulen  zu  prufeu. 
Hermann    Cohn,    D.    Med.    Wochenschr.,    Berlin    28,    1902    (85-86, 
102-104). 


200  TRANSACTIONS   I.    E.    S. — PART    I 

Ueber  eine  schuelle  methods  zur  prufund  der  lichtstarke  auf  den  arberls- 
platzen  in  schulen. 

E.   Pfeiffer,   Bureau  und   wekstatten   Munchence  med  Worheuschr 
49,  1902  (926). 
Public  School  Room  Lighting. 

Knight  and  Marshall,  Trans.  I.  E.  S.,  vol.  5,  1910,  p.  553. 
School  Lighting. 

Ilium.  Eng.,  London,  Sept.,  1910,  p.  557. 
The  Conservation  of  Vision. 

Dr.  E.  M.  Alger,  Trans.  I.  E.  S.,  vol.  5,  1910,  p.  1005. 
School  Lighting — Natural. 

Dr.  James  Kerr,  Ilium.  Eng.,  London,  Mar.,  191 1,  p.  154. 
Artificial  Lighting  of  Schools. 

Dr.  N.  Bishop  Harman,  Ilium.  Eng.,  London,  Mar.,  191 1,  p.  157. 
Notes  on  the  Lighting  of  Some  Schools  and  Colleges. 

L.  Gaster,  Ilium.  Eng.,  London,  May,  191 1,  p.  289. 
An  Analysis  of  Glare  from  Paper. 

M.  Luckiesh,  Electrical  Review  and  West.  Elect.,  June  1,  1914. 
Illumination  of  School  Buildings. 

V.  R.  Lansingh,  Amer.  School  Board  Jour.,  June,  1912. 
Zeichensall,  Bureau  und  Schul  Beleuchtung. 

Licht  u.  Lampe,  Heft  115,  1912,  p.  476. 
Distribution  of  Natural  and  Artificial  Light  in  Interiors. 

M.  Luckiesh,  Trans.  I.  E.  S.,  vol.  7,  p.  388. 
School  Lighting  and  Eye  Strain. 

Ilium.  Eng.,  London.  Nov.,  1912,  p.  515. 
School  Lighting. 

Ilium.  Eng.,  Feb.,  1913,  p.  106. 
Indirect  Lighting  at  Rugby  School. 

Elec.  Eng.,  July  10,  1913,  p.  406. 
Lighting  of  Schools  and  Libraries. 

Jour,  of  Gas  Ltg.,  July  15,  1913,  p.  161. 

Proceedings  of  Fourth  International  Congress  on  School  Hygiene. 
Buffalo,  N.  Y.,  1913. 

Lighting  of  Schools. 

Jour,  of  Gas  Ltg.,  Sept.  2,  1913,  pp.  601,  616. 
Organized  Health  Work  in  Schools. 

Bulletin  44,  1913,  U.  S.  Bureau  of  Education. 
Lighting  of  School  Rooms. 

T.  M.  Young,  Ilium.  Eng.,  Oct.,  1913,  p.  498. 
Value  of  School  Room  Lighting. 

Elec.  World,  Oct.  4,  1913,  p.  698. 
Die  beleuchtung  von  schulraumen  und  horsalen. 

Licht  u.  Lampe,  Oct.  9,  1913,  p.  807. 


LUCKIESH  :     SAFEGUARDING   THE   EYESIGHT  201 

The    Physiological    and    Mental    Disadvantages    of    Unscientific    School 
Illumination. 
L.  Gaster,  Ilium.  Eng.,  London,  Nov.,  1913,  P-  555- 

Natural  Lighting  of  Schools. 

Ilium.  Eng.,  Nov.,  1913.  P-  581. 
School  and  Library  Lighting. 

Elec.  Eng.,  Nov.  13,  19*3,  P-  628. 
Illumination  School  Lighting  and  Education. 

Gas  Light  Journal,  Nov.  24,  1913,  P-  322. 

School  Lighting. 

Electrician,  Nov.  21,  1913,  P-  275- 
Uber  lehrzimmerbeleuchtung  mittels  gas  in  den  wiener  stadtischen  schulen. 

F.  Pohl,  Jour.  f.  Gasbeleu.,  Jan.  3,  1914,  P-  *• 
The  Illumination  of  Burwash  Hall,  University  of  Toronto. 

Elec.  News,  Jan.  15,  1914.  P-  57- 
Daylight  Illumination  in  School  Planning. 

P.  J.  Waldram,  Lond.  Ilium.  Eng.,  Jan.,  1914. 
School  Room  Lighting. 

Romaine  W.  Myers,  Jour,  of  Elec,  Jan.  31,  1914,  P-  96. 
School  Lighting. 

E.  H.  Nash,  Ilium.  Eng.,  London,  Feb.,  19 14,  P-  1^- 
Some  Experiments  in  School  Lighting  by  Gas. 

F.  H.  Gilpin,  Light.  Jour.,  Mar.,  1914,  P-  5°. 

Illumination    in    the    New    Electrical    Engineering    Laboratory,    Sheffield 
Scientific  School  of  Yale  University. 

C.  E.  Clewell,  Light.  Jour.,  Mar.,  1914,  P-  53- 
School  Illumination. 

Gas  Age,  Mar.  16,  1914,  P-  274. 
Glare  in  School  Illumination. 

M.  Luckiesh,  Amer.  School  Board  Jour.,  Apr.,  1914. 
Report  on  Daylight  Illumination  of  Schools. 

London  Ilium.  Eng.,  July,  1914. 
Planning  for  Daylight  and  Sunlight  in  Buildings. 

Marks  and  Woodwell,  Trans.  I.  E.  S.,  vol.  9,  I9I4,  P-  643. 
Protection  of  the  Eyes  of  School  Children. 

X.  M.  Black  and  F.  A.  Vaughn,  Ophthalmic  Record,  Feb.,  1913- 

DISCUSSION. 
Mr.  S.  G.  Hibben:  Even  though  semi-indirect  lighting  is 
most  excellent  in  schools,  I  do  not  consider  direct  lighting  with 
open  bottom  reflectors  to  be  taboo.  Under  quite  a  number  of 
conditions,  such  as  with  units  placed  high  enough  to  be  well  out 
of  the  line  of  vision,  direct  lighting  reflectors  are  satisfactory— 


202  TRANSACTIONS    1.    E.    S. PART    1 

in  fact  advisable  whenever  a  good  systematic  maintenance  or 
cleaning  system  would  probably  be  lacking. 

A  larger  number  of  direct  than  of  semi-indirect  units  is  neces- 
sary, both  to  secure  a  close  approach  to  the  same  quality  of 
broadly  distributed  or  multidirectional  light,  and  also  in  order 
to  keep  down  the  intrinsic  brilliancies.  The  direct  reflectors  that 
are  recommended  for  the  schools  are  deep,  to  shield  the  fila- 
ments of  the  lamps,  so  that  the  proper  sized  shade  for  a  ioo-watt 
lamp  in  a  classroom  would  be  that  which  ordinarily  would  be 
used  with  a  150-watt  lamp  elsewhere. 

The  chief  factors  influencing  the  performance  of  the  semi- 
indirect  bowls  are  the  density  of  the  glass,  and  the  hanging 
height.  It  goes  without  saying  that  ceiling  colors  are  vital.  I  have 
found  that  of  identically  shaped  bowls  the  medium  density  glass 
will  produce  25  to  30  per  cent,  more  illumination  on  desk  tops 
than  the  heavy  density  opal.  When  a  medium  density  bowl  is 
lowered  from  the  ceiling,  the  illumination  beneath  it  increases; 
the  reverse  is  often  true  when  using  a  heavy  density  bowl. 

I  have  considered  it  much  better  policy  to  use  a  larger  sized 
light-density  glass  bowl,  rather  than  a  small  sized  heavy-density 
one.  The  common  objection  to  the  light-density  glass  is  the  rel- 
atively high  intrinsic  brilliancy.  This  may  be  overcome  by  using 
a  larger  bowl ;  and  even  though  the  first  cost  be  greater  than 
that  of  a  smaller  denser  bowl,  yet  the  increased  efficiency  or  the 
larger  amount  of  light  on  the  working  plane,  will  eventually 
more  than  over-balance  the  first  cost. 

Mr.  G.  W.  Roosa  :  It  might  be  a  good  plan  to  have  rules  on 
optical  hygiene  printed  on  small  sheets  and  pasted  in  every  school 
book.  The  necessity  of  safeguarding  the  eyesight  and  of  better 
school  lighting  cannot  be  too  strongly  enphasized. 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 

Vol.  X  APRIL  30,1915  NO.  3 

ON  THE  CHOICE  OF  A  GROUP  OF  OBSERVERS  FOR 
HETEROCHROMATIC  MEASUREMENTS.* 


BY  HERBERT  E.  IVES  AND  EDWIN  F.  KINGSBURY. 


Synopsis:  In  making  measurements  on  colored  light  with  the  flicker 
photometer  the  visual  characteristics  of  the  observers  are  of  the  utmost 
importance.  A  group  of  readers  should  be  chosen  whose  average  is  that 
of  an  average  eye.  In  this  paper  a  method  is  described,  by  means  of  two 
test  colors,  for  selecting  a  group  whose  average  characteristics  shall  be 
those  of  the  very  large  number  who  determined  the  photometric  scale 
used  by  the  authors. 


In  the  photometry  of  colored  lights  the  selection  of  observers 
is  of  exactly  equal  importance  as  the  selection  of  an  instrument 
and  of  conditions  of  illumination  and  photometric  field  size. 
Skill,  previous  experience  and  conscientiousness  cannot  make  a 
man  normally  color  sensitive  if  he  is  born  otherwise.  Conse- 
quently in  selecting  a  group  of  observers  who  shall  have  in  their 
mean  a  normal  eye,  one  may  pass  over  the  best  "reader"  in  a 
laboratory  and  use  in  his  place  the  newest  errand  boy.  In  short, 
where  colored  light  photometry  is  in  question,  one  must  in  the 
choice  of  observers  free  one's  mind  as  completely  as  possible 
from  any  previous  criterion  and  establish  a  new  one  based  on 
considerations  of  the  nature  of  the  observers'  color  vision. 

In  work  recently  presented  before  the  Illuminating  Engineer- 
ing Society1  we  have  carried  out  extensive  measurements  of 
differently  colored  lights,  using  throughout  a  definite  photo- 
metric method.     This  method  comprises  in  part  the  use  of  a 

*  A  paper  read  at  a  meeting  of  the  Philadelphia  Section  of  the  Illuminating 
Engineering  Society,  March  19,  1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 

1  Experiments  on  Colored  Absorbing  Solutions  for  Use  in  Heterochromatic  Photome- 
try; Trans.  I.  E.  S.,  No.  9,  p.  795;  1914. 

Additional  Experiments  on  Colored  Absorbing  Solutions  for  Use  in  Heterochromatic 
Photometry;  Trans.  I.  E.  S.,  1915. 


204 


TRANSACTIONS   I.    E.    S. — PART    I 


certain  design  of  flicker  photometer,  under  stated  conditions,  and 
for  the  other  part  the  use  of  a  group  of  observers  carefully 
selected  so  that  their  results  shall  be  the  same  as  for  a  normal  or 
average  eye.  The  instrument  and  method  of  use  have  already 
been  described.  It  is  the  purpose  of  this  paper  to  describe  both 
the  method  of  choosing  the  working  group  of  observers  and  also 
a  means  by  which  other  laboratories  can  select  a  group  of 
similar  characteristics. 

The  average  eye  now  used  in  the  laboratory  of  the  United 
Gas  Improvement  Company  is  based  on  measurements  made  by 
sixty-one  observers,  this  number  being  all  that  could  conveniently 
be  obtained  during  a  period  of  several  weeks,  and  being  as  well 


B 

V 

1 

) 

+c                        •< 

S                            -1 

I 

J-                .. 

if 

W 

C                               -7 

V 

WAVC-LtHJTH 

Fig.  i.— Spectral  transmissions  of  two  colored  solutions  used  in  the  selection 
of  a  group  of  observers  for  heterochromatic  measurements.  A — 53  grams 
copper  sulphate  to  1  liter  of  solution;  B— 72  grams  potassium  dichromate 
to  1  liter  solution. 

a  large  enough  number  so  that  the  inclusion  or  exclusion  of  any 
observer  in  the  group  would  affect  the  result  by  less  than  half 
of  1  per  cent.  The  color  measured  was  a  monochromatic  green 
against  the  light  of  a  carbon  lamp.  This  was  not  chosen  as  a 
criterion  for  general  use,  but  was  incidental  to  a  determination 
of  the  mechanical  equivalent  of  light  and  further  details  will  be 
found  in  the  account  of  that  investigation.2 

We  shall  first  describe  how  our  laboratory  luminosity  scale 
has  been  maintained  on  the  basis  of  these  measurements,  after 

-  The  Mechanical  Equivalent  of  Light;  Physical  Review,  1915. 
Measurements  on  a  Monochromatic  Green  Solution;  Physical  Review,  1915. 


IVES  AND  KINGSBURY  :    HETEROCHROMATIC  MEASUREMENTS      205 

which  we  shall  describe  means  by  which  this  same  scale  can  be 
worked  to  in  any  laboratory. 

The  transmission  of  the  special  monochromatic  green  solution 
as  given  by  the  mean  of  sixty-one  observers  is  0.0437.  Indi- 
vidual observers  available  in  our  laboratory  vary  from  this  as 
much  as  12  per  cent,  on  either  side.  In  selecting  a  group  for 
making  a  colored  light  measurement  the  procedure  is  simply  to 
pick  a  group  of  at  least  five  whose  mean  reading  on  the  test 
color  difference,  as  made  and  recorded  once  for  all,  is  the  true 
mean.  Thus  the  group  of  seven  used  in  one  of  the  measure- 
ments on  the  blue  solution  previously  described  had  obtained  the 
following  values  on  the  monochromatic  green : 

0.0474 
0.0432 
0.0416 
0.0453 
0.0398 
0.0471 
0.0418 


Mean  0.0437 

When  any  one  observer  of  such  a  group  was  not  available 
either  another  was  selected  of  very  nearly  the  same  character- 
istics or,  as  was  sometimes  necessary,  one  or  two  other  observers 
of  the  group  were  replaced  by  a  different  selection  whose  mean 
value  from  our  record  was  again  that  of  the  sixty-one. 

The  luminosity  scale  maintained  in  this  way  has  now  been  in 
use  in  our  laboratory  for  a  period  of  many  months.  It  has 
proved  eminently  satisfactory.  The  different  observers  consis- 
tently retain  their  characteristic  positions.  Measurements  made 
with  different  groups  at  various  times  have  shown  most  excellent 
agreement. 

In  order  to  make  this  method  of  selection  of  observers  gen- 
erally available,  and  insure  at  the  same  time  that  the  same 
luminosity  scale  is  adhered  to,  we  have  thought  it  advisable  to 
adopt  a  different  test  color  difference  than  that  incidentally 
obtained  in  the  study  of  the  mechanical  equivalent  of  light.  For 
this  purpose  we  have  worked  out  two  colored  solutions  of  inor- 
ganic salts  which  to  the  average  eye,  as  determined  by  our  meas- 
urements,  should  have   equal  transmissions   of   the   light   of   a 


206  TRANSACTIONS   I.   E.   S. — PART    I 

standard  carbon  lamp.  At  the  same  time  an  effort  was  made  to 
select  transmissions  each  of  which  should  give  practically  one 
end  of  the  spectrum  alone.  The  idea  of  this  was  that  if  a  group 
of  observers  measures  the  ratio  of  the  two  halves  of  the  spectrum 
correctly  it  will  probably  measure  any  of  the  ordinary  much  less 
pronounced  color  differences  right. 

The  test  colors  which  we  now  recommend  are  given  by  the 
following  aqueous  solutions : 

Yellow  solution :  potassium  dichromate — 72  grams  to  1  liter  of  solution. 
Blue-green  solution :  copper  sulphate — 53  grams  to  1  liter  of  solution. 

These,  placed  in  two  carefully  matched  tanks  of  1  centimeter 
thickness,  should  transmit  equal  amounts  of  the  light  of  a  stand- 
ard "4-watt"  carbon  lamp,  the  measurement  being  made  at 
20  deg.  C.  by  the  flicker  photometer  under  the  conditions  of 
illumination  and  field  size  previously  described.  In  regard  to 
the  illumination,  it  is  to  be  noted  that  the  actual  transmission  of 
these  solutions  is  close  to  70  per  cent.  In  order,  therefore,  to 
secure  the  equivalent  of  25  meter-candles  on  a  white  surface  the 
lamp  and  distance  should  be  arranged  to  give  35  or  more  meter- 
candles,  depending  on  the  absorption  of  the  optical  parts  of  the 
photometer.  Needless  to  say,  as  in  all  precision  photometry,  the 
test  should  be  carried  out  by  the  substitution  method,  the  two 
solutions  being  alternated  on  the  test  side. 

The  transmissions  of  these  solutions  have  been  established  by 
a  series  of  approximations  involving  a  large  number  of  measure- 
ments all  made  in  accordance  with  our  original  method  of  main- 
taining the  luminosity  scale.  This  scale  is  now  maintained  by 
using  the  new  test  colors  in  exactly  the  same  way  as  outlined 
for  the  monochromatic  green  and  agrees,  as  it  should,  with  the 
original  scale.  That  is,  a  group  selected  by  their  measurements 
on  these  test  colors  as  having  a  "mean  eye"  also  possesses  that 
characteristic  when  tested  by  their  measurements  on  the  mono- 
chromatic green  solution. 

A  number  of  questions  which  arise  in  connection  with  the 
choice  of  a  group  of  observers  in  this  way  can  be  answered  from 
our  experience.  For  instance,  the  question  of  what  to  do  if 
enough  observers  are  not  available  to  make  a  balanced  group  is, 
we  find,  taken  care  of  by  giving  double  weight  to  one  or  two,  in 
such  way  that  the  same  weighting  gives  equality  with  the  test 


IVES  AND  KINGSBURY:    HETEROCIIROMATIC  MEASUREMENTS      207 

colors.    Again  the  question  arises  as  to  the  minimum  number  of 

observers  necessary.     Is  one  observer,  for  instance,  enough,  if 

he  reads  the  test  color  difference  correctly?    We  find  in  general 

that  it  is  hardly  safe  to  depend  upon  one  observer  who  tests 

normal,  because  after  all  the  test  is  to  some  extent  arbitrary  and 

is  not  an  absolute  guide  to  an  observer's  performance  on  all  types 

of  color  differences.    We  have  actually  noted,  however,  that  the 

mean  result  of  a  certain  pair  of  rather  extreme  observers  (whose 

vellow  .     ,  .  N  .        . 

values  for  —r-. are  respectively  1.12  and  0.90)  m  a  long  series 

blue 

of  measurements  is  almost  uniformly  the  mean  of  the  group,  sug- 
gesting that  in  many  cases  as  few  as  two  balanced  observers 
would  be  sufficient,  but  we  would  nevertheless  recommend  at 
least  five  observers  for  precision  work. 

An  important  question  which  is  frequently  raised  is  that  of 
the  permanence  of  an  observer's  characteristics.  Will  the  mem- 
bers of  a  group  retain  their  relative  positions  over  a  period  of 
time?  A  large  number  of  observations,  extending  over  nearly  a 
year,  have  convinced  us  of  the  practical  permanence  of  individual 
color  vision  characteristics,  with  very  rare  exceptions.  We  shall 
publish  these  data  in  another  connection,  but  that  portion  obtained 
in  this  present  study  may  profitably  be  presented  here.  In  the 
series  of  measurements  by  which  these  two  equal  transmission 
solutions  were  developed,  the  preliminary  work  was  done  with  a 
physical  photometer  (to  be  described  shortly),  after  which  two 
series  of  visual  measurements  were  made,  at  an  interval  of  about 
a  month.  In  the  first  set  seven  observers  participated  and  in  the 
second  eleven.  Of  these,  six  measured  in  both  sets.  In  the 
following  table  we  give  the  values  of  the  ratios  of  transmission  of 
the  two  solutions  (the  actual  ratio  of  each  approximation  being 
taken  as  the  unit)  as  obtained  by  these  men  at  these  two  times: 


Observer 
I 
2 
3 
4 
5 
6 

Mean  0.992  °-997 


Ratio  — — 

1st  set. 

2nd  set. 

0.957 
o-973 

O.946 
O.965 

1.002 

I.052 

0.910 

O.904 

1.042 
1.068 

I.043 

I.074 

208  TRANSACTIONS   I.    E.    S. — PART    I 

It  will  be  seen  that  with  one  exception  the  observers  have 
repeated  to  i  per  cent,  or  better.  This  one  observer  (number  3) 
as  it  happens  had,  previous  to  this  work,  never  read  an  optical 
instrument  and  was  used  in  the  work  chiefly  because  of  his  avail- 
ability at  all  times.  The  one  exception  need  not,  therefore,  be 
given  great  weight.  Even  so,  the  mean  value  for  this  group  of 
six,  on  these  extreme  test  colors,  is  only  ]/2  per  cent,  different  in 
the  two  sets. 

Another  question  is  whether  this  method  of  selection  could  not 
be  used  for  observers  to  work  with  the  equality  of  brightness 
method.  The  answer  is  "yes>"  provided  it  were  possible  to  make 
sufficiently  definite  and  consistent  settings  by  that  method  on  the 
test  color  difference  to  yield  unambiguous  results.  Actually  the 
number  of  settings  and  the  time  which  would  be  required  defi- 
nitely to  determine  an  observer's  characteristics  by  this  photo- 
metric method  would  be  prohibitive.  The  method  of  selecting 
observers  is  planned  for  the  photometric  procedure  in  which  the 
flicker  photometer  is  used,  and  it  is  recommended  for  that  only. 

This  paper,  together  with  those  which  have  preceded,  to  which 
reference  has  been  made,  give  full  descriptions  of  instruments 
and  methods  by  which  uniform  results  may  be  obtained  in  differ- 
ent laboratories  in  the  photometry  of  colored  lights.  A  luminosity 
scale  has  been  developed — a  matter  of  as  much  importance  in 
photometry  as  is  a  temperature  scale  in  thermometry — to  which 
these  uniform  results  are  referred.  The  test  colors  just  described 
may  be  compared  to  the  fixed  points  by  which  a  thermometer  is 
calibrated. 


haskell:   lighthouse  illumination  209 

LIGHTHOUSE  ILLUMINATION.* 


BY  RAYMOND   HASKELL. 


Synopsis:  This  paper  describes  the  various  forms  of  illuminants  used 
in  the  lighthouse  service  and  discusses  their  application  by  means  of  lenses 
and  other  means  of  intensification  to  lighthouses,  buoys  and  light  vessels. 


In  some  form  or  other  practically  every  system  of  illumination 
and  every  type  of  primary  light  source,  has  at  some  time  been  in 
use,  or  at  least  tried,  for  the  purpose  of  lighthouse  illumination. 
Even  totally  indirect  lighting  has  been  seriously  advocated  in  the 
proposition  to  throw  a  strong  beam  upon  the  clouds.  This,  while 
it  theoretically  gives  height  to  the  signal  and  hence  greater  range 
of  visability,  would  be  impractical  on  account  of  the  enormous 
energy  required  and  the  uncertainty  of  clouds. 

History  informs  us  that  lighthouses  existed  long  before  the 
Christian  Era,  but,  in  comparison  with  modern  installations  they 
were  built  more  as  curiosities  or  monuments,  than  as  aids  to 
navigation.  Later,  however,  a  great  many  were  constructed  by 
the  Romans,  and  the  sites  of  these  are  indeed  in  many  cases 
identical  with  those  of  modern  lighthouses.  The  first  lighthouse 
structure  built  in  the  United  States  was  situated  in  Boston  har- 
bor. This,  however,  was  partly  destroyed  during  the  Revolution, 
and  the  present  Boston  lighthouse,  while  on  the  same  site,  is  a 
fairly  modern  structure. 

The  oldest  existing  lighthouse  towers  in  the  United  States  are 
situated  on  Sandy  Hook  and  Cape  Henlopen,  but  even  in  these 
cases  the  lanterns  and  superstructures  are  comparatively  modern. 

ILLUMINANTS. 

In  ancient  days,  and  in  fact  up  to  fairly  modern  times,  the 
illumination  for  lighthouse  towers  was  produced  by  burning 
piles  of  fagots  or  other  material  giving  a  comparatively  large 
flame.  These  were  followed  by  the  use  of  candles  and  various 
types  of  primative  seed  oil  lamps.     Oils  have  been,  and  still  are, 

*  A  paper  read  at  a  meeting  of  the  Philadelphia  Section  of  the  Illuminating  Engi- 
neering Society,  November  20,  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


210  TRANSACTIONS    I.    E.    S. PART    I 

the  principal  sources  of  light  used  in  lighthouses,  the  greatest 
advance  in  their  use  being  in  the  improvement  of  the  lamps  and 
the  manner  of  distribution  of  the  light.  Until  recent  times,  veg- 
etable or  animal  oils  were  the  only  ones  used,  the  principal  illum- 
inant  in  the  lighthouses  of  the  United  States  being  lard  oil,  but 
since  the  discovery  of  petroleum,  kerosene,  in  one  form  or  an- 
other, has  formed  the  basis  for  light  sources  in  the  greater  num- 
ber of  cases. 

Both  flat  and  round  wicks  are  used,  and  for  large  installations 
burners  with  as  high  as  eight  concentric  wicks  have  been  de- 
veloped. There  are  still  a  considerable  number  of  five  wick 
burners  in  use. 

Since  the  advent  of  the  mantle,  wick  lamps  for  the  more  power- 
ful lights  have  been  superseded  in  favor  of  the  kerosene  mantle 
type  of  lamp.  This  form  of  light  source,  at  the  present  time,  is 
the  best,  as  to  light  efficiency  and  cost,  known.  Its  only  drawback 
is  the  fallibility  of  the  mantle  and  hence  the  necessity  for  having 
a  keeper  to  watch  it  occasionally  and  also  to  keep  the  lamps  and 
accessories  in  proper  shape. 

In  large  installations  it  is  necessary  to  have  a  keeper  anyway, 
and  therefore  this  system  of  illumination  is  almost  universally 
used  in  these  cases. 

The  first  incandescent  oil-vapor  (kerosene  with  mantle)  lamps 
used  in  this  country  were  patterned  after  the  French  lamps,  in 
which  the  kerosene  is  vaporized  by  the  excess  and  waste  heat  of 
the  mantle  heating  a  tube  containing  the  oil  and  situated  over  the 
mantle.  This,  however,  had  its  drawbacks  in  efficiency  and  reg- 
ulation, and  another  type  has  been  developed  which  allows  free 
passage  of  the  light  in  all  directions  and  gives  a  very  high  intrinsic 
brilliancy.  This  high  intrinsic  brilliancy,  as  will  be  readily  under- 
stood, is  the  principal  characteristic  demanded  by  an  illuminant 
for  lighthouse  purposes.  The  cost  of  this  lamp  for  fuel  is  about 
i  cent  per  500  candlepower  per  hour,  or  including  repairs  and 
depreciation,  about  1.5  cents  per  500  candlepower  per  hour. 

Electricity,  on  account  of  the  high  intrinsic  brilliancy  as  exem- 
plified in  the  arc  and  concentrated  filament  lamps,  presents  itself 
as  the  ideal  source  of  lighthouse  illumination.  Its  great  drawback 
however  is  its  cost  and  the  difficulty  of  obtaining  it  at  most  light 


haskkll:    lighthouse  illumination  211 

stations.  Simplicity  and  reliability  are  the  watch  words  in  the 
lighthouse  service.  Unless  current  can  be  obtained  from  power 
companies  on  shore,  the  use  of  electricity  is  prohibited  by  the 
cost  of  generating  plants,  the  inability  to  make  repairs  on  account 
of  isolation  of  stations,  and  the  necessity  of  employing  skilled 
labor. 

'Where  current  can  be  obtained,  as  in  some  shore  stations,  the 
concentrated  filament  lamp  is  more  or  less  ideal  and  is  used  sat- 
isfactorily. Even  here  it  must  be  watched,  as  lamps  will  burn 
out  and  power  lines  will  fail,  but  a  lighthouse  must  stay  lighted 
regardless. 

The  electric  arc  is  theoretically  ideal  as  a  concentrated  light 
source  for  use  with  lenses,  but  practically  its  drawbacks  are  many 
and  various.  It  has  been  found  expedient,  therefore,  to  utilize 
this  source  only  in  a  few  instances,  the  most  notable  example 
being  Navesink  on  the  Highlands,  just  south  of  Sandy  Hook. 
This  is  the  most  powerful  signal  in  the  United  States,  and  cor- 
respondingly gives    an  exceedingly  quick  flash. 

Gas,  either  in  the  form  of  enriched  oil  gas  or  acetylene,  is  a 
very  important  source  of  light  in  the  lighthouse  service,  and  is 
used  particularly  in  buoys  or  small  beacons,  where  great  intensity 
is  not  demanded,  and  where  it  is  impractical  to  have  an  attendant. 
These  gas  installations  will  operate  without  attention  from  three 
to  six  months,  depending  on  the  size  of  the  burner  and  very  little 
trouble  is  experienced  with  them. 

LENSES. 

While  the  intensity  of  the  source  is  important,  the  greatest 
factor  in  lighthouse  illumination  is  the  means  of  intensifying  or 
directing  the  light  energy  in  order  to  obtain  the  most  usable  re- 
sult. 

This  was  first  accomplished  by  the  use  of  metallic  reflectors. 
These  are  still  used  on  some  small  light  vessels,  and  when  kept 
highly  polished  are  not  a  bad  installation.  In  these  cases  eight  of 
these  are  so  arranged  on  a  carriage  around  the  mast  that  they  can 
be  lowered  to  the  deck  and  attended  to  without  exposing  the  men 
to  the  weather. 

The  next  development  was  the  dioptric  Fresnel,  which  was 


212  TRANSACTIONS   I.    E.    S. — PART    I 

followed  by  the  complete  lighthouse  lens,  containing  both  diop- 
tric and  catadioptric  prisms.  By  catadioptric  prisms  is  meant 
those  above  and  below  the  central  belt  which  direct  the  light  in 
the  desired  direction,  both  by  refraction  and  also  by  total  reflec- 
tion from  the  inner  surface  of  the  glass.  This  is  shown  by  a 
lens  profile.  In  the  central  belts  the  light  energy  is  directed  hor- 
izontally by  refraction  only.  In  the  upper  and  lower  prisms  the 
light  is  first  refracted,  then  totally  reflected  and  finally  refracted 
again.  By  means  of  these  prisms  the  total  energy  from  the  source 
at  the  centre  is  theoretically  emitted  in  a  parallel  direction.  In 
cases  of  units  which  are  known  as  fixed  lenses,  the  prisms  are 
evolved  around  a  vertical  axis,  and  the  resultant  beam  is  a  series 
of  parallel  horizontal  planes  of  light  diverging  in  all  directions, 
in  azimuth.  With  flashing  and  range  lenses  the  prisms  are 
evolved  around  one  or  more  horizontal  axes,  and  the  resultant 
beams  are  theoretically  cylinders  of  light.  Practically  on  account 
of  the  sizes  of  the  sources  the  beams  are  solid  cones  of  light 
whose  divergence  depends  on  the  dimensions  of  the  source,  and 
whose  intensity  depends  practically  only  on  the  intrinsic  brilliancy 
of  the  source,  and  on  the  solid  angles  subtended  by  the  lens 
panels  at  the  focus.  The  flashing  is  produced  by  revolving  the 
lens  around  the  source. 

The  mariner  prefers  a  fixed  light  as  it  gives  him  something 
steady  to  run  by,  but  such  lights  are  naturally  lacking  in  intensity 
and  are  often  confused  with  shore  lights.  The  flashing  light  is 
very  powerful  but  is  of  short  light  duration.  With  lenses  of  the 
same  focal  length,  the  ratio  of  the  period  of  luminosity  to  period 
of  darkness  is  indirectly  proportional  to  the  intensity  of  flash. 
Where  high  power  is  not  needed,  but  where  it  is  desired  to  pro- 
duce a  distinctive  light,  it  is  customary  to  use  a  fixed  lens,  but 
to  cut  off  the  light  at  definite  periods  by  means  of  blanking 
sections  of  the  lens,  and  revolving  it  about  the  source  of  light. 
This  can  be  accomplished  by  extinguishing  or  blanking  shutters 
which  periodically  cover  up  or  cut  off  the  light  from  the  source. 

In  order  to  utilize  the  light  energy  which  is  lost  when  a  lens 
panel  is  blanked  off,  it  has  been  found  expedient  to  install  silvered 
spherical  mirrors  in  place  of  these  blanking  panels.  By  prop- 
erly arranging  the  mirrors  the  light,  which  would  strike  a  blank 


HASKELL:     LIGHTHOUSE    ILLUMINATION  213 

panel,  can  be  reflected  back  through  the  source  and  out  through 
the  lens  on  the  opposite  side,  thereby  intensifying  that  beam  very 
greatly.  With  sources  of  illumination  that  are  transparent,  as 
acetylene  gas,  this  method  is  very  efficacious,  but  with  sources 
which  are  quite  opaque,  as  mantle  lights,  the  gain  from  this 
scheme  is  scarcely  25  per  cent.  To  obviate  this  loss  the  idea 
was  conceived  that  instead  of  sending  the  energy  back  through 
the  focus,  it  could  be  sent  back  alongside  of  the  focus  just  missing 
the  mantle.  Theoretically  this  would  not  produce  good  results, 
as  the  lenses  are  designed  for  a  point  source  at  the  focus,  but 
practically  the  sources  are  generally  so  large  that  the  fact  that 
the  image  is  not  at  the  focus  is  scarcely  realized,  and  from  80  to 
85  per  cent,  of  the  otherwise  lost  energy  can  be  utilized  in  use- 
ful light.  With  fixed  lenses  this  intensifies  the  beam.  When  used 
with  flashing  lenses  it  increases  the  relative  light  period. 

In  using  this  principle  of  offset  mirrors  it  has  been  found  most 
practical  to  split  the  mirrors  vertically,  and  so  set  them  as  to 
send  the  reflected  light  on  both  sides  of  the  mantle  instead  of 
all  on  one  side. 

As  mentioned  above  the  usual  method  of  producing  occulting 
or  flashing  lights  when  gas  or  electricity  is  not  used  for  the  illum- 
inant  is  by  means  of  revolving  the  lens.  This  is  done  by  clock- 
work actuated  by  weights.  The  lenses  are  often  very  heavy  and 
are  generally  supported  on  chariots,  ball  bearings  or  floated  in 
mercury.  For  the  heavy  lenses  the  mercury  float  method 
is  found  to  be  the  best.  By  the  proper  design  of  mercury  float, 
a  two-ton  lens  can  be  carried  on  less  than  50  pounds  of  mercury 
and  the  whole  thing  can  be  revolved  by  a  few  ounces  constant 
force.  This  requires,  however,  that  the  parts  of  mercury  float 
outfit  shall  be  machined  and  set  up  exceedingly  true,  and  also 
that  the  lens  shall  be  very  well  balanced.  In  order  to  use  oil- 
vapor  lights,  it  is  necessary  on  account  of  the  tanks  containing 
oil  and  air  under  pressure,  that  the  lamp  shall  be  stationary  and 
the  lens  revolve  around  it. 

The  most  powerful  flashing  lens  ordinarily  used  is  what  is 
called  the  bivalve.  This  consists  of  two  hemispherical  shaped 
panels,  the  prisms  of  which  are  so  arranged  as  to  concentrate 
practically  all  the  light  emitted  by  the  source  into  two  diametri- 


214  TRANSACTIONS    I.    E.    S. — PART    I 

cally  opposite  beams.  The  flash  emitted  by  these  bivalve  lenses  is 
very  powerful,  but  is  of  short  duration,  in  many  cases  of  less  than 
one  tenth  second  duration.  When  it  is  desired  to  utilize  the 
beam  in  only  one  direction,  as  in  the  case  of  a  range  lens  show- 
ing light  only  in  one  direction  along  a  channel,  one  half  of  a  bi- 
valve can  be  used  and  intensified  by  the  substitution  of  mirrors 
for  the  other  half.  This  condenses  and  directs  all  the  light 
emitted  by  the  source  in  one  direction  in  a  search  light  beam. 

By  proper  design  of  prisms  and  panels  it  is  possible  to  flash 
numbers,  as  in  the  case  of  Minots  Ledge,  which  flashes  1-4-3,  or 
as  in  other  cases  to  make  combinations  of  red  and  white  flashes. 
These  special  combinations  are  used  in  cases  where  a  number  of 
lights  together  are  likely  to  produce  confusion. 

The  manufacture  of  lenses  is  quite  a  delicate  operation,  and 
until  lately  such  work  has  been  done  abroad.  This  has  been  due 
partly  to  the  fact  that  the  largest  factor  in  the  cost  is  labor,  which 
can  be  obtained  much  cheaper  abroad  than  here,  and  also  to  the 
fact  that  the  demand  has  not  been  sufficient  to  warrant  the  initial 
outlay  necessary. 

Recently,  however,  American  manufacturers  have  gone  into 
this  industry  and  by  the  use  of  machinery  are  making  better 
lenses  than  those  obtained  abroad,  and  it  is  believed  it  soon  will 
be  a  paying  proposition  to  them.  The  advantage  of  the  American 
made  lens  over  the  foreign  one  lies  in  the  use  of  machinery  in- 
stead of  hand  labor,  whereby  all  similar  prisms  are  exactly  alike 
and  interchangeable,  and  repairs  can  be  easily  made.  In  foreign 
lenses  the  prisms  rarely  are  the  same  and  repairs  are  very  ex- 
pensive. 

LIGHT  INTENSITY. 

A  great  many  attempts  have  been  made  to  compute  the  candle- 
power  values  produced  by  various  lenses,  but  there  are  so  many 
factors  entering  into  this  computation  that  a  formula  becomes  too 
loaded  down  to  be  workable.  They  all  end  up  by  making  some 
assumption  or  other  which  is  never  practical  and  vitiates  the 
whole  computation.  In  working  out  candlepower  values  the 
Unit  d  States  Lighthouse  Bureau  has  used  the  empirical  method, 
obtaining  all  the  data  it  could  and  then  using  simple  formula  for 
rpolation.     The  values  were  obtained  by  actually  measuring 


HASKELL:     LIGHTHOUSE    ILLUMINATION  215 

such  lenses  as  were  available  with  the  different  sources  of  lights 
used  in  the  service. 

The  following  results  are  worth  noting.  With  small  lenses  the 
candlepower  increases  up  to  150  feet  and  then  remains  constant 
no  matter  how  far  away  it  is  taken.  With  large  lenses  the 
maximum  is  reached  at  250  to  300  ft.  (75  to  90  m.),  and 
further  increase  of  distance  causes  no  change.  This  is  largely 
due  to  the  fact  that  the  sources  of  light  are  fairly  large.  As  a 
general  rule  the  maximum  is  reached  soon  after  a  point  is 
reached  where  all  the  prisms  fill  with  light. 

Fixed  lenses  with  the  same  light  source  are  found  to  vary 
in  candlepower  directly  with  the  diameter;  flashing  lenses  of 
similar  construction  vary  approximately  as  the  square  of  the 
diameter  decreasing  and  departing,  however,  from  this  law 
somewhat  as  the  larger  lenses  are  considered.  This  is  probably 
due  to  the  fact  that  the  prisms  in  the  larger  lenses  are  thicker  and 
not  so  well  set  as  the  medium  sized  ones.  With  fixed  lenses  the 
candlepower  varies  directly  as  the  intrinsic  brilliancy  and  as  the 
width  of  the  light  source,  but  does  not  depend  on  its  height.  With 
flashing  lenses  the  candlepower  depends  only  on  the  intrinsic 
brilliancy,  the  large  sources  producing  only  more  divergence  of 
beam  and  no  increase  of  candlepower. 

The  dioptric  portion  of  the  lens,  approximately  300  above  and 
below  the  central  plane,  produces  about  60  per  cent,  of  the  light, 
the  upper  catadioptric  portion  30  per  cent,  and  the  lower  10  per 
cent. 

All  of  the  above  facts  would  be  naturally  foretold  by  geomet- 
rical optics,  but  it  is  always  pleasing  to  have  theory  so  well  cor- 
roborated. 

The  brightest  light  in  the  United  States  is  on  the  Highlands 
of  the  Navesink  where  an  electric  arc  is  intensified  by  a  second 
order  bivalve  lens.    It  is  estimated  at  25,000,000  candlepower. 

BUOYS. 

The  lighted  buoy  is  more  or  less  a  modern  invention.  At  one 
time  an  attempt  was  made  to  have  a  string  of  buoys  in  one  of 
the  channels  of  New  York  harbor  lighted  by  electricity  and  sup- 
plied by  a  cable  from  the  shore.     They  gave  so  much  trouble, 


2l6  TRANSACTIONS    I.    E.    S. — PART    I 

however,  that  they  were  abandoned.  The  next  development  was 
the  use  of  oil  or  Pintsch  gas,  each  buoy  being  a  unit  by  itself. 
The  gas  is  contained  in  the  body  of  the  buoy  under  up  to  180 
pounds  (12  atmospheres)  pressure  and  burns  in  a  protected  lan- 
tern at  the  top.  In  order  to  save  gas  and  give  character  to  the 
light,  a  mechanism  is  installed  in  the  lantern  which  automatically 
and  periodically  turns  the  gas  on  and  oft*.  A  small  flame  or  pilot 
burns  continuously  in  order  to  light  the  gas  when  it  is  automati- 
cally turned  on.  The  mechanism  is  simple  and  operated  by  the 
gas  pressure,  and  barring  accidents  will  operate  as  long  as  there 
is  gas  in  the  buoy.  Ordinarily  these  buoys  will  run  without  at- 
tention from  four  to  nine  months,  depending  on  the  flashing 
period  of  the  light. 

These  buoys  are  very  easily  filled  at  their  stations  by  simply 
lashing  the  buoys  to  the  side  of  a  lighthouse  tender,  attaching  a 
hose  and  pumping  the  gas  into  them  from  a  large  storage  holder 
carried  on  deck.  The  crews  of  these  vessels  become  quite  expert 
in  securing  these  buoys  for  attention  even  in  rough  seas,  and  it 
is  surprising  how  little  damage  is  done  to  them. 

The  candlepower  of  an  ordinary  oil  gas  lantern,  however,  is 
low  and  in  hazy  weather  especially  it  cannot  be  seen  at  any 
great  distance.  To  increase  its  light  intensity,  in  many  cases 
the  gas  is  burned  with  a  mantle.  The  use  of  the  mantle  intro- 
duces, however,  a  more  or  less  uncertain  factor.  Sometimes  a 
mantle  will  operate  for  many  months  satisfactorily  without 
failure,  while  another  mantle  from  the  same  manufactured  lot 
will  fail  very  quickly.  These  lights  therefore  are  generally  used 
in  places  where  they  can  be  observed  every  few  days  and  given 
attention  if  necessary. 

The  most  modern  gas  illuminant  is  acetylene.  This  is  burned 
in  a  lantern  more  or  less  in  the  same  manner  as  oil  gas,  only  the 
mantle  is  not  used.  This  gas,  however,  cannot  be  compressed 
with  safety  into  the  body  of  the  buoy,  and  so  is  stored  in  tanks, 
dissolved  in  acetone.  These  tanks  fit  into  pockets  in  the  buoy 
and  are  so  arranged  that  they  can  be  easily  removed  and  replaced 
on  station  by  a  boat  alongside. 

Another  form  of  buoy  more  or  less  in  use  generates  the  acety- 
lene at  low  pressure  directly  from  calcium  carbide  stored  in  the 


HASKELL:     LIGHTHOUSE   ILLUMINATION  2\J 

buoy.  Theoretically  this  should  be  the  most  economical  method 
to  produce  acetylene,  but  practically  it  is  unsatisfactory.  Owing 
to  high  seas  and  waves  the  buoys  often  do  not  generate  evenly 
and  considerable  gas  is  lost.  It  is  impossible  to  tell  exactly  how 
long  a  buoy  is  going  to  run  which  makes  it  administration  costly 
on  account  of  tender  costs.  There  is  a  buoy  of  this  type  in  New 
York  harbor  which  ran  sixteen  months  on  a  single  charge,  and 
then  the  next  time  it  went  out  in  two  months. 

In  order  to  save  gas  in  the  day  time  it  is  possible  to  equip  gas 
apparatus  with  a  mechanism  which  is  operated  by  the  light  of  the 
sun  and  turns  the  gas  off  in  the  day  time.  These  so  called  "sun 
valves"  operate  quite  satisfactorily,  especially  on  large  installa- 
tions where  considerable  gas  is  consumed,  but  with  small  lanterns 
the  depreciation  and  repairs  of  the  sun  valve  is  greater  than  the 
cost  of  gas  saved.  This  is  especially  true  of  buoys  where  the 
danger  of  being  damaged  by  passing  vessels  is  great. 

LIGHT  VESSELS. 

Perhaps  the  most  important  aid  to  navigation  is  the  light 
vessel.  These  are  vessels  anchored  at  well  known  sailing  points 
whereby  the  mariner  can  get  a  perfect  idea  of  his  position  in 
thick  weather  without  the  danger  usually  attendant  in  running 
too  near  a  lighthouse.  Light  vessels  being  anchored  in  reason- 
ably deep  water,  the  mariner  runs  close  to  them  and  can  get  an 
accurate  point  of  departure  for  shaping  his  course,  while  light- 
houses being  on  land  the  mariner  cannot  run  near  to  them  and 
especially  in  thick  weather  must  more  or  less  guess  at  his  posi- 
tion. In  addition  to  signal  lights  these  vessels  all  carry  an  air 
fog  signal  and  most  of  them  submarine  bells. 

The  characteristic  lights  of  a  light  vessel  are  carried  at  or  near 
the  mast  head  and  consist  practically  of  the  same  systems  as 
enumerated  above.  The  small  vessels  are  equipped  with  oil 
lamps  with  reflectors  or  with  small  lenses  and  lanterns.  These 
are  arranged  on  frame  work  around  the  mast  so  designed  that  it 
can  be  lowered  to  the  deck  and  given  proper  attention  without 
the  necessity  of  the  men  going  aloft  in  bad  weather. 

A  large  number  of  vessels  are  being  equipped  with  gas  ap- 
paratus, particularly  acetylene  on  account  of  its  simplicity  and 


2l8  TRANSACTIONS   I.    E.    S. — PART    I 

ease  of  handling.  This  gas  apparatus  has  the  further  advantage 
that  the  lanterns  can  be  fixed  permanently  at  the  mast  head  and 
thus  gain  several  feet  in  height  over  the  oil  light  installations. 

Most  of  the  larger  vessels  are  equipped  with  electric  plants  and 
the  sources  of  illumination  are  concentrated  filament  250-watt 
tungsten  lamps  in  300  mm.  lanterns.  These  give  a  most  satis- 
factory light  and  require  little  attention,  the  only  drawback  being 
the  necessity  for  a  complete  electric  plant.  One  vessel, 
"Ambrose"  at  the  entrance  to  New  York  harbor  is  equipped  with 
flaming  arcs  in  300  mm.  lanterns.  These  of  course  give  a  very 
powerful  illumination,  but  it  is  really  greater  than  is  necessary 
to  correspond  with  the  elevation  of  the  lanterns.  These  lights 
are  so  bright  that  there  is  complaint  that  they  prevent  the  pilots 
from  detecting  other  ships  approaching  from  back  of  the  light 
vessel. 

Both  light  vessels  and  lighthouses  will  soon  be  displaced  in  a 
large  number  of  cases  with  big  buoys.  These  are  being  made 
now  with  very  heavy  bells  and  strong  whistles,  and  on  account 
of  the  lower  initial  cost  and  maintenance,  several  can  be  used 
instead  of  one  light  vessel,  for  the  same  cost  and  a  much  broader 
system  of  guide  posts  of  the  sea  can  be  established.  The  mariner 
will  simply  run  between  buoys,  a  few  miles  apart. 


sharp:   data  on  artificial  daylight  units  219 

SOME  DATA  ON  ARTIFICIAL  DAYLIGHT  UNITS.* 


BY   CLAYTON    H.  SHARP. 


By  projecting  a  spectrum  on  to  a  card  covered  with  skeins  of 
worsted  of  all  the  principal  spectral  colors,  including  also  purple, 
it  was  shown  how  the  colors  of  fabrics  vary  as  seen  in  different 
colored  lights.  Thus  a  red  worsted  is  black  in  green  and  blue 
light  and  a  blue  one  is  black  in  the  red  light.  Therefore  it  is 
necessary  in  order  that  colored  fabrics  may  always  be  seen  alike 
that  they  always  be  viewed  under  light  of  the  same  spectral  com- 
position, having  that  is,  the  same  relative  intensities  of  each  of 
the  colors.  As  a  standard  of  composition  of  this  sort,  daylight 
is  chosen  and  this  is  called  "white  light." 

The  colors  of  fabrics  are  obtained  in  one  of  two  ways;  either 
by  the  use  of  a  pure  dye  or  by  mixing  two  different  dyes  together. 
For  instance,  a  green  may  result  from  the  use  of  a  pure  green 
pigment  or  it  may  result  from  the  admixture  of  blue  and  yellow. 
Two  greens  differently  made  up  might  match  in  one  light, 
whereas  with  light  of  a  different  spectral  composition,  they  would 
be  differently  affected  and  hence  would  not  match.  The  use  of 
the  daylight  equipments  is  to  provide  this  standard  white  light 
of  a  given  spectral  composition  for  the  purpose  of  matching 
colors.  In  certain  respects  an  equipment  of  this  kind  is  better 
than  daylight,  inasmuch  as  it  is  always  of  a  fixed  value  and  does 
not  vary  continually  as  daylight  does,  both  in  color  and  intensity. 

The  following  daylight  equipments  were  exhibited  and  data 
obtained  at  the  Electrical  Testing  Laboratories  and  made  avail- 
able through  the  courtesy  of  the  Lamp  Committee  of  the  Asso- 
ciation of  Edison  Illuminating  Companies  were  given. 

The  principle  of  the  operation  of  these  equipments  is  that  by 
the  interposition  of  a  bluish  screen  between  the  light  source  and 
the  object  to  be  viewed,  the  excess  of  red  and  yellow  in  the  light 
source  is  removed,  and  the  spectral  composition  of  the  resultant 
light  becomes  the  same  as  that  of  daylight. 

*  Summary  of  a  lecture  delivered  before  a  meeting  of  the  Xew  York  Section  of  the 
Illuminating  Engineering  Society,  November  14,  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


220 


TRANSACTIONS   I.    E.    S. — PART    I 


Description  of 
equipment 


Character  of 
the  light  source 


A  Moore  carbon  dioxid  tube 

B  Special  Welsbach  mantle 

C  Intensified  arc 

D  Gas-filled  tungsten  lamp 

E  Gas-filled  tungsten  lamp 

F  Gas-filled  tungsten  lamp 


Character  of 
the  screen 

None. 

Greenish-blue  pebbled  glass 
and  purple  gelatin. 

Composite  of  small  pieces  of 
blue,  green  and  clear  glass 
with  diffusing  glass. 

Bluish  glass. 

Globe  of  bluish  glass,  sand- 
blasted on  the  interior. 

Globe  of  blue  glass  flashed 
with  opal. 


Data  on  Illumination  Produced. 
Equipment  B. 

The  illumination  values  found  are  shown  on  the  accompanying 
chart.  The  center  of  the  field  was  much  brighter  than  the 
edges. 

Equipment  C. 

The  following  values  were  obtained : 

Horizontal  foot-candles 

Location  of  test  station 
Directly  beneath  center  of  screen... 

1  ft.  out  from  center  of  screen 

2  ft.  out  from  center  of  screen 

3  ft.  out  from  center  of  screen 

4  ft.  out  from  center  of  screen 

Equipment  D. 

The  following  values  were  obtained : 

Horizontal  foot-candles 

i  ft.  iS  in. 

Location  of  test  station  below  screen    below  screen 

Directly  beneath  center  of  screen 52  18.0 

3  in.  out  from  center  of  screen 36  — 

6  in.  out  from  center  of  screen 11  8.5 

1   ft.  out  from  center  of  screen 4  3.0 

18  in.  out  from  center  of  screen —  1.5 

Note:     Illumination  very  non-uniform.  Bright  spot  directly 

beneath  unit. 


18  iii. 
below  screen 

3  ft. 
below  screen 

50.0 

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26.O 

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2.5 

— 

1.0 

A  (on  left)— Moore  carbon  dioxid  tube;  B  (on  right)— A  special  gas  mantle  daylight  producer. 


C — Intensified  carbon  arc  lamp  with 
color  screen. 


F — Tungsten  lamp  in  a  blue  glass  globe 
flashed  with  opal. 


1000 


410        450        490        550        570        6)0         650        690 
VIOLET       BLUE  GREEN  YELLOW      0RAM6E    RED 

WAVE-LENGTH 


Fig.  I.— Spectrophotometric  curves  of  the  daylight  equipments. 


sharp:    data  on  artificial  daylight  UNITS  221 

Absorption  Data. 

Equipment  C. 

Arc  lamp  unequipped,  mean  spherical  cp 151 

Arc  lamp  with  reflector,  mean  spherical  cp 107 

Arc  lamp  with  reflector  and  color  screen 11 

Absorption  due  to  screen 90     per  cent. 

Equipment  D. 

Lamp  equipped  with  reflector,  mean  spherical  cp.     57.8 
Lamp  equipped  with  reflector  and  color  screen...       3.56 
Absorption  due  to  screen 94     percent. 

Equipment  E. 

Absorption    64     per  cent. 

Equipment  F. 

Absorption    73.5  per  cent. 

The  spectrophotometric  curves  of  these  equipments  are  given 
in  the  accompanying  figure.  Daylight  curve  ascribed  to  Ives 
refers  to  the  blue  sky. 

The  Moore  carbon  dioxid  tube  has  been  suggested  as  a  stand- 
ard of  white  light  and  may  in  this  case  be  used  as  a  proper 
standard  for  comparison. 


222  TRANSACTIONS   I.    E.    S. — PART    I 

BOOKS  ON  ILLUMINATION. 


The  table*  on  the  following  pages  gives  a  classified  analysis  of  all  the 
available  books,  in  English,  pertaining  to  illuminating  engineering.  It 
indicates  the  possible  utility  of  these  books  for  illuminating  engineer- 
ing practise.  The  distributions  under  the  various  subject-headings  con- 
stitute, of  course,  an  index  rather  than  a  precise  analysis  of  the 
contents  of  the  books.  Moreover,  the  classification,  as  might  be 
expected,  is  necessarily  more  or  less  arbitrary.  For  example,  "  Private 
House  Electric  Lighting"  by  Taylor  describes  small  plants  for  generation 
of  electricity,  and  the  practical  wiring  and  placing  of  lamps  in  residences. 
It  has  been  classed  under  the  heading  "  G,"  but  there  are  also  good  reasons 
for  classing  it  under  "  D,"  "  M,"  "  Q,"  or  "  U." 


Catalog  of  Various  Subjects  Covered  by  Table  I. 

A.  Physical  basis  of  light  production. 

B.  Physical  characteristics  of  sources. 

C.  Chemistry  of  light  production. 

D.  Electric  illuminants. 

E.  Gas  and  oil  illuminants. 

F.  Incandescent  gas  mantle  lamps. 

G.  Electric  and  gas  lighting  (gen.  mfgr.  and  dist.) 
H.  Units,  standards  and  terminology. 

I.  Photometry. 

J.  Architecture. 

K.  Physiology  and  psychology. 

L.  Calculations. 

M.  Interior  illumination. 

N.  Exterior  illumination. 

O.  Reflectors,  glassware,  etc. 

P.  Fixtures. 

Q.  Commercial  aspects  of  electric  and  gas  lighting. 

R.  The  Illuminating  Engineering  Society. 

S.  Illuminating  engineering. 

T.  Color. 

U.  Miscellaneous. 

*  This  table,  which  was  prepared  by  Mr.  Norman  Macdonald,  has  been  abstracted 
from  the  annual  report  of  the  1913-1914  Committee  on  Education  of  the  Illuminating 
Engineering  Society. 


BOOKS   ON    ILLUMINATION 


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Illumination:    Its    Distribution 

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gove  and  porter:    car  lighting  problems  227 

A  PRACTICAL  STUDY  OF  CAR  LIGHTING  PROBLEMS.* 


BY   W.    G.   GOVE   AND  L.   C.    PORTER. 


Synopsis:  This  paper  describes  very  exhaustive  tests  conducted  by 
the  New  York  Municipal  Railway  Corporation  in  order  to  determine  the 
best  method  of  lighting  the  600  new  cars  under  construction  for  the  new 
subway  in  New  York  City.  Direct,  semi-indirect  and  totally  indirect 
lighting  systems  were  tried  in  a  full  sized  template  car,  built  for  the 
purpose.  Both  standard  equipment  and  equipment  especially  constructed 
for  the  purposes  were  tested,  the  construction  of  the  car  being  changed 
where  necessary.  As  a  result  of  the  tests,  the  system  finally  adopted 
consisted  of  a  single  row  of  56-watt  tungsten  railway  lamps  located  down 
the  center  line  of  the  ceiling  and  equipped  with  intensive  type  opal  glass 
reflectors,  this  system  offering  the  best  combination  of  desirable  factors, 
including  good  lighting,  reasonable  installation  cost  and  low  maintenance 
cost. 


When  the  plans  for  the  new  subway  in  New  York  City  were 
being  completed,  it  was  decided  that  the  six  hundred  cars  should 
be  the  latest  word  in  car  construction  in  every  detail.  Many  new 
and  interesting  mechanical  and  electrical  devices,  which  have 
been  described  in  the  various  technical  bulletins,1  were  decided 
upon  for  these  cars.  Not  the  least  of  these  most  up-to-date 
factors  was  the  lighting  of  the  cars.  The  size,  interior  seat  ar- 
rangement, finish  and  construction  of  the  cars  presented  many 
new  problems  to  be  solved  in  choosing  a  lighting  system  which 
would  meet  satisfactorily  the  following  desiderata : 

( 1 )  Quantity  of  light ;  it  being  desirable  to  have  an  average 

intensity  of  not  less  than  3  foot-candles  on  a  hor- 
izontal plane  42  in.  (1.06  m.)  above  the  floor,  at 
85  per  cent,  normal  voltage. 

(2)  General  effect  and  appearance  of  lighting  system  with 

lamps  lighted  or  extinguished. 

*  A  paper  read  at  a  meeting  of  the  New  York  Section  of  the  Illuminating  Engi- 
neering Society,  March  II,  1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 

1  Electric  Traction,  A.  E.  R.  A.,  Dec,  1914. 


JJS 


TRANSACTIONS    I.    E.    S. — PART    I 


(3)  Lack    of    eyestrain    for    both    seated    and    standing 

passengers,  involving  not  only  intensity  and 
direction  of  light,  but  also  glare  and  possible 
shadows  cast  by  standing  passengers  on  the  read- 
ing matter  of  seated  passengers. 

(4)  Efficiency. 

(5)  Installation  and  maintenance  expense. 

(6)  Depreciation  of  equipment  in  service. 

In  order  to  make  a  thorough  study  of  these  problems  a  series 
of  tests  were  conducted  in  a  full-sized  model  car  constructed  for 
the  purpose.  This  car  was  67  ft.  3  in.  (20.42  m.)  overall,  by 
9  ft.  10  in.  (3  m.)  wide,  by  12  ft.  3  in.  (3.73  m.)  high.    The  in- 


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Fig-  I. — I'lan  and  elevation  of  New  York  Municipal  Railway  Corporation's 
subway  tempate  car. 

terior  dimensions  of  the  body  used  in  the  tests  were  65  ft. 
(19.81  m.)  long  by  9  ft.  (2.74  m.)  wide.  Fig.  5  is  an  exterior 
view  of  the  car.  The  interior  car  finish  was  white  enameled 
headlining  and  walls,  down  to  the  window  sills.  Below  the  sills 
the  walls  were  painted  grey.  The  floor  was  concrete  and  the 
seats  upholstered  in  yellow  rattan.  Fig.  1  shows  the  interior 
seating  arrangement  and  gives  the  general  dimensions  of  the 
car. 

Photometer  tests  were  taken  to  supplement  such  data  as  ob- 
servation of  the  general  appearance,  installation  and  maintenance 
cost  figures,  etc.  The  photometric  measurements  were  not  made 
with  the  intention  of  comparing  the  efficiency  of  any  particular 
types  of  illuminating  devices  or  accessories  thereto;  though  the 


GOVE   AND   PORTER:     CAR   LIGHTING   PROBLEMS  229 

average  intensities  obtained  were  used  in  securing  the  relative 
utilization  efficiencies  of  the  various  lighting  sy6tems  tested. 

In  making  the  photometer  tests  stations  were  chosen  2  ft. 
apart  in  a  horizontal  plane  42  in.  (1.06  m.)  above  the  car  floor, 
over  one  quarter  of  the  floor  area.  The  entire  car,  however,  was 
equipped  with  lighting  units.  Five  readings  were  taken  at  each 
station,  on  a  portable  photometer,  recalibrated  before  each  test. 
In  order  to  make  one  reading  comparable  with  any  other,  sim- 
ultaneous voltage  readings  were  taken,  as  it  was  found  to  be 
impracticable  to  hold  constant  voltage  on  the  lamps.  Each 
photometer  reading  was  corrected  to  normal  voltage  from  the 
characteristic  curves  of  the  lamp  and  the  five  corrected  readings 
averaged  to  obtain  the  station  value.  In  obtaining  the  average 
intensity  for  the  entire  car,  weight  was  given  the  stations  in 
proportion  to  the  area  covered.  The  illumination  values  were 
also  calculated  for  85  per  cent,  normal  voltage,  in  order  to  see 
what  illumination  would  maintain  under  that  condition. 

The  same  lamps,  as  far  as  practicable,  were  used  in  the  various 
reflector  equipments.  As  the  tests  were  made  to  find  out  approxi- 
mately what  would  be  the  average  operating  condition  in  new 
cars,  and  not  to  determine  the  exact  efficiencies  of  the  different 
reflectors,  figures  were  based  on  the  manufacturers'  data  book 
ratings  of  the  lamps. 

It  was  decided  before  the  tests  started  that  tungsten  filament 
lamps  would  be  used  for  illuminants,  the  question  being  as  to  the 
best  method  of  applying  the  lamps.  Three  systems  of  illumina- 
tion were  tried  out,  i.  e.,  (a)  direct  lighting,  (b)  semi-indirect 
lighting,  (c)  totally  indirect  lighting.  In  working  up  various 
applications  of  these  three  systems,  a  study  was  made  of  existing 
installations,  supplemented  by  many  suggestions  for  improve- 
ment from  various  lighting  experts  and  practical  railway  men. 
In  order  to  carry  on  the  tests  the  interior  construction  of  the  car 
was  altered  when  necessary. 

Photographs  of  the  interior  of  the  car  were  taken  with  the 
lamps  burning.  The  exposures  were  timed  to  exactly  two  min- 
utes. These  photographs  were  intended  for  comparative  pur- 
poses only.     They  have  no  bearing  on  the  photometric  readings, 


230  TRANSACTIONS   I.    E.    S. — PART    I 

except  to  indicate   (in  a  comparative  way)   the  high  and  low 
lighting  throughout  the  car. 

The  direct  lighting  tests  made  were  as  follows: 

DIRECT  LIGHTING  TESTS. 

No.  1. — The  lighting  units  used  in  this  test  consisted  of  a 
single  row  of  14  6-in.  opal  glass  reflectors  (see  Fig.  6)  mounted 
along  the  center  line  of  the  ceiling  and  spaced  as  shown  in  Fig. 
2.  Ten  of  these  reflectors  were  equipped  with  56-watt  clear  bulb 
tungsten  railway  lamps  (wired  in  two  circuits  of  five  lamps  each 
in  series)  and  the  remaining  four  with  10- watt  clear  bulb  tung- 
sten emergency  lamps. 

The  variation  from  even  spacing  shown  on  Fig.  2  was  neces- 
sary on  account  of  the  construction  of  the  model  car,  but  would 
be  corrected  in  the  cars  as  finally  built.  The  light  distribution 
(Fig.  2)  was  good,  though  it  had  points  of  high  intensity  under 
the  emergency  lamps,  due  to  the  small  lamp  in  large  reflector. 
No  bare  lamp  filaments  were  visible  along  the  normal  line  of 
vision.  The  efficiency  of  the  system  was  high,  installation  costs — 
on  account  of  the  single  row  of  large  units — were  low,  and  main- 
tenance was  good,  the  smooth  surface  of  the  reflectors  facilitating 
rapid  cleaning.  The  general  appearance  of  the  lighting  system  in 
the  car  was  pleasing  (see  Fig.  7)  and  the  illumination  good, 
averaging  5.7  foot-candles  at  normal  and  3.2  at  85  per  cent, 
voltage,  with  an  energy  consumption  of  1.03  watts  per  square 
foot.  There  were  5.54  effective  lumens  per  watt  and  the  effective 
utilization  efficiency  was  68.7  per  cent.  It  is  interesting  to  note 
that  the  utilization  efficiency  in  an  ordinary  dark  yellow  trolley 
with  similar  equipment  is  about  30  per  cent.,  showing  the  great 
advantage  (from  an  efficiency-of-light-utilization  standpoint)  of 
the  white  enamel  interior  finish. 

No.  2. — The  second  direct  lighting  test  was  similar  to  the  first, 
except  that  clear  prismatic  reflectors  were  used.  The  change 
of  reflectors  raised  the  average  foot-candle  intensity  to  6.1  at 
normal  and  3.4  at  85  per  cent,  voltage.  The  effective  lumens  per 
watt  were  increased  to  5.90  and  the  utilization  efficiency  to  73.2 
per  cent.    The  maintenance  of  this  equipment  would  be  slightly 


GOVE    AND    PORTER:     CAR    LIGHTING    PROBLEMS 


231 


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2$2  TRANSACTIONS   I.   E.    S. — PART   I 

higher  than  with  the  glass  used  in  the  aforementioned  test,  due 
to  cleaning  the  prismatic  glass.  There  was  also  a  little  more 
glare,  though  not  an  objectionable  amount.  The  choice  between 
these  two  reflectors,  therefore,  is  largely  one  of  esthetic  taste. 

No.  3. — In  the  third  direct  lighting  test  5  94-watt  clear  tungsten 
filament  railway  lamps,  equipped  with  clear  prismatic  reflectors 
were  located  in  a  single  row  down  the  center  line  of  the  ceiling. 
Four  10-watt  tungsten  emergency  lamps  in  clear  prismatic  reflec- 
tors were  located  between  these.  The  resultant  average  intensity 
in  the  car  body  was  good,  but  due  to  the  relatively  low  hanging 
height  and  wide  spacing  of  the  units  the  distribution  was  very 
uneven  (see  Fig.  4).  The  installation  and  maintenance  of  the 
system  would  be  low,  on  account  of  the  small  number  of  large 
units  to  install  and  clean.  The  average  foot-candles  obtained 
were  5.0  at  normal  and  2.8  at  85  per  cent,  voltage.  The  energy 
consumption  was  0.87  watt  per  square  foot ;  effective  lumens  per 
watt  5.75;  and  effective  utilization  efficiency  71.5  per  cent. 

Xo  direct  lighting  tests  were  made  with  lighting  units  located 
on  the  half  decks.  Previous  experience  and  tests  had  shown 
that  center-deck  direct  lighting  may  produce  perfectly  satisfac- 
tory illumination,  free  from  sharp  shadows  and  glare.  It  was 
felt  that  the  possible  gain  of  a  few  per  cent,  in  efficiency  with  the 
half-deck  lighting  did  not  warrant  the  additional  installation  and 
maintenance  expense  (due  to  a  larger  number  of  smaller  units  to 
install  and  clean)  accompanying  this  system  of  lighting. 

SEMI-IXDIRECT  LIGHTING  TESTS. 

No.  1. — A  very  interesting  method  of  lighting  was  used  in  the 
first  test.  Twelve  special  80-watt  95-volt  turnip-shaped  tungsten 
lamps,  opal  dipped  over  the  tip  half,  were  installed  down  the 
center  line  of  the  ceiling.  Each  lamp  was  suspended  by  an 
inverted  white  enameled  cone,  shown  in  Fig.  8.  Three  10-watt 
tungsten  emergency  lamps  were  also  used  in  small  rosettes.  The 
80-watt  lamps  were  connected  six  in  series.  All  of  the  filament  of 
the  80-watt  lamps  was  located  below  the  center  of  the  bulb; 
hence,  none  of  it  was  in  the  line  of  vision.  The  opal  on  the 
lower  half  of  the  bulb  served  a  double  purpose,  i.  e.,  to  protect 


Fig.  5.— Outside  view  of  New  York  Municipal  Corporation's  subway  car. 


Fig.  6.— Showing  installation  of  56-watt  railway  tungsten  filament  lamps  in 
white  glass  reflectors. 


Fig   ;.— Lighting  effect  of  installation  shown  in  Fig.  6. 


Fig.  8.— Installation  of  12  special  80- watt,  95-volt,  turnip-shaped,  opal-dipped  bulb,  tungsten 
filament  lamps,  suspended  without  reflectors  from  white  euameled  cone  shaped 
fixtures. 


Fig.  9.— Installation  of  56-watt  tungsten  filament  railway  lamps  in  special  convex  reflector. 


Fig.  10.— Semi-indirect  lighting;  each  bowl  contains  two  94-watt  tungsten  filament 
railway  lamps  and  one  10-watt  tungsten  emergency  lamp. 


Fig.  ii. — fighting  effect  from  a  semi-indirect  installation  with  special  ceiling  insert. 


Fig. 12.—  Showing  installation  of  tungsten  filament  lamps  and  special  curved 
white  glass  screens. 


GOVE   AND   PORTER:     CAR   LIGHTING    PROBLEMS  233 

the  passengers'  eyes  from  the  glare  of  the  bare  filament  and  also 
to  reflect  the  light  up  to  the  ceiling.  The  particular  advantage  of 
this  system  of  lighting  was  that  it  eliminated  the  necessity  of 
reflectors,  special  holders  and  other  accessory  equipment;  thus 
lowering  both  installation  and  maintenance  costs.  The  illumina- 
tion was  fairly  uniform  (Fig.  3),  though  the  uneven  spacing 
necessitated  by  the  car  construction  made  it  unnecessarily  high  at 
the  center.  As  the  entrance  and  exit  doors  were  located  here, 
however,  this  was  no  great  objection.  The  average  intensity  was 
J.J  foot-candles  at  normal  and  5.1  at  85  per  cent,  voltage.  The 
energy  consumption  was  1.69  watts  per  square  foot,  the  effective 
lumens  per  watt  4.65,  and  the  utilization  efficiency  58.4  per  cent. 
The  appearance  of  the  car  lighted  was  pleasing.  The  lamps, 
being  located  on  the  center  line  of  the  car,  did  not  interfere  with 
the  clear  reading  of  advertising  signs  located  along  the  sides. 

Xo.  2. — In  the  second  semi-indirect  lighting  test  a  novel  equip- 
ment was  used  (Fig.  9).  Ten  56-watt  clear  tungsten  railway 
lamps  were  located  on  the  center  line  of  the  ceiling,  supplemented 
by  4  10-watt  tungsten  emergency  lamps.  Six  inches  (15.2  cm.) 
below  the  ceiling  and  extending  the  entire  length  of  the  car,  was 
suspended  a  reflector  consisting  of  a  white  enameled  board  11  in. 
(28  cm.)  wide,  convex  on  a  16- in.  (0.4  m.)  radius.  The  bowls 
of  the  56-watt  lamps  extended  through  holes  cut  in  this  reflector. 
Under  each  hole  was  fastened  a  white  glass  dish  to  diffuse  the 
glare  of  the  bare  lamp  filament.  The  spacing  of  the  lamps  is 
shown  in  Fig.  13.  The  plan  in  using  this  combination  was  to 
utilize  as  much  as  possible  of  the  direct  light  from  the  lamp,  to 
illuminate  the  advertising  signs ;  the  indirect  light  to  give  even 
distribution  and  the  direct  light  to  brighten  up  the  under  side 
of  the  reflectors.  Distribution  curves  from  this  equipment  are 
shown  in  Fig.  13.  The  light  distribution  was  good,  but  the 
intensity  low,  averaging  3.9  foot-candles  at  normal  and  2.2  at 
85  per  cent,  voltage.  The  watts  per  square  foot  were  1.03;  effec- 
tive lumens  per  watt  3.81 ;  and  the  effective  utilization  efficiency 
was  47.2  per  cent.  The  resultant  illumination  was  pleasant,  but 
the  appearance  of  the  lighting  equipment  was  rather  crude,  sug- 
gesting a  watering  trough  down  the  center  of  the  car.  It  was  a 
curious  fact  that  while  both  sides  of  the  reflector  and  the  ceiling 


234  TRANSACTIONS    I.    E.    S. — PART    I 

were  painted  alike,  the  under  side  of  the  reflector  appeared  grey. 
due  to  the  lower  intensity  of  light  on  it. 

Another  test  was  conducted  on  this  same  equipment  with  the 
interior  finish  of  the  car  silver  grey  instead  of  white.  This 
change  lowered  the  effective  utilization  efficiency  about  10  per 
cent. 

The  next  semi-indirect  equipment  tested  consisted  of  10  94- watt 
tungsten  railway  lamps  equipped  with  5  13-in.  (33  cm.)  white 
glass  bowls,  mounted  down  the  center  line  of  the  ceiling.  There 
were  2  94- watt  lamps  and  1  10- watt  emergency  lamp  in  each  bowl. 
(See  Fig.  10).  The  bowls  were  hinged,  allowing  of  lowering 
for  cleaning  and  lamp  replacement.  The  bowls  were  suspended 
with  their  tops  located  12  in.  below  the  center  of  the  ceiling. 
The  illumination  from  this  system  was  very  uneven,  being  high 
directly  under  the  units  and  low  between  them  (see  Fig.  14). 
The  average  intensity  was  5.7  and  3.2  foot-candles  at  normal  and 
85  per  cent,  voltage,  respectively;  watts  per  square  foot  1.69; 
effective  lumens  per  watt  3.36;  and  effective  utilization  efficiency 
41.5  per  cent. 

In  order  to  determine  the  effect  of  the  shape  of  the  ceiling  on 
the  light  distribution,  a  special  headlining  consisting  of  a  white 
enameled  insert,  having  a  3  ft.  (0.91  m.)  span  on  an  18  in. 
(0.45  m.)  radius,  was  inserted  and  the  test  repeated.  Fig.  11 
shows  the  appearance  of  the  insert  and  illumination  effect.  This 
resulted  in  raising  the  average  foot-candles  to  6.1  and  3.4  at 
normal  and  85  per  cent,  voltage,  respectively ;  effective  lumens  per 
watt  to  3.62 ;  and  the  utilization  efficiency  to  44.7  per  cent.  The 
distribution  curves  of  this  equipment  are  shown  in  Fig.  15. 

The  insert  was  then  removed  and  the  test  repeated  with  a  dif- 
ferent spacing  of  the  units.  This  resulted  in  a  little  improve- 
ment in  distribution.  The  principal  trouble  with  this  installation 
was  that  the  headroom  in  the  car  was  not  sufficient  to  allow  the 
lighting  units  to  be  hung  the  proper  distance  below  the  ceiling. 

The  next  equipment  tested  required  special  reflecting  devices. 
Ten  56-watt  clear  tungsten  railway  lamps  were  located  in  a  single 
line  down  the  center  of  the  ceiling,  with  5  10- watt  all-frosted  emer- 
gency lamps  in  rosettes  between  them.  Each  56-watt  lamp  was 
equipped  with  a  screen  made  from  a  circular  piece  of  glass  bent 


i 


GOVE   AND   PORTER:     CAR   LIGHTING    PROBLEMS  235 

over  a  cylinder  (Fig.  12).  This  resulted  in  a  screen  11  in. 
(27.9  cm.)  long  by  8  in.  (20.3  cm.)  wide  by  3  in.  (7.62  cm.) 
deep.  When  these  screens  were  hung  beneath  the  lamps  with 
their  open  ends  towards  the  sides  of  the  car,  it  was  impossible 
to  see  the  lamp  filaments  from  any  part  of  the  passenger  car 
body;  at  the  same  time  the  direct  light  from  a  considerable 
portion  of  the  lamp  fell  on  the  ceiling  and  reached  the  reading 
plane  with  but  one  reflection,  making  the  system  fairly  efficient. 
The  distribution  lengthwise  of  the  car  was  even,  though  the  out- 
board seats  received  considerably  less  light  than  the  center  aisle 
of  the  car  (Fig.  20).  The  average  intensity  was  4.8  and  2.7  foot- 
candles  at  normal  and  85  per  cent,  voltage;  the  energy  consump- 
tion 1.04  watts  per  square  foot;  effective  lumens  per  watt  4.63; 
and  effective  utilization  efficiency  57.6  per  cent.  The  chief  ad- 
vantage of  this  equipment  was  the  ease  with  which  the  reflectors 
could  be  cleaned.  The  appearance  of  the  car  lighted  was  rather 
pleasing. 

TOTALLY  INDIRECT  TESTS. 

No.  1. — The  first  totally  indirect  equipment  tried  consisted  of 
8  special  indirect  fixtures,  these  being  white  porcelain  enameled 
on  steel,  i$y2-'m.  (39.  cm.)  in  diameter  and  5^2  in.  (16.  cm.) 
deep  (Fig.  16).  Each  fixture  contained  3  36-watt  tungsten 
lamps  mounted  vertically.  The  fixtures  were  hung  in  a  single 
row  down  the  center  line  of  the  ceiling,  the  tops  of  the  reflectors 
being  13  in.  (33.  cm.)  below  the  ceiling.  The  spacing  of  the 
units  is  shown  on  Fig.  21.  The  resultant  illumination  was  uni- 
form and  of  fairly  good  intensity,  averaging  5.1  and  3.2  foot- 
candles  at  normal  and  85  per  cent,  voltage,  for  an  energy  con- 
sumption of  1.47  watts  per  square  foot.  The  effective  lumens 
per  watt  were  3.43  and  the  effective  utilization  efficiency  was 
46.3  per  cent.  The  chief  drawback  of  these  fixtures  was  their 
liability  to  catch  and  collect  much  dirt,  thus  materially  reducing 
their  efficiency ;  also,  to  obtain  good  distribution  it  was  necessary 
to  hang  them  so  low  that  they  might  be  in  the  way  of  tall  passen- 
gers. 

No.  2. — In  order  to  get  away  from  a  low  fixture  in  the  center 
line  of  the  car,  the  next  equipment  tested  consisted  of  20  36-watt 
tungsten  railway  lamps  in  indirect  reflectors.    These  were  mounted 


236 


TRANSACTIONS  I.   E.   S. — PART    I 


3*,y^  ,Z?  "O  aw*?  *o°j    -i,j~oz'*e/Y 


Fig.  16.— Installation  of  special  indirect  fixtures.    Each  fixture  contains  thtee  36-watt 
tungsten  filament  railway  lamps.    Light  distribution  shown  in  Fig.  15. 


Fig.  17.— Special  installation  of  indirect  lighting.    Reflectors  set  in  coves,  ten  on  each 
side.    Ceiling  rosettes  for  emergency  lighting. 


Fig.  iS.— Indirect  lighting  from  units  on  center  stanchions  and  grab  rails. 


pigi  i9— Lighting  equipment  finally  adopted,  consisting  of  fifteen  56-watt.  bowl-frosted 
tungsten  filament  railway  lamps  in  white  glass  reflectors,  supplemented  by  six  10-watt. 
round  bulb,  all-frosted  tungsten  filament  lamps  for  emergency  lighting.  Installation 
finally  adopted. 


GOVE    AND    PORTER:     CAR    LIGHTING    PROBLEMS  237 

in  two  rows  of  ten  each  on  the  sides  of  the  car,  just  above  the 
deck  sill  between  the  ventilators,  as  shown  in  Fig.  17.  Five  10-watt 
frosted  lamps  in  rosettes  were  mounted  on  the  ceiling  for  emer- 
gency lamps.  The  36-watt  lamps  were  mounted  horizontally  with 
their  centers  7  ft.  4  in.  (2.25  cm.)  above  the  floor.  The  spacing 
of  the  lighting  units  and  the  distribution  therefrom  is  shown  in 
Fig.  22.  The  resultant  illumination  was  of  low  intensity,  aver- 
aging 3.5  and  2.2  foot-candles  at  normal  and  85  per  cent,  voltage. 
The  wattage  consumption  was  1.32  per  square  foot;  effective 
lumens  per  watt  were  2.67 ;  and  effective  utilization  efficiency  was 
36.3  per  cent.  The  main  objection  to  this  system  was  the  prob- 
lem of  keeping  the  reflectors  clean. 

Xo.  3. — The  last  test  was  made  on  12  94- watt  tungsten  rail- 
way lamps  in  indirect  reflectors  and  5  10- watt  emergency  lamps 
in  rosettes,  located  down  the  center  line  of  the  ceiling.  In  order 
to  get  maximum  headroom  for  these  reflectors  and  still  have  them 
out  of  the  way  of  passengers,  special  inverted  cone-shaped  con- 
tainers for  the  reflectors  were  built  into  the  stanchions  along  the 
center  line  of  the  car  (Fig.  18).  Unfortunately  the  construction 
of  the  car  necessitated  spacing  the  units  rather  far  apart,  so  that 
uneven  illumination  resulted.  In  addition  to  the  bowls,  smaller 
inverted  bowls  were  mounted  on  the  horizontal  grab  rails,  at 
points  shown  in  Fig.  23.  Each  of  these  contained  1  94-watt 
tungsten  lamp,  making  a  total  of  12  94-watt  and  5  10-watt  lamps 
in  the  car.  The  average  foot-candles  were  8.5  and  4.7  at  normal 
and  85  per  cent,  voltage ;  watts  per  square  foot  2.01 ;  effective 
lumens  per  watt  4.21 ;  and  the  utilization  efficiency  was  53.4  per 
cent.  Considerable  difficulty  would  be  experienced  in  keeping 
this  equipment  clean  and  free  from  refuse. 

The  tables  in  the  Appendix  gives  general  summary  of  the 
tests. 

IMPORTANT  CONSIDERATIONS. 

In  studying  the  tests  to  choose  the  final  method  of  lighting,  the 
following  condsiderations  were  carefully  weighed : 

General  Effect  and  Appearance. — The  general  effect  and 
appearance  of  each  system  under  test  were  judged  by  comparison 
with  present  methods  (in  general)  of  car  lighting  for  similar 
service,  i.  e.,  with  the  use  of  tungsten  lamps  but  without  reflectors. 


238  TRANSACTIONS   I.    E.    S. — PART    I 

Under  this  item  was  also  considered  the  effect  of  the  distribution 
of  light  on  the  various  parts  of  the  car. 

Lack  of  Eyestrain. — In  comparing  the  various  systems  tested, 
the  effect  of  the  light  on  the  eyes  was  particularly  noted  by  a 
large  number  of  observers. 

Base  in  Reading  for  Seated  and  Standing  Passengers. — In 
comparing  the  three  methods  of  lighting — direct,  indirect  and 
semi-indirect — particular  attention  was  given  to  the  possible 
shadows  thrown  on  reading  matter  of  seated  passengers,  by  pas- 
sengers standing  in  a  crowded  car.  In  some  cases  it  was  found 
that  passengers  could  obtain  proper  light  in  any  position ;  in 
others  it  was  necessary  for  them  to  move  in  their  seats,  often  to 
uncomfortable  positions,  to  obtain  proper  light. 

Efficiency  of  System. — The  efficiencies  of  the  various  lighting 
systems  tested  differed  widely.  In  some  cases  this  was  largely 
due  to  the  type  of  reflector  used;  in  others  to  the  position  of  the 
reflector,  shape  of  the  ceiling,  etc.  In  several  tests  it  was  evi- 
dent that  improvement  could  be  made  by  changes.  Should  any 
one  system  meet  with  particular  favor  in  all  other  respects,  it 
was  considered  probable  the  efficiency  could  be  raised  by  a  more 
detailed  study. 

Maintenance. — The  question  of  maintenance  was  serious. 
Some  of  the  most  desirable  arrangements  of  reflectors  and  lights 
were  handicapped  by  the  dust  problem.  With  a  large  number  of 
small  units  this  difficulty  increases.  Various  methods  of  keeping 
reflectors  and  ceiling  clean  were  considered. 

Pozcer  Consumption. — In  order  to  secure  a  reasonable  oper- 
ating cost,  low  power  consumption  was  considered  one  of  the 
important  factors.  The  indirect  system  of  lighting  required  con- 
siderably more  power  than  the  direct,  while  the  semi-indirect 
came  between  these  two. 

Depreciation. — The  relative  loss  of  reflecting  power,  due  to 
accumulation  of  dust  on  the  various  types  of  reflectors,  was  also 
given  careful  consideration. 

Emergency  Lighting. — It  was  decided  that  sufficient  light 
would  be  obtained  from  the  emergency  lights  to  permit  clearly 
distinguishing  people  and  various  objects  in  the  car  with  main 
lamps  extinguished. 


GOVE   AND    PORTER:     CAR   LIGHTING    PROBLEMS 


239 


24O  TRANSACTIONS   I.    E.    S. — PART    I 

RESULTS. 

A  thorough  study  of  all  these  conditions  finally  led  to  the  adop- 
tion of  a  single  line  of  15  56-watt  bowl-frosted  tungsten  railway 
lamps  down  the  center  line  of  the  ceiling,  equipped  with  reflec- 
tors as  shown  in  Fig.  19,  supplemented  by  6  10-watt  all-frosted 
round  bulb  tungsten  emergency  lamps.  This  system  was  chosen 
as  the  one  containing  the  highest  percentage  of  the  desirable 
factors — satisfactory  illumination,  low  power  consumption,  low 
maintenance  and  upkeep  and  pleasing  appearance  with  the  lamps 
both  lighted  and  extinguished. 

The  spacing  of  the  reflectors  was  arranged  to  be  symmetrical. 
One  unit  was  placed  on  each  end  bulkhead  of  the  car  to  bring 
up  the  illumination  at  these  points.  The  emergency  lamps  were 
placed  in  rosettes,  one  being  located  on  the  side  wall  over  each 
pair  of  doors.  These  lamps  do  not  burn  while  there  is  power 
on  the  line,  but  the  instant  that  fails  the  emergency  lamps  are 
automatically  thrown  onto  a  storage  battery. 

Fig.  19  shows  the  interior  of  the  car  as  finally  equipped.  The 
illumination  averaged  5.94  foot-candles  at  normal  and  3.85  at 
85  per  cent,  voltage.  The  energy  consumption  was  1.44  watts 
per  square  foot;  effective  lumens  per  watt  4.14;  and  the  utiliza- 
tion efficiency  50.6  per  cent.  These  data  are  not  comparable  with 
the  other  tests,  due  to  the  use  of  bowl-frosted  lamps  (instead  of 
clear),  also  a  larger  number  and  different  arrangement  of  light- 
ing units.    Distribution  curves  are  given  in  Fig.  24. 

It  was  interesting  to  note  that  the  low  intensities  of  illumina- 
tion, at  stations  7  and  17  (Fig.  24),  are  opposite  the  entrance 
doors,  which  are  dark  green,  in  comparison  to  the  white  finish 
between  doors.  The  curves  were  slightly  high  at  stations  2,  3 
and  4,  due  to  the  fact  that  the  end  lamps  are  located  on  the  bulk- 
heads considerably  lower  than  the  rest  of  the  lamps  in  the  car. 

On  the  whole,  the  illumination  is  remarkably  soft,  even  and 
pleasing.  It  is  not  possible  to  note  any  unevenness  with  the  naked 
eye.  The  use  of  bowl-frosted  lamps  lowers  the  efficiency  a  little, 
but  also  eliminates  glare,  even  when  looking  directly  up  at  the 
lamp. 

In  addition  to  the  general  illumination  there  are  other  uses  of 
lamps,  in  connection  with  the  signal  system,  which  may  be  of 


GOVE    AND    PORTER:     CAR    LIGHTING    PROBLEMS 


241 


interest.  There  is  a  series  circuit  going  through  a  contact  on 
each  door  in  the  car  and  on  all  doors  in  the  train  when  more 
than  one  car  is  used.  This  circuit  also  goes  through  two  2-candle- 
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the  motorman.  When  all  doors  are  closed  one  of  the  lamps  lights 
up  and  until  this  occurs  it  is  impossible  to  start  the  train.  Two 
lamps  are  used  for  safety.     If  one  fails  the  other  is  thrown  in 


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from  the  system  of  indirect  illumination  bowl-frosted  railway  tungsten  lamps  in  white 
shown  in  Fig.  18.  Construction  of  car  glass  reflectors,  and  six  10-watt  frosted  emer- 
necessitated  spacing  units  rather  far  apart.         gency  in  rosettes  o\'er  side  doors.     Installation 

shown  in  Fig.  19.     Equipment  finally  adopted. 

circuit.  The  coupling  of  any  number  of  cars  together  auto- 
matically arranges  the  circuits  so  that  the  lamps  on  the  con- 
trollers, other  than  those  on  the  two  opposite  ends  of  the  train, 
do  not  burn. 

Block  signal  lights  are  located  in  the  cab,  i.  e.,  instead  of  hav- 
ing the  signals  aside  of  or  above  the  track,  as  is  usual ;  the  signal 
is  located  in  the  car  in  front  of  and  slightly  to  the  right  of  the 
controller.  The  signal  consists  of  three  lights — red,  green  and 
yellow — each  containing  a  32-volt  tungsten  filament  lamp  of  about 


242  TRANSACTIONS    I.    E.    S. — PART    I 

10  watts  capacity.  It  is  planned  to  use  double  filaments  in  these 
lamps,  so  that  when  one  fails  the  other  will  still  be  in  operation. 
If  the  signal  is  set  to  stop  and  is  not  obeyed,  within  a  certain 
distance,  a  warning  whistle  blows  near  the  motorman,  and  if 
the  signal  remains  unheeded  a  certain  further  distance,  the  brakes 
are  automatically  set.  Coupling  two  or  more  cars  together  also 
cuts  out  the  signals  in  the  cabs  other  than  the  two  on  the  ends 
of  the  train.  A  small  32- volt  ^-candlepower  tubular  carbon  lamp 
is  also  installed  over  each  air  gauge. 

The  end  of  each  car  carries  two  classification  lamps,  10-watt, 
34-volt,  on  the  roof  (Fig.  5).  Colored  screens  are  used  in  these 
to  obtain  the  different  destination  indications.  These  lamps  are 
also  automatically  cut  out  between  cars  where  two  or  more  are 
coupled  together. 

At  the  ends  of  each  car,  over  the  bumper,  are  located  4  10-watt, 
40-volt,  signal  lamps  back  of  lenses ;  one  above  the  other — two 
on  each  side  of  the  car.  The  upper  is  red  and  the  lower  white. 
On  the  front  end  the  white  ones  only  burn;  on  the  rear  the  red 
only.  Reversing  the  controller  automatically  changes  these  end 
indications.  These  lamps  also  are  cut  out  between  cars  of  a 
train. 


GOVE   AND    PORTER!     CAR   LIGHTING   PROBLEMS 


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J44  TRANSACTIONS   I.    E.    S. — PART    I 

BIBLIOGRAPHY. 

Street  Car  Lamp  Tests  in  Chicago. 

Electrical  Review  and  Western  Electrician,  Oct.  14,  191 1. 
High  Efficiency  Lamps  for  Street  Railway  Service,  by  S.  E.  Doane. 

Electric  Railway  Journal,  May  4,  1912. 
Test  of  Car  Lighting  with  Mazda  Lamps  and  Holophane  Reflectors. 

Electric  Railway  Journal,  Sept.  28,  1912. 
Tungsten  Lamps  in  Car  Lighting. 

Electrical  World,  Oct.  5,  1912. 
Car  Lighting. 

Electrical  Traction,  Mar.,  1913. 
Metallic  Filament  Lamps  for  Lighting  Street  Railway  Cars. 

Electrical  World,  Apr.  19,  1913. 
Illumination  of  Tramway  Cars. 

London  Electrician,  Sept.  5,  I9T3- 
Economical  Lighting  of  Street  Cars,  by  S.  G.  Hibben  and  E.  M.  Smith. 

Electric  Journal,  June,  1913. 
Street  Railway  Illumination,  by  S.  G.  Hibben. 

Electrical  Review  and  Western  Electrician,  Oct.  4,  1913. 
Street  Car  Lighting,  by  L.  C.  Porter. 

Lighting  Journal,  Oct.,  1913. 
Improvements  of  Street  Car  Illumination. 

Electrical  Review  and  Western  Electrician,  Oct.  22,  1913. 
Toledo  Railways  Adopt  Improved  Lighting  for  their  Cars. 

Electrical  Review  and  Western  Electrician,  Oct.  25,  1913. 
Argentine  Tram  Car  Lighting. 

Electrical  Review,  Nov.  7,  1913. 
Illumination  of  Street  Railway  Cars,  by  L.  C.  Porter. 

Electrical  Review  and  Western  Electrician,  Nov.  8,   1913. 
Electric  Railway  Car  Lighting,  by  J.  R.  Cravath. 

Electric  Railway  Journal,  Nov.  15,  1913. 
Improvement  of  Street  Car  Illumination. 

Electrical  Review  and  Western  Electrician,  Nov.  22,  1913. 
Illumination  of  Street  Railway  Cars,  by  H.  M.  Ryder. 

Lighting  Journal,  Dec,  1913. 
Latest  Practise  in  Street  Railway  Lamps,  by  V.  L.  Staley. 

General  Electric  Review,  Dec,  1913. 
Modern  Practise  in  Street  Railway  Illumination,  by  S.  G.  Hibben. 

Illuminating  Engineering  Society  Transactions,  Dec,  1913. 
Chicago  City  Railways'  New  Cars. 

Electric  Railway  Journal,  Dec.  20,  1913. 
The  Illumination  of  Street  Railway  Cars,  by  G.  H.  Stickney. 

Electric  Railway  Journal,  Dec.  20,  1913. 
The  Private  Car  "New  Jersey." 

Electric  Railway  Journal,  Dec.  27,  1913. 


GOVE   AND    PORTER:     CAR   LIGHTING    PROBLEMS  245 

The  Illumination  of  Street  Cars,  by  L.  C.  Porter  and  V.  L.  Staley. 

Illuminating  Engineering  Society  Transactions,  Jan.,  1914. 
The  1913  Motor  Cars  of  the  Chicago.  Railways. 

Electric  Railway  Journal,  Jan.  17,  1914. 
Report  of  Western  Association  of  Electrical  Inspectors  on  Car  Wiring. 

Electrical  World,  Jan.  31,  1914. 
Photometric  Tests  in  Railway  Cars,  by  L.  C.  Porter. 

Lighting  Journal,  Apr.,  1914. 
Recent  Progress  in  Street  Car  Lighting,  by  G.  H.  Stickney. 

Electric  Railway  Journal,  May  2,  1914. 
Car  Lighting  Discussed  by  Experts,  G.  H.   Stickney,  C.  O.  Bond,  P.   S. 
Millar,  E.  W.  Hoist,  J.  Corning  and  others. 

Street  Railway  Bulletin,  May,  1914. 
Storage  Battery  Lighting  on  New  York  Central  R.  R.  Cars. 

Electric  Railway  Journal,  June  6,  1914. 
Capitol  Traction  Company's  Semi-steel  Cars. 

Electric  Railway  Journal,  July  31,  1914. 
Report  of  Committee  of  American  Electric  Street  Railway  Association — 
Modern  Car  Lighting. 

Electric  Railway  Journal,  Oct.  24,  1914. 
Car  Lighting,  Chicago,  Lake  Shore  and  South  Bend  Railway. 

Electric  Railway  Journal,  Dec.  12,  1914. 

DISCUSSION. 

Mr.  T.  W.  Rolph  :  The  authors  of  this  paper  have  pre- 
sented us  with  some  extremely  valuable  data,  and  we  are  fortu- 
nate in  having  this  available  for  future  use,  in  car  lighting  prac- 
tise. There  is  an  interesting  point  which  I  would  like  to  bring 
out,  and  that  is  in  regard  to  per  cent,  utilization  efficiency  ob- 
tained. I  have  a  record  of  some  car  lighting  tests,  which  were 
conducted  by  the  Indianapolis  Traction  Terminal  Company,  in 
Indianapolis,  in  May  of  last  year.  There  were  recorded  in  a 
paper  presented  before  the  Pittsburgh  section  last  November  by 
Mr.  L,.  C.  Doane.f  The  efficiency  obtained  with  a  prismatic 
system,  using  56-watt  lamps,  was  46.1;  whereas  with  these  tests 
the  efficiency  obtained  was  73.2.  Similarly  with  a  unit  of  medium 
density  opal,$  the  efficiency  obtained  in  the  Indianapolis  test  was 
40.2 ;  while  the  efficiency  here  is  68.7.  This  difference  is  due  to 
the  finish  of  the  cars.  We  have  obtained  in  the  tests  recorded 
here,  probably  the  highest  utilization  efficiencies  that  have  ever 

t  Modern  Street  Car  Lighting,  Trans.  I.  E.  S.,  vol.  X,  p.  S2,  (1915). 
I  "Sudan"  glass. 


246  TRANSACTIONS   I.    E.    S. — PART    I 

been  obtained  in  general  commercial  work.  The  subway  people 
are  to  be  congratulated  on  obtaining  efficiencies  very  appreciably 
beyond  those  which  have  been  obtained  in  other  classes  of  light- 
ing. 

Mr.  S.  G.  Hibben  :  To  the  companies  which  have  made  such 
a  thorough  investigation  of  car  lighting  in  this  instance,  there  is 
more  than  ordinary  credit  due,  both  for  the  standard  and  detail 
of  the  work,  and  also  because  a  good  deal  of  this  car  lighting  is 
still  pioneering.  The  engineers  of  this  investigation  and  the 
authors  of  the  paper  deserve  a  large  measure  of  thanks. 

The  night  before  last  in  Pittsburgh  at  a  section  meeting  of  the 
society  certain  men,  who  are  supposed  to  know  a  great  deal  about 
car  lighting  equipment,  made  the  statement  that  in  several  cars 
where  the  tungsten  lamp  had  been  tried  in  conjunction  with 
globes,  the  illumination  was  poorer  and  of  less  amount  than  when 
bare  unshaded  carbon  lamps  were  used.  On  looking  into  that 
pessimistic  statement,  I  found  that  the  experience  of  those  par- 
ticular men  was  that  the  lamps  had  been  used  in  prismatic  hemis- 
pheres against  the  ceilings  of  the  cars.  The  comparative  inef- 
ficiency of  such  glassware  used  thus,  and  its  dustiness,  was  a  very 
unfair  argument  against  the  general  use  of  tungsten  lamps  and 
reflectors. 

Some  criticisms  that  have  been  made  against  the  economy  of 
tungsten  lamps  came  from  the  fact  that  the  lamps  were  stolen,  and 
not  broken,  and  that  loss  might  be  mentioned  here  in  connection 
with  the  comparison  between  center-deck  and  side-deck  lighting. 
I  have  experienced  cases  where  lamps  placed  low  along  the  side 
decks  were  stolen  quite  often.  The  lamps  along  the  center  deck 
were  out  of  reach  and  did  not  disappear  so  fast.  I  believe  these 
losses  may  be  reduced  through  the  use  of  the  marine  type  socket 
or  receptacle.  The  coiled  spring  into  which  the  lamp  base  screws 
not  only  prevents  the  lamp  from  shaking  out,  but  also  prevents 
it  from  being  easily  unscrewed  and  stolen. 

Concerning  the  glass  reflectors,  I  want  to  call  attention,  in  the 
first  place,  to  the  inadvisability  of  using  any  blown  glass  reflec- 
tors on  which  many  manufacturers  leave  a  ground  or  rough  edge. 
On  account  of  the  method  of  manufacture,  the  blown  reflectors 
in  their  first  stage,  are  completely  closed,  and  afterwards   are 


CAR   LIGHTING    PROBLEMS  247 

broken  off  at  the  bottom,  and  ground  straight.  If  this  roughed 
edge  is  not  fire-polished,  it  in  time  will  gather  dirt  and  appear 
as  a  dark  edge. 

There  is  just  one  experience  I  have  had  in  the  failure  from 
breakage  of  glass  reflectors  in  car  lighting  service  where,  under 
very  extreme  conditions  of  rough  service,  several  shades  which 
were  poorly  held  by  the  glass  lip  only,  were  broken  around  the 
upper  part.  The  type  of  holder  which  has  the  inner  flange  will, 
of  course,  prevent  that  sort  of  breakage. 

If  the  ceiling  finish  of  the  tested  car  as  herein  reported  was 
polished  or  glossy,  the  results  from  the  indirect  or  semi-indirect 
units  might  not  be  as  good  as  in  the  case  of  depolished  ceilings. 
Light  from  the  curved-plate  units  especially  would  be  directed 
against  the  sides  of  the  car  by  specular  ceiling  reflection,  and 
would  be  largely  lost. 

Regarding  cleaning  costs,  I  would  like  to  get  some  more 
figures  on  that  subject  if  there  are  any  available.  After  a  year 
or  two,  about  the  best  data  I  have  on  hand  shows  an  expense  of 
about  7  cents  to  10  cents  per  unit  per  month  for  cleaning  ex- 
penses. That  I  believe  involves  wiping  the  reflector,  dry,  three 
times  a  month  and  washing  it  with  water  once  a  month.  If  the 
reflectors  have  any  kind  of  crevices,  as  in  the  case  of  prisms,  or 
if  the  elaboration  is  a  design  with  horizontal  lines,  the  expense 
of  cleaning  may  be  considerably  greater. 

These  cars  are  I  suppose  arranged  with  three  circuits  of  lamps. 
In  case  of  one  lamp  failure  the  illumination  is  cut  down  to 
approximately  two  thirds  of  its  former  value,  which  still  is,  I 
believe,  sufficiently  high.  To  those  unacquainted  with  some  other 
practises,  fifteen  36-watt  lamps  for  a  car  are  sometimes  consid- 
ered too  many,  and  arrangements  have  been  made  with  either 
two  circuits  of  five  lamps  each,  or  one  circuit  of  five  larger 
lamps,  and  using  a  selector  switch  which  will  short-circuit  a 
burned-out  lamp,  and  simultaneously  place  in  the  circuit  an 
auxiliary  lamp.  One  good  feature  of  this  arrangement  is  that  by 
using  a  three-point,  or  three-way  switch,  interurban  cars  which 
load  and  unload  at  definite  stations  can  be  lighted  at  both  plat- 
forms or  at  either  platform,  while  one  regular  unit  in  the  center 
of  the  car  would  be  temporarily  cut  out. 
4 


248  TRANSACTIONS   I.   K.   S. — PART   I 

There  is  at  least  one  other  system  of  wiring  with  features  of 
special  interest,  where  there  are  ten  no-volt  lamps  in  series,  on  a 
circuit  of  1,100  or  1,200  volts.  One  of  the  peculiar  features  in 
this  case,  is  that  the  large  or  mogul  base  lamps  are  necessary, 
because  with  the  failure  of  one  lamp  the  open  circuit  voltage 
across  the  base  of  this  lamp  would  be  that  of  the  line,  and  would 
tend  to  arc  over  the  distance  separating  the  contact  points  of 
ordinary  Edison  base  lamps. 

Mr.  G.  H.  Stickxey:  This  paper  presents  a  more  complete 
and  comprehensive  set  of  car  lighting  data  than  has  heretofore 
been  available.  The  fact  that  the  different  lighting  arrangements 
have  been  tried  out  in  the  same  car  and  under  the  same  conditions 
gives  unusual  value  to  the  comparative  results.  In  the  past  it 
has  been  impossible  to  eliminate  variations  due  to  difference  in 
shape  of  cars,  finishes,  window  areas,  etc.  We  are  certainly 
indebted  to  the  New  York  Municipal  Railway  Corporation  and 
Brooklyn  Rapid  Transit  Company  for  giving  out  the  information. 
I  know  they  have  hesitated  to  do  so  lest  it  work  injury  or  injus- 
tice to  excellent  types  of  equipment  which  for  their  conditions 
were  not  so  suitable  as  some  other  types.  I  believe  this  factor 
had  something  to  do  with  the  omission  of  more  general  conclu- 
sions. The  practical  conclusion  of  the  tests  is,  of  course,  indi- 
cated by  the  lighting  plan  selected.  The  simple  presentation  of 
the  facts,  as  given  in  this  paper,  is  a  pleasant  contrast  to  some 
papers  in  which  authors  draw  sweeping  conclusions  apparently 
not  warranted  by  the  data  presented. 

The  effect  of  the  light  finish  of  cars,  brought  up  by  Mr.  Rolph, 
is  exceedingly  important  and  often  does  not  receive  sufficient 
attention  from  railway  companies.  A  light  finish  in  the  lower 
part  of  the  car  is  not  especially  advantageous  and  is  easily  soiled. 
In  the  upper  part,  however,  a  light  finish  not  only  helps  to  econo- 
mize the  light,  but  adds  to  the  diffusion  and  evenness  of  distri- 
bution. 

One  of  the  serious  problems  of  applying  the  reflector  method 
of  car  lighting  was  that  of  securing  a  satisfactory  holder  for 
the  reflectors.  The  holder  shown  here  to-night  has  more  good 
features  than  any  other  I  have  seen.  It  has  seemed  objectionable 
to  some  to  use  the  2>4  in.  fitter  rather  than  the  more  common 


CAR   LIGHTING   PROBLEMS  249 

2^4  m- 1  but,  as  both  prismatic  and  white  glass  reflectors  with 
this  fitter  are  available,  this  would  hardly  seem  to  me  serious ; 
while  the  other  advantages  which  can  be  obtained  with  the  larger 
fitter  would  seem  to  me  to  be  important.  The  holder  clamps  the 
reflector  in  such  a  way  that  it  cannot  possibly  fall  unless  com- 
pletely shattered.  The  glass  is  supported  from  below  independent 
of  the  flange.  The  larger  opening  permits  the  use  of  stronger 
porcelains  on  the  socket  and  therefore  provides  safer  insulation. 
The  large  wiring  space  makes  it  more  convenient  and  safer  to 
wire  with  the  heavily  insulated  cables  required  on  street  railway 
circuits. 

A  spring  socket  protects  the  lamp  from  excessive  vibration. 
While  this  does  not  entirely  prevent  stealing  of  lamps,  it  renders 
their  unauthorized  removal  more  difficult. 

Most  of  the  lock-sockets  with  which  I  am  familiar  cannot  be 
used  with  reflectors. 

Very  little  trouble  from  stealing  has  been  encountered  as  far 
as  I  am  able  to  learn.  Practically  all  lamps  stolen  are  taken  by 
employees  when  the  cars  are  in  the  car  houses.  It  would,  there- 
fore, seem  that  the  best  way  of  overcoming  it  would  be  through 
discipline  of  employees,  just  as  in  the  case  of  an  office  or  indus- 
trial establishment. 

Mr.  Frank  M.  BrinckerhofF:  This  paper  gives  very  inter- 
esting details  of  the  tests.  One  feature,  always  difficult  to  decide, 
is  the  commercial  value  of  any  lighting  system.  It  is  hard  to 
place  a  value  on  the  lighting  of  passenger  cars,  except  as  it  affects 
the  traffic  of  the  road.  If  two  car  lighting  methods  are  in  use 
on  the  same  train,  it  can  easily  be  noted  that  the  cars  which  are 
improperly  lighted  carry  but  few  passengers  as  compared  with 
cars  which  are  better  lighted,  and  one  can  thus  possibly  place  a 
relative  value  on  the  lighting  systems.  The  New  York  Municipal 
Railway  cars  are  to  be  in  the  subway  about  one  third  of  the 
entire  time  of  their  operation;  therefore,  the  lighting  problem  is 
of  considerable  interest,  during  the  day  as  well  as  during  the 
night.  Of  course,  with  the  ordinary  trolley  car,  operating  on  the 
surface  and  requiring  electric  lights  but  a  few  hours  of  each  day, 


250  TRANSACTIONS   I.    E.    S. — PART    I 

the  lighting  is  of  less  importance  than  in  subway  service  where 
it  is  an  all-day  proposition. 

One  possible  commercial  view  that  could  be  taken  of  the  light- 
ing problem  is  the  effect  on  the  advertising  cards.  Now,  that 
may  sound  rather  odd,  but  in  a  great  many  cars,  especially  in 
subway  service,  where  the  traffic  is  very  heavy,  the  income  from 
the  rental  of  advertising  space  is  very  considerable.  At  times 
the  cards  and  color  effects  are  made  very  attractive  to  catch  the 
attention  of  passengers.  The  advertiser  is  undoubtedly  influenced 
by  the  lighting  which  is  thrown  on  his  advertisement. 

Chairman  :  You  will  notice  in  all  these  cars  that  they  all  have 
full  windows  just  as  passenger  coaches ;  it  has  always  seemed  to 
me  a  considerable  waste  of  light  to  have  the  same  windows  in 
the  cars  that  you  would  use  with  daylight  cars.  There  seems  to 
be  no  good  reason  why  the  sides  of  the  cars  should  not  be  fin- 
ished with  white  enamel  and  just  a  narrow  window  near  the  top 
of  the  present  glass. 

Mr.  Frank  M.  Brinckerhoff:  The  reason  for  windows  in 
subway  cars  is  to  enable  the  passengers  to  see  out  at  the  stations ; 
so  that  passengers  can  see  at  what  station  they  are.  People  fre- 
quently have  trouble  in  determining  their  station.  The  seated 
passenger  needs  the  window  to  look  out  just  as  much  as  the 
standing  passenger  does,  and  you  will  find  the  windows  of  the 
subway  car  about  suitable  for  the  purpose. 

All  the  ceilings  have  been  rubbed  flat  finish  to  take  off  the 
high  gloss ;  this  surface  eliminates  a  great  deal  of  glitter  and 
affords  a  much  more  pleasing  illumination. 

Chairman  :  Peculiar  color  combinations  are  used  on  the  sub- 
way advertising  cards;  yellow  and  orange  are  used  in  certain 
words  or  lines  for  emphasis.  Has  an  advertiser  ever  complained 
that  these  cards  are  not  as  conspicuous  under  artificial  light  as 
he  thinks  they  should  be?  These  cards  are  probably  designed 
and  approved  under  daylight,  and  it  cannot  be  expected  that 
certain  color  combinations  will  be  as  striking  under  artificial 
light  as  they  would  be  in  daylight. 

Mr.  Frank  M.  Brinckerhoff:  I  do  not  think  the  color  of  a 
card  has  ever  been  discussed,  but  the  color  of  the  car  finish  has. 
I  have  never  heard  of  a  complaint  by  an  advertiser  that  his  pecu- 


CAR    LIGHTING    PROBLEMS  25  I 

liar  color  combination  was  not  properly  illuminated;  I  do  not 
think  that  I  have  ever  heard  of  that  being  brought  up;  but,  of 
course,  the  color  combination  of  the  car  itself  has  a  great  deal 
of  effect,  or  rather  it  influences  the  appearance  of  the  cards.  A 
good  frame  around  a  picture  brings  out  and  enhances  the  picture ; 
just  so,  this  moulding  around  the  advertising  card  either  pro- 
duces an  attractive  effect,  or  detracts  from  the  appearance  of  the 
cards.  For  example,  if  green  moulding  is  carried  along  beneath 
the  entire  row  of  advertising  cards,  it  gives  it  a  dignity  and  bal- 
ance that  is  rather  attractive.  If  advertising  cards  are  mounted 
against  a  flat  white  background  above  and  below,  it  rather  detracts 
from  their  color  scheme.  I  have  never  heard  of  the  color  of  the 
card  being  affected  by  the  illumination ;  but  I  can  easily  see  that 
it  could  do  so. 

Mr.  Young:  As  to  the  elaboration  on  the  glass  to  be  used, 
I  think  every  one  is  coming  more  and  more  to  an  absolutely 
plain  surface  on  any  lighting  glassware  that  they  use.  It  is  quite 
easy  to  get  up  a  line  of  glassware  comprising  reflectors,  hemis- 
pheres, etc.,  with  an  elaboration  that  is  quite  intricate;  but 
it  is  quite  hard  to  get  up  a  piece  of  glass  with  a  simple 
elaboration.  I  have  been  at  it  a  good  many  years,  and  I  know 
what  it  means.  Recently,  there  has  been  marketed  a  line,  as  you 
would  say,  of  absolutely  plain  glassware  as  shown  in  Fig.  12. 
The  disk,  or  fixture  shown  is  w-ithout  elaboration.  There  has 
been  some  discussion  to-night  in  regard  to  the  collection  of  dust 
on  reflectors,  etc.  The  glassware  shown  in  Fig.  12  could  be  more 
easily  cleaned  than  a  shade ;  the  glass  can  be  cleaned  with  a  piece 
of  chamois ;  or  it  can  be  cleaned  with  a  dry  rag,  provided  the 
atmosphere  is  not  greasy;  in  which  case,  of  course,  the  glass 
would  collect  grease  and  would  have  to  be  washed. 

Mr.  L.  C.  Porter  (In  reply)  :  One  speaker  asked  what  fac- 
tors were  against  the  special  turnip-shaped  lamps  without  re- 
flectors, and  against  the  indirect  system.  One  of  the  chief  draw- 
backs of  these  two  systems  was  the  lack  of  headroom  in  a  car 
either  to  get  an  indirect  fixture  or  a  special  lamp  with  opal  on 
the  bottom  sufficiently  low  from  the  ceiling  so  that  it  would  light 
the  ceiling  fairly  evenly,  instead  of  just  throwing  a  little  spot  of 
light  on  the  ceiling.    To  do  this  it  was  necessary  to  put  the  lamp 


-'D- 


TRANSACTIONS    I.    E.    S. — PART    I 


or  fixture  so  far  down  that  it  would  necessarily  be  in  the  way  of 
tall  passengers,  particularly  those  wearing  opera  hats.  One  of 
the  other  chief  factors  against  those  two  systems  was  the  col- 
lection of  dirt,  etc. 

In  regard  to  light  distribution,  it  is  true  that  the  outside  dis- 
tribution curve  is  probably  the  most  important  one,  but  even  with 
passengers  facing  sideways  in  the  car  it  was  found  that,  under 
average  conditions,  they  held  their  papery  at  least  two  feet  out 
from  the  side  of  the  car,  which  brought  them  within  the  range  of 
the  distribution  curve  shown. 

You  will  note  that  so  far  car  lighting  problems  have  dealt 
with  fitting  the  lighting  to  cars  at  present  in  service — that  is,  cars 
already  designed. 

In  one  of  the  tests  described  in  the  paper,  you  will  find  that  a 
special  ceiling  insert  was  made  to  see  if  the  lighting  could  be 
improved.  This  opens  quite  a  field;  in  other  words,  why  should 
not  the  roof  of  the  car  be  designed  to  fit  the  lighting? 

Mr.  Frank  M.  Brinckerhoff:  If  a  car  could  be  designed 
with  a  cross  section  similar  to  that  headlight  that  we  have  looked 
at  this  evening,  it  would  insure  the  most  even  distribution  of 
light ;  in  other  words,  if  the  roof  of  the  car  could  be  given  a 
parabolic  form  and  the  lamps  could  be  placed  on  the  exact  focal 
center  of  the  parabola,  an  absolutely  even  distribution  of  light 
over  the  entire  width  of  the  car  could  be  obtained.  The  height 
of  the  New  York  Municipal  Railway  cars  made  it  necessary  to 
take  a  certain  definite  width,  with  the  result  that  it  is  impossible 
to  place  the  light  sources  exactly  as  we  would  have  desired ;  it 
was  necessary  to  accept  a  compromise  position.  The  distribution 
of  light  finally  secured  is  about  as  good  as  can  be  obtained  in  a 
car  of  this  height  and  width. 


IVES  AND  KINGSBURY  :    HETEROCHROMATIC  PHOTOMETRY     253 

ADDITIONAL  EXPERIMENTS  ON  COLORED  ABSORB- 
ING SOLUTIONS  FOR  USE  IN  HETERO- 
CHROMATIC PHOTOMETRY.* 


BY    HERBERT  E.    IVES  AND   EDWIN    F.    KINGSBURY. 


Synopsis:  This  paper  is  a  continuation  of  one  recently  presented 
under  a  similar  title.  It  describes  a  blue  solution  which  used  over  a 
standard  carbon  lamp  duplicates  the  color  of  lamps  of  higher  efficiency. 
The  photometric  calibration  of  this  solution  is  given.  Simple  equations 
have  been  developed  to  represent  the  transmission  of  both  this  new  solu- 
tion and  the  previously  described  yellow  solution. 


In  a  previous  paper1  before  the  Illuminating  Engineering  So- 
ciety we  have  described  a  yellow  absorbing  solution  which  can 
be  used  in  varying  concentrations  to  eliminate  the  difference  in 
color  between  black  bodies  at  different  temperatures.  We  present 
herewith  an  account  of  a  blue  solution  of  similar  properties,  which 
may  be  used  over  the  present  carbon  incandescent  standards,  to 
produce  with  them  all  the  incandescent  lamp  colors  up  to  the  most 
efficient  lamps  now  obtainable.  In  the  previous  paper  details  are 
given  as  to  the  mode  of  use  of  the  solutions  and  upon  the  method 
of  calibration.  The  present  communication  may  be  considered 
as  a  continuation  of  the  other,  containing  only  matter  not  therein 
included. 

Constitution  of  New  Blue  Solution. — The  blue  solution  has  the 
following  composition : 

Nickel  ammonium  sulphate 50  gr. 

Ammonium  sulphate   10  gr. 

Ammonia  0.90  gr 55  cc. 

Water  to    1  liter  of  solution 

Dilute  with  water  containing  10  gr.  ammonium  sulphate  per 
liter. 

The  solution  should  be  used  as  fresh  as  possible,  because  on 
standing  it  slowly  dissolves  the  glass  of  the  containing  vessel,  and 

*  A  paper  read  at  a  meeting  of  the  Philadelphia  Section  of  the  Illuminating  Engineer- 
ing Society,  March  19,  1915. 

The  Illuminating  Engineering  Society  is  not  responsible   lor  the  statements  or 
opinions  advauced  by  contributors. 

1  Ives  aud  Kingsbury,  Experiments  with  Colored  Absorbing  Solutions  for  Use  in 
Heterochromatic  Photometry;  Trans,  I.  E.  S.,  vol.  VIII  (1914),  p.  795. 


254 


TRANSACTIONS    I.    E.    S. — PART    I 


because  alkaline  solutions  such  as  this  are  inherently  less  stable 
than  acid  solutions  like  the  yellow  one. 

Calibration. — The  same  method  of  calibration  was  used  as 
before.  One  advance  lay  in  the  fact  that  our  average  observer 
was  obtained  from  the  mean  of  sixty-one  instead  of  twenty-five, 
as  in  the  earlier  work.  The  working'  group  from  whom  the 
seven  observers  were  taken  was  only  in  part  the  same  as  before, 
but,  if  the  method  of  selection  is  reliable,  their  mean  result  should 
be  the  same  as  that  of  the  similarly  selected  group  used  in  the 
yellow  solution  work,  since  the  mean  value  for  the  test  green 
light  was  little  affected  by  the  inclusion  of  the  larger  number  of 
observers  now  used  in  establishing  the  standard  eye. 


100 
90 
80 
.70 

|  50 
?40 

30 

.20 

.10 

fll L-i_ 

10        .20        30        10        SO        60         70         80       .90       100 
CONCENTRATION 

Fig.  i.— Transmission  of  blue  solution.    Equation  of  curve:  logi0T 


\ 

Jy 

\^ 

s 

X 

z 

z 

N 

V 

s 

s 

z 

g 

3 

S 

s 

z 

f*^ 

u 

1 

% 

5 

539C'- 


The  observations  are  plotted  in  Fig.  I,  on  which  are  also  shown 
the  approximate  concentrations  called  for  by  typical  illuminants. 

Temperature  Coefficient. — An  undesirable  feature  of  the  yellow 
absorbing  solution  is  the  existence  of  a  pronounced  temperature 
coefficient,  making  it  imperative  either  to  work  at  the  temperature 
used  in  calibrating  or  to  apply  corrections. 

We  find  the  blue  solution  to  have  practically  no  temperature 
coefficient  over  the  range  of  temperature  to  be  expected  in  the 
laboratory     This  is  a  very  fortunate  thing,  especially  as  the  field 


IVES  AND  KINGSBURY:    HETEROCHROMATIC  PHOTOMETRY     2 


33 


of  usefulness  of  the  blue  solution  may  be  expected  to  be  much 
greater  than  that  of  the  yellow. 

Spectral  Transmission. — Fig-.  2  shows  the  transmission  through 
the  spectrum,  as  measured  on  the  spectrophotometer,  for  the 
100  per  cent,  solution.  When  plotted  in  terms  of  log.  absorption 
against  i/A  an  approximation  only  to  a  straight  line  results,  as  with 
the  yellow  solution.  This  means  that  the  color  match  obtained 
by  using  the  solution  is  a  subjective  one  and  will  not  hold  abso- 
lutely with  observers  of  abnormal  color  vision.  This  divergence 
from  actual  identity  of  the  two  compared  spectra  is,  however,  too 
small,  we  believe,  to  cause  trouble  in  practical  work.  We  find 
as  well  that  Beer's  law  does  not  hold,  so  that  the  concentration 


6 

in 

2 
Z.    , 

<  ' 

a. 

1- 

.2 

/ 

' 

A 

3            4 

5           .5 

3           .5 

WAVE- 

5           .6 
l-ENGTH 

3          .6 

5           .70 

Fig.  2. — Spectral  transmission  of  100  per  cent,  blue  solution. 

necessary  for  any  particular  case  cannot  be  obtained  by  experi- 
ments on  thickness.     Trial  of  various  concentrations  is  necessary. 

Comparison  of  Results  Using  Yellow  and  Blue  Solutions. — 
The  yellow  solution  when  used  on  the  test  side  performs  the 
same  color  difference  eliminating  function  as  the  blue  solution  on 
the  comparison  lamp  side. 

It  is  a  matter  of  interest  to  know  how  closely  the  value  to  be 
assigned  by  using  one  solution  agrees  with  that  from  the  other. 
This  constitutes  a  test  of  the  method  of  calibration.  If  the 
method  is  reliable  and  self-consistent  the  same  value  should  be 
obtained  upon  measuring  a  high  efficiency  lamp  by  the  use  of 
either  solution. 

This  point  was  tested  by  the  measurement  of  a  type  "C"  tung- 
sten lamp,  efficiency  0.65  w.  p.  c,  against  a  4-watt  standard.    The 


256  TRANSACTIONS   I.    E.    S. — PART    I 

requisite  concentration  of  the  yellow  solution  was  determined  by 
the  use  of  the  wedge  cells  described  in  the  previous  paper;  that 
of  the  blue  by  several  trials.  The  relative  intensity  of  the  two 
lamps  was  then  found  to  be  the  same  to  about  y2  per  cent,  or 
within  the  errors  of  photometric  setting. 

This  test,  involving  as  it  does  two  different  series  of  measure- 
ments made  several  months  apart,  with  largely  different  groups 
of  observers,  shows  clearly  the  reliability  of  the  photometric  pro- 
cedure. 

Mathematical  Expressions  for  the  Transmission  Curves. — In 
order  that  these  colored  solutions  may  not  only  be  made  up  but 
also  used  from  written  specifications,  it  is  desirable  that  their 
transmission  be  expressible  in  some  simple  mathematical  form. 
This  we  find  to  be  possible. 

In  the  case  of  monochromatic  light  the  equation  connecting 
transmission  with  concentration  is  of  quite  simple  form,  namely, 

T  =  T0eac 
where  T  is  transmission,  T0  is  the  transmission  for  zero  concen- 
tration, e  is  the  base  of  the  natural  system  of  logarithms,,  a  is  a 
constant  and  c  is  concentration.     In  the  present  case  T0  is  unity, 
so  that  the  relationship  may  be  written  simply : 

T  =  kc 
or 

log  T  =  ck' 

Now,  we  are  not  dealing  here  with  monochromatic  light,  but  it 
is  well  known  that  over  considerable  ranges  of  color  change  in 
black  body  illuminants  the  total  change  in  intensity  is  very  closely 
the  same  as  the  change  of  intensity  for  a  certain  single  wave- 
length.2 We  should,  therefore,  expect  the  above  equation  to 
hold  over  a  fairly  large  range  of  concentrations.  When,  how- 
ever, this  range  is  exceeded  the  deviation  is  slow  and  can  be 
taken  care  of  by  a  slight  modification  of  the  simple  law.  Thus 
we  find  that  over  the  whole  range  of  concentrations  called  for  by 
the  present  practical  illuminants  the  transmissions  of  our  solu- 
tions are  represented  with  extreme  accuracy  by  equations  of  the 
form 

log  T  =  c*k 

-  Ives.  II.  B.|  Note  on  Crova's  Method  of  Heterochromatic  Photometry;  Physical  Review, 
XXXII,  3,  Mar.  1911,  p.  316. 


IVES  AND  KINGSBURY:    HETEROCHROM  ATIC  PHOTOMETRY     257 


where  x  is  a  number  only  slightly  differing  from  unity.     The 

actual  equations  for  the  yellow  and  blue  solutions  are  as  follows : 

Blue  solution  on  comparison  lamp  side  •  • -log10  T  =  — o.539^I-°3 

Yellow  solution  on  comparison  lamp  side-tog10  T  =  — o. 245^-9 

Yellow  solution  on  test  lamp  side log10  T  =  -j-o. 366^1 -°5 

where  T  and  c  are  expressed  in  decimal  fractions  of  unity  (i.  e., 
20  per  cent,  transmission  or  concentration  is  expressed  as  0.20). 
The  curves  represented  by  these  equations  lie  everywhere  distant 


1.40 
135 
130 
125 

ST  120 

S 

z   115 

1   IIC 

2 

u.  105 
3  100 
g   .95 

I    90 

z 
<c 

.80 

75 
.70 

{     i 

\\ 

i 

|[\    ! 

§i   ^\S 

\j 

s! 

s\ 

SOLUTION  ON  COMPARISON 
1  LAMP'  SCl 

1  ||K 

% 

I  1 

\?l 

z 

si 

SO 

UTI0N 

0NTE 

-  lam 

SIDE 

. 

SO      .40        30       .20 


.10        0         ID 
CONCENTRATION 


.20       .30      .40       50 


Fig.  3.— Transmission  of  yellow  absorbing  solution  at  20  deg.  C.     Equations  of  curve: 
comparison  lamp  side,  log10T  =  — 0.245C9;  test  lamp  side,  logi0T  =  0.366c1"*5. 

from  the  experimentally  determined  points  by  no  more  than  the 
uncertainty  of  the  experimental  work.  The  full  line  in  Fig.  I 
has  been  drawn  with  the  aid  of  the  first  equation,  and  in  Fig.  3 
the  data  on  the  yellow  solution  have  been  reproduced  along  with 
the  curves  represented  by  the  second  and  third  equations. 

DISCUSSION. 
In  the  previous  paper  we  dealt  rather  insistently  on  the  diffi- 
culties of  working  with  absorbing  solutions.     Among  these  dim- 


258  TRANSACTIONS   I.    E.    S. — PART    I 

culties  the  care  of  the  glass  tanks  and  the  complications  caused  by 
the  temperature  coefficient  figured  prominently.  In  the  light  of 
our  more  extended  experience  we  now  feel  it  permissible  to  speak 
somewhat  more  favorably  of  this  method.  We  have  found  that 
the  absorbing  tanks  in  the  form  developed  in  the  course  of  the 
investigation  maintain  their  similarity  in  spite  of  nearly  con- 
tinuous use  for  months.  The  new  blue  solution  with  its  freedom 
from  temperature  coefficient  removes  another  objection.  And, 
finally,  the  possibility  of  representing  the  transmissions  by  simple 
equations  places  these  solutions  squarely  in  the  category  of 
primary  color  standards,  entirely  reproducible  from  specification 
at  any  time  or  place.  By  their  careful  use  all  laboratories  can 
insure  a  high  degree  of  uniformity  and  agreement  in  measure- 
ments involving  the  commonest  type  of  color  differences,  once 
agreement  has  been  reached  on  the  values  to  be  assigned  to  the 
transmissions.  The  scale  upon  which  we  have  determined  these 
transmissions  is  based  upon  a  careful  study  of  photometric 
methods  and  is,  we  believe,  entitled  to  most  serious  consideration 
for  adoption  as  standard. 


IVES    AND    KINGSBURY!     COLOR   VISION  259 

METHOD    OF    CORRECTING    ABNORMAL    COLOR 
VISION  AND  ITS  APPLICATION  TO  THE 
FLICKER  PHOTOMETER.* 


BY    HERBERT   E.    IVES   AND   E.    F.    KINGSBURY. 


Synopsis:  A  study  is  made  of  the  manner  in  which  the  spectral 
luminosity  curves  of  individuals  differ.  It  is  pointed  out  that  when  the 
flicker  photometer  is  used  any  observer  can  be  corrected  to  normal  by  the 
interposition  of  the  proper  absorbing  medium  over  his  eye.  Practical 
approximations  to  such  absorbing  media  are  developed  and  tried.  By 
their  means  color-blind  observers  are  made  to  read  substantially  the  same 
as  normal. 


Various  investigations  on  the  spectral  luminosity  curves  of 
individuals  of  normal  and  abnormal  color  vision  have  clearly  es- 
tablished that  these  curves  differ  from  individual  to  individual. 
The  differences  are  small  between  those  who  would  be  classed  as 
of  normal  vision,  but  of  increasing  magnitude  as  observers  are 
included  of  the  various  types  of  recognized  color  blindness.  This 
fact  is  illustrated  by  the  luminosity  curves  of  normal  and  color- 
blind observers  shown  in  Fig.  i. 

Now,  an  individual  of  abnormal  color  vision  suffers  from  two 
characteristic  disabilities,  both  probably  due  to  the  same  funda- 
mental defect.  One  is  the  distortion  of  color  values,  the  other  the 
distortion  of  luminosity  values.  These  two  disabilities  are  of 
differing  gravity'  to  an  individual,  depending  upon  the  use  he 
makes  of  his  eyes.  If  his  work  demands  the  discrimination  or 
harmonizing  of  colors,  then  inability  to  differentiate  hues  is  suf- 
ficient to  disqualify  him.  If,  however,  his  work  involves  the 
measurement  of  luminous  intensity  the  fact  that  one  color  has  to 
his  eye  the  same  quality  as  another  embarrasses  him  not  at  all, 
but  the  fact  that  the  different  colors  do  not  have  the  same  relative 
intensity  as  to  a  normal  eye  is  a  serious  handicap. 

One  of  the  present  writers  suggested  some  time  ago1  that  an 
abnormal  eye  might  be  corrected  for  purposes  of  photometry  by 

*  A  paper  read  at  a  meeting  of  the  Philadelphia  Section  of  the  Illuminating  Engineer- 
ing Society,  March  19,  1915. 

The  Illuminating  Engineering  Society  is  not  responsible   for  the  statements  or 
opinions  advanced  by  contributors. 

1  Ives,  Discussion  of  a  paper  by  Fabry  ;  Trans.  I.  E.  S.,  June,  1913,  p.  320. 


2(5o 


TRANSACTIONS    I.    E.    S. PART    I 


the  aid  of  an  absorbing  screen  which  would  reduce  the  intensity 
of  certain  portions  of  the  spectrum.  Dr.  Louis  Bell  more  re- 
cently2 has  suggested  that  in  certain  types  of  abnormal  color 
vision,  where  one  sensation  is  only  partly  deficient,  correcting 
glasses  might,  in  restoring  the  balance  between  the  different  parts 
of  the  spectrum,  enable  the  wearer  to  see  colors  in  their  normal 
hue  relationships.  This  latter  possibility  of  course  only  applies 
where  all  three  fundamental  sensations  (in  the  Young-Helm- 
holtz  sense)  are  present  to  some  degree.  The  photometric  possi- 
bility is  equally  good  whether  the  observer  perceives  color  or  not, 
provided  he  sees  something  in  all  parts  of  the  normally  visible 
spectrum.    That  is,  even  an  individual  who  sees  the  spectrum  as 


Fisr.  I. — Spectral  luminosity  curves  of  three  normal  and  one  totally  color-blind 
observers.  (Three  "normal"  from  data  of  Ives;  color-blind  from  measure- 
ments by  Bender.) 


a  mere  colorless  band  should  be  able  to  obtain  normal  photo- 
metric results  once  the  luminosity  curve  of  his  spectrum  is  nor- 
malized. 

The  type  of  observer  just  mentioned  would  in  fact  have  a  cer- 
tain advantage  in  ordinary  direct  comparison  photometry,  be- 
cause he  would  not  be  distracted  by  the  difference  of  quality 
which  causes  the  fundamental  difficulty  in  colored  light  pho- 
tometry. So  serious  is  this  distraction  that  definite  and  satis- 
factory results  can  be  obtained  in  colored  light  photometry  only 
by  the  use  of  the  flicker  photometer.    Consequently  in  this  paper, 

1  Bell,  L..  Types  of  Abnormal  Color  Vision  ;  Pioc.  Amer.  Acad.,  50,  pp. 3-13,  May,  1914. 


IVES    AND    KINGSBURY:     COLOR   VISION  26l 

which  deals  chiefly  with  the  application  of  this  correction  method 
to  photometry,  the  flicker  method  alone  will  be  considered,  it  being 
understood  that  the  method  of  correction  should  be  equally  ap- 
plicable to  direct  comparison  photometry  were  this  latter  a  prac- 
tical means  of  precision  measurement. 

The  peculiar  applicability  of  the  flicker  photometer  to  this 
proposed  method  of  correction  lies  in  its  entire  elimination  of 
the  question  of  quality.  The  system  composed  of  the  flicker 
photometer  and  the  eye  is  a  physical  null  instrument,  in  which 
the  eye  acts  merely  as  the  sensitive  detector  of  a  lack  of  balance 
in  which  color  or  quality  plays  no  part  and  only  the  luminosity 
differences  remain.  Such  a  system  may  be  subjected  to  the 
action  of  colored  absorbing  media  in  exactly  the  same  way  as 
can  a  thermopile  or  a  photo-electric  cell,  with  a  similar  alteration 
of  its  spectral  sensibility  curve. 

Once  this  fact  is  clearly  recognized  the  possibility  of  altering 
a  known  individual  luminosity  curve  into  a  normal  one  by  ap- 
propriate colored  absorbing  media  is  obvious.  It  is,  however, 
possible  that  the  production  of  a  correcting  screen  for  each  in- 
dividual might  be  a  task  of  great  difficulty.  How  much  do  in- 
dividuals differ?  Can  an  average  type  of  correction  be  worked 
out  practically?  If  so  what  is  its  field  of  successful  application? 
These  questions  were  the  object  of  the  investigation  here  re- 
ported. 

I.-THE  DIFFERENCES  BETWEEN  INDIVIDUAL  LUMINOSITY 
CURVES  AND  THE  CORRECTIONS  CALLED  FOR. 

Some  forty  spectral  luminosity  curves,  obtained  by  the  flicker 
method,  are  available  for  study,  obtained  by  Ives  and  by  Nutting, 
and  probably  half  as  many  more,  obtained  under  somewhat  dif- 
ferent conditions  by  workers  with  the  Lummer-Pringsheim 
flicker  photometer.  For  the  present  purpose  a  single  group  is 
sufficient,  and  for  this  the  curves  obtained  by  Ives  are  used; 
Nutting's  lead  to  exactly  similar  conclusions,  as  do  probably  also 
the  other  curves  quoted.  In  Fig.  I  are  shown  several  luminosity- 
curves  selected  from  the  larger  group  of  18  3.  In  Fig.  2  these 
are  plotted  in  percentages  of  the  mean  at  each  wave-length.  From 

3  Ives,  The  Spectral  Luminosity  Curves  of  the  Average  Eye;  Phil.  Mag.,  Dec.  1912, 
P-  §59- 


262 


TRANSACTIONS    I.    E.    S. PART    I 


these  selected  curves  it  is  apparent  that  deviations  from  the  mean 
are  of  two  kinds:  First,  that  characterized  by  a  uniformly 
changing    deviation    of    the   type    represented    by    the    equation 

I  =  —  -\-   B,  and,  second,  small  localized  variations  from  this 

A 

simple  type  of  variation,  resulting  in  more  or  less  extended  con- 


S6  58 

WAVE-LENGTH 


Fig.  2. — Characteristic  deviations  from  normal  spectral  luminosity  curve, 
and  effect  of  applying  correcting  medium. 

cavities  or  convexities  in  the  plotted  lines.  These  latter,  which 
are  in  most  cases  undoubtedly  real  and  not  errors  of  observa- 
tion, are  due  probably  to  individual  differences  of  pigmentation 
of  the  fovea  and  similar  causes,  superposed  on  the  main  basis  of 
difference,  namely  the  relatively  different  proportion  of  the  three 
color  sensations.    In  Fig.  3  we  have  plotted  the  average  deviation 


> 



-. 

,  ^^_^~ 

»- 

■■—■J. 

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8         5 

G          5 

2         .5 

4         .5 

6       a 

8         i> 

0          i 

2         t 

4           i 

M 

WAVC  -  LENGTH 


Fig.  3.— Average  deviation  from  normal  luminosity  curve  of 
red-sensitive  and  blue-sensitive  groups. 

from  normal  of  all  those  observers  lying  clearly  on  the  blue  side 
of  the  mean  and  all  those  lying  clearly  on  the  red  side.  It  is  at 
once  seen  that  the  small  localized  irregularities  are  largely  ironed 
out  and  that  the  average  type  of  deviation  from  normal  consists 


IVES    AND    KINGSBURY:     COLOR   VISION  263 

in  the  simple  gradual  variation  with  wave-length  represented  by 
the  equation  already  given. 

It  may  be  stated  without  further  discussion  that  an  average 
type  of  corecting  medium  would  be  one  whose  spectral  trans- 
mission is  the  reciprocal  of  the  average  deviation  just  shown,  as 

T  =  — \-  b.     Such  a  medium  with  varying  values  of  a  and  b 

A 

should  correct  the  main  deviation  from  normal  vision.  At  the 
same  time  such  an  average  correction  cannot  fit  the  smaller  in- 
dividual differences. 

At  this  point  it  may  be  remarked  that  this  study  might  have 
been  carried  through  on  merely  one  or  two  individuals  whose 
luminosity  curve  would  first  be  accurately  determined,  exact  cor- 
rection screens  then  being  developed,  and  their  performance 
examined.  We  have  not  done  this  because  the  well  established 
physical  characteristics  of  the  flicker  photometer  already  men- 
tioned tell  us  in  advance  that  such  an  individually  worked  out 
correction  would  be  exact.  The  labor,  however,  of  working  out 
individual  screens  for  every  member  of  a  laboratory  staff  would 
make  the  scheme  at  once  a  dubiously  practical  one.  Our  interest 
has,  therefore,  been  in  studying  the  possibility  of  adapting  this 
method  in  such  simplified  form  as  to  make  it  practical.  We 
have  accordingly  worked  out  an  average  correcting  medium  and 
have  investigated  the  extent  of  its  usefulness. 

tt— THE  PERMANENCE   OF  THE   COLOR   CHARACTERISTICS 
OF  INDIVIDUAL  OBSERVERS. 

Will  a  correction  once  found  adequate  always  be  so?  This  of 
course  depends  upon  the  permanency  of  the  luminosity  curve. 
In  previous  papers  on  the  flicker  photometer,  evidence  has  been 
presented  that  an  observer's  characteristics  are  permanent.  In 
the  course  of  nearly  a  year's  continuous  use  of  the  photometric 
method  advocated  by  us,  we  have  accumulated  a  mass  of  data 
from  which  very  definite  information  on  this  point  is  available. 

We  have  arranged  some  of  these  data  graphically  in  Fig.  4. 
At  our  disposal  were  the  following  sets  of  observations :     two 
series  of  readings  on  monochromatic  green  light  compared  with 
5 


264 


TRANSACTIONS    I.    E.    S. — PART    I 


the  light  of  a  "4-watt"  lamp*;  four  series  of  measurements  on 
a  special  yellow  solution  which  in  varying  concentrations  takes  up 
the  color  differences  between  incandescent  lamps  of  various  effi- 
ciences5 ;  two  series  on  a  blue  solution  of  similar  characteristics8, 
which  ultimately  proved  unsatisfactory  (A)  and  two  on  the 
satifactory  solution  (B)  ;  two  sets  on  a  pair  of  test  colors  used  in 
the  selection  of  groups  of  observers  for  colored  light  photometry.7 
These  are  plotted  in  such  manner  that  measurements  on  the  blue 
side  of  the  normal  fall  above  the  axis  of  abscissa,  those  on  the 


M0N0- 
;HR0MAT 
GREEN 

:     BLUE  SOLUTION  A 

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YELLOW  SOLUTION 

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COLORS 

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Fig.  4. — Photometric  history  of  four  observers. 


yellow  below.     The  ordinates  are  the  percentage  deviations  from 
the  mean.     In  the  case  of  the  yellow  and  blue  solutions  the 

4  Ives  and  Kingsbury,  Measurements  with  the  Flicker  Photometer  on  a  Monochro- 
matic Green  Solution  ;  Physical  Review,  March,  1915,  p.  230. 

6  Ives  and  Kingsbury,  Experiments  with  Colored  Absorbing  Solutions  for  Use  in 
Heterochromatic  Photometry  ;  Trans   I.  E.  S.,  vol.  VIII,  p.  795  ;  1914. 

•  Ives  and  Kingsbury,  Additional  Experiments  on  Colored  Absorbing  Solutions  for 
Use  in  Heterochromatic  Photometry  ;  Trans.  I.  E.  S.,  1915. 

'•  Ives  and  Kingsbury,  On  the  Choice  of  a  Group  of  Observers  for  Heterochromatic 
Measurements;  Trans.  I.  E.  S.,  1915. 


IVES    AND    KINGSBURY:     COLOR   VISION  265 

greatest  color  difference  is  to  the  left,  decreasing  to  a  very  small 
color  difference  at  the  right.  The  observations  on  these  solutions 
should,  therefore,  in  general  converge  toward  the  axis,  as  they 
do.  The  scattering  of  these  points  is  not  to  be  taken  as  evidence 
of  lack  of  sensibility  of  the  photometric  method,  as  all  kinds  of 
possible  errors  influence  the  results. 

With  very  few  exceptions  our  observers  have  maintained 
throughout  their  positions  relative  to  the  mean.  This  is  strikingly 
shown  in  the  case  of  observers  I,  2  and  3,  whose  observations 
practically  all  fall  on  one  side  of  the  normal  line.  We  have 
found  but  one  actual  reversal  of  position  in  the  case  of  the 
monochromatic  green  reading  by  an  observer,  not  here  shown. 
The  first  reading  was  made  upon  a  green  absorbing  solution 
which  afterwards  proved  of  unstable  composition  so  that  even  this 
case  is  not  clearly  proven.  Fluctuations  of  color  vision  do  how- 
ever undoubtedly  occur,  caused  for  instance  by  exposure  to  the 
eyes  to  intense  light,  by  working  with  colored  light,  as  in  the 
spectrophotometer,  etc.,  and  these  show  up,  as  they  should,  in 
the  flicker  photometer  measurements.  But  apart  from  these 
there  is  no  doubt  that  an  individual's  spectral  luminosity  curve 
is  as  much  a  personal  characteristic  as,  for  instance,  the  con- 
figuration of  the  eye-ball,  for  which  we  prescribe  spectacles. 

An  interesting  piece  of  information  is  obtained  by  studying  the 
relative  amounts  of  the  deviations  from  normal  with  the  different 
kinds  of  color  differences.  These  are  not  entirely  parallel  with 
different  observers.  Thus  the  percentage  deviation  from  the 
mean  of  observer  4  is,  with  the  very  saturated  colors  of  the  first 
and  last  columns,  quite  large,  but  with  the  less  saturated  colors  of 
the  middle  columns  his  readings  average  very  near  normal.  On 
the  other  hand  the  more  extreme  observers,  such  as  numbers 
1  and  2,  show  up  consistently  away  from  the  mean,  although 
measuring  the  monochromatic  green  no  further  off  than  observer 
4.  These  differences  are  clear  cases  of  those  localized  differences 
in  the  luminosity  curves  already  noticed.  We  may  from  them 
expect  that  no  average  type  of  correction  will  cut  finely  enough 
to  take  up  with  great  success  rather  small  differences  in  color 
vision,  or  do  more  with  abnormal  observers  than  bring  them  near 
normal. 


266 


TRANSACTIONS    I.    E.    S. PART    I 


III.— THE  PRACTICAL  DEVELOPMENT  OF  CORRECTING 

MEANS  APPLICALBLE  TO  THE  AVERAGE  TYPE 

OF  DEVIATION  FROM  NORMAL. 

The  absorbing  media  which  we  sought,  to  be  used  over  the  eye 
for  correcting  the  luminosity  curve,  were  two,  a  generally  blue 
one,  and  a  generally  yellow  one,  each  having  a  transmission 
represented  by  a  straight  line  from  one  end  of  the  visible  spec- 
trum to  the  other,  and  capable  in  varying  concentrations  of 
giving  all  ordinarily  necessary  corrections  without  serious  depart- 
ure from  that  type  of  transmission.     Of  course  the  exact  attain- 


"H\ 

• 

»■»**"" 

/ 
/ 

• 

/ 
/ 
/ 

\ 

3-^ 

/ 

i 

.50         54        5)        K 

WAVE-LENGTH 


7C^ 


Fig.  5.— Spectral  transmission  of  correcting  solutions;  full  line, 
blue  solution,  dashed  line,  yellow  solution. 

ment  of  the  desired  characteristics  is  hardly  to  be  expected.  The 
media  which  we  finally  selected  after  considerable  experimenta- 
tion are  for  the  blue: 

Cupric  sulphate    2.0  gr. 

Ammonia  (0.90  gravity)    200     cc. 

Add  water  to  make  1  liter  of  solution.     (Dilute  with  water 
4  parts,  ammonia  I  part.) 

and  for  the  yellow  : 

Bayer's  Fast  Brown,  0.025  gram  per  liter  of  water. 

The  spectral  transmissions  of  these  are  shown  for  100  per  cent, 
concentration  in  thickness  of  5  mm.  in  Fig.  5.  It  will  be  seen 
that  they  approximate  fairly  closely  to  the  required  charac- 
teristics, especially  through  the  middle,  of  the  more  important 
part  of  the  spectrum. 

The  result  of  applying  the  60  per  cent,  solution  to  the  lumin- 
osity curve  A.  W.  of  Fig.  1  is  given  in  Fig.  2.  By  the  use  of 
the  correction  the  general  slope  of  the  curve  is  removed,  whereby 


IVES    AND    KINGSBURY:     COLOR   VISION 


267 


it  is  reduced  to  the  same  class  as  those  possessing  merely  localized 
irregularities. 

The  practical  means  for  applying  the  correction  consisted  of 
small  glass  tanks,  made  very  simply  by  drilling  one  centimeter 
diameter  holes  in  pieces  of  plate  glass  5  mm.  thick  and  two  and 
one-half  centimeters  square,  riling  a  groove  for  filling  and  fasten- 
ing thin  glass  faces  on  with  paraffin.  These  were  slipped  over 
the  eye-piece  of  the  flicker  photometer. 

We  have  worked  with  liquid  solutions  as  simpler  for  the  ex- 
perimental work.  Doubtless  colored  glasses  could  be  found 
which  would  serve.     These  could  be  used  in  the  form  of  wedges. 

IV.— THE  EFFICACY  OF  THE  CORRECTING  SCHEME  ON 
A  GIVEN  COLOR  DIFFERENCE. 

In  order  to  determine  the  amount  of  correction  needed  by  the 
various  observers  at  our  disposal,  we  have  made  use  of  the  test 


^ 
/ 

< 

:~Z 

~~~~~ 
»--- 

• 
/ 

^ 

■ 

r-" 

■ 

20  40  60  80  100% 

CONCENTRATION  OF  CORRECTION   SOLUTIONS 

Fig.  6. — Effect  of  color  vision  correcting  solutions  on  test 
color  intensity  ratio  with  four  observers. 

colors  by  which  we  select  a  group  of  observers  for  heterochro- 
matic  measurements7. 

Each  observer  measured  the  ratio  of  these  two  colors,  which 
should  measure  equal  to  a  normal  eye,  then  with  progressively 
greater  concentrations  of  the  correcting  solution  which  was  indi- 
cated as  necessary.  With  each  concentration  a  different  ratio  of 
the  two  intensities  was  obtained.  The  series  of  points  thus  found 
were  then  joined  by  a  line  the  intersection  of  which  with  the  axis 
indicated  that  exact  correction  demanded.  These  lines  were  found 
fortunately  to  be  straight.     In  Fig.  6  are  plotted  the  results  ob- 


268  TRANSACTIONS   I.    E.    S. — PART    I 

tained  by  four  observers.  It  is  evident  that  in  the  case  of  a  given 
color  difference  the  method  of  correction  is  perfectly  definite. 

An  interesting  fact,  in  accordance  with  the  known  types  of 
differences  in  the  luminosity  curves,  is  that  individuals  who 
measure  the  test  colors  nearly  alike  do  not  take  the  same  correc- 
tion. This  is  exhibited  by  the  two  red-sensitive  observers  of 
Fig.  6.  One  evidently  has  a  much  narrower  luminosity  curve 
than  the  other,  for  the  correction  is  much  less,  and  it  is  obvious 
that  a  monochromatic  luminosity  "curve"  would  not  respond  to 
the  connecting  scheme  at  all. 

Before  going  on  to  the  case  of  other  color  differences  we  may 
point  out  that  in  cases  where  a  definite  type  of  color  difference 
is  to  be  measured  repeatedly  a  correction  determined  in  this  way 
makes  it  possible  for  any  member  of  a  laboratory  force  to  make 
normal  measurements.  Thus  a  correction  determined  for  the 
difference  between  standard  and  high  efficiency  incandescent 
lamps  would  work  for  all  lamps  of  the  same  relative  efficiencies 
and,  what  is  more,  it  may  be  expected  to  work  for  all  smaller 
differences  of  the  same  type,  as  those  between  lamps  differing  less 
in  efficiency. 

V.— TEST  OF  THE  CORRECTING  SCHEME  ON  OTHER 
COLOR  DIFFERENCES. 

While  this  development  opens  up  a  number  of  interesting  possi- 
bilities we  have  been  interested  in  pushing  the  question  still 
farther.  Will  a  correction  determined  from  our  test  colors,  be 
correct  for  other  types  of  color  differences  ?  To  obtain  an  answer 
to  this  question  we  have  tried  our  various  observers  with  their 
eye  correctors  on  a  commonly  met  color  difference,  namely,  that 
between  the  standard  "4-watt"  carbon  lamp,  and  a  type  "C" 
tungsten  lamp  at  0.65  w.  p.  c.  We  were  specially  fortunate  in 
securing  the  cooperation  of  one  observer  who  was  known  to  be 
color-blind,  and  of  one  other,  who  from  our  previous  work  we 
knew  to  be  rather  far  from  normal  in  the  opposite  direction  to  the 
individual  just  mentioned.  The  first  observer  required  a  300 
per  cent,  concentration  of  the  yellow  correcting  solution8,  the 
second  a  150  per  cent,  concentration  of  the  blue  correcting  solu- 

8  Working  backward  from  the  transmission  curve  of  the  correction  solution  required, 
we  find  that  the  luminosity  curve  of  this  observer  is  closely  that  of  the  totally  color-blind, 
as  shown  in  Fig.  I, 


IVES   AND    KINGSBURY:     COLOR   VISION 


269 


tion,  as  against  a  maximum  of  100  per  cent,  for  any  of  our  other 
observers. 

The  results  are  shown  graphically  in  Fig.  7.  To  the  left  are 
the  relative  values  of  the  two  lamps,  in  arbitrary  units,  as  meas- 
ured by  the  nine  observers  without  the  correcting  device.  To  the 
right  are  shown  the  relative  values  as  obtained  by  the  corrected 
eyes,  the  dashed  line  through  the  middle  is  the  true  relative  value 
of  the  lamps.  It  is  seen  at  once  that  all  the  observers,  color- 
blind and  normal,  have  been  brought  quite  close  together  and 


RATIOS  WITH 
P\   CORRECTED  EYES. 


—.RATIOS  WITH 
UNCORRECTED  EYES 


Fig.  7.— Results,  with  uine  observers,  of  applying  correction  calculated 
from  test  color  measurements  to  the  color  difference  of  4-w.  p.  c. 
carbon  lamp  and  0.65-w.  p.  c.  tungsten  lamp. 

every  observer,  without  exception,  has  been  brought  nearer  to 
the  true  value.  An  extreme  variation  of  15  per  cent,  has  been 
reduced  to  five.  Broadly,  therefore,  the  corrections  determined 
from  the  color  difference  represented  by  the  two  test  colors  serves 
for  the  new  color  difference. 

Upon  examination,  however,  it  will  be  evident  that  while  the 
improvement  with  the  more  abnormal  observers  is  striking,  the 
ones  initially  nearer  normal  have  not  all  profited  equally.  We 
have  cases  of  under-correction  and  cases  of  over-correction.  The 
corrected  points  do  not  lie  within  1  per  cent,  of  each  other  as 
they  should  if  the  correction  were  perfect.    This  is  exactly  what 


2/0  TRANSACTIONS   I.    E.    S. — PART    I 

we  had  anticipated  from  the  preliminary  study  of  the  luminosity 
curves.  No  average  correction  can  be  expected  to  fit  the  smaller 
differences.  We  have  decided  from  our  work  that  if  an  observer 
measures  the  test  colors  off  by  less  than  5  per  cent,  that  there  is 
no  object  in  applying  this  correcting  medium  for  general  work, 
for  his  deviation  from  normal  in  all  probability  consists  in  local 
irregularities  of  the  spectrum  luminosity  curve  not  to  be  over- 
come by  an  average  correction. 

The  correcting  scheme  does  not,  therefore,  as  we  have  worked 
it  out,  obviate  the  necessity  for  selecting  a  group  of  individuals 
for  making  general  heterochromatic  measurements,  as  it  would 
do  were  the  correction  exact  for  each  individual.  We  can,  how- 
ever, modify  our  requirement  for  five  or  more  observers  whose 
mean  value  of  the  test  colors  is  naturally  correct,  into  a  require- 
ment of  five  or  more  corrected  observers. 

SUMMARY. 

A  method  for  correcting  the  spectrum  luminosity  curve  of  an 
abnormal  or  color-blind  eye  has  been  developed.  By  a  practical 
application  of  this  method  to  the  flicker  photometer  it  is  possible 
to  (1)  equip  any  observer  so  that  he  will  read  correctly  color 
differences  of  a  given  type;  (2)  equip  a  color-blind  observer  so 
that  he  will  not  only  read  correctly  color  differences  of  a  given 
type,  but  also  measure  other  color  differences  no  farther  from 
correct  than  a  random  observer  of  "normal"  vision  will  do. 

The  account  we  have  given  here  is  concerned  chiefly  with  the 
experimental  study  of  the  eye  correcting  scheme.  The  means 
developed,  involving  the  use  of  liquids  in  glass  tanks,  are  ex- 
perimental laboratory  means.  We  believe  it  to  be  possible  to 
reduce  the  results  of  the  work  to  a  more  practical  form  for  gen- 
eral use  by  the  use  of  special  glasses.  Such  practical  develop- 
ment may  be  reported  upon  later. 


bailey:    headlights  271 

INCANDESCENT  HEADLIGHTS  AND  PROJECTORS.* 


BY  P.  S.  BAILEY. 


Synopsis:  This  paper  is  intended  to  outline  the  commercial  develop- 
ment of  incandescent  headlights  and  projectors.  It  gives  a  brief  descrip- 
tion of  the  manufacture,  application  and  operation  of  various  types  of 
headlights. 


The  appearance  of  the  gas-filled  tungsten  lamp  with  a  focus- 
type  filament,  in  commercial  form,  has  stimulated  the  design  of 
several  devices  for  the  projection  of  light  from  an  incandescent 
source.  The  field  for  apparatus  of  this  description  appears  to  be 
very  broad.  Aside  from  its  application  to  the  stereopticon  and 
to  street  railway  requirements,  there  is  an  active  tendency  among 
the  steam  railroads  to  adopt  the  incandescent  head-lamp.  In 
addition,  there  is  apparently  a  considerable  opportunity  for  the 
incandescent  projector  in  marine  work,  such  as  in  the  equipment 
of  tow-boats,  launches,  and  other  small  craft,  to  enable  the  pilots 
to  locate  buoys,  landing  places,  etc.  Then,  too,  there  is  display 
lighting,  involving  the  illumination  of  flags  and  decorations,  public 
buildings,  signs  and  the  advertisement  of  seashore  resorts.  And 
lastly,  in  the  case  of  war,  for  military  and  naval  operations. 
Searchlights  are  being  employed  in  Europe  in  the  present  hostili- 
ties, as  an  aid  in  the  digging  of  trenches,  picking  up  the  wounded, 
burying  the  dead,  detecting  aeroplanes,  blinding  a  charging 
enemy,  and  assisting  in  attack. 

The  high  powered  arc  searchlights  with  the  necessary  engines, 
motors  and  generators  or  storage  batteries  to  operate  them,  are 
extremely  heavy  and  cumbersome.  For  this  reason,  the  incan- 
descent projector,  operated  from  a  portable  gasoline  electric  set 
would  appear  attractive  and  worthy  of  the  consideration  of  mili- 
tary representatives. 

Problems  concerning  the  lighting  of  thoroughfares  and  interiors 
of  practically  all  descriptions,  require  light  sources  of  relatively 

*  A  paper  read  at  a  meeting  of  the  New  England  Section  of  the  Illuminating  Engi- 
neering Society,  November  10,  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


272  TRANSACTIONS    I.    E.    S. — PART    I 

large  dimensions,  as  they  tend  to  reduce  intrinsic  brilliancy  and 
glare  and  improve  diffusion.  But  the  effectiveness  of  an  illumi- 
nant  when  used  with  parabolic  reflectors  or  lenses  depends  greatly 
upon  its  concentration  into  small  dimensions.  In  fact,  the  nearer 
the  illuminant  approaches  zero  dimensions  the  nearer  do  the 
resultant  effects  approximate  the  sharply  outlined  beams  so  impor- 
tant in  light  projection. 

Undoubtedly  these  conditions  are  better  met  by  the  crater  of 
the  carbon  arc  than  by  any  other  form  of  illuminant,  for  high 
power  work,  but  the  purpose  of  this  paper  is  to  call  attention  to 
the  demand  for  apparatus  using  a  lower  power  concentrated  light 
source,  which  does  not  require  expert  adjustment,  trimming  and 
other  minor  attention. 

After  testing  different  lenses,  reflector  lens  combinations  and 
reflectors,  I  have  come  to  the  conclusion  that  for  a  general  com- 
mercial proposition,  combining  effectiveness  of  beam,  low  initial 
cost,  maintenance,  etc.,  the  polished  parabolic  reflector  of  metal 
or  silvered  glass  has  many  points  of  superiority. 

A  parabolic  reflector  is,  of  course,  understood  to  be  a  concave 
reflector  having  a  specular  surface,  so  designed  that  all  sections 
through  the  axis  of  the  reflector  are  parabolas  of  identical  focal 
length.  Such  a  reflector  has  the  unique  property  of  reflecting  all 
rays  of  light,  emitted  from  the  exact  focal  point  and  impinging 
on  its  surface,  along  lines  parallel  to  its  axis.  Since  it  is  impos- 
sible to  obtain  mechanically  a  perfect  parabolic  reflector  and 
since  no  true  point  source  of  light  is  available,  the  ideal  parallel 
beam  is  never  realized.  Thus,  granting  that  all  sources  of  light 
have  more  or  less  definite  dimensions,  a  distinct  angular  dis- 
persion is  caused.  A  ray  of  light  proceeding  from  the  light  source 
at  the  true  focal  point  and  impinging  upon  the  reflector  will  be 
reflected  in  a  direction  parallel  with  the  axis.  Another  ray  pro- 
ceeding from  a  point  in  the  light  source  forward  of  the  focus 
will  be  converged  across  the  axis,  while  a  ray  emanating  from  a 
point  back  of  the  focus  will  diverge.  So  it  may  be  said  that  dis- 
persed cones  of  light  will  be  emitted  from  all  points  on  the  reflec- 
tor surface,  each  cone  having  an  angle  equivalent  to  that  which 
the  source  subtends  with  reference  to  the  particular  points. 

It  follows,  therefore,  that  the  angle  of  dispersion  will  increase 


BAILEY :     HEADLIGHTS  273 

with  increased  dimensions  of  the  light  source  and  decrease  with 
increased  distance  of  the  light  source  from  the  reflector,  or  in 
other  words,  with  increased  focal  length.1  Considering  the 
reflector  from  the  light  source  a  distance  sufficiently  great  that  it 
becomes  essentially  a  point,  all  the  light  cones  may  be  considered 
to  merge  into  a  single  cone  and  the  relation  which  exists  for  one 
cone  holds  approximately  for  all.  So  in  considering  the  effect  of 
a  projector  at  a  distance  of  two  or  three  hundred  times  its  diam- 
eter, it  can  be  said : 

First,  with  a  light  source  of  given  dimensions,  everything  else 
being  equal,  a  reflector  having  the  greater  focal  length  will  give 
the  greater  concentration  of  beam. 

Second,  for  a  reflector  of  a  given  focal  length,  the  angle  of 
dispersion  of  reflected  light  will  be  approximately  proportional 
to  the  dimensions  of  the  light  source. 

As  the  focal  length  is  increased,  the  parabolic  curve  opens  out 
very  rapidly  so  that  in  cases  where  the  diameter  is  limited,  a 
reflector  of  long  focal  length  will  cover  a  smaller  solid  angle  about 
the  light  source.  The  focus-type  lamp  gives  approximately  the 
same  intensity  in  all  directions,  so  that  the  light  flux  striking  the 
reflector,  which  avails  in  producing  the  beam  is  nearly  propor- 
tional to  the  solid  angle  covered  by  the  reflector.  Therefore, 
for  a  given  diameter  of  reflector,  the  shorter  the  focus  the 
greater  the  amount  of  light  flux  impinging  upon  the  reflector  and 
redirected  to  the  beam. 

In  the  practical  design  of  a  projector,  the  reflector  and  lamp 
are  of  first  importance.  The  diameter  of  the  reflector  is  usually 
limited  by  the  cost  and  the  possibility  of  mechanically  accurate 
work,  as  well  as  by  the  space  at  the  disposal  of  the  user.  For 
example,  in  the  case  of  application  to  the  automobile,  it  is  neces- 
sary for  the  designer  to  consider  proportion  as  well  as  efficiency ; 
so  that  the  diameter  of  the  reflector,  as  well  as  the  size  of  the 
incandescent  lamp,  is  limited.  Thus  a  short-focus  reflector  is 
essential  in  producing  the  most  efficient  beam,  since  it  covers  the 
greater  solid  angle  about  the  light  source. 

Electric  railway  requirements  may  be  divided  into  three  classes  : 
city,  suburban  and  interurban.    The  first  requires  in  most  cases 

1  G.  H.  Stickney,  General  Electric  Review,  Dec,  1912.  F.  Nerz,  Searchlights  ;  Their 
theory  and  Application,  Franklin,  Electric  lighting. 


2J4  TRANSACTIONS    I.    E.    S. — PART    I 

simply  a  marker  on  the  front  end  of  the  car,  as  the  streets  are 
usually  well  illuminated  from  other  sources.  The  second  requires 
sufficient  illumination  to  enable  the  motorman  to  discern  objects 
on  dimly  lighted  streets  of  the  outlying  districts.  In  the  third 
case  powerful  projected  beams  are  necessary,  since  there  is  often 
no  light  on  the  right  of  way  and  the  speed  of  the  cars  is  accele- 
rated in  many  cases  to  sixty  miles  an  hour,  or  over,  and  it  is 
imperative,  therefore,  that  the  motorman  discern  an  object  at  a 
sufficient  distance  to  allow  him  to  bring  his  car  to  a  stop  that 
he  may  avoid  striking  it. 

It  is  at  present  customary  in  practically  all  suburban  and  inter- 
urban  work  to  use  a  portable  headlight,  which  may  be  carried 
from  one  end  of  the  car  to  the  other.  Thus,  the  size  and  weight 
of  the  head  lamp  must  be  kept  within  reasonable  limits. 

Fig.  i  shows  a  type  of  incandescent  headlight  for  suburban  or 
moderate  speed  interurban  cars.  Fig.  2  is  a  headlight  for 
interurban  cars. 

A  word  on  the  development  of  the  spun  parabola  may  be  of 
interest  to  those  who  are  not  familiar  with  the  process.  First, 
a  wooden  or  steel  form  is  turned  out  on  a  lathe  so  that  the  out- 
side surface  conforms  to  the  drawing  of  the  inside  surface  of 
the  parabola  which  is  about  to  be  produced.  Then  a  piece  of 
circular  metal  stock,  of  sufficient  area  to  cover  the  form,  is 
selected  and  held  centrally  between  the  form  and  a  disk  chuck 
on  a  lathe.  The  spinner  then  proceeds  to  cause  the  circular  blank 
and  form  to  rotate  and  by  the  use  of  blunt  nose  spinning  tools 
proceeds  to  force  and  stretch  the  metal  over  the  form.  The 
piece  is  then  trimmed  at  the  edge,  skimmed  inside  and  then  sent 
to  the  finishing  room  for  plating  and  buffing.  Metal  parabolas 
may  be  produced  with  dies,  but  the  larger  sizes  are  more  success- 
fully spun. 

Glass  parabolas  are  often  pressed,  while  in  a  hot  pliable  con- 
dition, into  moulds  and  then  accurately  ground,  polished  and 
silvered.  Such  reflectors  are  naturally  truer  than  spun  metal 
ones.  Other  glass  parabolas  are  blown  into  moulds  and  prove 
sufficiently  accurate  for  all  practical  purposes.  The  pressed, 
ground  and  polished  parabolas  are  naturally  very  expensive  and 


ZT4 


Figs,  i  and  2. — Two  types  of  incandescent  headlights. 


Fig.  3  (on  left)— locomotive  headlight;  Fig.  4.— Dasher  type  headlight. 


in- 

jf^^^\ 

W 

\ 

m. 

Fig.  5  (on  left)— Incandescent  projector;  Fig.  6.— locomotive  headlight. 


Fig.  7.— A  locomotive  headlight  in  place. 


Pig.  8. — A  special  rear-end  equipment. 


BAILEY  :     HEADLIGHTS  2/5 

their  cost  precludes  their  universal  use  in  the  larger  sizes  for 
railways. 

The  shallow  parabola  n  in.  (27.9  cm.)  in  diameter,  4  in. 
(10. 1  cm.)  focus,  in  the  suburban  headlight  referred  to  above,  was 
designed  to  permit  the  use  of  lamps  having  bulbs  as  large  as 
5  in.  (12.7  cm.)  in  diameter  operating  between  80  and  125  volts, 
with  wattages  of  from  100  to  320.  The  filaments  of  these  lamps 
do  not  reach  the  degree  of  concentration  of  the  low  voltage  high 
current  lamps.  Thus  the  shallow  parabola  aids  in  preventing  too 
great  dispersion,  as  wrell  as  permitting  the  use  of  the  large  sized 
bulb. 

The  deeper  parabolas  12  in.  (30.48  cm.)  diameter,  1^  in. 
(3.49  cm.)  focus,  with  which  the  suburban  headlights  are 
equipped,  permit  the  efficient  use  of  the  more  concentrated  fila- 
ment focus-type  lamps,  operating  at  6  volts  and  105-125  volts  at 
wattages  of  36,  72  and  108,  and  23,  36,  46,  56,  y2  and  94,  respec- 
tively, having  bulbs  as  large  as  2]/%  in.  (5.39  cm.)  in  diameter. 
The  silvered  glass  parabola  is  the  more  efficient  as  it  has  the 
truer  reflecting  surface. 

The  rough  usage  to  which  this  class  of  apparatus  is  subjected, 
makes  it  imperative  that  the  lamps  and  reflectors  be  encased  as 
strongly  as  possible.  Struck-up  steel  cylinders  are  used,  which 
are  formed  from  deep  drawing  steel  in  a  die.  There  are  no 
seams,  as  this  method  provides  a  one-piece  casing  which  is  ex- 
tremely rigid.  The  doors  which  contain  the  glass  fronts  are  also 
struck-up  and  punched  hinges  are  used.  The  hanger  straps  and 
supporting  legs  are  punched  and  riveted  to  the  casing. 

Another  and  more  powerful  headlight  (Fig.  3)  having  a  rolled 
steel  casing  supported  on  a  cast  iron  base,  with  classification 
number  boxes  is  available.  This  has  been  designed  for  use  on 
electric  locomotives  but  can  be  applied  as  well  to  steam  locomo- 
tives. Here  a  larger  reflector  (20  in.  (50.8  cm.)  diameter,  2^4 
in.  (6.98  cm.)  focus)  has  been  designed.  It  can  be  furnished  in 
either  brass  or  copper,  silver  plated  and  buffed  or  in  buffed 
aluminum.  Copper  is  generally  used  for  steam  road  sen-ice  as 
the  metal  resists  the  action  of  the  gases  so  prevalent  about  large 
stations  and  roundhouses.  It  is  easier  to  spin  than  brass,  but 
does  not  usually  take  on  so  good  a  finish  as  brass,  as  the  metal  in 


276  TRANSACTIONS   I.   E.    S. — PART    I 

sheet  form  seems  of  somewhat  coarser  grain.  Aluminum  retains 
its  polished  surface,  as  a  rule,  a  little  longer  than  silver  and  is 
to  be  preferred  in  some  instances,  although  the  coefficient  of 
reflection  for  silver  plate  is  approximately  86  per  cent,  against 
approximately  61  per  cent  for  sheet  aluminum. 

It  is  quite  important  that  electric  and  steam  locomotives  em- 
ployed in  hauling  passenger  and  freight  trains  be  equipped  with 
classification  numbers  as  a  means  of  identification  for  tower  and 
switch  men.  This  has  been  taken  care  of  by  the  employment  of 
number  boxes  riveted  to  the  sides  of  the  casing.  Each  box  is 
provided  with  an  opal  glass  diffusing  member  and  a  hinged  door 
containing  a  stencil  and  clear  glass.  Both  glasses  are  puttied  into 
their  frames  to  keep  out  the  water  and  the  doors  are  made 
water-tight  where  they  fit  the  number  boxes,  being  held  tightly 
by  latches  and  wing  nuts.  Light  from  the  incandescent  lamp  is 
permitted  to  pass  through  slits  in  the  reflector  and  is  diffused  by 
the  opal  glass  sharply  defining  the  numbers  cut  in  the  black 
stencil. 

There  is  a  growing  demand  for  a  headlight  for  city  and  sub- 
urban use  which  will  project  a  beam  comparable  with  that  of  the 
more  powerful  automobile  headlights,  as  the  usual  dasher  type 
headlights  are  in  many  cases  insufficient.  Such  a  headlight 
(Fig.  4)  has  been  developed  and  apparently  meets  the  conditions 
very  nicely.  It  has  so  far  been  constructed  with  a  cast  iron  cas- 
ing, but  it  can  as  well  be  furnished  in  cast  aluminum.  A  cir- 
cumferential flange  for  attachment  to  the  car  dasher  projects 
midway  between  front  and  back,  so  that  the  device  can  be  set 
into  the  dasher.  The  casing  contains  a  deep  glass  parabolic 
mirror  approximately  8jHs  in.  (21.27  cm.)  in  diameter  and  a 
reliable  focusing  mechanism,  which,  by  the  way,  is  somewhat 
conspicuous  by  its  absence  in  similar  types  on  the  market  to-day. 
Tests  on  this  device  have  proven  quite  satisfactory.  It  could  be 
easily  converted  for  automobile  service  by  a  redesign  of  the 
casing. 

Too  much  cannot  be  said  about  the  necessity  of  accurately 
focusing  the  lamps.  A  slight  variation  from  the  proper  focal 
point  oftentimes  causes  an  amazing  reduction  in  apparent  beam 
candlepower.     The  better  forms  of  focusing  devices  permit  of 


BAILEY :     HEADLIGHTS  277 

adjustment  backward  and  forward  along  the  axis  of  the  reflec- 
tor, as  well  as  radially. 

In  such  cases  as  the  wattage  of  the  lamps  employed  will  per- 
mit, it  is  desirable  to  exclude  all  free  air  from  headlight  casings, 
as  this  prolongs  the  life  of  the  surface  of  metal  reflectors.  This 
is  accomplished  by  means  of  felt  gaskets  applied  between  the 
door  and  casing.  In  cases  where  the  wattage  of  lamps  is  so  high 
as  to  reduce  their  normal  rated  life  where  enclosed,  there  is  no 
alternative  but  to  ventilate  them  well. 

Another  problem  is  the  use  of  suitable  glass  in  the  doors.  The 
glass  must  be  of  good  quality,  low  absorption  and,  when  high 
wattage  lamps  are  used,  must  be  composed  of  two  layers  of  sec- 
tional glass,  one  section  staggered  with  respect  to  the  other,  to 
reduce  the  effects  of  unequal  expansion  and  contraction,  or  of  a 
special  single  pane  of  very  refractory  glass  to  answer  the  con- 
ditions. Oftentimes  birds,  blinded  and  dazed  by  the  glare  of  the 
headlight,  have  come  to  grief  within  the  confines  of  the  reflector 
when  the  door  glass  perchance  was  not  sufficiently  strong  to  with- 
stand the  impact. 

Fig.  5  shows  a  simple  form  of  incandescent  projector  with 
swivel  and  trunnion  base.  This  device  is  equipped  with  a  20  in. 
(50.8  cm.)  silvered  metal  parabola  with  2^4  m-  (6.98  cm.)  focus 
and  a  special  1,500  mean  horizontal  candlepower  focus-type 
tungsten  filament,  which  operates  at  approximately  30  volts,  in 
series  with  a  variable  resistance  on  no-volt  direct  current.  It 
will  operate  as  well  from  a  transformer  or  compensator  from  an 
alternating  current  cicuit. 

In  general,  I  might  say  that  for  the  highest  speed  interurban 
direct  current  service  the  tungsten  filament  lamp  so  far  has  its 
limitations  and  the  present  luminous  arc  head-lamp  will  without 
doubt  be  used  for  this  purpose  for  some  time  to  come.  The 
reason  for  this  is  that  in  order  to  reduce  the  dimensions  of  the 
tungsten  filament  sufficiently  to  put  it  on  a  competitive  basis  with 
the  arc,  it  is  necessary  to  operate  it  at  very  low  voltage  and  com- 
paratively high  current,  so  that  operating  from  a  550-volt  circuit 
the  total  wattage  becomes  a  prohibitive  factor.  Where  alter- 
nating current  circuits  are  available  a  compensator  may  be  intro- 
duced so  that  in  this  case  no  obstacle  presents  itself.    The  same 


278  TRANSACTIONS   I.    E.    S. — PART    I 

is  true  with  respect  to  storage  batteries.  Also  on  existing  25-cycle 
alternating  circuits,  the  incandescent  headlight  is  a  boon  as  the 
fluctuations  of  any  appreciable  extent  are  not  observable,  while 
in  the  electric  arc  they  are  plainly  visible. 

If  it  were  possible  to  obtain  the  ideal  case  of  parallel  rays, 
candlepower  could  not  apply  on  account  of  the  failure  of  the 
inverse  square  law.  But,  practically,  at  distances  where  the 
beam  can  be  considered  as  a  single  cone  of  light  it  is  apparent 
that  the  section  of  the  beam  will  vary  proportionally  in  area  with 
the  square  of  the  distance  from  the  reflector.  This  being  granted 
and  ignoring  the  absorption  of  the  atmosphere,  intensities  at 
various  distances  will  be  inversely  proportional  to  the  square  of 
the  distances.  Thus,  in  working  at  long  range,  there  appears  to 
be  no  reason  why  the  intensity  cannot  be  referred  to  as  apparent 
beam  candlepower,  since  this  defines  it  as  compared  with  the 
candlepower  of  the  original  light  source,  if  the  distance  at  which 
the  test  is  made  is  given. 

Apparent  beam  candlepowers  obtained  with  parabolic  reflectors 
are  enormous  as  compared  with  the  original  light  sources  without 
reflectors.  The  reason  for  this  is  that  a  large  part  of  the  flux 
of  light,  instead  of  being  radiated  in  all  directions  is  condensed 
into  a  relatively  small  angle  and  thus  reaches  a  much  higher 
intensity.  The  ratio  between  the  apparent  beam  candlepower 
and  the  mean  spherical  candlepower  of  the  light  source  is  often 
referred  to  as  the  multiplying  factor.  This  depends  upon  the 
diameter  and  focal  length  of  the  reflector,  the  dimensions  of  the 
light  source  and  the  percentage  reflection  of  the  surface. 

The  multiplying  factor  of  the  20  in.  (50.8  cm.)  diameter  sil- 
vered metal  reflector  with  2)4  in.  (6.98  cm.)  focus  equipped  with 
a  special  6- volt,  126.3-cp.  concentric  helix  filament  tungsten  lamp 
has  been  proven  by  actual  test2  to  be  approximately  5.500. 

Much  discussion  has  arisen  concerning  what  constitutes  a 
proper  apparent  beam  candlepower  for  steam  railroad  service. 
Certain  states  have  statutes  requiring  1,500  unreflected  candle- 
power.  The  special  1,500-candlepower  focus-type  tungsten  lamp 
previously  referred  to,  when  placed  at  the  focal  point  of  the 
20   in.    diameter   parabola    shown,    will   give   an    apparent    beam 

1  Test  by  I,.  C.  Porter,  Harrison,  N.  J. 


bailey:    headlights 


2/9 


candlepower  of  approximately  1,100,000.  Other  states  require 
that  an  object  the  size  of  a  man,  in  dark  clothes  be  observed  at 
a  distance  of  800  ft.  in  front  of  the  locomotive  on  a  dark  night. 

The  Report  of  the  Committee  on  Locomotive  Headlights  issued 
by  the  American  Railway  Master  Mechanics  Association  calls 
for  a  headlight  having  a  maximum  beam  candlepower  not  greater 
than  3,000,  referred  to  the  center  of  a  reference  plane,  from 
500  to  1,000  ft.   (15.24  to  30.48  km.)   ahead  of  the  locomotive 


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36-watt  focus-type  tungsten  headlight  lamp. 


and  not  greater  than  2,800  at  the  same  distances  in  front  of  the 
locomotive,  but  taken  at  20  ft.  (6.09  m.)  either  side  of  the  axis. 
(Height  of  the  headlight  9  ft.  7  in.  (2.92  m.)  above  the  rail.) 
The  20  in.  (50.8  cm.)  diameter  reflector  previously  referred  to 
in  this  article  will  accomplish  these  results  when  equipped  with 
a  suitable  tungsten  lamp. 

In  due  time  it  is  to  be  hoped  that  a  national  law  will  be  made 
to  regulate  the  intensities  of  headlight  beams.  Such  a  step  will 
serve  towards  a  considerably  greater  uniformity  in  design  than 
is  now  possible. 

Fig.  9  shows  curves  obtained  from  a  headlight  (Fig.  2) 
6 


28o  TRANSACTIONS    I.    K.    S. —  PART    1 

equipped  with  6-volt,  36-watt  focus-type  tungsten  headlight  lamp. 
The  full  line  curve  was  taken  with  a  clear  glass  door  pane.  The 
dotted  line  curve  was  taken  with  an  amber  glass  door  pane. 
Observation  tests  made  at  Lynn  show  no  apparent  reduction  in 
glare  at  the  same  measured  apparent  beam  candlepower  for  the 
amber  glass  screen  over  the  clear. 

Fig.  7  shows  a  Boston  &  Maine  locomotive  equipped  with 
turbo-generator  headlight  outfit.  Capacity  of  set  is  100  watts 
and  generator  delivers  6  volts,  9  amperes  to  the  lamp.  The 
headlight  is  here  shown  mounted  on  the  smoke-box  door  of  the 
locomotive,  while  the  turbine  and  generator  are  located  on  top 
of  the  engine  just  ahead  of  the  cab  roof. 

Fig.  8  shows  an  incandescent  headlight  applied  to  gasoline 
electric  cars.  Approximately  seventy-five  of  these  headlights  are 
in  service,  using  35-volt,  1 10-watt  focus-type  tungsten  lamps 
operated  in  series  with  a  resistance  from  a  65-volt  direct  current 
car  lighting  generator  and  are  giving  very  satisfactory  service. 

Thus  it  may  be  observed  that  considerable  attention  has  been 
given  to  the  design,  construction  and  operation  of  incandescent 
headlights  and  projectors  for  practically  all  service  requirements. 


BAYNES:     STREET    LIGHTING    IN    CHICAGO  28l 

STREET  LIGHTING  IN  CHICAGO.* 


BY    PIERRE    E.    HAYNES. 


Synopsis:  This  paper  describes  a  few  of  the  most  interesting  engi- 
neering problems  met  with  during  the  rehabilitation  of  the  street  lighting 
system  of  the  City  of  Chicago.  The  method  of  arc  lamp  selection  is  sug- 
gested as  a  method  of  approximation  which  is  generally  acceptable  to 
arc  lamp  manufacturers,  and  still  enables  the  purchaser  to  obtain  the  very 
best  value  for  his  money.  The  subway  illumination  design  is  a  distinct 
refinement  in  outdoor  lighting  where  comparatively  high  intensities  are 
desired  on  both  horizontal  and  vertical  surfaces  with  a  minimum  of  glare. 


The  first  attempt  to  illuminate  the  public  streets  of  Chicago 
was  made  in  the  year  1805.  At  that  time  the  hunters  and  trappers 
following  an  old  pathway  along  what  is  now  Archer  Avenue 
extended  their  operations  down  as  far  as  18th  or  22nd  Streets. 
The  trip  was  at  that  time  quite  difficult  and  in  order  to  guide 
the  hunters  back  to  the  fort  a  pine  knot  was  fastened  to  a  tall 
pole  and  lighted  every  night.  This  improvised  lamp  was  set  up 
probably  a  little  east  of  the  south  end  of  the  present  Rush  Street 
bridge. 

Little  or  no  attempt  at  street  lighting  was  made  until  the 
manufacture  of  coal  gas  was  started  in  the  year  1850.  The 
council  proceedings  subsequent  to  that  time  contain  many  orders 
for  the  setting  and  operation  of  flat  flame  gas  lamps.  Many 
lamps  of  this  type  remained  in  service  up  to  two  or  three  years 
ago. 

In  the  year  1887,  105  electric  arc  lamps  were  installed  east  of 
the  Chicago  River  from  Kinzie  to  Polk  Streets  and  since  that 
time  the  total  number  of  such  units  in  service  has  increased  while 
the  number  of  gas  lamps  decreased. 

The  adequate  illumination  of  the  streets  of  Chicago  requires 
the  use  of  electric  arc  lamps,  tungsten  incandescent  lamps,  ordi- 
nary and  ornamental  gas  lamps  and  incandescent  gasoline  lamps. 

The  use  of  electric  arc  lamps  is  confined  as  nearly  as  possible 
to  business  streets,  traffic  streets,  and  unshaded  residence  dis- 

*  A  paper  read  at  a  meeting  of  the  Chicago  Section  of  the  Illuminating  Engineering 
Society,  June  10,  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


2&2  TRANSACTIONS    I.    E.    S. — PART    I 

tricts  or  in  districts  where  the  density  of  population  is  not  suffi- 
ciently high  to  warrant  the  high  initial  cost  of  ornamental 
tungsten  lamp  post  construction.  The  total  number  of  arc  lamps 
in  service  is  about  19,000,  of  which  11,444  are  10-ampere  alter- 
nating current  flame  arc  lamps.  The  remainder  of  the  lamps  in 
service  consist  of  direct  current  open  and  alternating  current 
enclosed  arc  lamps,  there  being  about  1,000  of  the  former  and 
6,000  of  the  latter. 

The  keen  quality  competition  of  the  American  arc  lamp  manu- 
facturers and  the  price  competition  of  the  foreign  manufacturers 
necessitated  more  exact  methods  of  comparison  than  has  hereto- 
fore been  used  in  the  selection  of  such  units.  The  American 
manufacturers  took  ready  advantage  of  many  of  the  suggestions 
made  by  the  city's  engineers  and  as  a  consequence  changed  some 
points  in  their  lamp  design  very  materially. 

SELECTION  OF  ARC  LAMPS. 

The  proper  selection  of  an  arc  lamp  must  take  cognizance  of 
many  points  and  in  order  that  a  proper  grading  may  be  given  to 
each  type  of  lamp  submitted,  each  of  these  points  must  be  given 
a  weighting  so  that  the  grading  given  to  each  type  will  fairly 
represent  the  value  of  that  unit  under  the  conditions  for  which 
it  is  selected.  Out  of  a  total  of  168  points  allowed  for  a  perfect 
lamp,  the  various  characteristics  were  graded  as  follow- : 

Total  light  flux 10 

Light  distribution 10 

Light  constancy   10 

Light  efficiency 10 

Mechanical  efficiency    ....    5 

Regulation  of  voltage 5 

Power  factor 3 

Accessibility  of  mechanism 20 

Design 20 

Materials    20 

Reliability 30 

Orbon  consumption 25 

Attention  will  be  directed  to  the  methods  used  in  estimating  only 
two  of  the  points  listed  above,  the  other  methods  being  obvious 
from  the  name  assigned  to  the  different  characteristics. 

In  a  large  shop  the  matter  of  standardizing  stocks  of  materials, 
spare  parts,  and  shop  routine  becomes  extremely  important  if  any 


HAYNBS:     STREET   LIGHTING    IN    CHICAGO  283 

efficiency  is  to  be  obtained,  and  an  attempt  was  made  in  this  case 
to  reduce  the  number  of  parts  in  a  lamp  to  a  minimum,  to  make 
these  parts  accessible  as  they  are  assembled  in  the  lamp,  and  to 
reduce  the  number  of  special  parts  as  far  as  was  practicable.  In 
order  to  determine  which  of  the  competing  lamps  was  best 
according  to  this  standard,  accessibility  or  dissembly  tests  were 
made.  The  various  lamps  submitted  were  taken  to  the  city  shop 
and  placed  in  the  hands  of  any  operator  which  the  manufacturer 
desired  to  furnish.  This  operator  was  required  to  dissemble  and 
assemble  some  eighteen  or  twenty  parts  characteristic  to  all  lamps 
competing.  The  number  of  smallest  parts  handled  and  the  num- 
ber of  operations  were  recorded  and  the  total  for  each  lamp 
taken  inversely  represented  to  a  fair  degree  the  relative  value  of 
the  lamp  to  its  competitors.  In  every  case  the  lamp  showing  the 
best  grade  was  given  the  maximum  value  shown  on  the  table 
previously  given.  It  was  interesting  to  note  that  three  distinctly 
different  types  of  lamps  did  not  vary  more  than  25  per  cent,  from 
each  other  in  accessibility  by  this  method  of  test  while  the  various 
estimates  based  purely  upon  the  judgment  of  experienced  men 
varied  as  much  as  100  per  cent. 

In  the  matter  of  design,  the  grades  were  assigned  after  a  very 
careful  consideration  of  the  fundamental  principles  involved  and 
the  manner  and  extent  in  which  the  manufacturer  had  adhered 
to  them.  Attention  is  called  to  the  fact  that  some  serious  depart- 
ures from  a  theoretically  perfect  lamp  were  found. 

The  posts  (Fig.  3)  used  for  mounting  flame  arc  lamps  have 
been  approved  by  the  Chicago  Art  Commission  and  are  standard 
in  this  city  for  this  type  of  construction. 

LIGHTING  OF  SUBWAYS. 

In  Chicago  the  steam  railroads  are  elevated  and  at  intersections 
of  these  elevations  with  public  streets  there  are  found  what  are 
termed  "subways."  These  subways  or  viaducts  were  a  source 
of  considerable  danger  on  account  of  lack  of  illumination  until 
a  short  time  ago.  Where  the  elevation  ordinances  specifically 
require  it,  the  railroads  have  or  are  planning  to  illuminate  these 
subways  according  to  specifications  drawn  by  the  commissioner 
of  gas  and  electricity.     The  remainder  are  now  lighted  by  the 


284  TRANSACTIONS    I.    E.    S. PART    I 

city   according   to   specifications   considerably   better   than   those 
under  which  the  railroads  are  required  to  work. 

The  railroads  first  proposed  a  method  of  installation  of  sub- 
way illumination  and  one  subway  was  wired  according  to  this 
method.  Fig.  1  shows  this  subway  at  night  time  under  the  illum- 
ination provided  by  the  railroad  method.  The  shadows  and 
glare  spots  are  quite  noticeable.  The  department  of  gas  and 
electricity  then  made  an  installation  according  to  what  seemed 
to  be  the  best  and  most  practicable  method.  Fig.  2  shows  the 
result.  Here  it  is  plain  that  practically  all  shadows  have  been 
eliminated.  Subsequent  tests  showed  that  the  illumination  de- 
rived from  the  railroad  method  was  inadequate.  The  city 
method  provides  more  uniform  illumination  in  the  line  of  most 
rapid  travel,  the  vertical  surfaces  are  adequately  illuminated,  and 
the  angle  reflectors  shade  the  eyes  from  the  intense  glare  of  the 
lamps  in  the  driveway. 

Following  the  subway  illumination  work  attention  was  turned 
to  grade  crossing  illumination.  Fig.  7  shows  a  sheet  used  in  the 
department  of  gas  and  electricity  by  foremen  in  laying  out  sub- 
way and  grade  crossing  jobs.  Over  4,000  25- watt  tungsten 
lamps  are  in  use  in  the  subways  lighted  by  the  city.  Each  lamp 
serves  approximately  400  sq.  ft.  (36.8  sq.  m.)  of  subway  area. 
All  lamps  are  installed  in  high  grade  porcelain  steel  reflectors. 
Driveway  lamps  are  installed  in  angle  reflectors  and  are  placed 
over  the  curb  and  the  horizontal  axis  of  illumination  turned  45 
deg.  toward  the  direction  of  traffic. 

INCANDESCENT  LAMP  LIGHTING. 

Electric. — The  construction  of  the  ornamental  tungsten  lamp 
post  lighting  system  (Fig.  4)  made  use  of  old  gas  lamp  posts. 
This  installation  consists  of  the  old  post  with  a  top  casting  which 
supports  the  globe  and  contains  a  series  lamp  socket  with  a  film 
cut  out.  The  illumination  obtained  from  this  unit  is  of  very 
low  intensity,  quite  uniform,  and  extremely  pleasing.  Moreover, 
visual  efficiency  under  the  illumination  provided  is  very  high 
considering  the  low  foot-candle  values  found. 

Gasoline. — The  gasoline  lamp  has  been  used  for  many  years  for 
the  illumination  of  isolated  locations  where  gas  or  electricity  are 
not  available. 


Fig.  i. — Railroad  subway  lighting. 


Fig.  2. — Railroad  subway  lighting. 


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Fig.  3. — Flame  arc  lamp  and 
standard  post. 


Fig.  4.— Electric  incandescent  lamp  post 
with  street  sign  attached. 


i-u    J.     ornamental  gas  lighting 
standard. 


Fig.  6. —Standard  post  for  commercial 
lighting. 


HAYNES:     STREET   LIGHTING    IN    CHICAGO 


285 


The  amount  of  gasoline  consumed  is  65  grams  per  hour  per 
lamp  and  the  candlepower  obtained  is  in  excess  of  50  at  the  hor- 
izontal. 


~-fc- 


SUBWAY  LIGHTING 


TYPE-A 


TYPE-B 


TYPEC 


TYPED 


3  COLUMN  SUBWAY 


2  COL.  SUBWAY  Z  COL.NARROW  SUB.  OPEN  SUBWAY 
GRADE  CROSSING  LIGHTING 


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BETWEEN  TRACKS  IS  IN- 
SUFFICIENT ARCS  MUSTBE  USED 


Fig.  7. — Plan  used  in  laying  out  subway  lighting. 

Gas. — Up  until  a  very  few  years  ago  the  city  used  an  old  type 
of  incandescent  gas  lamp  which  was  capable  of  giving  from  25 
to  30  cp.  on  the  average.  This  unit  now  yields  in  excess  of  50  cp. 
measured  horizontally  and  uses  less  fuel  than  before. 


CANDLEPOWER 


Fig.  8.— Light  distribution  from  10-atnp.  alternating 
current  flame  arc  lamp  shown  in  Fig.  i. 


Fig.  9.— Light  distribution 
from  tungsten  lamp  unit 
shown  in  Fig.  2. 


The  increase  in  efficiency  of  street  lighting  in  this  city  has 
been  remarkable  during  the  last  three  years.  Both  the  number 
and  efficiency  of  units  have  been  increased  while  costs  with  the 
exception  of  the  cost  of  gasoline  units  have  decreased.  The  cost 
of  operation  of  gasoline  units  has  increased  on  account  of  the 


286  TRANSACTIONS    I.    E.    S. — PART    I 

change  in  market  price  of  the  fuel  used.  This  cost  is  now  so 
high  that  the  gasoline  lamp  is  being  replaced  as  rapidly  as  possible 
by  other  and  cheaper  types. 

The  method  used  in  checking  the  candlepower  and  continuity 
of  service  of  gas  and  gasoline  lamps  is  worthy  of  mention. 
Twenty-five  per  cent,  of  all  gas  and  gasoline  lamps  in  each  class 
of  service  are  inspected  each  month  during  the  lighted  period. 
The  condition  of  all  lamps  inspected  is  considered  as  indicative 
of  the  condition  of  all  lamps  of  that  class  of  service  for  the 
whole  month  and  a  deduction  is  made  from  the  contractor's  bill 
based  on  whatever  percentage  of  lamps  tested  or  inspected  fall 
within  the  limits  of  the  following  classes: 

Candlepower 

45     Excellent No  reduction 

35-45  Good 5% 

25-35  Fair 20% 

15-25  Bad 80% 

Out 100%         " 

Photometric  measurements  are  made  from  time  to  time,  meas- 
urements being  taken  of  horizontal  candlepower  with  all  glass- 
ware in  place  These  tests  are  made  on  the  street  using  a  port- 
able photometer  in  connection  with  a  special  adjustable  stand 
which  is  carried  on  a  wagon.  All  tests  are  taken  directly  from 
the  wagon  and  it  is  unnecessary  to  climb  out  except  to  measure 
the  distance  from  the  lamp  to  the  photometer  screen. 

ORNAMENTAL  LAMP  POSTS. 
A  demand  has  arisen  for  an  ornamental  gas  lamp.  The  use 
of  the  present  type  of  lamp  with  diffusing  glass  did  not  appear 
to  be  the  best  thing  obtainable.  Single  and  upright  mantle  lamps 
were  tried  in  spherical  globes  and  finally  a  vase  shaped  globe 
was  tried.  The  effect,  using  this  globe,  was  very  satisfactory, 
the  internal  reflection  of  the  globe  making  the  single  inverted 
unit  as  efficient  with  diffusing  glassware  as  it  was  in  the  old  type 
of  lantern  with  clear  glassware.  Exhaustive  tests  of  this  type  Of 
globe  (Fig.  5)  showed  that  it  increased  the  amount  of  downward 
illumination  with  all  mantle  combinations,  but  that  the  maximum 
increase  of  23  per  cent,  was  obtained  using  the  single  inverted 
mantle.  This  unit  will  be  used  wherever  it  is  desirable  to  have 
an  ornamental  gas  unit. 


IIAVXES:     STREET   LIGHTING   IN    CHICAGO 


287 


Various  special  problems  come  up  from  time  to  time  and 
these  are  handled  with  the  general  idea  that  fixtures  and  opera- 
tive methods  are  to  be  standard  and  that  intensity  must  be  uni- 
form and  brilliancy  low. 


CANDLEPOHER 


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Fig.  10.  — Light  distribution  from  (1)  single  upright  mantle  with  round 
white  glass  globe;  (2)  single  upright  mantle  with  vase  shaped 
white  glass  globe;  (3)  single  inverted  mantle  with  round  white 
glass  globe;  (4)  single  inverted  mantle  with  vase  shaped  white 
glass  globe;  (5)  double  inverted  mantle  with  round  white  glass 
globe;  (6)  double  inverted  mantle  with  vase  shaped  white  glass 
globe. 

The  development  of  the  new  commercial  lighting  post  (Fig.  4) 
used  principally  by  the  Commonwealth  Edison  Company  followed 
out  these  ideas  very  strictly.  The  post  itself  was  designed  by  the 
Art  Commission  and  the  choice  of  lamps,  lamp  heights,  and  glass- 
ware was  prescribed  by  the  city. 

In  the  business  districts  this  post  must  be  16  ft.  (4.87  m.) 
from  the  street  level  to  the  center  of  the  suspended  globes  and 
in  outlying  districts  this  dimension  must  be  12  ft.  (3.65  m.). 
The  increase  in  efficiency  was  remarkable  when  the  old  height 
of  10  ft.  (3.04  m.)  was  compared  with  the  newer  heights  of  12 
and  16  ft.  All  the  new  cluster  lighting  upon  Chicago  streets  must 
be  of  this  type  (Fig.  6)  at  the  end  of  five  years. 


DISCUSSION. 

Mr.  Hans  Schaedlich  :  The  lighting  system  of  Chicago  is 
different  from  that  of  any  other  city  in  the  world  in  that  the 
series  circuits  are  fed  in  multiple  from  250  kv-a.  transformers. 


_'SX  TRANSACTIONS    I.    E.    S. PART    I 

These  transformers  supply  current  for  from  six  to  fifteen  circuits 
at  a  potential  of  5,050  volts.  In  order  that  a  ground  upon  one 
circuit  may  not  react  upon  the  operation  of  the  other  circuits 
operating  from  the  same  transformer,  one  side  of  the  transformer 
must  be  grounded  permanently.  The  transformers  are  connected 
in  banks  of  three,  delta  on  the  primary  and  star  on  the  secondary 
side,  with  the  neutral  grounded.  This  system  of  operation  has 
two  special  features,  one  is  that  the  occurrence  of  a  ground 
causes  a  short  circuit  upon  the  line  and  the  other  is  that  on 
underground  circuits  there  is  a  considerable  difference  of  current 
between  the  phase  and  neutral  ends  of  the  circuit.  The  first  of 
these  peculiarities  is  taken  care  of  by  the  careful  selection  of  the 
current  regulating  device,  and  the  second  by  the  proper  balancing 
of  the  capacity  and  reactance  of  the  lines. 

The  question  of  the  gas-filled  tungsten  lamp  standing  up  under 
the  shocks  of  operation  due  to  grounds  was  satisfactorily  settled 
by  repeatedly  subjecting  two  of  these  units  to  the  worst  condition 
possible.  For  this  test  the  lamps  were  placed  upon  an  experi- 
mental circuit  fully  loaded  and  all  the  load  with  the  exception  of 
these  two  lamps  was  suddenly  short-circuited  through  an  oil 
switch.  This  test  was  repeated  some  twenty  times  and  the  lamps 
withstood  this  treatment  perfectly.  The  lamps  are  now  burning 
upon  arc  circuits.  This  test  subjected  the  lamps  to  more  excess 
rushes  of  current  than  would  occur  during  several  years  of  actual 
operation. 

The  size  of  the  unit  selected  is  the  300- watt  600-candlepower 
20-ampere  lamp.  The  lamp  housing  was  designed  by  the  city's 
engineers,  as  the  appearance  of  the  units  on  the  market  were  so 
radically  different  from  that  of  the  flame  arc  units  now  in  service 
as  to  hamper  the  uniformity  of  the  lighting  system.  Further- 
more, the  ventilation  of  the  fixtures  on  the  market  was  not  suffi- 
cient, in  the  opinion  of  the  city's  engineers,  to  properly  dissipate 
the  heat  generated  by  the  lamp. 

The  600-candlepower  lamp  is,  due  to  the  steadiness  of  its  light 
and  due  to  lack  (if  depreciation  of  the  volume  of  light  (as  during 
a  trim  of  an  arc  lamp)  at  periodic  intervals,  slightly  superior  to 
the  flaming  arc  lamp  with  its  initial  maximum  eandlepower  of 
1.1 -1  through  a  diffusing  outer  globe. 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 

VOL.  X  JUNE  lO.  1915  NO.  4 

THE  THEORY  OF  COLD  LIGHT.* 


BY  WILDER  D.  BANCROFT. 
Professor  of  Physical  Chemistry,  Cornell  University. 


Synopsis:  It  is  claimed  that  all  chemical  reactions  tend  to  emit  light 
and  that  they  all  emit  light  if  made  to  take  place  very  rapidly.  It  is 
shown  that  the  luminescence  of  salt  flames  is  a  chemiluminescence,  and 
the  method  of  determining  the  reaction  is  outlined  for  the  specific  case 
of  cupric  chloride.  If  a  suitable  chemical  reaction  can  be  made  to  take 
place  sufficiently  rapidly,  without  any  marked  evolution  of  heat,  cold 
light  is  obtained.  The  firefly  has  solved  this  problem,  though  the  nature 
of  the  substance  which  oxidizq^  is  not  known.  The  chemist  will  some  day 
solve  it  in  another  way.  The  Moore  light  is  probably  a  case  of  chemi- 
luminescence ;  but  most  commercial  forms  of  lighting  depend  on  tem- 
perature radiation  for  their  efficiencv. 


When  opaque  substances  such  as  carbon,  platinum  or  earthen- 
ware are  heated  sufficiently  they  emit  light,  the  quality  and  inten- 
sity of  which  depends  on  the  temperature  and  not  on  the  nature 
of  the  substance  heated.  Radiation  of  this  sort  is  called  tempera- 
ture radiation.  An  opaque  gas  would  also  emit  light  if  heated 
to  a  suitable  temperature.  Iodine  vapor,  for  instance,  glows1 
when  heated  to  above  5000  C.  While  this  may  not  be  entirely  a 
temperature  radiation,  it  is  usually  so  considered.  The  law  of 
temperature  radiation  holds  only  for  opaque  substances,  which 
are  sometimes  called  perfect  radiators.  An  absolutely  trans- 
parent substance  would  give  no  temperature  radiation.  At  the 
end  of  the  eighteenth  century  Wedgwood2  showed  that  heated 
air  is  not  luminous.  Subsequent  experiments  have  confirmed  this 
conclusion  of  Wedgwood's. 

Most  artificial  lighting  is  due  to  temperature  radiation  from 

*  A  paper  read  at  a  meeting  of  the  Pittsburgh  Academy  of  Sciences  and  the  Illuminat- 
ing Engineering  Society,  December  10,  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 

1  Salet;  Ann.  Chim.  Phys.  (9)  vol.  28,  p.  34  ;  1873.  Cf.  Bancroft  and  Weiser;  Jour.  Phys. 
Ch'm..  vol.  18,  p.  295  ;  1914. 

-  Phil.  Trans.,  vol.  82,  p.  272;  1892.  Cf.  Bancroft  and  Weiser;  Jour.  Phys.  Chem.,  vol  18 
p    2"!  ;   1914. 


290  TRANSACTIONS   I.   E.   S. — PART   I 

solid  particles.  In  the  kerosene  lamp  the  light  is  due  to  glowing 
particles  of  carbon.  The  difference  between  the  kerosene  lamp 
and  the  gas  jet  is  that  the  temperature  of  the  latter  is  higher. 
If  all  the  solid  particles  are  burned,  as  in  the  Bunsen  burner,  a 
so-called  non-luminous  flame  is  obtained,  even  though  the  tem- 
perature is  much  higher  than  in  the  burner  with  a  luminous 
flame.  The  brilliancy  of  the  lime  light  is  due  to  temperature 
radiation  from  intensely  heated  lime.  In  the  Welsbach  mantle 
and  in  the  Xernst  lamp  there  are  suitable  mixtures  of  rare  earth 
oxides  instead  of  the  calcium  oxide  used  in  the  lime  light.  There 
is  some  question  whether  the  light  from  the  Welsbach  mantle  is 
exclusively  due  to  temperature  radiation,  but  it  is  unnecessary 
to  go  into  that  matter  now. 

At  first  one  would  suppose  that  the  incandescent  lamp  would 
give  the  most  efficient  temperature  radiation  known  because 
graphite  melts  at  a  higher  temperature  than  any  other  known 
substance.  The  carbon  lamp  can  be  made  to  give  an  extraordi- 
nary light  efficiency,  but  its  life  is  extremely  short  under  these 
conditions.  The  graphite  vaporizes  or  disintegrates  and  the  fila- 
ment breaks.3  There  has  therefore  been  a  systematic  search  for 
substances  with  high  melting  points  and  low  vapor  pressures. 
As  a  result,  there  have  been  produced  successively  the  osmium, 
the  tantalum,  and  the  tungsten  lamps.  In  the  nitrogen-filled 
tungsten  lamp  the  thermal  radiation  has  been  cut  down  and  con- 
sequently less  power  is  needed  to  heat  the  filament  to  a  given 
temperature. 

While  it  would  be  foolish  to  claim  that  the  limit  of  efficiency 
has  been  reached,  it  must  be  remembered  that  a  large  number  of 
very  able  men  have  been  attacking  this  problem  of  temperature 
radiation  systematically  and  that  consequently  the  limit  of  effi- 
ciency is  probably  being  approached.  That  brings  up  the  question 
whether  light  may  not  be  produced  in  other  ways  than  by  tem- 
perature radiation  and,  if  so,  whether  it  is  possible  to  produce 
cold  light.  The  possibility  of  cold  light  cannot  be  disputed 
because  the  firefly  produces  it.  Langley's  studies  of  the  firefly 
have  shown  that  the  insect  gives  about  95  per  cent,  efficiency, 
meaning  thereby  that  95  per  cent,  of  the  radiations  are  in  the 

•  Werner  von  Bolton  obtained  0.3-watt  per  candlepcwer  for  a  moment  with  r  antalum 
lamp. 


BANCROFT:     THF,   THEORY   OF    COLD   LIGHT  291 

portion  of  the  spectrum  visible  to  the  human  eye  while  only 
about  5  per  cent,  of  the  radiations  are  in  the  ultra-red  portion  of 
the  spectrum  and  what  are  popularly  called  heat  rays.  The  light 
of  the  firefly  cannot  be  due  to  a  temperature  radiation  because 
the  firefly  does  not  burn  up  instantaneously.  It  is  not  a  question 
involving  life  because  the  abdominal  portion  of  the  firefly  can 
be  dried,  pulverized  in  a  mortar,  and  kept  for  two  years.  At 
the  end  of  that  time  the  powder  will  glow  if  moistened  and 
exposed  to  oxygen.  It  is  simply  an  oxidation  process.  The  fire- 
fly has  the  power  of  secreting  a  substance  which  burns  with  a 
luminous,  cold  flame.  If  one  were  to  make  in  the  laboratory  the 
unknown  substance  which  the  firefly  makes,  it  would  behave  in 
exactly  the  same  way  as  the  natural  product.  It  would  be 
amusing  to  do  this;  but  that  is  all  that  it  would  be,  because  the 
product  would  be  too  expensive  to  use  as  a  source  of  light. 
Nobody  claims  for  the  firefly  a  low  cost  of  production.  In  fact, 
it  is  not  known  how  one  would  estimate  the  firefly's  cost  of 
production. 

Under  certain  circumstances  cold  light  can  be  produced  in  the 
laboratory.  Angstrom4  has  calculated  that  he  gets  about  95  per 
cent,  light  efficiency  when  he  passes  a  current  through  nitrogen 
under  0.1  mm.  pressure.  The  losses  at  the  electrodes  and  at  the 
walls  of  the  tube  cut  the  working  efficiency  down  to  about  8  per 
cent.  From  this  work  of  Angstrom's,  it  seems  probable  that  the 
Moore  light  is  not  a  temperature  radiation  but  is  due  to  chemical 
reactions. 

Phosphorescing  substances,  such  as  zinc  sulphide,  emit  light 
at  low  temperatures  and  do  not  involve  temperature  radiations. 
As  yet,  however,  such  substances  as  Balmain's  paint,  etc.,  have 
to  be  exposed  to  light  before  they  will  emit  light.  Until  some 
other  way  of  stimulating  them  is  found,  they  are  of  more  theo- 
retical than  practical  importance.  At  present  very  little  is  known 
about  the  chemical  reactions  involved,  because  these  substances 
have  been  studied  chiefly  by  physicists. 

The  luminescence  of  salt  flames  are  of  great  importance  theo- 
retically. By  putting  different  salts  into  the  non-luminous  flame 
of  a  Bunsen  burner  different  colored  flames  are  obtained :  yellow 

4  Wied.  Ann.,  vol.  48,  p.  493 ;  1893. 


292  TRANSACTIONS    I.    E.    S. — PART    I 

with  sodium,  pink  with  lithium  or  strontium,  blue  or  green  with 
copper.  Since  the  temperature  of  the  flame  is  about  the  same  in 
all  these  cases  and  since  one  cannot  very  well  claim  selective 
absorption  in  each  case,  it  seems  certain  that  the  colors  of  these 
flames  are  not  due  to  temperature  radiation  and  the  problem  is 
to  find  out  what  does  produce  the  luminescence. 

One  usually  gets  the  same  yellow  color  with  different  sodium 
salts  and  one  is  consequently  tempted  to  say  that  the  yellow  color 
is  due  to  the  sodium  atom  when  heated  to  a  suitable  temperature. 
This  is  not  true,  however,  because  sodium  salts  emit  little  or  no 
yellow  light  in  the  hydrogen-chlorine  flame,  even  though  this  is 
fully  as  hot  as  the  flame  of  the  Bunsen  burner. "'  The  next 
assumption  is  that  the  yellow  color  is  due  in  some  way  to  sodium 
metal  and  that  the  metal  is  present  in  one  flame  and  not  in  the 
other.  The  presence  of  free  metal  in  the  flame  is  not  impossible. 
Almost  all  salts  are  formed  with  evolution  of  heat  and  conse- 
quently will  dissociate  if  the  temperature  is  high  enough.  It 
therefore  becomes  a  question  of  fact  whether  a  given  salt  dis- 
sociates in  a  given  flame  or  not.  To  test  this,  use  has  been  made 
of  a  modification  of  Deville's  hot-cold  tube.  Cold  water  was 
run  through  a  porcelain  tube  and  the  chilled  porcelain  tube  was 
held  in  the  colored  flame.  With  salts  of  copper,  cadmium,  tin, 
silver,  lead,  bismuth,  zinc,  antimony,  and  arsenic  in  the  Bunsen 
flame,  mirrors  of  the  metals  were  obtained  on  the  porcelain  tube.0 
With  salts  of  mercury  a  grey  deposit  was  obtained  consisting 
of  drops  of  mercury.  No  experiments  were  made  with  gold  or 
with  the  platinum  metals.  No  mirrors  of  tungsten  or  molyb- 
denum could  be  obtained  from  oxides  of  these  metals  in  the 
Bunsen  flame,  but  good  mirrors  were  obtained  with  the  hotter 
oxyhydrogen  flame.  From  the  cooler  portions  of  the  oxyhydro- 
gen  flame  tungsten  blue  and  molybdenum  blue  were  precipitated 
on  the  tube.  When  sulphur  dioxide  was  led  into  the  hydrogen- 
air  flame,  sulphur  was  precipitated  on  the  porcelain  tube.  No 
copper  was  obtained  when  copper  salts  were  fed  into  the  hydro- 
gen-chlorine flame,  showing  that  the  amount  of  metallic  copper 
it  in  this  flame  is  at  any  rate  very  much  less  than  in  the 
Bunsen  flame. 

*  Cf.  Bancroft  and  Weiser;  Jour  P/iys   Client.,  vol.  J>).  p.  310;  1915. 

*  Bancroft  and  Weiser  ;  J<>u> .  I'hys.  Chem.,  rol.  18,  p.  261  ;  1914. 


BANCROFT:     THE   THEORY   OF   COLD   LIGHT  293 

It  is  not  to  be  expected  that  mirrors  of  metallic  sodium  and 
potassium  would  be  produced.  There  is,  however,  some  evidence 
that  the  metals  are  actually  precipitated.  The  sodium  chloride 
is  distinctly  alkaline  when  precipitated  from  the  hottest  flames. 
This  is  probably  not  due  to  hydrolysis  in  the  heated  gases,  because 
caustic  soda  is  more  volatile  than  sodium  chloride  and  consequently 
should  be  found  in  larger  amounts  in  the  outermost  portions  of 
the  flame.  This  is  not  the  case,  for  the  sodium  chloride  from  the 
outside  of  the  flame  is  neutral.  The  greatest  alkalinity  is  obtained 
under  the  conditions  under  which  one  should  expect  to  have  the 
largest  amount  of  free  metal.  While  this  is  not  absolutely  con- 
clusive in  itself,  it  is  pretty  satisfactory  when  taken  in  connection 
with  the  behavior  of  the  other  metals. 

It  is  evident  that  a  number  of  reactions  are  taking  place  simul- 
taneously in  a  flame  colored  with  a  salt.  It  is  now  believed  that 
all  reactions  tend  to  emit  light7  and  that  they  all  emit  light  if 
made  to  take  place  very  rapidly,  the  critical  reaction  velocity 
varying  enormously  in  different  cases.  It  is  known  that  increas- 
ing the  rapidity  of  a  reaction  which  emits  light  increases  the 
intensity  of  the  light8  without  producing  much  change  in  the 
quality.  While  the  vaporized  salts  are  sometimes  colored,  as  in 
the  case  of  cupric  chloride,  and  may  therefore  give  temperature 
radiation  to  some  extent,  it  is  clear  that  most  of  the  light  emitted 
by  salt  flames  is  due  to  chemical  reactions  and  is  to  be  classified 
as  chemiluminescence. 

Some  progress  has  been  made  in  determining  the  reaction  cor- 
responding to  a  given  color.  The  following  results9  were  obtained 
for  copper  salts  in  the  Bunsen  flame: 

I.  Cuprous  ion  to  cuprous  salt  =  red. 
II.  Copper  to  cuprous  ion  =  green. 
III.  Cuprous  ion  to  cupric  salt  =  blue. 
The  first  conclusion  is  based  on  the  action  of  cathode  rays  on 
cuprous  iodide,  the  third  on  the  combustion  of  cuprous  chloride  in 
chlorine,  and  the  second  on  the  combustion  of  copper  in  oxygen. 
A  number  of  experiments  were  made  on  the  rapid  reduction  of 
cupric  and  cuprous  salts  with  sodium  and  aluminum  as  reducing 

'  Bancroft ;  Jour.  Franklin  Inst.,  vol.  175,  p.  129  ;  1913. 

8  Trautz,  Zeit.  Eleklrockemie,  vol.  10,  p.  595;  1904.     Zeit.  Phys.  Chem.,  vol.  53,  p.  10S;  1905. 
»  Bancroft  and  Weiser;  Jour.  Phys.  Client.,  vol.  18,  p.  323;  Trans.  Am.  EUctrochem . 
Soc.  vol.  25,  p.  123  ;  1914. 


294  TRANSACTIONS   I.   E.    S. — PART    I 

agents.  No  characteristic  luminescence  could  be  obtained,  pre- 
sumably because  these  reverse  reactions  were  not  made  to  go 
sufficiently  rapidly.  However  that  may  be,  it  is  clear  that  reduc- 
tions play  no  important  part  as  regards  the  light  emitted  by 
copper  salts  in  the  Bunsen  flame. 

When  a  solution  of  cupric  chloride  in  aqueous  hydrochloric  acid 
is  sprayed  into  the  Bunsen  flame,  there  is  a  red  or  violet  tip  to 
the  flame  and  when  the  flame  is  burning  steadily  one  can  often 
see  a  violet  sheath  around  the  flame.  This  is  not  a  true  lumines- 
cence, though  it  looks  like  one.  It  is  merely  the  color  of  cupric 
chloride  vapor.  It  can  be  obtained  in  mass  by  heating  copper  in 
an  electric  furnace  and  then  running  in  chlorine  or  by  volatilizing 
cupric  chloride. 

When  cupric  chloride  is  sprayed  into  a  hydrogen-chlorine  flame 
or  when  a  mixture  of  cupric  chloride  and  hydrochloric  acid  is 
sprayed  into  a  Bunsen  flame,  the  hydrochloric  acid  cuts  down 
the  dissociation  of  the  cupric  chloride  and  there  is  a  reaction  from 
cuprous  ion  to  cupric  salt  but  not  the  reaction  from  copper  to 
cuprous  ion.  Consequently  the  flame  is  blue  and  not  green.  The 
same  result  ought  to  be  obtained  without  the  acid  if  one  used  a 
flame  the  temperature  of  which  was  not  sufficient  to  dissociate 
cupric  chloride  into  free  metal  and  chlorine.  The  alcohol  flame  is 
just  on  the  dividing  line.  Cupric  chloride  colors  a  hot  alcohol 
flame  green  and  a  cooled  alcohol  flame  blue. 

Since  the  yellow  of  the  sodium  flame  is  due  to  the  reaction 
from  sodium  to  sodium  ion,  the  hydrochloric  acid  from  a  hydro- 
gen-chlorine flame  will  force  back  the  dissociation  and  cause  the 
yellow  to  disappear  practically  completely.10 

Since  the  bulk  of  the  light  in  salt  flames  is  due  to  chemical 
reactions  and  not  to  temperature  radiation,  there  is  a  possibility 
of  duplicating  the  effect,  if  one  can  cause  the  reactions  to  take 
place  sufficiently  rapidly  at  low  temperatures;  in  other  words,  if 
they  are  done  electrolytically.  Some  years  ago  Schluederberg11 
showed,  in  the  Cornell  laboratory,  that  light  is  emitted  when  an 
alternating  current  is  passed  through  lead  electrodes  in  sulphuric 
acid.    Later,  Wilkinson1-  obtained  flashes  of  light  with  a  number 

'«  Bancroft  and  Weiier  ;  Jour.  Phys.  Client.,  vol.  19,  p.  310  ;  11,15. 
>•  Jour.  Phys.  Chrm.,  vol.  12,  p.  623  ;  1908. 
>-  /old.,  vol.  13,  p.  695;  1909. 


BANCROFT:     THE   THEORY   OF   COLD   LIGHT  295 

of  metals  as  anodes,  using  a  direct  current.  Owing  to  film 
formation,  the  light  could  only  be  seen  for  an  instant.  By  press- 
ing a  tooth  brush  against  a  rotating  anode,  it  is  possible  to 
remove  the  film  as  it  gets  too  thick  and  thus  to  obtain  light  con- 
tinuously for  an  indefinite  period,  ten  minutes  for  instance.  So 
far  we  have  not  been  able  to  obtain  an  electrolytic  flame  with 
copper  which  could  be  shown  to  a  large  audience,  but  we  can  do 
this  readily  with  mercury.13 

When  mercurous  bromide  or  mercury  is  burned  in  bromine  an 
orange  light  is  emitted.  When  mercurous  or  mercuric  bromide  is 
exposed  to  the  cathode  rays  a  similar  orange  light  is  obtained. 
When  mercury  is  made  anode  in  a  cold,  fairly  concentrated, 
potassium  bromide  solution  (25  per  cent.,  for  instance)  with  an 
anode  current  density  of  about  2  amperes  per  square  decimeter, 
the  mercury  first  becomes  coated  with  a  film  of  bromide  and 
then  appears  to  glow  with  a  brilliant  orange  light.  This  will 
last  for  at  least  ten  minutes,  at  the  end  of  which  time  the  film 
of  bromide  will  have  become  so  thick  as  to  prevent  the  light 
being  seen.  By  looking  carefully  from  the  side,  light  can  still 
be  seen  between  the  film  and  the  surface  of  the  mercury.  The 
light  can  be  obtained  at  as  low  a  voltage  as  3  volts,  but  the 
intensity  is  then  very  low.  With  increasing  voltage — or  really 
with  increasing  current  density — the  intensity  of  the  light  in- 
creases, the  upper  limit  coming  when  visible  sparking  takes  place. 
The  phenomenon  is  shown  very  well  with  a  voltage  of  24-28  volts. 

This  is  not  cold  light.  It  is  not  even  a  very  efficient  light.  The 
importance  of  it  lies  in  the  fact  that  it  is  a  striking  illustration 
of  the  principle  that  reactions  emit  light  and  that  a  high  tempera- 
ture is  not  essential.  To  obtain  cold  light  one  must  find  a  reac- 
tion which  can  be  made  to  go  rapidly,  which  absorbs  heat  or 
evolves  but  a  small  amount  of  heat,  and  which  has  a  high  con- 
version factor  for  light.  A  number  of  other  requirements  come 
in.  if  it  be  stipulated  that  the  light  shall  be  suitable  for  commer- 
cial purposes.  There  is  no  immediate  prospect  of  the  present 
methods  of  lighting  being  superseded;  but  the  theoretical  feasi- 
bility of  cold  light  and  the  general  conditions  under  which  it  is  to 
be  obtained  have  been  demonstrated. 

is  Bancroft  and  Weiser  ;  Jour.  Phys.  Chem.,  vol.  18,  p.  762  ;  1914. 


296  TRANSACTIONS   I.    E.    S. — PART    I 

PIPINCx  HOUSES  FOR  GAS  LIGHTING.* 


BY  II.  R.  STERRETT. 


Synopsis:  This  paper  emphasizes  the  importance  of  having  a  specifi- 
cation which  will  thoroughly  cover  the  installation  of  all  interior  gas 
piping.  The  method  of  handling  this  phase  of  the  distribution  system  in 
one  city  is  described.  The  desirability  of  illuminating  engineers  deciding 
on  the  location  of  outlets  is  also  discussed. 


Although  the  Illuminating  Engineering  Society  has  primarily 
to  do  with  the  utilization  of  energy  in  the  form  of  light,  the  de- 
sign of  burners  and  reflectors,  the  study  of  the  effect  of  light 
upon  the  human  eye,  the  determining  of  the  quality  and  proper 
amount  of  illumination  for  the  great  number  and  variety  of  con- 
ditions under  which  artificial  light  is  necessarily  used,  it  is  the 
object  of  this  paper  to  tell  something  of  the  means  used  to  convey 
that  form  of  light  energy  commonly  known  as  illuminating  gas  to 
the  various  outlets  or  points  where  it  is  to  be  converted  by  com- 
bustion into  light  or  heat. 

Broadly  speaking,  any  distribution  system  may  be  divided  into 
four  component  parts;  mains,  sen-ices,  meters  and  house  piping, 
each  of  which  contributes  equally  to  the  satisfactory  supply  of 
gas.  Of  these  divisions  the  first  three  are  under  the  gas  com- 
pany's control,  and  hence,  are  usually  properly  installed  and 
maintained. 

A  brief  description  of  a  typical  low  pressure  distribution  sys- 
tem might  now  be  apropos. 

From  the  works  where  the  gas  is  made  there  is  a  net  work 
of  trunk  or  principal  mains,  which  act  as  feeders  for  the  thous- 
ands of  branch  pipes  which  supply  gas  to  all  parts  of  the  city. 
In  a  large  plant  gas  as  manufactured  is  forced  through  pusher 
mains  usually  of  20  in.  or  30  in.  pipe   (  go.8  or  76.2  cm.)   pipe, 

•  A  pnper  rod  at  a  meeting  of  the  Philadelphia  Section  of  the  Illuminating  Engi- 
neering Society.  March  ai,  1915. 

The  Illuminating  Kngineering  Society   is   not   responsible   for  the   statements  or 
opinions  advanced  by  contributors. 


STERRETT:     PIPING    HOUSES    FOR   GAS   LIGHTING  297 

under  a  pressure  of  from  10  to  70  in.  (0.25  to  1.78  m.)  water 
column,  the  latter  being  a  little  less  than  3  pounds  (1.36  kg.) 
per  square  inch  (6.45  sq.  cm.),  to  the  various  holders  or  re- 
serve tanks. 

The  pusher  mains  are  so  interconnected  that,  if,  for  any  reason, 
something  unforeseen  should  happen  to  either  of  the  manufac- 
turing plants,  the  other  could  instantly  take  up  the  additional 
load  without  endangering  the  continuity  of  supply.  During  the 
periods  of  low  demand  the  holders  are  filled,  and  when  the  peak 
load  conies  on  the  gas  supply  is  ample.  The  gas  is  discharged 
from  the  holder  through  governing  valves  into  the  distribution 
system,  which  is  under  a  pressure  averaging  about  3  inches  of 
water  column.  The  distribution  mains,  which  range  from  6  to 
48  in.  in  diameter,  are  so  cross  connected  and  interconnected 
that  any  break  in  the  system  affects  but  a  few  consumers.  Con- 
tinuously recording  pressure  gauges  are  set  in  different  parts  of 
the  city  so  that  any  change  in  the  gas  pressure,  due  to  increased 
or  diminished  consumption,  perhaps  caused  by  a  shifting  pop- 
ulation, can  be  adjusted  by  partly  closing  or  opening  the  holder 
valve.  In  this  way  the  general  pressure  conditions  are  kept  con- 
stant within  certain  limits. 

The  remaining  division  of  the  distribution  system,  house 
piping,  is  usually  installed  by  plumbers  or  gas  fitters,  and  does 
not  come  under  the  direct  control  of  the  gas  company.  It  is, 
therefore,  necessary  that  this  work  be  properly  inspected. 

The  importance  of  a  specification  which  will  thoroughly  cover 
the  installation  of  all  interior  gas  piping,  cannot  be  too  greatly 
emphasized.  In  order  that  such  a  specification  be  of  any  real 
value,  it  is  very  necessary  that  proper  laws  be  enacted  to  insure 
to  the  gas  company  the  enforcement  of  the  various  rules  em- 
bodied in  the  specification. 

In  one  large  city,  before  any  gas  piping  may  be  installed  in  a 
building,  it  is  necessary  to  obtain  a  permit  from  the  bureau  of 
buildings,  which  also  inspects  the  work  when  completed  and 
issues  an  approval  card  before  a  meter  may  be  set.  In  another 
city  all  piping  must  be  installed  in  accordance  with  specifications 
issued  by  the  gas  company,  whose  inspectors  supervise  the  work ; 
while  in  still  another  city  all  gas  fitters  must  be  licensed  and  file  a 


TRANSACTION'S    I.    IC.    S. — PART    I 

plan  of  the  proposed  piping  with  the  building  department  fur 
its  approval,  the  gas  company  supervising  the  installation. 

In  one  city  where  about  375,000  meters  are  in  use,  the  city 
government  by  ordinance  requires  the  gas  company  to  exercise  a 
supervision  over  the  character  of  material  used  and  work  done 
in  installing  gas  piping  and  fixtures.  In  accordance  with  the  ob- 
ligation thus  created,  the  company  has  adopted  a  specification 
for  fuel  and  illuminating  piping  and  fixtures.  This  specification 
includes  the  kind  of  material,  methods,  locations,  etc.,  to  be  used 
and  avoided  in  making  installations,  a  schedule  of  pipe  sizes  and 
lengths  for  various  consumptions,  instruction  how  to  properly 
draft  a  piping  plan,  and  an  explanation  of  just  what  is  required 
in  the  way  of  inspections  by  the  gas  company's  representatives. 

The  piping  schedule  is  based  on  Prof.  Pole's  well  known  for- 
mula for  the  flow  of  gas  through  pipes, 

n  _  r     K'(P,  -  p,) 

where  Q  =  cubic  feet  per  hour ;  d  =  diameter  pipe  in  inches 
Px   =   initial  pressure,   inches  water;   P_.   =   terminal  pressure, 
inches  water ;  L  =  length  in  yards ;  \V  =  specific  gravity  of  gas 
(air  =  1);  C  =  constant. 

A  computer  designed  by  Wm.  Cox  is  based  on  this  formula. 
and  saves  much  time  which  otherwise  would  be  spent  in  making 
calculations.     With  the  computer,  either  the  discharge,  the  re 
quired  size  pipe,  or  the  difference  in  pressure  can  be  determined, 
provided  the  other  two  are  known. 

If  the  sizes  specified  in  the  schedule  are  checked  with  the  for- 
mula they  will  be  found  somewhat  in  excess  of  the  figures  de- 
rived from  the  latter,  it  being  the  desire  of  the  gas  company  to 
make  provision  for  the  future  installation  of  additional  ap- 
pliances without  necessitating  an  increase  in  the  size  of  piping. 

The  smallest  diameter  pipe,  and  therefore  the  smallest  outlet 
permitted,  is  }$  in.  (9.52  mm.),  and  this,  it  is  assumed,  will 
usually  supply  i<>  cu.  ft.  (0.28  cu.  m.)  per  hour  at  the  average 
ire.  The  capacity  of  a  larger  outlet  as  compared  with  a 
\s-in.  outlet,  varies  directly  as  the  areas.  In  designing  a  system 
of  piping,  after  the  sizes  of  the  various  outlets  and  the  best  di- 
rection to  run  the  pipes  have  been  determined,  it  remains  to  de- 


STERRETT:     PIPING    HOUSES   FOR   CAS   LIGHTING  299 

cide  the  proper  size  piping  to  install.  This  is  accomplished  by 
starting  at  that  part  of  the  system  farthest  from  the  meter  and 
working  toward  the  latter,  determining  the  proper  sizes  by  con- 
sulting the  piping  schedule.  When  the  first  branch  line  is  reached 
the  sizes  are  again  determined  by  starting  at  the  far  end  of  the 
branch  and  proceeding  to  the  junction,  where  the  quantities  of 
gas  for  the  two  pipes  are  added  and  the  same  process  repeated 
until  finally  the  meter  is  reached. 

In  drawing  a  piping  plan,  vertical  lines  show  vertical  piping, 
horizontal  lines  show  horizontal  piping  running  the  length  of  the 
building,  while  the  slanting  lines  show  horizontal  piping  running 
the  width  of  the  building. 

When  no  outlets  are  open  the  pressure  in  a  system  of  house 
piping  is  uniform,  except  the  small  difference  due  to  elevation, 
each  10  ft.  (2.54  m.)  being  equal  to  about  V10  in.  (2.5  mm.) 
water  column.  Just  as  soon  as  a  burner  is  lighted,  gas  begins  to 
flow  through  the  piping  and,  as  a  result  of  frictional  losses,  the 
pressure  by  the  time  the  gas  reaches  the  burner  is  reduced.  Since 
it  is  necessary  to  have  a  certain  volume  of  gas  at  a  burner,  and 
since  the  volume  depends  on  the  pressure  as  well  as  on  the  size 
of  piping,  a  certain  pressure  loss  through  a  system  of  piping  must 
be  used  as  a  basic,  so  that  in  the  piping  schedule  mentioned  before 
a  loss  of  2/io-in.  water  pressure  between  the  meter  and  the  farth 
est  outlet  is  considered  as  maximum.  Then  since  there  is  from 
2Vio_  to  35/10-in.  (63.5  to  90.  mm.)  pressure  on  the  mains  and 
services,  the  pressure  at  an  appliance  connected  to  the  extreme 
outlet  would  be  from  2%0  or  3%0  in.,  there  being  about  a  3/10-in. 
drop  through  the  meter. 

Due  to  the  fact  that  there  is  a  certain  unavoidable  range  in 
pressure  over  an  area  as  great  as  that  included  by  the  limits  of 
a  large  city,  gas  appliances  are  usually  equipped  with  the  neces- 
sary means  of  adjusting  the  burner  to  take  care  of  the  different 
pressures. 

In  one  large  city  where  the  gas  company  is  responsible  to  the 
city  government  for  all  material  and  workmanship  in  the  installa- 
tion of  house  piping  three  inspections  of  interior  piping  are  made, 
the  inspectors  being  employees  of  the  gas  company,  impartial  and 
working  for  the  combined  interest  of  the  consumer  and  the  com- 


300  TRANSACTIONS   I.    E.    S. — PART    I 

pany.  When  an  installation  is  ready  for  the  first  inspection,  which 
is  made  while  the  piping  is  still  exposed,  a  plan  of  the  system  or 
extension,  plotted  on  a  regular  form,  is  forwarded  to  the  gas 
company.  The  inspector  compares  the  actual  installation  with 
the  plan,  and  tests  the  piping  for  leaks,  a  pressure  of  3  pounds 
(1.36  kg.)  per  square  inch  (6.45  sq.  cm.)  as  indicated  by  a 
6-in.  (15.24  cm.)  mercury  column,  being  applied  for  10  minutes. 
If  the  rules  have  been  complied  with,  and  the  system  is  tight, 
a  certificate  of  first  inspection  is  issued  and  the  piping  may  be 
covered.  If  any  changes  are  necessary,  they  must  be  made  be- 
fore the  certificate  is  granted.  After  all  carpenter  and  other 
building  work,  that  might  disturb  the  piping,  has  been  finished, 
and  after  the  last  coat  of  white  plaster  is  on,  the  gas  fitter 
applies  for  the  second  inspection,  which  is  principally  one  of 
pressure  and  is  made  before  any  fixtures  are  hung.  A  pressure 
test  identical  with  that  of  the  first  inspection,  is  made,  and  if  the 
piping  is  tight  a  certificate  of  second  inspection  is  given.  After 
the  fixtures  are  installed  and  the  system  is  ready  to  receive  gas, 
the  third  inspection  is  applied  for.  This,  the  last  inspection,  is 
principally  one  of  fixtures ;  the  entire  system  is  put  under  a 
pressure  of  6-in.  water  column,  which  must  show  no  drop  in  10 
minutes.  Fixtures  are  examined  for  poor  workmanship,  ob- 
jectionable design,  etc.,  and  all  gas  fixture  cocks  are  carefully 
measured  with  a  special  gauge  made  for  the  purpose  of  deter- 
mining whether  they  comply  with  the  fixture  cock  specification. 

There  is  very  little  to  say  about  the  actual  physical  house 
piping.  It  is  simply  a  case  of  determining  the  proper  location 
of,  and  the  approximate  consumption  of  gas  for,  each  outlet, 
joining  the  various  outlets  to  the  riser,  care  being  exercised  so 
that  the  piping  is  of  the  correct  size,  properly  supported,  sloping 
in  the  right  direction,  etc. 

In  ordinary  dwelling  houses,  which  form  the  great  majority  of 
cases,  a  system  of  house  piping  usually  consists  of  a  riser  or  pipe 
running  vertically  from  a  point  in  the  basement  near  the  meter, 
and  supplying  gas  at  each  floor  to  a  branch  pipe,  to  which  are 
connected  the  various  outlets  on  that  floor.  In  larger  dwellings 
two  or  more  risers  may  be  run,  all  being  supplied  by  one  meter; 
while  in  the  case  of  apartment  houses  a  separate  riser  and  meter 


STERRETT:     PIPING    HOUSES    FOR   GAS   LIGHTING  301 

supplies  each  apartment.  The  meters  are  always  installed  in  the 
basement,  and  in  some  cases  where  the  number  warrants,  a  special 
meter  room  is  built.  In  modern  manufacturing  buildings  it  is 
the  custom  to  install  a  trunk  or  common  riser,  the  meter  or  meters 
being  set  on  each  floor,  according  to  the  number  of  tenants 
occupying  it. 

In  most  cases  horizontal  gas  piping  is  run  parallel  with,  and 
under,  the  floor  boards,  which  not  only  makes  it  more  convenient 
if  the  piping  should  ever,  for  any  reason,  need  to  be  uncovered, 
but  also  assures  that  it  will  be  supported  by  the  joists  which  may 
be  notched  out  as  near  their  points  of  support  as  is  possible. 
Vertical  pipes  are  usually  run  in  hollow  partition  walls.  When- 
ever possible  it  is  preferable  to  have  the  gas  piping  exposed  to 
view. 

Piping  may  be  laid  level,  but  if  not  it  should  be  sloped  toward 
an  outlet  where  it  can  be  properly  dripped,  that  is,  where  any 
condensation  formed  might  be  conveniently  drained  off. 

After  a  system  of  piping  has  been  properly  installed,  it  needs 
very  little  attention  under  normal  conditions.  In  time  a  certain 
amount  of  scale  may  form,  and  if  this  collects  at  any  point  the 
area  will  be  reduced  and  the  pressure  lowered,  thus  causing  a 
complaint  from  the  consumer  that  the  supply  has  been  insuf- 
ficient. By  shutting  off  the  gas  at  the  meter  and  forcing  air 
through  the  pipes  by  means  of  a  hand-pump,  these  obstructions 
can  usually  be  removed.  The  decision  as  to  where  each  outlet 
should  be  placed  to  afford  the  proper  distribution  of  light,  should 
be  made  by  an  illuminating  engineer.  Of  course,  there  are  in- 
numerable little  houses  where  the  small  rooms,  usually  square 
or  oblong,  do  not  allow  fixtures  other  than  central  pendants  or 
side  wall  brackets  to  be  installed,  and  in  these  cases  it  is  of  little 
importance  that  the  various  outlets  are  located  by  one  who,  per- 
haps, knows  little  or  nothing  about  lumens,  foot-candles,  glare, 
coefficients  of  reflection,  etc.  On  the  other  hand,  there  are 
thousands  of  larger  residences,  apartment  houses,  commercial 
buildings,  and  school  houses,  where  the  size  of  the  rooms  does 
not  limit  the  type  or  location  of  lighting  fixtures.  In  structures 
such  as  these,  the  location  of  the  light  sources  should  rest  with 
one  who  is  familiar  with  the  principles  of  illumination. 


302  TRANSACTIONS   I.   E.    S. — PART   I 

The  writer's  attention  was  recently  called  to  an  instance  where, 
in  an  operation  of  the  better  class  of  dwellings,  the  living  room 
was  very  poorly  illuminated,  due  to  the  improper  location  of  the 
outlet.  By  placing  the  fixture  a  few  feet  to  one  side,  the  lighting 
could  have  been  greatly  improved.  This  is  a  case  where  good 
illumination  was  evidently  sacrificed  in  order  to  do  away  with 
running  the  extra  pipe  extension. 

In  piping  houses  for  gas,  the  outlets  should  be  properly  located 
and  the  piping  run  to  the  outlets,  instead  of,  as  is  the  rule  in  so 
many  cases,  locating  the  outlets  according  to  the  easiest  and 
least  costly  system  of  piping.  If  the  members  of  the  Illuminating 
Engineering  Society  when  the  opportunity  presents  itself,  will 
emphasize  this  point,  better  illumination  will  result  in  many  in- 
stances. 

The  cost  of  installing  a  complete,  modern  system  of  gas  piping, 
if  put  in  at  the  time  the  building  is  erected,  varies  from  about 
one-eighth  of  I  per  cent,  to  I  per  cent,  of  the  total  cost  of 
the  building.  These  figures  are  based  on  the  analysis  of  a  large 
number  of  cases,  ranging  from  an  ordinary  residence  to  large 
office  and  commercial  buildings. 


CRAVATH  :     THE   LIGHTING  OF   SMALL   INTERIORS  303 

KXOWNS  AND  UNKNOWNS  IN  THE  LIGHTING  OF 
SMALL  INTERIORS.* 


BY  J.   R.    CRAVATH. 


Synopsis:  This  paper  attempts  to  summarize  briefly  the  principal 
known  facts  to  be  observed  in  planning  the  lighting  of  small  interiors. 
Some  of  the  points  in  controversy  and  undetermined  are  stated  and  the 
author's  views  are  given  as  to  a  safe  course  to  pursue  pending  the 
acquisition  of  more  definite  knowledge  on  these  points. 


In  attempting  to  summarize  in  this  paper  some  of  the  principal 
known  and  established  facts  in  the  illumination  of  small  rooms 
I  can  necessarily  present  but  one  point  of  view,  my  own,  because 
no  two  workers  in  the  field  would  be  likely  to  agree  as  to  just 
what  can  be  considered  "known"  what  "questionable"  and  what 
"unknown."  In  my  presentation  of  this  matter  I  shall  endeavor 
to  take  what  appears  to  me  a  rather  conservative  attitude.  In 
doing  so  I  shall  doubtless  incur  the  criticism  of  some  for  having 
gone  too  far  and  that  of  others  for  not  having  gone  far  enough. 
Much  that  will  be  said  here  concerning  the  lighting  of  small 
interiors  applies  equally  to  all  classes  of  interior  lighting. 

Lighting  of  small  interiors  affects  the  comfort,  convenience 
and  pleasure  of  far  more  people  than  any  other  class  of  lighting. 

This  subject  will  be  taken  up  under  three  headings  as  fol- 
lows : 

(1)  Comfort,  efficiency  and  safety  of  the  eyes. 

(2)  Physical  efficiency  in  the  utilization  of  the  light  gen- 

erated. 

(3)  Esthetic  or  artistic  effects. 

Of  these  three  the  first  relating  to  comfort  and  efficiency  of 
the  eyes  is  by  all  means  first  in  order  of  importance.  As  to  the 
others,  whether  efficiency  in  light  utilization  or  artistic  effect  is 
the  most  important  depends  altogether  on  the  purpose  for  which 
the  small  room  is  used.  For  the  benefit  of  those  who  might  say 
that  psychology  should  be  introduced  somewhere  in  my  general 

*  A  paper  read  at  a  meeting  of  the  Chicago  Section  of  the  Illuminating  Engineering 
Society,  April  22,  1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


304  TRANSACTIONS    I.    E.    S. PART    I 

classification,  it  may  be  pointed  out  that  psychology  undoubtedly 
enters  both  into  questions  of  comfort  and  efficiency  of  the  eyes 
and  into  esthetic  effects. 

COMFORT  AND  EFFICIENCY  OF  THE  EYE. 

As  a  broad  principle  the  comfort  and  efficiency  of  the  eye  de- 
pends upon  the  distribution  of  brightness  within  the  range  of 
vision.1'2-18  It  should  be  kept  constantly  in  mind  that  what- 
ever is  said  in  this  paper  regarding  brightness  values  which  are 
good  or  bad  for  the  eye  assumes  that  the  brightness  under  con- 
sideration is  actually  within  the  range  of  vision.  The  eye  is  con- 
cerned only  with  what  it  sees.  Consequently  if  bright  light 
sources  are  not  within  the  range  of  vision  they  are  out  of  con- 
sideration except  for  the  reflection  from  them  which  may  come 
from  glossy  surfaces  which  are  within  the  range  of  vision. 

What  is  said  here  as  to  the  known  effects  of  light  upon  the  eye 
under  a  given  set  of  conditions  does  not  necessarily  apply  to  all 
individuals  because  there  is  fully  as  much  difference  between 
what  different  eyes  will  stand  as  there  is  between  the  physical 
strength  and  endurance  of  different  persons.  What  is  said  here 
is  intended  as  applying  to  most  of  the  people  most  of  the  time. 

In  the  discussion  of  brightness  values  in  this  paper  figures  will 
be  given  both  in  candlepower  per  square  inch  and  in  "apparent 
foot-candles."  An  apparent  foot-candle  of  brightness  will  be 
here  used  as  meaning  a  brightness  equivalent  to  that  of  a  perfect 
mat  diffusing  and  reflecting  surface  illuminated  to  an  intensity 
of  1  foot-candle.  It  is  452  times  the  candlepower  per  square  inch. 
While  this  is  not  yet  a  generally  accepted  method  of  expression 
I  believe  it  is  valuable  in  conveying  a  more  definite  mental  picture 
than  an  expression  in  candlepower  per  unit  area  to  those  of  us 
who  are  constantly  dealing  with  illumination  as  measured  in 
foot-candles. 

Taking  certain  well  known  natural  conditions  as  a  starting 
point,  it  is  known  that  a  clear  blue  sky  having  a  brightness  of 
about  2  candlepower  per  square  inch,  or  904  apparent  foot- 
candles,  can  be  faced  with  entire  comfort  when  it  fills  the  upper 
part  of  our  field  of  vision  outdoors  in  the  open  or  near  a  window, 
provided  the  lower  part  of  our  field  of  vision  consists  of  green 
or  gray  fields  or  some  equally  dark  surface.    It  is  only  when  the 


CRAVATH:     THE   LIGHTING   OF    SMALL    INTERIORS  305 

lower  part  of  our  visual  field  is  filled  with  light  reflected  from 
snow  or  desert  or  light  colored  roadway  that  a  normal  person 
will  experience  discomfort  facing  a  blue  sky.  However,  if  one 
faces  a  small  patch  of  this  same  blue  sky  and  from  the  rear  of  a 
small  narrow  office  so  that  it  stands  as  a  bright  patch  amid  dark 
surroundings,  it  may  be  put  down  as  a  known  fact  that  the 
majority  of  people  will  experience  discomfort  within  an  hour  or 
two  if  not  sooner. 

The  second  known  fact  in  connection  with  the  comfort  of  the 
eye  and  brightness  of  surfaces  is  that,  even  though  a  given  sur- 
face may  be  comfortable  to  face  continuously  under  bright  sur- 
roundings, a  surface  of  the  same  brightness  if  presented  so  as 
to  be  in  sharp  contrast  with  its  surroundings  (that  is  very  much 
brighter  than  its  surroundings)  may  cause  decided  discomfort  if 
continually  within  the  field  of  vision  for  some  time. 

In  the  artificial  lighting  of  small  rooms  it  is  well  known  from 
the  personal  experience  of  many  observant  people  that  the  ex- 
posure of  certain  undiffused  light  sources,  if  of  sufficient  candle- 
power,  to  adequately  light  the  room  according  to  modern  ideas 
will  cause  discomfort  to  the  eyes.  This  is  assuming,  as  said 
before,  that  those  bright  sources  are  exposed  to  the  eye  for  some 
considerable  period. 

Beginning  at  the  top  of  the  list  the  brightest  source  of  artificial 
light  with  which  one  commonly  deals  in  the  lighting  of  small  inte- 
riors is  the  tungsten  lamp  with  a  brightness  of  over  1,060  candle- 
power  per  square  inch,  or  about  479>ooo  apparent  foot-candles, 
or  more.  The  gas-filled  lamp  is  probably  2.500  to  3.000  or  more 
candlepower  per  square  inch,  or  1,130,000  to  1.350,000  apparent 
foot-candles.  As  to  the  bad  effect  of  exposed  lamps  of  such 
brilliancy  in  small  rooms  where  persons  must  face  them  con- 
tinuously there  is  practical  agreement  among  illuminating  engi- 
neers and  oculists,  although  it  is  by  no  means  known  or  agreed 
just  what  is  the  real  cause  of  the  discomfort  or  fatigue  which  is 
commonly  experienced. 

Coming  down  from  tungsten  lamps  to  sources  of  less  intrinsic 
tightness  there  is  the  carbon  lamp  which  is  still  uncomfortably 
bright,  namely,  from  400  to  600  candlepower  per  square  inch, 
corresponding  to  180,000  to  270,000  apparent  foot-candles. 


306  TRANSACTIONS   I.   E.    S. — PART   I 

The  Welsbach  mantle  of  about  31  candlepower  per  square 
inch,  or  14,000  apparent  foot-candles,  may  also  be  included 
among  the  uncomfortably  bright  sources  without  much  question. 

Next  comes  a  class  of  bright  surfaces  or  light  sources  about 
which  there  has  been  some  controversy.  These  are  the  light 
sources  just  enumerated  when  enclosed  in  diffusing  glass. 

A  frosted  tungsten  lamp  bulb  has  a  brightness  of  2  to  8  candle- 
power  per  square  inch,  or  900  to  3,600  apparent  foot-candles. 
In  this  case  there  is  an  approach  to  brightness  values  comparable 
with  the  sky  in  its  various  aspects.  However,  I  have  already 
shown  that  sky  brightness  amid  comparatively  dark  surroundings 
can  be  uncomfortable,  and  in  this  case  the  surroundings  in  an 
artificially  lighted  room  are  very  dark  compared  with  the  frosted 
tungsten  lamp.1 

The  evidence  seems  to  be  steadily  accumulating  against  the 
use  of  exposed  sources  of  this  order  of  brightness  where  they 
must  be  faced  continuously.  To  the  personal  experience  of  the 
many  who  find  it  unpleasant  to  sit  and  face  such  sources  there 
have  been  added  the  investigations  of  Dr.  C.  E.  Ferree  of  Bryn 
Mawr  College  who,  by  the  use  of  his  method  of  testing  for  eye 
fatigue,3'  4,  5  has  been  able  to  reduce  to  a  quantitative  basis 
some  observations  which  heretofore  could  be  made  only  in  a 
somewhat  haphazard  fashion.  While  it  is  true  that  the  work  of 
Dr.  Ferree's  test  so  far  has  been  confined  largely  to  his  own 
laboratory  supplemented  by  some  confirmatory  work6  done  by 
myself  in  1914,  I  personally  believe  that  as  a  result  of  these  rather 
extensive  experiments  it  may  be  put  down  as  one  of  the  knowns 
that,  in  the  lighting  of  small  rooms  where  the  exposed  sources 
are  such  as  to  have  a  brightness  of  over  1  candlepower  per  square 
inch  or  452  apparent  foot-candles,  trouble  from  eye  fatigue  and 
discomfort  will  follow  from  continuous  work  with  the  light  from 
such  concentrated  sources  shining  in  the  eyes. 

Below  1  candlepower  per  square  inch  or  452  apparent  foot- 
candles  brightness  for  the  exposed  light  sources  one  enters  a 
region  of  uncertainty  and  controversy  as  to  the  effects  on  the 
eye.  The  heavy  pressed  bowls  used  for  semi-direct  lighting  at 
the  present  time  as  actually  used  in  the  lighting  of  small  interiors 
generally  have  a  brightness  from  about  2  candlepower  per  square 


CRAVATH  :     THE   LIGHTING   OF   SMALL   INTERIORS  307 

inch,  or  904  apparent  foot-candles,  down  to  about  0.075  candle- 
power  per  square  inch,  or  34  apparent  foot-candles.  With  pure 
indirect  lighting  the  brightness  of  the  ceiling  (which  is  the  visible 
source  of  light)  usually  falls  between  50  and  4  apparent  foot- 
candles  in  small  rooms. 

The  researches  of  Dr.  Ferree3  seem  to  indicate  that  there  is 
some  eye  fatigue  when  facing  units  of  0.71  candlepower  per 
square  inch,  or  320  apparent  foot-candles  in  a  room  with  light 
colored  walls.  Extensive  tests  which  I  made  last  year6  indicated 
no  more  fatigue  with  the  subjects  facing  a  brightness  of  0.35 
candlepower  per  square  inch,  corresponding  to  156  apparent 
foot-candles,  in  the  shape  of  certain  semi-direct  lighting  bowls 
than  was  experienced  with  a  pure  indirect  system.  It  is  of  course 
obvious  that  the  pure  indirect  system  offers  the  minimum  of 
surface  brightness  with  which  it  is  possible  to  accomplish  arti- 
ficial illumination  at  the  present  time.  As  far  as  present  informa- 
tion goes  from  the  tests  cited  and  from  experience  it  seems  prob- 
able to  me  that  a  brightness  of  about  0.5  candlepower  per  square 
inch,  or  230  apparent  foot-candles,  for  semi-direct  or  luminous 
bowl  indirect  lighting  equipment  for  small  rooms  should  be 
about  the  maximum  limit.  Some  semi-direct  bowls  at  the  present 
time  offer  considerably  greater  brightness  than  this  to  the  eye, 
while  others  fall  well  under  the  limit.7 

What  has  just  been  said  applies  to  semi-direct  and  luminous 
bowl  fixtures  of  the  sizes  commonly  necessary  to  light  a  room.  If 
the  bright  area  exposed  is  small,  however,  so  that  the  total  candle- 
power  is  low  the  limits  just  suggested  may  be  comfortably  ex- 
ceeded. 

So  far  in  considering  this  subject  of  the  effect  of  the  brightness 
of  the  exposed  light  sources  upon  the  eye  in  small  interiors  only 
the  effect  of  the  light  which  goes  directly  from  the  sources  to  the 
eye  has  been  considered.  However,  there  is  another  class  of 
effects  closely  allied  to  the  first,  namely,  the  reflection  from 
smooth  or  polished  surfaces,  one  example  of  which  is  commonly 
known  as  "glare  from  paper."  One  of  the  thoroughly  known 
facts  is  the  annoyance  and  eye-straining  effects  of  this  glare 
from  paper,  polished  tables,  and  all  smooth  polished  surfaces. 
This  glare  is  simply  the  result  of  reflection  from  the  original 


308  TRANSACTIONS    I.    E.    S. PART    I 

light  sources.  It  is  obvious  that  whatever  is  done  to  diffuse  the 
light  from  such  sources — that  is,  to  enlarge  the  area  from  which 
the  light  comes — and  reduce  the  brightness  will  be  beneficial  in 
reducing  the  glare  from  paper.  The  same  things  that  are  bene- 
ficial in  diffusing  the  light  from  exposed  surfaces  for  the  comfort 
of  the  eye  are  beneficial  in  reducing  this  glare  from  paper. 

In  some  cases  as  with  a  shaded  reading  or  desk  lamp  the  source 
of  light  is  shaded  from  the  eyes  of  the  occupants  of  the  room,  but 
is  not  shaded  from  the  papers  which  are  being  read.  In  such 
cases  the  position  of  the  lamp  with  reference  to  the  paper  and  the 
eye  is  all  important  as  the  eye  should  not  be  in  a  position  to 
receive  glare  from  the  page.  The  correct  position  may  or  may 
not  be  easy  to  attain. 

It  may  be  taken  as  fully  known  and  demonstrated  that  diffused 
light  is  best  for  reading  and  working  on  papers  and  polished  sur- 
faces. Much  of  the  pleasing  quality  of  daylight  for  reading  is 
due  to  its  diffuse  character.  For  sewing  on  cloth  where  the 
direction  of  the  light  is  such  that  shadows  do  not  interfere, 
direct  light  is  equally  satisfactory. 

The  result  of  hundreds  of  tests  on  many  individuals  9- IQ.  Ir  on 
the  amount  of  light  preferred  for  reading  shows  that  the  majority 
asked  for  a  lower  intensity  with  diffuse  than  with  direct  or  more 
uni-directional  lighting.  In  my  opinion,  considering  the  method 
of  making  these  tests,  these  results  should  be  interpreted  as  mean- 
ing that  the  diffuse  lighting  is  more  satisfactory  rather  than  as 
indicating  that  one  can  with  safety  plan  for  less  illumination  with 
diffused  or  indirect  systems.  When  the  quality  of  illumination 
is  not  satisfactory  most  people  ask  for  more  quantity  regardless 
of  the  real  trouble. 

It  is  established  beyond  controversy  that  a  purely  localized 
illumination  is  not  satisfactory.8- I9  The  eye  has  not  been  evolved 
under  conditions  such  as  prevail  with  a  bright  area  in  the  center 
of  the  visual  field  with  the  surroundings  dark.  This  is  the  con- 
dition that  one  finds  with  purely  localized  light  such  as  is  fur- 
nished with  an  opaque  shade  concentrating  light  on  some  spot 
upon  which  we  are  working  with  the  eye;  the  rest  of  the  room 
being  in  darkness. 

If  we  cannot  get  all  our  light   for  working  purposes   from 


cravath:    the  lighting  of  small  interiors  309 

diffusing  sources  such  as  day  skylight  and  indirect  artificial  light 
we  should  at  least  provide  as  large  a  portion  of  the  total  light  in 
the  shape  of  general  diffuse  light  as  possible.  If  necessary  for 
reasons  of  economy  this  can  then  be  supplemented  by  such  amount 
of  localized  light  as  is  necessary  for  the  particular  purpose  in 
hand.  The  presence  of  a  considerable  amount  of  general  light- 
ing, especially  if  it  is  well  diffused,  greatly  enhances  the  comfort 
with  which  work  can  be  done  under  the  localized  light. 

In  the  lighting  of  small  offices,  daylight  coming  through  win- 
dows usually  has  one  important  advantage  over  diffused  arti- 
ficial light  coming  from  a  ceiling,  namely,  the  direction  of  the 
light.  Even  with  the  best  diffused  indirect  artificial  light  or 
natural  skylight  from  windows  there  is  some  trouble  from  specu- 
lar reflection  or  glare  from  paper.  It  is  easier  to  avoid  this 
specular  reflection  when  the  light  is  coming  from  one  side  as  it 
does  from  a  window  than  when  it  comes  from  above.  In  a  large 
interior  these  difficulties  largely  disappear  because  of  the  large 
expanse  of  lighted  ceiling  which  increases  the  diffuse  character 
of  the  light  received  upon  a  page. 

Those  who  would  put  unshaded  bracket  or  table  lamps  almost 
in  the  line  of  vision  in  a  small  room  should  remember  that  it  has 
been  well  demonstrated  in  connection  with  experiments  on  street 
lighting  both  by  Mr.  A.  J.  Sweet12'  '3  and  by  Mr.  Preston  S. 
Millar14  that,  when  a  lamp  is  brought  within  a  range  of  about 
25  degrees  of  the  object  which  one  is  looking  at,  it  has  a  blind- 
ing effect  which  necessitates  more  illumination  on  the  object  in 
order  to  see  it  with  equal  clearness.  This  effect  increases  as  the 
light  is  brought  nearer  to  the  line  of  the  center  of  vision. 

When  the  edge  of  a  lamp  shade  is  below  the  level  of  the  eye 
all  that  is  necessary  to  guard  the  eye  from  the  direct  light  of  the 
filament  is  to  have  the  source  slightly  above  the  edge  of  the 
shade.  When,  however,  the  edge  of  the  shade  is  above  the  eye 
of  a  person  sitting  in  the  room  much  more  care  must  be  used  as 
to  the  correct  position  of  the  source  with  reference  to  the  shade 
or  reflector.  A  lamp  at  ordinary  chandelier  heights  can  only  be 
properly  shaded  when  the  edge  of  the  reflector  protects  the  eyes 
from  direct  rays  emanating  from  the  lamp  at  angles  in  excess  of 
about  25  degrees  from  the  vertical.     If  this  rule  is  adopted  the 


310  TRANSACTIONS   I.    E.    S. — PART   I 

eyebrows  of  the  average  person  will  shade  the  eyes  when  the 
person  approaches  within  the  25-degree  zone  and  the  reflector  will 
shade  the  eyes  when  the  person  is  outside  of  the  25-degree  zone. 
Of  course,  this  angle  will  vary  somewhat  for  different  individuals, 
but  25  degrees  is  a  good  working  average. 

As  to  effect  of  color  on  eye  efficiency  and  comfort  little  is 
known  save  that  a  nearly  monochromatic  or  one  color  light  like 
the  mercury  vapor  is  better  for  work  on  fine  details.15' l6 

In  the  lighting  of  small  offices  and  desk  lighting  in  residences 
shadows  play  an  important  part  in  determining  the  satisfactory 
or  unsatisfactory  character  of  the  illumination  from  an  ocular 
standpoint.  The  more  diffused  the  lighting  the  greater  the  free- 
dom from  sharp  shadows.  If  semi-direct  or  indirect  lighting 
with  luminous  bowl  fixtures  is  employed  the  minimum  amount  of 
shadow  is  obviously  obtained  when  the  brightness  of  the  bowl 
does  not  exceed  that  of  the  ceiling.  The  more  the  brightness  of 
the  bowl  exceeds  that  of  the  ceiling  the  greater  the  noticeable 
shadow  to  cause  annoyance.  Annoyance  from  shadows  is  not 
serious,  however,  until  the  light  direct  from  the  bowl  exceeds  15 
per  cent,  of  the  total,  as  determined  by  Mr.  T.  W.  Rolph.1T 

The  brightness  of  the  fixture  bowls  in  semi-direct  lighting  of 
offices  and  most  work  rooms  is  limited  more  by  the  importance  of 
avoiding  shadows  than  by  the  brightness  values  which  will  be 
comfortable  to  face.  In  other  words,  it  is  usually  permissible  to 
use  a  somewhat  brighter  bowl  in  a  living  room  or  dining  room 
than  in  an  office. 

EFFICIENCY  OF  LIGHT  UTILIZATION. 

By  efficiency  is  meant  the  percentage  of  the  light  generated 
which  is  delivered  on  a  plane  level  with  a  common  table  top, 
30  inches  (76.2  cm.)  from  the  floor.  This  depends  on:  (1)  The 
color  or  reflecting  power  of  ceiling,  walls  and  floor;  (2)  the  shape 
of  the  room;  (3)  the  reflector  and  globe  equipment;  (4)  the 
locations  of  the  lamps. 

Color  of  ceilings,  walls  and  floors  may,  it  has  been  demon- 
strated by  Lansingh  and  Rolph,  make  a  difference  of  over  4  to  1 
in  the  illumination.  When  dealing  with  common  colors,  however, 
I  think  a  difference  of  2  to  1  would  be  the  ordinary  range  unless 


CRAVAT H  :     THE   LIGHTING  OF    SMALL   INTERIORS  31  I 

it  is  attempted  to  use  indirect  lighting  with  a  dark  ceiling  when 
the  ratio  would  be  very  high. 

A  low  square  room  will  show  the  least  loss  of  light  by  absorp- 
tion and  a  high  narrow  room  the  greatest.  In  other  words,  the 
greater  the  wall  area  in  proportion  to  the  floor  area  the  lower  the 
efficiency. 

The  globe  or  reflector  equipment  has  a  great  influence  on  effi- 
ciency, but  comparative  figures  on  this  must  necessarily  apply  to 
only  one  given  set  of  conditions  because  the  comparative  rank 
of  the  different  equipments  will  change  with  room  colorings  and 
lamp  locations.  For  example,  an  indirect  system  obviously  is 
more  affected  by  ceiling  color  than  a  direct  system. 

As  to  locations  of  lamps  a  central  location  is  more  efficient 
than  locations  near  the  walls. 

A  table  covering  efficiencies  even  for  the  commonest  of  prac- 
tical conditions  would  be  too  bulky  for  ordinary  use.  However, 
the  following  will  serve  to  give  some  idea  of  the  usual  ranges  of 
efficiency  figures  for  certain  conditions. 

For  a  typical  room  15  feet  (4.57  m.)  square  by  9  feet  (2.74  m.) 
high,  assuming  a  light  ceiling  in  each  case  the  light  falling  upon 
the  working  plane  in  percentage  of  total  light  emitted  by  the  lamp, 
with  the  light  all  generated  by  a  tungsten  or  gas  mantle  lamp  at 
one  central  outlet  will  be  about  as  Table  I : 

TABLE  I. 
Efficient  bowl-shaped  opal  or  prismatic  reflec- 
tors at  ceiling  45  to  60  per  cent. 

Frosted  enclosing  globe  at  ceiling 25  to  40  per  cent. 

Bare  unshaded  lamp  near  ceiling 30  to  45  per  cent. 

Indirect,  mirrored  reflectors   25  to  35  per  cent. 

Indirect,   white  enameled  reflectors 21  to  31  per  cent. 

Mirrored  reflector,  at  ceiling,  deep 70  to  80  per  cent. 

Aluminum  finished  metal  at  ceiling,  deep 45  to  60  per  cent. 

White  enameled  metal  at  ceiling 45  to  60  per  cent. 

The  foregoing  figures  apply  to  clean  lamps  and  reflectors. 

In  office  buildings  of  our  larger  cities  where  soft  coal  is  used,  a 
decrease  of  illumination  due  to  accumulation  of  dirt  may  be  fig- 
ured at  about  n  per  cent,  in  one  month  in  all  systems  where 
reflectors  are  employed. 


312  TRANSACTIONS    I.    E.    S. PART    I 

ESTHETIC  OR  ARTISTIC  EFFECTS. 

This  is  the  most  difficult  part  of  the  subject  in  which  to  lay 
down  definite  laws  and  establish  facts  for  the  reason  that  indi- 
vidual tastes  and  opinions  vary  so  greatly.  The  old  saying  that 
'"there  is  no  accounting  for  tastes"  is  simply  one  way  of  express- 
ing the  difficulty  of  formulating  any  rules  regarding  matters 
which  involve  individual  opinion  as  to  what  does  or  does  not 
"look  well."  The  most  that  can  be  done  is  to  make  a  few  obser- 
vations as  to  the  observed  trend  of  public  opinion  in  some  of 
the  more  important  matters  relating  to  lighting  small  interiors. 

First  it  must  be  recognized  as  a  general  principle  that  a  large 
number  of  people  will  not  consider  that  any  arrangement,  style 
or  design  looks  right  unless  it  corresponds  closely  with  present 
conditions.  With  another  class  of  people  novelty  and  change 
rather  than  adherence  to  present  conditions  are  sought  after. 

On  the  question  of  color  it  must  be  recognized  that  for  genera- 
tions artificial  lighting  has  been  done  with  illuminants  rich  in 
yellow  and  deficient  in  green  and  blue.  The  only  exception  to 
this  is  the  Welsbach  gas  mantle  and  to  judge  from  the  state- 
ments made  at  the  last  meeting  of  our  section  by  Mr.  Luther 
that  type  of  mantle  is  most  popular  in  the  lighting  of  small  rooms 
which  tends  to  bring  out  the  reds  and  yellows  and  suppresses  the 
greens  and  blues.  It  may  be  taken  as  established  that  any  light 
which  does  not  have  a  sufficient  percentage  of  red  and  yellow  in 
its  composition  or  has  too  much  green  and  blue  is  likely  to  create 
a  ghastly  appearance  of  hands  and  faces.  It  also  renders  unat- 
tractive rugs,  carpets  and  wall  paper  in  which  yellow  and  red  hues 
are  prominent. 

It  is  a  matter  of  controversy  and  personal  taste  and  opinion  as 
to  whether  the  gas  filled  tungsten  lamp  and  amber  tint  Welsbach 
mantle  give  a  light  which  needs  modification  toward  the  yellow  in 
order  to  be  most  acceptable  for  common  use  in  residences.  As 
these  sources  are  considerably  more  yellow  than  any  kind  of  day- 
light it  seems  probable  that  a  part  of  the  objections  to  these 
illuminants  is  due  to  the  fact  that  they  are  whiter  than  the  arti- 
ficial illuminants  to  which  we  have  been  formerly  most  accus- 
tomed, and  that  some  of  these  objections  will  gradually  become 
less  as  the  whiter  types  of  illuminants  become  more  common. 


CRAVATH  :     THE   LIGHTING   OF   SMALL    INTERIORS  313 

Nevertheless  it  must  be  accepted  as  demonstrated  that  the  yellow 
illuminants  of  the  older  types  or  the  present  illuminants  modified 
by  globes  or  ceiling  tints  to  make  them  more  yellow  produce  some 
very  agreeable  effects  on  complexions  and  on  some  kinds  of 
room  furnishings.  With  direct  lighting  the  color  can  be  easily 
controlled  for  most  practical  purposes  by  the  use  of  the  proper 
glassware  and  for  indirect  lighting  the  color  of  the  ceiling  largely 
influences  the  ultimate  results.  Such  color  modifications,  how- 
ever, always  means  loss  of  efficiency  and  allowance  must  be 
made  for  this. 

The  direction  and  character  of  shadows  have  important  effects 
on  objects  in  a  room  and  these  shadow  effects  have  to  be  more 
considered  in  small  interiors  where  the  sources  of  light  are  fewer 
in  number  than  in  large  interiors.  Where  light  is  largely  uni- 
directional, that  is,  direct  from  a  small  bright  source  with  insuffi- 
cient diffuse  lighting  to  modify  it,  the  sharp  shadows  which  result 
help  to  bring  out  wrinkles  and  give  a  harsh  appearance  to  com- 
plexion and  features.  Diffuse  lighting  either  from  ceilings  and 
walls  or  from  windows  and  skylight  does  not  in  practice  do  away 
entirely  with  shadows,  but  rather  softens  them  to  an  extent  which 
renders  the  general  appearance  of  persons  and  objects  much  more 
pleasing. 

As  to  whether  there  should  be  a  visible  source  of  light  on  the 
lighting  fixture  there  is  no  agreement.  Many  like  to  see  a  little 
light  coming  from  the  fixture  itself  for  decorative  purposes. 
Others  care  nothing  about  this. 

To  some  the  localized  lighting  effect  produced  by  a  dome  over 
the  dining  room  table  or  by  a  table  reading  lamp  which  lights 
one  spot  brightly  and  leaves  the  rest  of  the  room  somewhat  in 
shade  produces  a  cozy  effect  which  is  pleasant.  Others  feel  that 
they  cannot  feel  cheerful  without  having  the  whole  room  brightly 
lighted. 

Objections  have  been  raised  to  indirect  and  semi-direct  light- 
ing that  the  ceiling  is  too  bright  and  that  it  reverses  the  old  order 
of  things  too  much.  Others  seldom  think  of  this  effect.  Tastes 
in  these  matters  are  largely  a  question  of  environment  and 
education. 


314  TRANSACTIONS   I.   E.    S. — PART   I 

BIBLIOGRAPHY. 

1.  Cravath,  J.  R.,  Brightness;  Trans.  I.  E.  S.,  1914,  p.  394. 

2.  Ives,  Herbert  E.,  The  Measurement  of  Brightness  and  Its  Significance ; 

Trans.  I.  E.  S.,  1914,  p.  183. 

3.  Ferree,  C.  E.,  and  Rand,  G.,  Further  Experiments  on  the  Efficiency  of 

the   Eye   under   Different   Conditions   of   Lighting;    Illuminating 
Engineering  Society,  Cleveland  Convention,  1914. 

4.  Ferree,  C.  E.,  The  Efficiency  of  the  Eye  under  Different  Systems  of 

Illumination ;   Illuminating  Engineering  Society,   Pittsburgh  Con- 
vention, 1913. 

5.  Ferree,  C.  E.,  Tests  for  the  Efficiency  of  the  Eye  under  Different  Sys- 

tems of  Illumination  and  a  Preliminary  Study  of  the  Causes  of 
Discomfort;  Trans.  I.  E.  S.,  1913,  p.  40. 

6.  Cravath,   J.   R.,    Some   Experiments   with   the   Ferree   Test   for   Eye 

Fatigue;  Trans.  I.  E.  S.,  1914,  p.  1033. 

7.  Rowe,  E.  B.,  and  Magdsick,  H.  H.,  A  Photometric  Analysis  of  Diffus- 

ing Glassware  with  Varying  Indirect  Components ;  Trans.  I.  E.  S., 
1914,  p.  220. 

8.  Light :  Its  Use  and  Misuse ;  Illuminating  Engineering  Society  publi- 

cation. 

9.  U.  S.  Postal  Car  Lighting  Tests  on  B.  &  O.  R.  R. ;  Proceedings  Asso- 

ciation of  Railway  Electrical  Engineers,  1912. 

10.  Standard  Specifications  for  U.  S.  Postal  Cars  issued  by  the  Govern- 

ment. 

11.  Cravath,  J.  R.,  The  Effectiveness  of  Light  as  Influenced  by  Systems 

and  Surroundings;  Trans.  I.  E.  S.,  191 1,  p.  782. 

12.  Sweet,  Arthur  J.,  An  Analysis  of  Illumination  Requirements  in  Street 

Lighting;  Journal  of  the  Franklin  Institute,  May,  1910. 

13.  Sweet,  Arthur  J.,   Glare  as  a  Factor  in   Street   Lighting;   Electrical 

Review  and  Western  Electrician,  Mar.  6,  1915. 

14.  Millar,  Preston  S.,  Some  Neglected  Considerations  Pertaining  to  Street 

Illumination;  Trans.  I.  E.  S.,  1910,  p.  653. 

15.  Luckiesh,  M.,  The  Influence  of  Spectral  Character  of  Light  on  the 

Effectiveness  of  Illumination;  Trans.  I.  E.  S.,  1912,  p.  135. 

16.  Bell,  Louis;  Electrical  World,  May  11,  1911,  p.  1163. 

17.  Rolph,  Thomas  W.,  The  Engineering  Principles  of  Indirect  and  Semi- 

indirect  Lighting;  Trans.  I.  E.  S.,  1912,  p.  549. 

18.  Woodwell,  J.  E.,  The  Intrinsic  Brightness  of  Lighting  Sources ;  Trans. 

I.  E.  S.,  1908,  p.  573. 

19.  Cobb,  Percy  W.,  Vision  as  Influenced  by  the  Brightness  of  Surround- 

ings ;  Trans.  I.  E.  S.,  1913,  p.  292. 


IVES:    DEFINITIONS,  STANDARDS,  PHOTOMETRIC  METHODS     315 

PROPOSALS  RELATIVE  TO  DEFINITIONS,  STAND- 
ARDS AND  PHOTOMETRIC  METHODS.* 


BY  HERBERT  E.  IVES. 


A  series  of  studies  in  photometry,  more  particularly  in  connec- 
tion with  lights  of  different  color,  has  led  the  writer  to  suggest 
the  adoption  of  a  new  standard  of  luminous  flux  and  of  a  definite 
photometric  method  in  heterochromatic  photometry.  The  steps 
leading  to  these  suggestions,  and  the  arguments  in  favor  of  their 
adoption,  are  to  be  found  in  the  papers  listed  in  the  bibliography 
at  the  end.  What  is  here  presented  for  publication  in  the 
Transactions  of  the  society  is  a  specific  set  of  suggestions  in 
tabular  form,  to  be  taken  up  later  for  consideration,  if  desired, 
by  the  appropriate  committee  of  the  society. 

DEFINITIONS. 

Pozver  consumed  by  a  light  source  =  P ;  expressed  in  watts,  a 
portion  of  which  is  dissipated  by  radiation,  the  remainder  by  con- 
duction and  convection. 

Power  radiated  by  a  source  =  R  =    I    RA  d\  =   power  emitted 

Jo 

by  a  light  source  in  the  form  of  radiation  between  wave-lengths 
o  and  00  ,  expressed  in  watts. 

Radiation  efficiency  =  —   =  ratio  of  the  power  dissipated  as 

radiation  to  the  total  amount  of  power  consumed  by  the  source. 
(A  pure  numeric.) 

Luminous  flux  =  F  =  radiant  power  evaluated  according  to 
its  capacity  to  produce  the  sensation  of  light. 

Light  evaluating  factor  or  stimulus  coefficient  of  any  radiation 
is  the  ratio  of  the  luminous  flux,  in  its  appropriate  units,  to  the 
radiant  power  producing  it,  in  its  appropriate  units. 

The  luminous  efficiency  of  any  radiation  =  Lr  =  the  relative 
capacity  of  the  radiation  to  produce  the  sensation  of  light,  com- 

*  A  paper  presented  at  a  meeting  of  the  Philadelphia  Section  of  the  Illuminat- 
ing Engineering  Society  May  21,  1915. 

The  Illuminating   Engineering    Society  is  not   responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


3l6  TRANSACTIONS    I.    E.    S. PART    I 

pared  with  the  capacity  of  the  same  quantity  of  radiation  of  the 
maximum  possible  light  producing  capacity  .  (A  pure  numeric.) 
The  luminous  efficiency  of  any  radiation  is  the  mean 
value  of  the  luminous  efficiencies  of  its  component  mono- 
chromatic spectral  radiations.  These  latter  are  specified 
by  the  luminosity  curve  of  the  normal  equal  energy  spec- 
trum, of  maximum  value  unity.  The  spectral  luminosity 
curve  is  obtained  by  the  standard  photometric  method  for 
colored  light  photometry. 

To  a  close  approximation  the  spectral  luminosity  curve 
is  represented  by  the  expression : 

R3 
\ 


La 

-A(4 

•  e         a 

r 

+>(. 

R2 

A 

1  — 
-  e 

wh 

ere 

A  = 

=  0.999 

Ri  = 

=  0 

556 

B  = 

=  0.04 

R2  = 

=  0 

465 

C  = 

=  0.095 

Rs  = 

=  0 

.610 

y+c(- 


a  =  200 
/?=  400 

7=1 000 

Total  luminous  efficiency  of  a  light  source  =  Lt  =  the 
relative  capacity  of  the  power  applied  to  a  light  source  to  produce 
the  sensation  of  light,  compared  with  the  capacity  of  the  same 
quantity  of  power  in  the  form  of  radiation  of  maximum  possible 
luminous  efficiency.     (A  pure  numeric.) 

Units. — Luminous  flux  is  connected  to  radiant  power  by  a 
numerical  evaluating  factor.  The  unit  of  power  is  the  watt.  The 
present  arbitrary  practical  unit  of  luminous  flux  is  the  lumen. 
The  light  evaluating  factor  or  stimulus  coefficient  is  consequently 
expressed  in  lumens  per  watt.  If  for  this  evaluating  factor  is 
taken  the  luminous  efficiency  as  above  defined,  the  unit  of  lumi- 
nous flux  is  the  same  as  that  of  radiant  power  or  applied  power, 
namely  the  watt. 

In  the  symbols  proposed: 

PXyXLR  =  PXLT  =  F. 

In  order  to  go  over  to  the  watt  as  the  unit  of  luminous  flux  it 
is  necessary  to  know  the : 

Mechanical  Equivalent  of  Light  =  the  value  of  the  lumen  in 
watts  of  luminous  flux. 


IVES:    DEFINITIONS,  STANDARDS,  PHOTOMETRIC  METHODS     317 

(The  lumen  is  approximately  0.00162  watt  of  luminous  flux, 
or  light  watts.) 

(The  terms  "specific  consumption,"  "specific  output,"  etc., 
involving  relationships  between  watts  and  lumens,  are  super- 
seded by  the  method  of  defining  luminous  efficiency,  and  by  the 
adoption  of  the  watt  as  the  unit  of  luminous  flux.) 

The  quantities  derived  from  luminous  flux,  e.  g.,  illumination, 
luminous  intensity  and  brightness,  are  to  be  defined  as  at  present, 
with  the  necessary  substitution  of  the  watt  of  luminous  flux  for 
the  lumen  wherever  occurring.  It  is  suggested  that  the  new 
unit  of  luminous  intensity  on  the  watt  basis,  might  be  called  the 
"pyr." 

METHODS  OF  MEASURING  LIGHTS  OF 
DIFFERENT  COLOR. 

Visual  Method. — The  visual  method  is  specified  by  the  type  of 
photometric  instrument,  the  conditions  of  its  use  and  the  choice 
of  observers. 

The  instrument  shall  be  the  flicker  photometer,  in  which  the 
photometric  field  shall  be  two  degrees  in  diameter,  with  a  sur- 
rounding field  of  as  large  diameter  as  feasible,  of  approximately 
the  same  brightness.  The  photometric  field  shall  be  maintained 
at  an  approximately  constant  brightness  of  0.013  watt  of  lumi- 
nous flux  per  square  meter  per  unit  solid  angle  (the  brightness 
of  a  white  mat  surface  under  an  illumination  of  25  meter- 
candles,  present  practical  units). 

Precision  measurements  should  be  made  by  a  group  of  at  least 
fifty  observers  who  possess  no  marked  abnormalities  of  vision,  or 
by  a  group  of  not  less  than  five  whose  average  readings  are  the 
same  as  those  of  the  larger  group. 

(A  group  of  five  or  more  may  be  considered  as  constituting  a 
normal  eye  group  when  their  average  value  on  the  following 
color  difference  is  equality. 

Color  A — 72  grams  potassium  dichromate  -\-  water  to  1  liter. 

Color  B — 53  grams  cupric  sulphate  -f-  water  to  1  liter. 

These  solutions  at  20 °   C.  to  be  contained  in  matched  clear 
white  glass  tanks,   1  centimeter  in  thickness,  and  measured  by 
the  instrument  and  conditions  above,  over  a  standard  "4-watt" 
carbon  lamp.) 
3 


3l8  TRANSACTIONS    I.    E.    S. PART    I 

Physical  Method. — The  characteristics  of  the  average  eye  may 
be  incorporated  in  a  physical  artificial  eye,  consisting  of  a  radiom- 
eter whose  spectral  wave-length  sensibility  curve  is  that  of  the 
average  eye. 

(A  close  approximation  to  such  an  artificial  eye  is  furnished 
by  a  non-selective  radiometer,  over  which  is  placed  the  follow- 
ing solution,  in  a  thickness  of  I  centimeter: 

Cupric  chloride 60.0  grams 

Cobalt  ammonium  sulphate 14.5  grams 

Potassium  chromate 1.9  grams 

Nitric  acid  (1.05  gr.) 18.0  cc. 

Water  to 1     liter) 

This  solution  should  be  protected  from  overheating  by  the 
interposition  of  a  layer  of  clear  water  at  least  2  cm.  thick. 

SUGGESTIONS  FOR  RECOMMENDATIONS  TO  BE  MADE 
BY  THE  SOCIETY. 

The  establishment  of  the  watt  as  the  unit  of  luminous  flux, 
and  the  development  of  the  precision  physical  photometer,  depend 
upon  the  exact  determination  of  the  spectral  luminosity  curve  of 
the  average  eye.  The  luminosity  curve  and  the  ratio  of  the 
lumen  to  the  watt  have  been  determined  with  considerable  ac- 
curacy, but  to  meet  the  needs  of  the  future  they  should  be  even 
more  definitely  fixed. 

It  is  suggested  that  determinations  of  these  factors  would  be 
most  appropriately  made  by  the  Bureau  of  Standards,  and  that, 
therefore,  the  Illuminating  Engineering  Society  recommend  to 
the  Bureau  as  specific  problems  of  value  to  the  science  of  light 
measurement : 

1.  A  determination  of  the  average  spectral  luminosity  curve 
by  measurements  upon  at  least  fifty  individuals,  by  the  photo- 
metric method  above  specified. 

2.  A  determination,  using  the  results  of  the  luminosity  curve 
study,  of  the  ratio  of  the  lumen  to  the  watt  of  luminous  flux. 

BIBLIOGRAPHY. 
The  Status  of  Heterochromatic  Photometry. 

Electrical  Review,  Sept.  10,  1910,  p.  514. 
Some  Spectral  Luminosity  Curves  Obtained  by  Flicker  and  Equality  of 
Brightness  Photometers. 
Trans.  I.  E.  S.,  Nov.,  1910,  p.  711. 


IVES:    DEFINITIONS,  STANDARDS,  PHOTOMETRIC  METHODS     319 

Spectral  Luminosity  Curves  Obtained  by  the  Equality  of  Brightness  Pho- 
tometer and  the  Flicker  Photometer  under  Similar  Conditions. 

Phil.  Mag.,  July,  1912,  p.  149. 
Spectral  Luminosity  Curves  Obtained  by  the  Method  of  Critical  Frequency. 

Phil.  Mag.,  Sept.,  1912,  p.  352. 
Distortions  in  Spectral  Luminosity  Curves  Produced  by  Variations  in  the 
Character  of  the  Comparison  Standard  and  of  the  Surroundings 
of  the  Photometric  Field. 

Phil.  Mag.,  Nov.,  19 12,  p.  744. 
The  Addition  of  Luminosities  of  Different  Color. 

Phil.  Mag.,  Dec,  1912,  p.  845. 
The  Spectral  Luminosity  Curve  of  the  Average  Eye. 

Trans.  I.  E.  S.,  Nov.,  1912. 
An  Experiment  Bearing  on  the  Theory  of  the  Flicker  Photometer. 

Lighting  Jour.,  April,  1914,  p.  82. 
The  Theory  of  the  Flicker  Photometer. 

Phil.  Mag.,  Nov.,  19 14,  p.  708. 

kA   New   Design   of   Flicker   Photometer   for   Laboratory    Colored   Light 
Photometry. 
Phys.  Review,  Sept.,  1914,  p.  222. 
The  Selection  of  a  Group  of  Observers  for  Heterochromatic  Measure- 
ments. 
Trans.  I.  E.  S.,  vol.  X,  No.  3  (1915). 
Experiments  with  Colored  Absorbing  Solutions  for  Use  in  Heterochro- 
matic Photometry. 
Trans.  I.  E.  S.,  No.  8,  1914,  p.  795. 
Additional    Experiments    on    Colored    Absorbing    Solutions    for    Use    in 
Heterochromatic  Photometry. 
Trans.  I.  E.  S.,  vol.  X,  No.  3  (1915). 
Physical  Photometry. 

Trans.  I.  E.  S.,  No.  1,  1915,  p.  101. 
Physical  Photometry  with  a  Thermopile  Artificial  Eye. 

Physical  Review,  1915. 
The  Mechanical  Equivalent  of  Light. 

Physical  Review,  1915. 
The  Primary  Standard  of  Light. 

Astrophysical  Jour.,  Nov.,  1912,  p.  322. 
Heterochromatic  Photometry  and  the  Primary  Standard  of  Light. 

Trans.  I.  E.  S.,  Oct.,  1912,  p.  376. 
A  Method  of  Correcting  Abnormal  Color  Vision  and  its  Application  to 
Flicker  Photometry. 
Trans.  I.  E.  S.,  vol.  X,  No.  3  (1915). 


DR.  CHARLES  P.  STEINMETZ,  PRESIDENT-ELECT  OF  THE  ILLUMINATING 
ENGINEERING  SOCIETY. 


ALTEN  S.   MILLER,  GENERAL  SECRETARY-ELECT  OF   THE   ILLUMINATING 
ENGINEERING  SOCIETY. 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 

Vol.  X  JULY  20,  1915  NO.  5 

ILLUMINATING  ENGINEERING  AS  A  BRANCH  OF 
TECHNICAL  INSTRUCTION.* 


BY  C.  E.  CLEWELL, 

ASSISTANT    PROFESSOR    OF    ELECTRICAL    ENGINEERING, 

UNIVERSITY   OF   PENNSYLVANIA. 


Synopsis:  Through  the  efforts  of  the  Committee  on  Education  the 
amount  of  instruction  in  illumination  given  by  various  technical  schools 
and  colleges  has  been  gathered  into  a  most  interesting  report  covering  its 
investigations  into  the  field  of  college  instruction  along  these  lines.  Some- 
what with  the  idea  of  supplementing  the  summary  of  this  committee  and 
also  for  the  purpose  of  presenting  a  more  detailed  description  of  the  work 
which  has  been  carried  out  at  two  of  the  institutions  investigated  by  the 
committee,  this  paper  has  been  prepared  with  special  reference  to  the 
illumination  courses  given  at  different  times  during  the  past  three  years 
at  the  Sheffield  Scientific  School  of  Yale  University  and  at  the  University 
of  Pennsylvania.  Among  the  various  features  included  in  the  paper  are 
the  points  which  give  to  illumination  a  wide  range  of  interest  for  students 
in  practically  all  courses  whether  academic  or  technical.  After  describing 
methods  used  in  the  work  for  undergraduate  and  graduate  students  at 
these  two  institutions,  general  conclusions  are  tentatively  drawn  as  to  the 
best  methods  to  follow  in  planning  out  such  work,  and  the  views  of  heads 
of  electrical  engineering  departments  in  leading  universities  are  quoted  in 
their  bearing  on  this  general  subject. 


A  number  of  plans  have  been  developed  during  the  past  year 
or  two  for  broader  general  education  along  the  lines  of  illum- 
ination. These  plans  have  included  various  movements  instituted 
by  the  Illuminating  Engineering  Society  typified,  for  example, 
by  the  formation  of  the  following  committees:  (a)  Committee 
on  Education,  (b)  School  Lighting  Committee,  (c)  Committee 
on  Popular  Lectures,  (d)  Committee  on  Lighting  Legislation. 
(e)  Exhibition  Booth  Committee  (Gas).  (/)  Exhibition  Booth 
Committee  (Electric),  (g)  Committee  on  Reciprocal  Relations 
with  other  Societies. 

The  Committee  on  Education  also  has  for  one  of  its  objects 

*  A  paper  presented  under  the  auspices  of  the  Committee  on  Education  at  a 
meeting  of  the  New  York  Section,  Illuminating  Engineering  Society.  May  13,  1915. 

The  Illuminating  Engineering   Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


322     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

an  effort  to  promote  the  study  of  illuminating  engineering  in  the 
technical  schools  and  colleges  as  a  general  or  specific  branch.  It 
seems  particularly  appropriate,  therefore,  to  present  under  the 
auspices  of  this  committee  a  brief  summary  of  the  work  which 
has  been  done  at  two  representative  universities  during  the  past 
few  years  in  offering  to  undergraduate  and  graduate  students 
work  pertaining  to  lamps  and  artificial  lighting. 

Prof.  Chas.  F.  Scott  of  the  Sheffield  Scientific  School  of  Yale 
University  has  made  the  statement  that  illumination  has  a  far 
wider  scope  and  the  college  has  a  far  greater  opportunity  in 
illumination  than  the  training  of  a  few  specialists.  Adding  to 
this,  he  continues,  "There  must  be  specialists  for  research,  in- 
vention and  development,  as  well  as  expert  illuminating  engineers, 
but  their  number  is  infinitesimal  compared  with  those  who  apply 
lamps  and  use  lighting."  These  statements  at  once  classify  the 
teaching  of  illuminating  engineering  into  two  broad  divisions, 
i.  e.,  work  especially  adapted  to  those  few  who  plan  to  become 
experts  either  in  research  or  practical  illuminating  engineering, 
and,  in  contrast,  those  who  must  apply  lamps  and  use  light, 
typical  of  practically  every  student  who  enters  a  university  when 
interpreted  in  a  liberal  way. 

WIDE  RANGE  OF  INTEREST. 

It  might  seem  at  first  thought  that  to  make  the  following  notes 
fairly  definite,  reference  should  be  made  in  particular  to  electrical 
engineering  students  who  would  ordinarily  have  more  than  a 
passing  interest  in  illumination  on  account  of  its  close  alliance 
with  electrical  engineering  activity  in  general. 

On  the  other  hand  a  student  in  architecture  will  ultimately  be 
confronted  with  the  problem  of  the  arrangement  and  number  of 
lamps  in  the  building  over  which  he  has  supervision ;  the  medical 
student  should  be  interested  in  the  relation  of  proper  lighting  to 
the  human  eye;  the  mechanical  engineer,  who  may  be  a  works 
manager  in  an  industry,  should  be  concerned  with  proper  illumi- 
nation in  its  influence  on  the  comfort,  wellbeing  and  working  ef- 
ficiency of  his  employees;  the  director  of  municipal  engineering 
may  be  confronted  with  the  proper  lighting  of  city  streets;  the 
electrical  engineer  as  well  as  the  gas  engineer,  is  vitally  con- 
cerned with  the  principles  of  illumination  because  artificial  light- 


clewell:   illuminating  engineering  323 

ing  may  be  looked  upon  as  the  basis  of  the  electrical  and  gas  in- 
dustries; and,  lastly,  the  average  citizen,  through  the  proper 
lighting  of  his  own  home  or  his  office  as  the  case  may  be,  unless 
posted,  is  at  the  mercy  of  others  in  the  planning  of  such  lighting, 
which  from  common  experience  is  more  apt  to  be  wrong  than 
right. 

To  quote  Prof.  Scott  in  this  connection,  and  in  summarizing 
these  different  branches  of  engineering  study,  it  is  only  necessary 
to  point  out  in  passing  that  a  large  majority  of  students  coming 
under  these  various  heads  do  not  expect  to  become  illuminating 
engineers  or  lighting  experts,  but  in  every  case  should  be  given 
a  training  in  the  fundamentals  of  illumination,  and  in  the  rela- 
tions of  proper  lighting  to  their  professions. 

ELECTRIC  MACHINERY  ANALOGY. 

This  statement  has  an  analogy  in  a  great  deal  of  engineering 
work.  Thus  in  the  study  of  electric  machinery,  the  general  tend- 
ency has  been  to  modify  the  old  attitude  which  looked  to  the 
training  of  designers,  and  rather  to  concentrate  more  and  more 
attention  upon  the  principles  which  govern  operation  and  intelli- 
gent application  of  electrical  aparatus  This  does  not  imply  that 
designers  are  not  needed,  but  merely  emphasizes  the  much  larger 
number  of  men  who  go  into  the  operation  and  application  side  of 
engineering  than  in  designing  work. 

In  like  manner,  men  are  required  for  research  and  development 
of  lamps  and  new  methods  of  applying  lamps,  while  on  the  other 
hand  a  much  larger  number  of  men  is  concerned  with  the  way 
these  lamps  should  be  applied  in  practical  every  day  cases,  due  to 
the  relation  of  such  lighting  to  their  own  comfort,  convenience 
or  efficiency  as  workmen. 

THREE  GROUPINGS  OF  THE  SUBJECT. 
Prof.  Scott  advances  the  idea  that  one  way  to  interest  students 
in  illumination  is  to  get  them  to  observe  lighting  conditions  in 
the  study  room,  class  room,  lecture  hall,  public  hall,  store  and 
street,  and  to  analyze  the  methods  of  this  lighting  and  the  results 
which  the  lighting  produces,  always  endeavoring  to  compare 
these  with  ideal  conditions.  What  constitutes  "ideal"  conditions 
in  various  cases  is  a  subject  which  the  student  should  always 
be  asked  to  consider  carefully.     He  has  further  presented  three 


324     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ways  in  which  the  subject  may  be  given  to  college  students,  as 

follows  :* 

(o)  For  students  in  all  departments,  a  few  illustrative  lectures  pre- 
senting important  facts  of  illumination  in  relation  to  different  phases  of 
life  and  indicating  that  the  questions  of  lighting  are  not  to  be  decided 
haphazardly ;  that  illumination  is  a  science ;  and,  above  all,  that  there  are 
experts  from  whom  advice  can  be  secured. 

(b)  For  students  in  architecture,  medicine  and  engineering  in  general, 
courses  covering  the  requisites  of  good  lighting,  the  kinds  of  lamps  and 
their  application. 

(c)  For  those  students  who  expect  to  become  experts  in  this  par- 
ticular field,  an  advanced  and  special  course. 

WORK  AT  THE  SHEFFIELD  SCIENTIFIC  SCHOOL. 

At  the  Sheffield  Scientific  School  of  Yale  University  the  op- 
portunity presented  itself,  and  in  making  the  effort  to  interest  the 
students  of  various  courses  in  illumination  Prof.  Scott  followed 
several  methods.  One  of  these  was  to  assign  to  the  junior  stu- 
dents, in  their  seminar  course,  the  topic  of  shop  window  lighting, 
for  example,  requiring  each  student  during  a  given  week  to  ob- 
serve as  many  shop  windows  throughout  New  Haven  as  he  could 
conveniently  see,  and  to  report  specifically  on  several  instances 
of  good  and  bad  lighting  which  had  come  under  his  observation. 
This  scheme  resulted  in  excellent  returns;  was  productive  of 
many  valuable  points  brought  out  in  the  seminar  hours;  and  in- 
creased the  powers  of  observation  on  the  part  of  the  student, 
who  came  to  observe  the  lighting  effect  in  various  places  where 
he  happened  to  be,  more  or  less  as  a  matter  of  course. 

At  these  seminar  hours  the  students  also  presented  various 
papers  on  lamps  and  lighting  which  were  prepared  beforehand 
with  the  aid  of  articles  and  books  in  the  reading  room,  and  these 
papers  were  discussed  and  commented  upon  in  such  a  way  that 
valuable  and  interesting  points  were  often  brought  out  to  better 
advantage  than  could  well  have  been  accomplished  by  other 
means. 

In  another  case  the  students  were  asked  to  prepare  a  state- 
ment of  the  lighting  in  their  study  rooms  either  in  the  dormitory 
or  private  boarding  house,  this  report  to  contain  a  plan  and  ele- 
vation of  the  room  or  desk  showing  the  general  arrangement  of 
lamps,  together  with  a  summary  of  the  various  items  which  the 

*  Lighting  Journal,  vol.  II,  p.  73.  April,  1914. 


clewell:    illuminating  engineering 


325 


student   had   observed    in    connection    with    the   lighting   effect. 
These  reports  proved  both  interesting  and  helpful,  and  in  quite  a 


•II 


fc- 


f~ 


h- w 


POSITION  0F800K 


»»■  n 


_#— ZSW  TUNGSTEN  LAMP- 


OESK 


ELEVATION 


Fig.  i. 


Figs.  2  and  3. 


'i;  ;6.t|     NOTE  NEITHER  REFLECTOR  NOX 
SHADE  IS  USEO.BUTANEYE 
SHIELD  IS  WORN.  NO  SHAOOWS 
ARE  CAST 

LIGHTING  BY  TWO  60-WATT 
CARBON  LAMPS 


FRONT  VIEW 

Figs.  4  and  5. 


//in  - 
/ '// .'  1  * 

'  /  /  I  i  I 


few  cases  led  the  student  to  see  that  certain  very  bad  conditions 
existed  which  they  had  not  before  realized,  and  also  to  inquire  as 
to  the  best  ways  for  remedying  such  conditions.  Figs,  i  to  8 
indicate  typical  diagrams  which  were  handed  in  as  a  result  of 


326     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

this  plan,  and  the  following  summary  of  the  points  which  were 
brought  out  by  these  students  in  their  own  words  with  regard 


ELEVATION. 


ELEVATION 
Figs.  6,  7  and  8. 


ELEVATION 


to  the  lighting  of  their  rooms  is  of  interest  in  connection  with  the 
diagrams  and  the  general  subject. 

Fig.  1. — These  views  give  an  idea  of  the  illumination  in  my  study 
room.  My  desk  is  3  ft.  high.  Directly  3  ft.  above,  mounted  on  a  hori- 
zontal fixture  1  ft.  in  length,  is  an  inverted  lamp  burning  artificial  gas. 
This  lamp  consists  of  the  inverted  fixture  as  shown,  an  inverted  mantle, 
a  globe  marked  B,  and  an  outer  globe  marked  A.  The  chief  difficulty 
seems  to  rest  in  the  regulation  of  the  flow  of  gas.  The  part  directly  above 
the  mantle  generally  becomes  clogged  with  soot.  The  outer  globe  A, 
which  was  probably  made  for  a  shade,  was  found  to  cut  off  too  much  of 
the  light.  Now  I  merely  use  the  lamp  with  the  smaller  globe  B,  which 
affords  a  more  intense  light. 

Fig.  2. — Light  is  intense  enough  and  dark  shadows  are  avoided.  Also 
there  is  no  glare  on  the  paper.  Pretty  satisfactory  for  studying,  but  lamps 
are  too  low  for  general  illumination,  as  they  are  directly  in  the  line  of 
vision. 

Fig.  3. — Illumination  is  sufficient  because  very  little  work  is  done 
except  on  desk  areas,  which  receive  strong  light  from  desk  lamps.  More- 
over, lighting  aims  to  be  ornamental  as  well  as  useful  in  a  study  and 
lounging  room.  Working  plane  is  not  illuminated  with  entire  uniformity, 
but  this  is  not  necessary  where  work  is  concentrated  on  two  small  areas. 
However,  there  is  sufficient  light  throughout  room  to  allow  of  ordinary 
intercourse  and  affairs  at  any  point  in  it.  Glare  from  desk  lamps  is 
avoided  by  turning  the  intensive  reflectors  away  from  the  eyes  and  by 
use  of  non-glazed  paper.    The  average  foot-candle  intensity  is  only  1,  but 


clewell:   illuminating  engineering  327 

the  light  is  so  concentrated  on  the  working  area  as  to  be  fully  sufficient 
for  all  working  purposes.  Thus  if  the  whole  working  plane  were  to  be 
thoroughly  lighted,  the  intensity  should  be  about  3  foot-candles,  or  three 
times  as  much.    Hence  the  arrangement  is  economical. 

Fig.  4. — The  lighting  consists  of  three  40- watt,  no-volt  tungsten 
lamps;  two  in  a  central  fixture  overhead,  with  a  mounting  height  of 
1  ft.,  and  one  desk  lamp,  its  energy  being  supplied  from  the  central  fixture. 
The  working  plane  is  3  ft.  above  the  floor.  The  regular  intensive  type 
prismatic  reflectors  are  used  in  the  central  fixture,  while  the  desk  lamp 
has  a  green  glass  shade.  The  central  lighting  fixture  is  mounted  in  the 
center  of  the  plaster  ceiling.  The  room  is  sufficiently  lighted,  the  desk 
lamp  alone  supplying  sufficient  light  for  studying  and  reading.  Except 
for  the  extreme  corners,  the  whole  room  is  rather  uniformly  lighted, 
though  the  working  plane  could  not  be  said  to  be  uniformly  lighted 
throughout  owing  to  the  arrangement  of  the  fixture.  There  is  more  or 
less  glare  on  the  desk,  due  to  papers,  which  is  avoided  by  dispensing  with 
said  papers  and  moving  the  desk  lamp. 

Fig.  5. — Neither  reflector  nor  shade  is  used,  but  an  eye  shield  is  worn. 
No  shadows  are  cast.    Lighting  by  two  60- watt  no-volt  carbon  lamps. 

Fig.  6. — The  lamps  used  are  all  25-watt  tungstens  and  are  eight  in 
number,  the  fixture  on  the  table  taking  two  lamps.  The  lamps  on  the 
desks  are  ordinary  flexible  desk  lamps.  The  reflectors  are  all  intensive. 
The  illumination  on  the  desks  is  sufficient,  but  there  is  a  glare  from  the 
papers.  The  table  lamp  is  very  poor  as  it  is  very  intensive  and  is  more 
ornamental  than  useful.  The  lamps  about  the  wall  are  more  for  artistic 
purposes  than  for  real  lighting.    The  economy  is  very  low. 

Fig.  7. — For  study,  and  reading  close  to  the  desk,  the  study  lamp  is 
sufficient;  the  lamp  overhead,  being  directly  over  the  desk,  does  not  add 
much  to  the  light  on  the  desk.  For  reading  away  from  the  lamp,  the 
light  is  hardly  sufficient,  even  with  the  overhead  lamp.  The  light  is  much 
poorer  on  the  left  side  of  the  desk,  since  the  lamp  is  at  the  right  for 
convenience.  Glare  is  usually  annoying,  since  my  eyes  are  usually  in  line 
with  lamp  and  book;  I  usually  shift  the  book,  but  it  might  perhaps  save 
time  to  change  the  lamp.  I  rarely  use  the  lamp  overhead;  the  mantle 
usually  gives  less  and  less  light  till  a  new  one  is  necessary,  which  is  once 
in  every  two  months  or  so ;  I  should  call  the  economy  about  average. 

Fig.  8. — The  lighting  for  this  room  was  furnished  by  gas,  burned  with 
mantles.  An  opalescent  globe  is  used  to  cut  down  the  glare,  but  no 
reflector  is  used.  There  are  but  two  of  these  lamps  for  the  room,  being 
mounted  a  foot  or  more  above  the  working  surface  of  the  desks.  The 
illumination  is  sufficient  for  reading  and  working  at  the  desks  without 
eye-strain,  but  at  a  distance  of  3  or  4  ft.  from  the  lamp  the  illumination 
is  too  poor  even  to  attempt  to  read.  Owing  to  the  translucent  globe  sur- 
rounding the  mantle,  there  is  no  noticeable  glare  from  papers  lying  on 
the  desks.    I  think  that  on  account  of  the  necessity  of  cutting  down  the 


328     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

light  from  the  gas  lamp,  it  is  a  poor  type  to  use  for  individual  lighting, 
and  that  it  would  have  been  better  to  have  a  couple  of  these  mantles  in 
the  center  of  the  room  equipped  with  proper  reflectors,  so  that  individual 
lamps  would  not  be  necessary. 

The  foregoing  statements  taken  from  a  large  number  of  similar 
opinions  represent  the  ideas  of  typical  senior  and  graduate  stu- 
dents before  giving  any  appreciable  attention  to  the  subject  of 
lighting.  The  various  instances  cited  are  selected  from  written 
reports  of  men  in  both  the  electrical  and  mechanical  courses  and 
the  opinions  advanced  are  of  special  interest  and  importance  be- 
cause they  show  an  appreciation  of  many  illumination  features, 
even  if  expressed  in  a  crude  way,  which  ordinarily  are  not  given 
attention  by  the  average  user  of  light.  The  features  brought 
out  by  these  simple  reports  are  also  considered  important  because 
they  indicate  how  readily  a  student  takes  up  an  analysis  of  a 
lighting  problem  as  simple  as  that  involved  in  the  lighting  of  his 
own  study  room  after  his  attention  is  called  to  the  fact  that  there 
is  something  to  analyze. 

A  summary  of  these  eight  opinions  indicates  that  the  attention 
collectively  has  been  directed  to  items  which  include  intensity, 
shadows,  glare  from  lamps  and  reflecting  surfaces,  general  il- 
lumination, regulation  of  gas  flow,  deterioration,  sizes  and  types 
of  lamps  and  reflectors,  ornamentation  versus  usefulness, 
economy  and  uniformity.  To  me  this  has  seemed  like  a  consid- 
erable return  for  practically  the  first  inspection  of  a  system  often 
consisting  of  one  gas  burner  used  to  illuminate  a  desk  and  its 
books  and  papers.  With  a  physical  conception  of  these  items  as 
a  working  basis,  a  course  in  illumination  should  easily  result  in 
favorable  progress  when  related  to  the  proper  combination  of 
such  basic  items  for  obtaining  good  illumination  in  specific  cases. 

It  is,  of  course,  important  to  follow  up  a  general  report  like 
this  on  the  part  of  the  students  with  a  discussion  either  in  the 
lecture  or  class  room,  and  this  might  possibly  be  increased  to 
several  such  talks  pointing  out  the  various  items  which  must  be 
considered  if  good  lighting  is  to  result. 

ILLUMINATION  AND  MECHANICAL  ENGINEERS. 

In  my  own  work  given  to  senior  mechanical  engineers  at  the 
Sheffield  Scientific  School,  in  addition  to  the  fundamentals  of 


CLEWELL:     ILLUMINATING   ENGINEERING  $2() 

electric  circuits  and  machinery,  a  short  time  was  allotted  to  a 
treatment  of  factory  lighting  in  its  specific  relation  to  shop  man- 
agement. 

The  formation  of  this  part  of  the  work  for  senior  mechanical 
engineers  resulted  largely  from  a  conference  with  a  former 
graduate  in  mechanical  engineering  who  was  employed  in  the 
works  management  side  of  a  Connecticut  industry,  and  who 
stated  on  the  occasion  of  a  visit  to  the  university,  that  one  of  the 
first  jobs  which  he  had  to  undertake  after  leaving  college  was 
that  of  improving  the  artificial  lighting  in  his  plant.  His  request 
for  some  kind  of  information  or  a  reference  which  might  lead 
him  to  gain  a  little  understanding  of  the  methods  of  handling 
such  a  problem  seemed  so  clearly  to  indicate  the  necessity  for 
at  least  some  work  along  this  line  for  mechanical  engineers  that 
it  was  decided  to  incorporate  a  short  course  in  factory  lighting 
for  these  men  as  part  of  their  work  in  the  electrical  engineering 
department.  This  work  involved  one  lecture  and  one  recitation 
per  week  for  about  three  weeks. 

COURSE  FOR  GRADUATE  ELECTRICAL  ENGINEERS. 

About  two  years  ago  a  specific  course  was  outlined  in  illumina- 
tion at  the  Sheffield  Scientific  School  for  graduate  students  in 
electrical  engineering.  This  course  consisted  of  classroom  and 
problem  work,  and  also  a  limited  amount  of  lecture  work.  The 
text  book  used  as  a  basis  for  the  course  was  Clewell's  "Factory 
Lighting"  supplemented  by  frequent  explanations  and  discussions 
and  by  a  number  of  practical  problems. 

The  course,  given  as  it  was  to  graduate  students,  assumed  a 
certain  degree  of  preparation  in  the  physics  of  light,  and  em- 
phasized more  particularly  the  practical  or  application  side  of 
lamps  and  illumination.  In  a  general  way  the  following  topics 
may  be  considered  as  representative  of  the  work  given:  i.  Types 
and  operating  features  of  lamps;  2.  Reflectors  and  their  effect 
on  the  resulting  illumination;  3.  The  objects  to  be  obtained  from 
a  lighting  system ;  4.  Bad  features  of  certain  lighting  methods ; 
5.  Methods  of  design,  installation  and  maintenance;  6.  Study  of 
the  lighting  in  specific  locations,  such  as  offices,  drafting  rooms, 
and  factories. 


330     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  work  was  covered  in  one  term  with  two  exercises  per 
week,  and  in  addition  to  the  regular  time  allotted,  illumination 
tests  were  made  in  one  of  the  rooms  of  the  engineering  building 
with  different  types  of  reflectors  so  as  to  check  up  the  predeter- 
mined values  of  illumination  intensity  which  had  been  calculated 
for  this  same  room,  on  a  basis  of  the  reflector  distribution  curves 
measured  by  the  student. 

In  addition  to  the  foregoing,  the  Yale  Branch  of  the  American 
Institute  of  Electrical  Engineers  was  used  as  a  medium  on  one 
or  more  occasions  throughout  the  year  for  presenting  papers  by 
experts  on  artificial  lighting.  For  example,  Mr.  Bassett  Jones  of 
New  York,  and  Mr.  T.  J.  Litle  of  the  Welsbach  Company,  came 
to  New  Haven  at  different  times  to  give  talks  on  the  subject  of 
illumination  at  such  meetings.  The  students  also  had  the  oppor- 
tunity of  attending  the  semi-annual  New  Haven  Branch  meetings 
of  the  American  Society  of  Mechanical  Engineers  held  at  the 
Sheffield  Scientific  School,  at  one  of  which  Prof.  Scott  and  the 
writer  presented  discussions  on  "Factory  Lighting."  These 
meetings  gave  the  undergraduate  student  an  opportunity  of 
getting  the  broader  viewpoint  of  illuminating  engineering  in  its 
relation  to  practical  work  and  they  proved  valuable  in  their  rela- 
tion to  the  efforts  for  promoting  a  wider  interest  in  the  subject. 

COURSES  AT  THE  UNIVERSITY  OF  PENNSYLVANIA. 

At  the  University  of  Pennsylvania  the  formation  of  the  new 
electrical  engineering  department  in  the  Towne  Scientific  School 
in  June,  1914  has  given  an  opportunity  for  certain  modifications 
in  the  curriculum,  one  of  which  has  been  to  establish  a  definite 
course  in  illumination.  This  work  has  been  planned  for  senior 
electrical  engineers  under  a  course  entitled  "Illumination,"  which 
extends  throughout  the  first  term  of  the  senior  year,  with  one 
lecture  and  one  recitation  per  week.  The  work  during  the  past 
half  year  has  involved  the  solution  of  a  number  of  practical 
problems,  one  of  these  in  particular  having  proved  valuable. 
This  problem  related  to  a  given  floor  area  with  a  certain  class 
of  work.  With  a  given  type  of  lamp  available,  the  problem  was 
to  arrange  a  lighting  plan  so  as  to  give  satisfactory  illumination 
on  the  working  area. 


clewell:   illuminating  engineering  331 

This  scheme  of  solution  has  included  both  the  flux  of  light  and 
point  by  point  methods,  and  with  a  number  of  dark  rooms  and 
a  portable  photometer  outfit,  the  distribution  curves  of  typical 
lamps  and  reflectors  are  later  to  be  taken,  followed  by  the  in- 
stallation of  these  lamps  in  a  given  room.  The  student  is  then 
to  calculate  the  illumination  intensity  which  will  result  on  a 
basis  of  the  distribution  curve  which  he  himself  has  measured, 
and  this  is  to  be  checked  up  with  the  actual  illumination  as  meas- 
ured with  the  portable  photometer,  as  a  part  of  the  regular 
laboratory  course  supplementing  the  recitation  and  lecture  work. 

This  procedure  has  worked  out  thus  far  in  a  particularly  suc- 
cessful manner  because  of  the  interest  stimulated  by  working 
out  a  given  problem,  with  the  anticipation  of  following  it  up  by 
actual  measurement.  Obviously,  also  a  problem  like  this  will 
bring  out  many  points,  such  as  the  discrepancy  between  calculated 
and  actual  values  due  to  the  effect  of  ceiling  and  wall  reflection 
and  similar  items. 

To  senior  mechanical  and  chemical  engineers  also  some  work 
has  been  given  in  factory  lighting  as  a  part  of  their  course  in  the 
electrical  engineering  department,  this  work  having  been  covered 
in  about  eight  to  ten  weeks,  and  involving  one  lecture  and  two 
recitations  per  week.  The  interest  displayed  by  mechanical  and 
chemical  engineers  has  been  increased  by  pointing  out  how  good 
illumination  is  related  to  efficiency  of  production  in  the  kinds  of 
industries  in  which  they  are  apt  to  be  engaged  later. 

SOME  CONCLUSIONS. 

The  writer's  experiences  at  the  Sheffield  Scientific  School  and 
at  the  University  of  Pennsylvania  seem  to  indicate  the  wisdom 
of  taking  up,  first,  the  physical  characteristics  of  the  different 
types  of  lamps,  and,  second,  following  this  by  a  study  of  con- 
ditions related  to  the  objects  to  be  illuminated,  typified,  for  ex- 
ample, by  office  or  manufacturing  spaces,  making  a  careful  study 
of  the  needs  of  given  cases  and  then  determining  which  types  of 
lamps  are  best  adapted  to  the  work  and  how  they  should  be  ar- 
ranged and  installed. 

The  point  which  is  intended  here  is  a  little  difficult  to  make 
clear,  but  is  nevertheless  important.     A  course  of  this  kind  if 


332     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

made  entirely  descriptive,  i.  e.}  based  on  existing  methods  of 
lighting  in  various  kinds  of  locations,  loses  force  because  the 
average  student  lacks  the  experience  and  perspective  to  form 
physical  ideas  of  the  items  involved  and  their  relative  importance. 
He  should,  during  the  course,  be  given  photometric  problems  in 
the  laboratory  and  should  make  illumination  measurements  under 
actual  installations  so  that  the  stimulus  produced  by  the  element 
of  personal  initiative  is  added  to  the  interest  so  often  passive  in 
merely  descriptive  courses. 

This  general  principle  is  not  limited  merely  to  the  teaching  of 
illumination,  but  applies  with  equal  force  to  many  engineering 
branches,  like  that,  as  an  illustration,  of  motor  applications  where 
the  physical  characteristics  of  motors  can  to  advantage  precede 
the  study  of  the  speed  and  torque  requirements  of  the  machinery 
to  be  driven  These  specific  items  supplemented  by  numerous 
problems  can  then  be  followed  by  other  more  elaborate  problems 
illustrating  the  selection  and  application  of  the  motor  to  the  ma- 
chine. 

Briefly,  then,  the  teaching  of  illumination  in  its  practical  as- 
pects seems  to  lend  itself  to  the  same  general  methods  as  does 
that  of  motor  applications,  and  a  rational  basis  in  each  case  seems 
to  be,  in  order  of  treatment : 

(a)  The  purpose  or  object  to  be  accomplished,  i.  e.,  the  supply 
of  light  (or  power)  as  a  means  to  an  end. 

(b)  Physical  characteristics  of  lamps  (or  motors). 

(c)  Physical  characteristics  of  the  location  (or  machine)  to 
which  the  application  is  to  be  made. 

(d)  A  study  of  the  conditions  involved  in  the  selection  and 
application  of  the  lamp  (or  motor)  in  conformity  to  the  pre- 
liminary information  gained  in  (a),  (b)  and  (c). 

NOT  DIFFICULT  TO  GAIN  INTEREST  OF  STUDENTS. 

Taken  as  a  whole,  there  seems  to  be  no  difficulty  in  gaining  the 
attention  and  interest  of  undergraduate  students  in  illumination 
because  it  is  so  intimately  related  to  every  day  experiences.  Quite 
a  number  of  men  come  into  the  office  off  and  on  with  problems 
which  they  run  up  against,  in  a  dining  room,  or  the  hall  of  a 
fraternity  house,  or  a  church,  in  connection  with  which  some 


CLEWELL:     ILLUMINATING   ENGINEERING  333 

friend  has  asked  advice;  in  nearly  every  case  the  man  being  in- 
terested in  the  accomplishment  of  a  certain  result,  which  had 
either  been  a  case  of  bad  lighting  before,  or  in  which  his  friends 
had  desired  to  assure  themselves  of  a  good  result  instead  of 
placing  themselves  at  the  pleasure  of  an  architect  or  a  wiring 
contractor. 

It  has  been  found  very  helpful  in  this  work  at  the  University 
of  Pennsylvania  to  point  out  the  present  status  of  lighting  legis- 
lation in  the  various  states  throughout  the  country.  To  this  end 
the  Committee  on  Lighting  Legislation  of  the  Illuminating 
Engineering  Society  has  been  a  distinct  help,  because  through 
their  cooperation  a  summary  of  the  laws  in  a  number  of  states 
has  been  made  available  in  the  reading  room  to  which  the  students 
go  between  recitation  hours.  From  the  writer's  personal  experi- 
ence, it  would  seem  that  a  great  compensation  awaits  those  in- 
stitutions which  undertake  work  of  this  kind,  even  if  it  be  only 
for  accomplishing  a  better  appreciation  on  the  part  of  the  student 
of  what  good  lighting  consists  without  any  regard  to  his  entering 
illuminating  engineering  as  a  special  field  of  later  activity.  In  a 
few  instances,  however,  undergraduate  students  have  come  to 
look  upon  the  lighting  field  as  one  of  distinct  opportunity. 

The  recent  report  of  the  Committee  on  Education  has  gone  to 
show  that  at  the  present  time  the  teaching  of  illuminating 
engineering  in  technical  schools  and  universities  is  not  by  any 
means  standardized,  nor  even  definite  in  many  cases.  This,  how- 
ever, need  be  no  discouragement  because  electrical  engineering 
education  as  a  whole  is  far  from  standardized;  in  fact  it  would 
probably  show  almost  as  great  a  number  of  discrepancies  in  a 
summary  of  other  more  or  less  time  honored  subjects  as  now 
given  in  the  various  schools.  The  main  point  at  issue  at  the 
present  time  is  rather  to  arouse  enthusiasm  for  this  work  and  to 
place  it  on  a  par  with  other  subjects  in  electrical  engineering 
courses,  which  either  by  long  usage  or  an  account  of  actual  merit 
are  termed  fundamental. 

VIEWS  OF  ELECTRICAL  ENGINEERING  DEPARTMENT 

HEADS. 

The  writer  recently  addressed  personal  letters  to  the  heads  of 
the  electrical  engineering  departments  in  a  number  of  the  leading 


334     TRANSACTIONS  OF  IIXUMINATING  ENGINEERING  SOCIETY 

technical  schools  and  universities  to  find  out  how  much  of  a  field 
there  might  be  for  the  lantern  slide  talks  of  the  Committee  on 
Popular  Lectures  before  student  audiences,  in  the  hope  that  the 
opinions  expressed  would  indicate,  at  least  in  a  general  way,  the 
attitude  of  the  men  in  the  educational  field  to  broadening  the  in- 
formation of  college  students  along  the  lines  of  illumination. 

These  letters  asked  specifically  for  two  opinions:  (a)  the 
amount  of  theory  which  should  be  incorporated  in  the  popular 
lectures;  and  (b)  whether  the  possible  use  of  such  lectures  before 
classes  of  college  students  should  influence  the  method  of  treat- 
ment, and  in  regard  also  to  the  field  for  such  lectures  before 
student  audiences.  Quotations  relating  to  the  second  item  are  of 
interest  in  showing  something  of  the  attitude  held  at  this  time  by 
the  heads  of  representative  electrical  engineering  departments 
and  the  following  paragraphs  bearing  on  this  particular  phase  of 
the  popular  lecture  movement  are  quoted  because  they  bring  out 
some  interesting  points  related  to  the  educational  problem. 

1.  I  believe  the  average  student  will  derive  more  benefit  from  lectures 
intended  for  the  public  than  from  technical  treatments  of  the  subject. 
Let  us  give  them  the  technicalities  in  the  class  room.  Even  there  we  are 
inclined  to  proceed  too  fast  in  our  effort  to  cover  ground  in  a  short  course. 

2.  I  believe  that  such  lectures  will  be  welcome  and  well  received  in 
almost  any  college  in  the  country. 

3.  To  be  successful  before  the  student  body,  it  would  be  necessary  to 
have  the  treatment  somewhat  technical ;  otherwise  they  would  fail  to  hold 
the  respect  of  the  students  and  I  do  not  think  that  a  technical  treatment 
is  inconsistent  with  popular  comprehension. 

4.  If  the  lecture  does  not  comprise  a  sound  basis  on,  and  in  connec- 
tion with  theoretical  principles,  I  think  it  should  not  be  used  before  college 
students.  To  my  mind  one  of  the  greatest  troubles  of  our  educational 
system  to-day  in  all  its  branches  is  superficiality  and  the  failure  to  give 
a  thorough  grounding  in  underlying  principles.  My  feeling  on  this  point 
might  be  modified  somewhat  in  the  case  of  a  lecture  which  was  accom- 
panied by  exceptional  illustrations  both  on  the  screen  and  on  the  lecture 
table. 

5.  Since,  in  my  estimation,  the  college  student  audience  is  not  very 
different  in  mental  ability  from  the  audience  that  would  be  attracted  by 
such  lectures,  I  can  see  no  good  reason  why  there  should  be  any  modifica- 
tion of  the  plan  of  the  lectures  on  account  of  the  probability  that  they 
will  be  presented  in  colleges. 

There  are  too  small  a  number  of  the  students  in  our  colleges  who 
are  taking  courses   in   illumination.     A   still   larger  number  are   getting 


CLEWELL:     ILLUMINATING   ENGINEERING  335 

acquainted  with  the  meaning  of  the  term  "Photometry"  and  know  the 
purpose  of  a  photometer  in  their  work  in  physics.  Of  these  students  a 
large  number  may  have  but  a  hazy  recollection  of  the  subject,  but  I 
believe  those  who  remember  will  profit  by  the  lectures.  I  also  believe  it 
to  be  true  that  college  students,  many  times,  hear  with  pleasure  and 
profit,  from  an  outsider,  the  same  things  to  which  they  give  almost  no 
attention  if  heard  in  class  from  their  regular  instructor. 

In  regard  to  the  field  for  such  lectures  before  college  audiences,  I 
imagine  it  is  a  case  in  which  the  demand  has  to  be  created.  The  subject 
is  of  the  greatest  importance  and  the  colleges  should  be  compelled  to 
take  heed. 

6.  As  I  understand  it,  your  object  is  general  education  and,  since  the 
college  student  forms  an  exceedingly  small  proportion  of  the  total  popu- 
lation of  the  country,  I  should  hesitate  to  include  modifications  in  the 
lecture  simply  intended  for  that  class. 

7.  Regarding  the  field  for  lectures  before  student  audiences,  I  think 
there  is  a  very  considerable  opportunity  for  such  lectures.  For  instance, 
we  have  an  hour  each  week  at  which  the  whole  student  body  is  gathered 
to  listen  to  an  address  by  some  outside  man,  and  such  custom  is  followed 
in  a  large  number  of  other  institutions.  There  are  a  great  many  lectures 
given  before  various  departments  of  our  colleges  and  I  am  sure  that  if 
you  can  enlist  a  few  well  known  illuminating  engineers  they  would  find 
a  large  number  of  invitations  to  speak  before  college  audiences.  When 
you  consider  the  very  large  number  of  colleges  in  the  country,  academic 
as  well  as  technical,  and  the  large  number  of  young  men  and  women  who 
can  be  reached  in  this  way,  it  seems  to  me  to  offer  one  of  the  very  best 
fields  of  endeavor  for  the  work  of  your  committee. 

8.  The  possible  use  of  these  lectures  before  student  bodies  should  not 
modify  or  influence  their  mode  of  treatment.  The  student  should  obtain 
the  same  amount  and  the  same  kind  of  benefit  as  the  practical  man  in  the 
one  or  the  other  business  of  life.  The  treatment  should  be  no  more 
technical  or  theoretical  in  the  one  case  than  in  the  other.  Anyhow  I 
should  venture  the  opinion  that  for  the  average  student  in  our  colleges 
and  engineering  schools  much  of  the  highly  mathematical  theory  of  some 
of  the  subjects  presented  would  be  productive  of  greater  results  if  the 
time  were  spent  in  teaching  how  to  apply  the  simpler  mathematics  and 
the  really  usable  theory.  Of  course,  I  am  speaking  of  the  average,  not 
the  exceptional  student. 

Such  lectures  should  afford  the  student  a  splendid  opportunity  to  get 
the  layman's  point  of  view— to  meet  him  on  common  ground,  and  possibly 
because  of  his  own  more  complete  technical  training  be  the  readier  in 
the  application  of  the  important  principles  of  illumination,  and  thus  be 
in  position  to  be  of  greater  service  as  a  practical  engineer  than  he  may 
otherwise  have  been. 

9-  As  far  as  the  method  of  treatment  is  concerned,  if  these  lectures 


336     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

are  intended  for  popular  consumption,  and  for  the  purpose  of  directing 
the  popular  mind  regarding  the  proper  methods  of  using  lights,  which  is 
a  large  and  desirable  field  to  cultivate,  no  subsidiary  use  of  the  lectures, 
such  as  using  them  before  college  students,  should  be  allowed  to  influence 
the  method  of  treatment.  That  is,  if  the  best  effect  is  to  be  expected 
from  these  lectures  as  popular  lectures,  they  ought  to  be  planned  and 
executed  without  any  deviation  from  their  primary  object. 

I  don't  doubt  that  there  would  be  a  good  deal  of  use  for  such  lec- 
tures before  arts  students  in  the  colleges,  and  perhaps  before  the  engi- 
neering students  of  the  weaker  engineering  schools,  but  the  popular 
character  of  these  lectures  would  probably  not  injure  them  for  that 
purpose. 

10.  It  seems  to  me  that  unless  it  is  done  with  extraordinary  skill,  this 
kind  of  thing  is  pretty  sure  to  scare  out  a  popular  audience  before  the 
lecture  really  gets  started.  Of  course,  in  so  far  as  such  lectures  were  to 
be  used  with  college  students,  there  would  not  be  so  much  objection  to 
presenting  the  theoretical  side,  but  even  here  I  should  think  it  would  be 
as  well  to  confine  the  lecture  mostly  to  the  more  practical  and  to  demon- 
strative features. 

11.  Lectures  before  classes  of  college  students  by  outside  illuminating 
engineers  ought  to  be  of  great  value.  I  doubt,  however,  if  they  would  be 
of  such  direct  value  as  talks  before  the  general  public.  The  average 
student  feels  himself  about  surfeited  with  the  work  he  has  to  do  and  is 
not  prone  to  hasten  to  lectures  not  required  of  him  unless  the  subject  is 
somewhat  unique  or  the  lecturer  of  considerable  reputation.  I  would 
venture  to  suggest  that  the  best  way  to  get  such  lectures  before  the 
students  is  to  have  them  given  in  regular  class-room  time.  In  colleges 
which  have  a  branch  of  the  American  Institute  of  Electrical  Engineers, 
there  should  be  no  trouble  at  all  in  getting  these  lectures  before  the 
student  body.  I  wish  there  could  be  more  of  this  done  in  this  way.  If 
our  student  branches  are  to  flourish  it  will  only  be  when  they  are  actively 
aided  by  engineers  and  lecturers  from  outside. 

Again,  I  believe  that  these  lectures  if  they  are  to  be  successfully  given 
before  our  students  should  not  go  too  much  into  the  physics  of  the  matter, 
but  deal  largely  with  the  practical  side  of  the  question,  and  should  include 
practical  demonstrations,  commercial  data  and  the  like.  The  college 
departments  can  be  relied  upon  to  give  the  student  the  theoretical  side  of 
the  subject.  The  trouble  so  often  is  that  we  have  only  time  for  the 
theoretical  side  and  can  spare  little  or  no  time  to  the  practical  side. 

12.  It  would  seem  to  me  that  the  method  of  treatment  should  be 
adapted  to  each  individual  audience.  There  is  some  field  in  colleges  of 
engineering  for  such  lectures,  but  I  am  not  able  to  state  what  the  different 
colleges  offer  in  this  branch  of  engineering. 

13.  I  believe  that  lectures  more  or  less  popular  before  college  students 
may  have  a  very  beneficial  influence  on  the  practical  use  of  light.     Such 


CLEWELL:     ILLUMINATING   ENGINEERING  337 

lectures  could  be  much  more  technical  than  those  for  the  general  public, 
for  the  training  in  physics  prepares  the  audience  for  understanding  the 
subject.  How  much  of  a  field  there  is  for  such  lectures  before  student 
audiences  is  difficult  to  say,  but  I  believe  that  a  well  illustrated  more  or 
less  popular  talk  would  prove  interesting  and  draw  good  audiences  at 
practically  all  colleges,  but  particularly  those  where  the  work  is  indus- 
trial or  scientific  in  character. 

It  is  gratifying  to  find,  therefore,  that  in  a  majority  of  cases 
the  heads  of  electrical  engineering  departments  look  upon  the 
availability  of  such  lectures  as  a  valuable  aid  in  undergraduate 
instruction  work.  Only  a  few  cases  have  come  to  my  attention 
where  the  head  of  an  electrical  engineering  department  looks 
upon  illuminating  engineering  work  as  without  the  range  of  an 
ordinary  electrical  engineering  course.  This  may  be  due  partly 
to  a  different  viewpoint,  or  there  is  a  possibility  that  it  may  be 
due  to  a  lack  of  appreciation  of  just  what  has  been  accomplished 
during  the  past  three  or  four  years  in  this  important  and  growing 
field.  It  it  fortunate,  therefore,  that  the  Committee  on  Educa- 
tion is  at  work  in  helping  to  post  such  cases  on  the  actual  status 
of  illumination  at  the  present  time. 

It  is  no  discouragement  in  looking  over  the  report  of  the  Com- 
mittee on  Education,  to  find  that  the  number  of  kinds  of  ways 
in  which  lighting  and  illumination  is  taught  is  very  diverse  both 
in  kind  and  in  amount.  On  the  other  hand,  it  is  most  encouraging 
to  note  that  very  few  of  the  various  institutions  investigated  can 
be  found  which  have  not  in  some  way  outlined  work  in  this  field. 
It  is  quite  possible  that  if  an  investigation  like  this  had  been  made 
ten  years  ago  practically  no  work  along  this  line  would  have 
been  found  in  the  various  college  schedules ;  it  seems  hardly  too 
much  to  say  that  a  corresponding  summary  five  years  hence  will 
indicate  almost  as  much  uniformity,  at  least  as  regards  amount 
of  scheduled  time,  in  the  teaching  of  illumination  to  under- 
graduate students  as  is  found  to-day  in  such  subjects  as  electric 
railways,  power  plants  and  the  distribution  and  transmission  of 
power. 


338     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

DISCUSSION. 

Prof.  Charles  F.  Scott  (Sheffield  Scientific  School  of  Yale 
University)  :  The  significant  thing  in  Prof.  Clewell's  paper  on 
"Illuminating  Engineering  as  a  Branch  of  Technical  Instruction" 
is  the  fact  that  the  orthodox  method  of  instruction  from  a  text 
book  leading  up  logically  from  the  mathematical  and  physical 
laws  of  light  is  supplemented  by  a  great  many  other  methods. 
The  general  educational  work  of  the  Illuminating  Engineering 
Society  is  contributed  to  by  half  a  dozen  or  more  committees,  and 
the  education  in  the  technical  school  is  along  varied  lines  which 
have  to  do  with  the  engineering  principles  in  the  application  and 
use  of  illumination,  as  well  as  the  mathematical  and  physical  and 
chemical  laws  in  accordance  with  which  light  is  produced  and 
distributed.  Illumination  is  fortunate  in  having  so  many  rela- 
tions that  it  admits  of  treatment  in  many  ways.  Furthermore, 
illumination  is  a  matter  entering  into  the  experience  of  everyone, 
so  that  its  importance  is  apparent  to  all  and  an  interest  naturally 
arises.  Interest  is  quite  easily  awakened  when  we  find  new  facts 
and  laws  and  new  relations  with  regard  to  things  with  which  we 
are  already  familiar  and  have  assumed  that  we  knew  all  about. 
When  a  simple  illustration  or  explanation  or  a  little  analysis 
shows  that  conditions  which  have  entered  into  our  own  experience 
are  really  not  satisfactory,  but  violate  some  common  sense  con- 
dition which  we  had  never  thought  of,  we  are  apt  to  be  startled ; 
we  realize  that  our  powers  of  observation  and  simple  reasoning 
have  not  been  active.  In  brief,  illumination  is  a  fine  opportunity 
for  the  cultivation  of  the  observing  and  reasoning  powers.  Some- 
times the  highest  order  of  invention  consists  in'  accomplishing 
something  which  everybody  may  recognize  at  once  as  the  obvious 
and  proper  thing,  although  they  somehow  did  not  happen  to 
think  of  it  at  first. 

Prof.  Clewell's  paper,  therefore,  indicates  new  and  varied  ways 
of  technical  instruction,  which  are  of  great  value  as  a  type  of 
training,  as  well  as  a  source  of  information  for  the  engineer. 
Illumination,  the  new  branch  of  engineering,  is  fortunate  in 
being  able  to  give  a  stimulation  to  engineering  education. 

Prof.  Harold  Pender  (University  of  Pennsylvania)  :  In  this 
paper  Mr.  Clewell  describes  the  work  conducted  for  two  years 


ILLUMINATING   ENGINEERING  339 

in  conjunction  with  Prof.  Scott  at  Yale  University  in  giving  work 
in  illumination  to  undergraduate  and  graduate  students,  also  the 
work  of  the  past  year  at  the  University  of  Pennsylvania  along 
these  same  lines.  The  object  of  the  paper,  apparently,  is  not  to 
set  forth  the  idea  that  these  courses  are  looked  upon  as  all  that 
could  be  desired,  but  merely  to  describe  what  has  actually  been 
accomplished  at  two  institutions  thus  far.  The  underlying  object 
of  the  paper  has  been  to  invite  discussion  which  would  tend  to 
help  the  author  in  any  future  work  conducted  in  the  development 
of  this  particular  line  of  instruction. 

At  the  University  of  Pennsylvania  the  aim  in  the  electrical 
engineering  department  is  to  place  each  line  of  work  as  far  as 
possible  in  the  hands  of  men  fitted  by  practical  experience  or 
special  study  to  make  them  competent  to  plan  the  courses  to  the 
best  advantage.  In  this  way  the  instructor  is  able  to  concentrate 
his  attention  on  relatively  few  subjects  and  satisfactory  results  in 
such  specialized  courses  as  telephony,  railways,  illumination  and 
motor  applications  have  thus  been  possible.  The  course  in  illumi- 
nation involves  a  relatively  small  amount  of  time  in  the  prin- 
ciples of  illumination,  supplemented  by  photometric  and  illumina- 
tion experiments  in  the  laboratory.  The  laboratory  is  equipped 
with  all  types  of  modern  electric  illuminants. 

Mr.  Clewell  points  out  the  value  of  a  course  in  illumination  not 
only  to  electrical  but  to  non-electrical  students.  Thus  the  mechan- 
ical engineer  from  the  standpoint  of  the  future  works  manager 
should  have  almost  if  not  as  keen  an  interest  in  factory  lighting 
as  has  the  electrical  engineer  in  other  special  lighting  fields. 

The  fact  that  there  is  at  present  only  a  limited  call  for  men 
specially  trained  in  the  principles  and  practise  of  illumination  is 
largely  due  to  a  failure  on  the  part  of  those  in  responsible  charge 
of  shops,  factories  and  large  offices  to  appreciate  the  importance 
of  good  illumination  from  the  standpoint  of  the  efficiency  of  the 
worker.  The  remarkable  increase  in  defective  eyesight  in  the 
last  fifty  years  is  probably  due  more  to  poorly  designed  lighting 
installations  than  to  lack  of  light ;  it  is  proper  distribution  rather 
than  brilliancy  that  is  of  primary  importance.  A  better  under- 
standing of  the  principles  of  illumination  by  all  kinds  of  engineers 
will  in  the  long  run  mean  not  only  an  improvement  in  the  "public 


340     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

health,"  but  also  an  actual  saving  in  dollars  and  cents  to  the 
employer  of  labor. 

Mr.  William  J.  Serrill  :  Prof.  Clewell  has  given  us  in  this 
paper  a  very  interesting  discussion  of  the  educational  side  of 
illuminating  engineering.  In  the  engineering  schools  of  the 
country  there  is  to-day  noticeable  a  marked  tendency  away  from 
specialized  courses,  and  in  favor  of  a  thorough  instruction  in 
general  principles  that  underlie  all  engineering.  This  refers  to 
undergraduate  four-year  courses.  In  the  practise  of  law, 
there  are  probably  as  many  different  branches  of  work  as  there 
are  in  engineering.  In  the  law  schools,  the  instruction  for  all 
students  is  uniform,  and  they  all  get  the  one  degree  of  doctor  of 
laws.  I  look  forward  to  the  time  when  a  similar  situation  will 
exist  in  engineering  schools.  The  principles  underlying  engineer- 
ing in  general  will  be  thoroughly  taught,  and  the  one  degree  of 
doctor  of  engineering  will  be  given.  The  graduate  will  equip 
himself  for  specialized  work  in  a  post-graduate  course,  or  will 
do  so  by  his  own  efforts  after  leaving  college. 

The  principles  underlying  illuminating  engineering  are  of  such 
importance  that  they  should  undoubtedly  be  included  among  those 
general  principles  which  are  taught  to  undergraduates.  The  engi- 
neering school  of  the  future  will  undoubtedly  be  equipped  to  turn 
out  a  finished  illuminating  engineer  as  a  post-graduate  product. 

The  presentation  of  the  principles  and  practises  of  good  illumi- 
nation before  students  other  than  those  in  the  engineering  depart- 
ments is  desirable,  and  the  popular  lectures  which  Prof.  Clewell's 
committee  is  preparing,  as  well  as  other  illustrated  lectures  on  the 
subject,  are  undoubtedly  an  admirable  means  of  spreading  the 
propaganda  of  better  illumination  among  educated  people.  The 
thing  is  to  overcome  the  natural  indifference  to  the  question  of 
illumination,  and  to  awaken  an  interest  in  this  subject  among  the 
students.  Especially  is  it  important  that  students  in  the  archi- 
tectural schools  and  those  in  the  medical  schools  be  made  aware 
of  the  importance  of  illumination  as  affecting  the  great  profes- 
sions of  architecture  and  medicine.  In  both  professions  there  is 
great  ignorance  of  the  principles  of  illumination,  and  the  most 
effective  way  of   improving  this   condition  is   to   work  on  the 


ILLUMINATING   ENGINEERING  341 

students  in  these  departments,  rather  than  to  attempt  to  influence 
the  practising  architect  or  physician. 

Mr.  Norman  Macbeth  :  There  seems  to  be  a  question  in  the 
minds  of  many  when  considering  the  employment  of  graduates 
as  to  the  value  of  a  course  in  illuminating  engineering.  To  my 
mind  this  situation  is  due  to  a  failure  to  appreciate  the  value 
of  such  a  course,  or  perhaps  to  the  usual  conception  of  what 
the  present  illuminating  engineer  stands  for.  The  so-called  and 
self-styled  illuminating  engineer,  who  has  been  most  prominent 
in  the  commercial  field  within  the  past  five  or  six  years,  has  in 
many  instances  been  neither  an  engineer  nor  a  commercial  man, 
and  has  left  a  deep  impression  in  many  minds  as  lacking  more 
than  he  possessed. 

There  is  no  disagreement  as  to  the  value  or  usefulness  of  an 
electrical  engineering  course,  and  graduates  find  employment  in 
widely  diversified  fields  of  electrical  apparatus  design,  manu- 
facture or  application.  There  is  no  confusion  as  to  where  and 
how  the  electrical  engineer's  education  may  be  applied.  The  elec- 
tric railway  field,  telegraph,  telephone  and  wireless,  electric  trucks, 
power  applications,  etc.,  afford  many  opportunities.  The  course 
for  the  electrical  engineering  graduate  covers  a  wide  range  of 
electrical  applications.  So  far  as  the  course  itself  is  concerned, 
however,  many  of  these  applications  have  been  merely  touched 
upon,  and  the  final  usefulness  of  the  training  of  the  graduate 
most  likely  comes  through  a  specialization  of  some  one  branch. 

And  so  it  will  be  with  the  illuminating  engineering  graduate. 
There  are  thousands  of  opportunities  for  trained  men  in  the 
lighting  field  to-day.  The  entire  lighting  field  is  largely  in  the 
hands  of  mechanics  and  men  quite  unfitted  so  far  as  training  or 
an  appreciation  of  their  responsibilities  is  concerned.  And  the 
results  so  much  desired  are  largely  based  on  thumb  rule  and 
guess  to  say  nothing  about  indifference. 

In  the  United  States  alone  in  1913  our  sales  of  lighting  equip- 
ment totaled  over  $65,000,000  and  of  central  station  energy  for 
lighting  over  $300,000,000  per  annum.  It  may  be  noted  that  the 
central  station  receipts  from  lighting  are  more  than  twice  that 
from  the  much  talked  of  and  consistently  sought  power  load. 
Surely  a  business  of  $400,000,000  annually — and  it  is  greater  than 


342     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

this  if  we  include  gas  lighting — a  business  which  is  so  closely  and 
intimately  associated  with  our  lives  and  with  the  health  and  en- 
joyment of  the  people,  and  admittedly  so  ineffectively  handled 
to-day,  presents  opportunities  for  illuminating  engineering  grad- 
uates. 

In  the  applications  of  lamps,  glassware  and  lighting  fixtures,  in 
contracting  and  construction,  there  are  opportunities  for  men  who 
know  the  fundamentals  of  illuminating  engineering  and  have  the 
common  sense  to  apply  their  knowledge.  A  graduate  illumin- 
ating engineer  with  a  course  which  is  at  all  comparable  with  that 
of  the  electrical  engineer,  retaining  as  much  of  his  course  as  the 
average  electrical  engineering  graduate,  has  vastly  greater  oppor- 
tunities for  usefulness;  and  it  is  this  usefulness  which  in  any 
field  commands  salaries  worth  while. 

The  illuminating  engineer  has  not  as  yet  sold  his  proposition 
either  to  the  management  of  his  company  or  to  the  general  public, 
but  when  he  does,  and  that  time  is  not  far  off,  he  will  readily 
secure  his  proportion  of  the  many  millions  expended  in  this  field. 

Mr.  P.  S.  Milear:  The  New  York  Section  is  privileged  to 
have  presented  before  it  this  paper  on  the  educational  phases  of 
illuminating  engineering.  I  am  sure  that  we  have  been  interested 
in  the  accounts  of  the  introduction  of  these  two  courses  in  Yale 
University  and  the  University  of  Pennsylvania.  It  seems  to  me, 
however,  that  a  great  part  of  the  moral  of  this  paper  must  lie  in 
its  application  and  that  to  make  it  most  useful  it  must  be  placed 
in  the  hands  of  members  of  faculties  of  colleges  and  universities 
which  might  utilize  it  and  apply  it  to  their  advantage. 

It  occurs  to  me  that  we  are  about  to  issue  a  report  of  last  year's 
Committee  on  Education  and  that  it  would  be  an  excellent  plan 
to  include  copies  of  Mr.  Clewell's  paper  with  copies  of  the  report. 

With  regard  to  this  question  of  illuminating  engineering  educa- 
tion it  seems  to  me  that  there  are  three  points  of  view,  respec- 
tively that  of  the  educator,  that  of  the  employer  and  that  of  the 
Illuminating  Engineering  Society.  In  university  education  it 
apparently  is  the  tendency  to  broaden  under-graduate  engineering 
instruction,  and  to  include  in  a  graduate  course  such  special 
instruction  as  illuminating  engineering.  With  reference  to  em- 
ployees, this  year's  Committee  on  Education,  under  the  direction 


ILLUMINATING   ENGINEERING  343 

of  Prof.  Richtmyer,  is  planning  a  canvass  to  ascertain  what 
demand  corporations  might  have  for  engineers  who  graduate 
from  a  special  course  in  illuminating  engineering,  such  as  is  con- 
templated. If  I  rightly  understand  the  point  of  view  of  the 
society  it  is  that  we  are  not  prepared  to  urge  instruction  in  illumi- 
nating engineering  at  the  present  time.  We  are  anxious  to  do 
all  we  can  to  pave  the  way  for  it,  and  wish  to  be  prepared  to 
supply  such  information  as  it  is  within  our  power  to  make  avail- 
able whenever  there  exists  a  demand  for  it.  We  want,  of  course, 
to  promote  the  movement,  but  at  the  present  time  we  do  not  see 
that  the  time  is  ripe  to  urge  any  extension  of  this  form  of 
education. 

Prof.  Clewell's  paper,  it  seems  to  me,  if  properly  applied  in 
colleges  and  universities,  is  going  to  do  much  toward  assisting 
in  creating  this  demand  which  the  society  wants  to  meet. 

Prof.  Arthur  J.  Rowland  (Drexel  Institute) :  Educational 
work  in  illuminating  engineering  is  so  constantly  connected  with 
electrical  engineering  courses  only  that  I  am  glad  to  note  the 
remarks  in  Prof.  Clewell's  paper  and  emphasize  the  fact  that  such 
education  has  a  far  wider  application.  I  have  been  constantly 
surprised  that,  though  electrical  engineering  courses  invariably 
contain  a  course  on  electric  lighting,  in  connection  with  which 
the  study  of  electric  lamps  themselves  and  some  study  of  illumin- 
ation by  these  lamps  at  least  are  taken  up,  nothing  of  a  correspond- 
ing kind  exists  in  mechanical  engineering  courses.  It  seems  to 
me  that  the  place  to  start  with  training  in  illuminating  engineering 
is  in  the  regular  college  physics  courses.  It  is  true  that  the  text- 
books are  not  adapted  to  this,  but  it  is  surely  time  that  along  with 
the  study  of  light  the  terms  and  nomenclature  of  illuminating 
engineering  should  be  introduced.  The  application  of  light  for 
illumination  should  be  made  at  least  as  much  of  as  the  use  of 
lighting  appliances  to  which  considerable  time  is  given  in  our 
college  physics  courses. 

Taking  two  hours  per  week  through  the  senior  year  of  engineer- 
ing, a  really  valuable  course  in  illuminating  engineering  can  be 
given.  In  the  electrical  engineering  course  at  Drexel  Institute 
this  amount  of  time  has  been  given  for  a  number  of  years.  In  it 
can  be  included  not  only  all  the  fundamental  principles  of  illumin- 


344     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ating  engineering  practise,  but  a  number  of  problems  relating  to 
indoor  illumination,  including  arrangement  of  lamps  and  circuits 
to  supply  them,  as  well  as  a  study  of  the  various  illuminants  avail- 
able for  everyday  service.  Students  seem  to  enjoy  this  course 
very  much  and  take  hold  of  its  practical  problems  with  avidity, 
even  when  considerable  outside  time  is  required  of  them.  It 
seems  to  me  that  the  actual  photometric  and  illumination  measure- 
ments which  are  to  be  done  must  inevitably  be  carried  along  as 
part  of  the  engineering  laboratory  work.  It  is  impossible  to  or- 
ganize or  to  spare  the  time  for  a  special  course  in  photometry  and 
illumination  measurements. 

While  I  believe  in  such  a  course  not  only  for  electrical  en- 
gineers but  for  others,  I  have  grave  doubts  as  to  the  real  value  of 
such  training  in  comparison  with  that  found  in  other  branches  of 
engineering  knowledge.  This  is  because  in  my  experience  there 
is  very  slight  demand  indeed  for  men  who  have  been  trained 
specially  in  illuminating  engineering  work.  Philadelphia  is  a 
rather  large  town  and  it  is  possible  to  judge  the  importance  of 
various  engineering  subjects  by  the  demand  for  them  in  evening 
class  work  here.  For  half  a  dozen  years  among  the  college  sub- 
jects offered  in  the  evening  classes,  Drexel  Institute  has  offered  a 
course  in  lighting  and  illumination.  I  have  personally  taught  this 
class,  and  I  think  I  am  well  enough  known  in  the  Philadelphia 
Section  of  the  Illuminating  Engineering  Society  to  have  as  good 
a  chance  as  anyone  else  to  secure  a  class.  A  very  small  class 
was  carried  in  this  subject  for  two  years.  We  have,  however, 
now  decided  to  abandon  the  work  since  we  have  given  up  any 
expectation  of  finding  any  demand  for  such  training.  There  is 
a  much  larger  demand,  for  example,  for  training  in  telephony, 
which  seems  to  be  a  highly  specialized  line.  In  fact,  those  who 
study  telephony  must  nearly  all  of  them  of  necessity  hold  posi- 
tions with  a  single  telephone  company.  There  are  many  firms  in 
Philadelphia  and  many  consulting  engineers'  offices  in  whose 
business  lighting  and  illumination  plays  an  important  part. 
Nevertheless  there  is  clearly  no  interest  in  and  demand  for  such 
courses  of  training  here. 

Prof.  A.  A.  Atkinson  (Ohio  University)  :  The  subject  of 
illumination  offers  not  only  a  very  interesting  field  for  scientific 


ILLUMINATING   ENGINEERING  345 

investigation,  but  also  furnishes  one  of  the  most  useful  and 
delightful  forms  of  study  for  a  great  body  of  students,  even  those 
in  domestic  science  and  educational  courses.  It  takes  rank  in 
the  technical  field  alongside  the  finest  lines  of  research;  in  prac- 
tical every-day  importance  alongside  hygiene,  sanitation,  etc. 
Scarcely  any  other  line  of  thought  or  investigation  touches  so 
many  phases  of  practical  life,  offers  so  many  opportunities  for 
the  cultivation  of  the  artistic  and  esthetic  sense,  or  is  allied  with 
so  many  other  technical  professions. 

The  method  of  Prof.  Scott  quoted  by  the  author  of  the  paper 
should  prove  an  excellent  means  of  arousing  an  interest  in  closer 
and  more  intelligent  observation  of  illuminating  conditions  and 
of  cultivating  powers  of  analysis  and  the  formation  of  correct 
judgment.  I  note,  however,  that  most  of  the  student  reports 
quoted  by  Prof.  Clewell  ended  with  the  statement  of  found  con- 
ditions only.  I  believe  that  senior  and  graduate  students  should 
be  required  to  draw  conclusions  from  their  observations  as  to 
methods  of  improvement  of  the  conditions  found  and  reported, 
and  even  to  propose  plans  showing  how  they  would  proceed  to 
make  the  modifications  suggested. 

The  general  course  outlined  by  the  author  as  the  result  of  his 
experiences  in  teaching  the  subject  seems  to  be  an  excellent  mode 
of  procedure.  The  combination  of  the  observational  and  descrip- 
tive phases,  calculations  based  on  specified  conditions,  and  finally 
actual  illumination  measurements  both  in  the  laboratory  and 
factory  should  make  up  a  course,  when  supplemented  by  lectures 
given  by  experts  engaged  in  practical  illumination,  of  great  edu- 
cational value  and  absorbing  interest  to  every  student. 

I  hope  the  time  will  come  shortly  when  the  teaching  of  this  very 
interesting  subject  will  be  very  general  and  uniform  in  the  col- 
leges throughout  the  whole  country. 

Mr.  R.  E.  Simpson  :  Graduates  of  mechanical  and  electrical 
engineering  departments  of  our  technical  schools  and  colleges  are 
very  often  in  a  position  in  which  they  are  called  upon  to  approve 
or  disapprove  the  present  lighting  system,  or  a  new  lighting 
system,  in  a  factory.  Much  more  than  the  mere  saving  of  a  few 
dollars  on  the  monthly  lighting  bill  is  dependent  on  the  decision 
made.    Generally  speaking,  the  increase  or  decrease  in  the  light- 


346     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ing  bill  should  not  be  the  determining  factor,  for  this  is  of  minor 
importance  when  the  ultimate  results  are  considered.  Decrease 
in  spoilage  and  seconds,  increase  in  production  and  efficiency  of 
the  workmen,  and  the  safety  of  the  employees  are  of  far  more 
importance  than  the  saving  in  the  lighting  bill.  Referring  to  the 
last  one  of  these  items,  namely,  the  safety  of  the  workmen,  the 
influence  of  the  lighting  installation  may  be  felt  in  the  profit  and 
loss  item  because  of  damage  claims.  Assuming  that  an  engineer, 
because  of  his  unfamiliarity  with  illuminating  engineering,  should 
decide  on  a  lighting  system  that  will  not  provide  proper  illumina- 
tion for  the  work,  but  which  will  save  an  average  of  $25.00  per 
month  compared  with  the  cost  of  the  old  system.  He  then  will 
have  saved  his  company  $300.00  per  year,  provided  no  one  of 
the  workmen  is  injured  because  of  the  inadequate  or  improper 
illumination.  At  the  present  time  I  am  gathering  statistics  on 
illumination  and  accidents  and  although  the  investigation  has 
only  recently  been  started,  the  average  of  the  figures  so  far 
obtained  indicates  that  the  cost  of  one  accident  would  more  than 
offset  the  saving  in  the  lighting  bill  for  the  year.  Any  additional 
accidents  which  might  be  charged  to  the  lighting  conditions 
simply  add  so  much  more  to  the  cost  of  the  illumination.  In 
states  having  workman's  compensation  laws  the  question  of  acci- 
dent prevention  is  a  matter  of  real  concern  to  the  factory  owner 
or  manager.  It  is  decidedly  to  his  interest  to  keep  informed  on 
every  item  that  enters  into  accident  prevention  work.  The 
mechanical  or  electrical  engineering  graduate  who  intends  to 
enter  the  manufacturing  field  should  therefore  have  as  thorough 
training  in  the  fundamentals  of  illuminating  engineering  as  in 
other  subjects,  if  in  him  is  to  be  lodged  the  authority  to  pass  on 
lighting  questions,  as  well  as  on  other  engineering  matters. 

Prof.  W.  E.  Barrows  (University  of  Maine)  :  I  have  read 
Prof.  Clewell's  paper  with  much  interest  and  at  this  time  I  wish 
to  express  my  appreciation  of  the  good  work  which  the  Committee 
on  Education  is  doing. 

It  was  my  privilege  to  give  the  course  in  illuminating  engin- 
eering at  the  Armour  Institute  of  Technology  in  1907  when  the 
subject  was  offered  there  for  the  first  time,  and  I  have  been 
teaching  that  subject  each  year  since  that  time.     When  I  became 


ILLUMINATING   ENGINEERING  347 

associated  with  the  University  of  Maine,  the  electrical  course  was 
changed  somewhat,  and  the  subject  of  illumination  added  to  those 
of  the  curriculum.  It  was  received  with  interest  and  has  proved 
a  success. 

One  of  the  features  of  the  course  which  has  received  much 
attention  has  been  the  arrangement  of  the  subject  matter  of  the 
course  so  as  to  secure  the  greatest  amount  of  interest  on  the 
part  of  the  students  and,  at  the  same  time,  cover  the  subject  in 
a  logical  order. 

While  using  my  book  "Light,  Photometry  and  Illumination" 
as  the  basis  for  the  course,  it  has  seemed  advisable  from  the 
standpoint  of  interest  on  the  part  of  the  class  to  first  take  up  in  a 
general  way  the  subject  of  illuminants  in  their  different  forms, 
together  with  their  characteristics  and  uses.  By  so  doing,  the 
student  at  once  becomes  aware  of  things  more  general  than  he 
had  learned  in  physics  and  is  keen  to  refer  to  these  illuminants 
when  taking  up  the  fundamentals  of  luminous  radiators,  photom- 
etry, illumination  calculations  and  interior  and  exterior  lighting. 

It  has  been  found  valuable  to  assign  a  certain  lighting  instal- 
lation to  each  student  to  study,  criticize,  redesign  and  discuss. 
The  reports  are  then  taken  up  in  the  class  and  there  discussed. 
The  results  have  been  valuable  and  interesting.  Several  of  the 
fraternities  have  halved  their  lighting  bills,  and  the  dormitories 
exhibit  the  recent  lighting  systems  using  various  devices  from  a 
new  tin  dish  to  a  mirror  reflector  for  the  indirect  lighting 
system. 

I  believe  there  is  an  excellent  field  here  in  Maine  for  popular 
lantern  slide  lectures  not  only  before  student  audiences  but  be- 
fore commercial  and  business  organizations  throughout  the  state. 
The  vast  amount  «of  available  water  power  in  this  part  of  the 
country,  with  prospects  of  additional  development  in  the  near 
future,  indicate  low  rates  and  there  must  follow  a  more  extensive 
use  of  electricity  for  lighting  purposes.  Moreover,  the  practise 
with  regard  to  lighting  equipment  is  in  general  not  in  accord  with 
the  times.  This  should  make  an  excellent  field  for  the  illumin- 
ating engineer. 

Prof.  Alan  E.  Flowers  (Ohio  State  University) :  Mr.  Cle- 
well  is  to  be  congratulated  for  giving  an  excellent  description  of 


348     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

successful  courses  in  illumination.  I  am  strongly  inclined  to 
favor  placing  courses  dealing  with  specialized  branches  of  engi- 
neering in  the  graduate  school,  as  was  done  with  the  course  in 
illumination  at  Yale,  but  I  think  that  every  engineering  curri- 
culum should  include  a  general  engineering  course  extending 
throughout  the  senior  year,  which  would  include  a  brief  treat- 
ment of  each  of  the  important  engineering  fields,  in  such  a  way 
as  to  bring  out  their  interrelations,  relative  industrial  and  techni- 
cal importance  and  their  possible  future  developments.  This 
course  should  consist  of  lectures,  correlated  reading  and  problems. 
Illuminating  engineering  should  find  a  place  in  this  general  course 
and  its  treatment  should  be  designed  to  give  every  student  a  grasp 
of  the  principles  of  illumination,  some  conception  of  the  im- 
portance of  good  illumination  and  some  idea  of  the  magnitude  of 
the  technical  work  being  accomplished  in  this  line  and  what  the 
professional  prospects  would  be  for  a  man  entering  this  field. 

Dr.  Clayton  H.  Sharp  :  The  paper  by  Mr.  Clewell  is  a  most 
useful  one,  both  on  account  of  the  information  which  it  brings 
together  and  of  the  practical  ideas  which  it  contains.  The  teach- 
ing of  illuminating  engineering  is  making  its  way  in  our  techni- 
cal schools  with  certainty,  but  perhaps  not  with  the  rapidity 
which  we  should  wish  for.  The  reasons  for  the  latter  condition 
may  be,  beside  natural  inertia  and  indisposition  of  men  to  take 
up  new  things,  and  the  lack  of  time  both  on  the  part  of  the 
instructors  and  the  students  for  treating  them,  first,  that  the 
importance  and  the  many-sidedness  of  the  subject  are  not  entirely 
appreciated  on  the  part  of  the  instructors,  and  second  that  the 
point  of  departure  and  method  of  attack  in  teaching  the  subject 
have  not  been  indicated  in  a  sufficiently  definite  and  practical  way. 
In  both  these  regards  the  hints  contained  in  Mr.  Clewell's  paper 
should  be  most  helpful.  When  it  is  fully  realized  that  illumin- 
ating engineering  presents  a  field  which  touches  the  every-day 
life  of  everyone  more  intimately  than  any  other  branch  of  en- 
gineering, with  the  exception  of  heating  and  ventilating,  and 
when  the  educational  value  of  a  course  in  illuminating  engineering 
in  training  the  observational  faculties,  the  judgment  and  the  use 
of  common-sense  on  the  part  of  students,  as  well  as  their  ability 
to  make  precise  measurements  along  lines  where  only  in  recent 


ILLUMINATING   ENGINEERING  349 

years  it  has  come  to  be  realized  that  measurements  are  both  feas- 
ible and  necessary,  the  progress  of  the  teaching  of  this  subject 
should  be  greatly  accelerated.  It  seems  to  me  that  Mr.  Clewell's 
paper  should  be  of  very  great  assistance  to  the  propaganda  car- 
ried on  by  the  Committee  on  Education  of  this  society  and  that 
a  great  many  copies  of  it  might  be  used  to  good  advantage  for 
this  purpose. 

Prof.  F.  K.  Richtmyer  (Cornell  University)  :  The  paper  is 
particularly  interesting  to  me  not  only  because  of  the  excellent 
material,  which  is  a  valuable  contribution  to  the  subject,  but  more 
important  still,  from  the  broader  standpoint,  because  of  that  for 
which  the  paper  stands:  a  pedagogical  experiment.  We  need 
more  experiments  of  this  kind,  and  less  generalization  as  to  the 
methods  to  be  employed  in  teaching. 

Prof.  Clewell  has  mentioned  the  keen  interest  shown  by  stu- 
dents of  illumination.  I  have  found  a  similar  attitude  among 
students  whom  I  have  taught.  And  not  until  recently,  did  I 
realize  the  reason.  Those  of  you  who  are  familiar  with  college 
students,  say  seniors,  know  that  they  have  reached  a  point  in 
their  educational  career  where  they  like  to  criticize.  When  you 
send  a  student  on  such  an  expedition  as  Prof.  Clewell  has  de- 
scribed, to  investigate  conditions  of  lighting  in  shops,  stores,  show 
windows,  etc.,  he  finds  so  much  to  criticize  that  he  is  perfectly 
happy.  It  is  not  difficult  to  get  his  interest.  Twenty  years  from 
now,  when  you  engineers  have  standardized  lighting  practise,  so 
that  there  are  not  so  many  "glaring"  examples  of  poor  lighting, 
you  will  probably  make  it  more  difficult  for  us  teachers  to  interest 
our  students. 

There  is  one  point  regarding  which  I  would  like  Prof.  Clewell's 
opinion:  where,  in  the  course  of  the  instruction  is  the  proper 
place  to  introduce  some  of  those  things  which  the  engineer  does 
not  meet  in  his  curriculum?  I  refer  to  the  close  connection  be- 
tween illuminating  engineering,  and  architecture,  physiological 
optics,  psychology,  art,  etc.  For  example,  it  is  obvious  that 
every  illuminating  engineer  should  know  something  of  archi- 
tecture. Yet  how  can  we  make  the  student  appreciate  the  archi- 
ectural  principles  involved  when  we  who  teach  him  have  never 
had  a  course  in  architecture  ourselves  ? 
3 


350     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Prof.  Clewell  has  mentioned  the  difficulties  encountered  in  in- 
teresting the  directors  of  educational  institutions  in  instruction  in 
illuminating  engineering.  I  think  the  reason  is  not  so  much  due 
to  the  jealousy  with  which  each  professor  guards  his  subject,  as 
to  the  point  brought  out  by  the  comments  of  Mr.  Serrill,  as  read 
by  the  chairman.  Your  practising  engineer  of  to-day,  in  order 
to  be  a  real  successful  engineer,  must  be  more  or  less  of  a  spec- 
ialist, and  just  in  so  far  as  he  must  be  a  specialist,  his  education, 
his  fundamental  education,  must  be  broad.  Our  colleges  are 
therefore  compelled  to  cut  out  a  great  deal  of  specialization  in 
the  course  of  instruction  and  in  its  place  put  broadening  subjects 
— a  more  sure  foundation  for  work  which  is  to  follow.  In  a  cer- 
tain university  for  example  we  used  to  have  courses  in  marine 
engineering,  in  railway  mechanical  engineering,  in  steam  power 
engineering,  in  gas  power  engineering,  mechanical  engineering 
and  perhaps  a  half  dozen  other  courses  in  which  the  student  was 
supposed  to  specialize  in  his  senior  year.  These  have  been  prac- 
tically all  cut  down  to  two  or  three  branches  and  at  the  present 
time  there  seems  to  be  little  room,  little  tendency,  for  branching 
out  again  by  adding  a  course  in  illuminating  engineering.  It  is 
assumed  that  the  young  engineer,  in  the  first  few  years  of  his 
practise,  will  on  his  college  course  as  a  basis,  build  up  a  knowl- 
edge of  his  specialty.  But  there  is  this  difficulty.  It  seems  to 
me  that  the  course  in  illuminating  engineering  is  not  quite  on  a 
par,  so  far  as  instruction  in  mechanical  engineering  is  concerned, 
with  courses  in  say  marine  engineering  or  railway  mechanical 
engineering  because  there  are  so  many  factors — architecture, 
physiology,  psychology,  and  so  on — which  the  student  does  not 
meet  in  his  general  course,  and  which  he  is,  therefore,  not 
familiar  with  when  he  comes  to  his  professional  practise. 

Proe.  C.  B.  LePage  (Stevens  Institute  of  Technology)  :  I 
have  followed  Prof.  Clewell's  paper  very  carefully  and  believe 
it  to  contain  many  very  valuable  suggestions  for  those  of  us  who 
are  teaching  illuminating  engineering  or  its  related  subjects.  This 
paper  is  certainly  a  very  clear  and  concise  report  of  some  good 
work  which  is  being  actually  accomplished.  I  expect  to  study  it 
with  a  great  deal  of  interest  and  I  desire  now  to  thank  Prof. 
Clewell  for  presenting  it  at  this  time. 


ILLUMINATING   ENGINEERING  351 

At  Stevens  Institute  of  Technology  we  have,  as  yet  no  con- 
nected course  in  illumination.  During  the  sophomore  year  we 
give  the  students  the  physics  of  light,  photometry,  and  illumin- 
ation by  lectures,  recitations  and  laboratory  exercises.  This  work 
is  followed  in  the  senior  year,  by  lectures  on  the  modern  light 
sources  and  laboratory  work  in  distribution  measurements,  all 
given  as  part  of  the  electrical  engineering  laboratory  course.  All 
our  graduates,  as  you  know,  receive  the  degree  of  mechanical 
engineer. 

Prof.  C.  E.  CeEwell  (In  reply)  :  It  has  been  very  interesting 
to  me  to  hear  the  various  views  brought  out  in  this  discussion, 
and  in  particular  to  hear  from  Prof.  Scott  and  Prof.  Pender. 
Both  of  these  men  stand  for  new  electrical  engineering  depart- 
ments in  two  of  the  largest  universities  in  the  country,  and  it  is 
significant  that  they  have  manifested,  as  their  discussions  show, 
a  decided  interest  in  illumination  as  a  branch  of  technical  in- 
struction. 

Mr.  Semll's  suggestion  that  the  coming  engineering  curri- 
culum will  probably  lead  to  a  degree  in  engineering  is  certainly 
somewhat  of  a  departure  from  the  ordinary  views  of  college 
education  as  manifested  by  present  specialized  courses.  How- 
ever, if  one  keeps  pace  with  the  times,  he  cannot  fail  to  see  that 
engineering  work  in  the  schools  is  coming  more  and  more  to  be 
looked  upon  as  a  training  in  the  broad  fundamentals  of  engineer- 
ing, rather  than  to  separate  the  courses  into  electrical,  mechani- 
cal or  civil  engineering  as  the  case  may  be.  These  different 
courses  will  doubtless  continue  under  the  jurisdiction  of  given 
departments,  but  at  the  same  time  the  concentration  on  funda- 
mentals of  engineering  in  its  broadest  sense  can  receive  due  at- 
tention. 

Prof.  Rowland's  statement  that  in  his  evening  classes  he  has 
found  no  demand  for  illumination  work  must  be  looked  upon,  I 
believe,  from  the  standpoint  of  the  call  for  particular  lines  of 
work  which  normally  follows  the  demand  for  men  trained  in  these 
directions.  As  Mr.  Macbeth  has  pointed  out,  there  is  a  proba- 
bility that  in  the  future  there  will  be  a  great  demand  for  men 
trained  in  this  field,  and  when  such  a  time  arrives,  the  demand  for 
illumination  courses  will  follow  as  a  logical  result. 


352     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Regarding  Prof.  Atkinson's  suggestion  that  in  reports  like 
those  mentioned  in  the  paper  conclusions  should  always  be  in- 
cluded by  the  student,  it  should  have  been  stated  that  in  these 
particular  reports  conclusions  were  added  although  they  formed 
no  part  of  the  paper. 

Prof.  Barrows  calls  attention  to  the  importance  of  proper  ar- 
rangement of  work  in  engineering  courses  so  as  to  secure  the 
best  results.  This  feature  coincides  exactly  with  my  own  views 
as  outlined  in  the  paper. 

I  want  to  express  my  appreciation  to  Prof.  Richtmyer  for  his 
comments  on  the  paper  and  in  particular  for  the  fact  that  he 
classes  the  work  back  of  the  paper  as  an  educational  experiment. 
This  is  the  manner  in  which  the  work  has  been  looked  upon 
during  the  past  three  years  and  his  view  that  it  is  both  stimulating 
and  healthful  in  educational  work  to  have  such  experiments  from 
time  to  time  seems  most  appropriate.  Answering  Prof.  Richt- 
myer's  question  as  to  the  proper  place  for  the  introduction  of  the 
kinds  of  things  which  do  not  normally  find  their  way  into  the 
engineering  curriculum,  such  as  architecture  and  psychology  for 
example,  the  student  branches  of  the  national  engineering  so- 
cieties might  well  be  used  as  an  opportunity  for  lectures  from  men 
in  these  other  lines  of  educational  activity. 

It  was  not  intended  in  the  introductory  remarks  of  the  paper 
to  give  the  idea  that  the  jealousies  of  college  professors  are  re- 
sponsible for  the  difficulty  in  finding  room  for  new  lines  of  in- 
struction work.  As  pointed  out  by  Prof.  Richtmyer,  college 
courses  are  already  too  crowded  in  many  cases  to  warrant  more 
than  the  broad  fundamental  items  which  are  required  by  the 
future  specialist.  There  must  then  be  a  good  and  sufficient  rea- 
son when  one  or  another  existing  courses  are  replaced  by  some- 
thing which  is  new  and  different. 

In  conclusion,  the  approval  which  Mr.  Millar  has  placed  on  the 
efforts  which  have  resulted  in  this  paper  is  gratifying  and  if  the 
material  should  be  considered  by  the  Committee  on  Education 
of  sufficient  interest  to  be  sent  out  as  a  supplement  to  the  annual 
report  of  that  committee,  this  may  be  the  means  for  hearing  from 
others  who  receive  the  paper  and  who  may  be  in  a  position  to 
offer  new  and  improved  ways  for  conducting  this  particular  line 
of  educational  work. 


OPTICAL   PROPERTIES   OP   DIFFUSING    MEDIA  353 

THE  OPTICAL  PROPERTIES  OF  DIFFUSING 
MEDIA,  I* 


Synopsis:  This  report  is  the  first  of  a  series  dealing  with  the  classifi- 
cation of  diffusion  and  the  general  properties  of  diffusing  materials.  The 
reflection  and  transmission  of  light  is  either  specular,  semi-specular,  semi- 
diffuse  or  diffuse.  These  four  classes  are  defined  and  illustrated.  Defi- 
nitions of  turbidity,  gloss,  glare,  density  and  other  terms  are  suggested. 
The  various  kinds  of  data  obtainable  and  required  in  practise  are  out- 
lined. The  theory  of  contrast  is  given,  and  finally  the  physical  theory  of 
scatter. 


TYPES  OF  DIFFUSION. 

Light  reflected  from  or  transmitted  through  various  materials 
is  scattered  in  varying  degree.  Part  of  the  light  may  be  highly 
diffused  and  the  remainder  reflected  specularly,  as  in  a  mirror, 
or  all  the  light  may  be  more  or  less  scattered.  Further,  the  dif- 
fusing properties  of  many  materials  vary  markedly  with  the 
quality  of  the  light.  Colored  objects  with  surface  polish,  specu- 
larly reflect  all  wave-lengths,  but  the  ratio  of  diffusely  to  specu- 
larly reflected  light  is  much  greater  for  the  color  exhibited.  Thin 
opal  transmits  a  red  image  of  a  lamp  filament,  but  viewed  through 
opal  and  a  blue  filter  no  specular  image  of  the  filament  is  seen. 
It  is  convenient  in  treating  diffusion  to  distinguish  four  quite 
distinct  glasses. 

1.  Specular  Reflection  and  Transmission. — Specular  reflection 
is  exhibited  by  plane  polished  surfaces  not  scratched,  dirty,  wavv, 
nor,  if  not  opaque,  reflecting  diffusely  from  within  the  surface. 
Bodies  transmit  specularly  if  their  surfaces  are  plane  and  clean 
and  if  they  contain  no  imbedded  diffusing  bodies  or  particles. 
Scratches,  dirt  or  undulations  on  surfaces  or  imbedded  particles 
in  a  material  produce  diffusion  in  general  only  if  their  least 
dimension  be  large  compared  with  half  the  length  of  a  light  wave; 
i.  e.,  a  quarter  of  a  thousandth  of  a  millimeter  or  a  hundred 

*  Report  No.  2  ot  the  I.  E.  S.  Committee  on  Glare,  submitted  in  March,  1915. 


354     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


thousandth  of  an  inch.  Smaller  irregularities  may  absorb  but 
never  scatter  light.  Larger  irregularities  produce  diffusion  of 
either  the  second  or  third  type. 

The  brightness  of  a  specularly  reflected  image  is  equal  to  that 
of  the  source  of  light,  viewed  on  a  line  through  the  point  of  in- 
cidence, times  the  reflecting  power  of  the  surface.  Reflecting 
powers  range  from  about  0.02  for  water  to  0.064  f°r  glass>  and 
from  0.16  to  0.98  for  metals.  A  specularly  transmitted  beam  suf- 
fers loss  by  reflection  from  surfaces  and  from  internal  absorption. 
Transmission,  T  =  (1-R)2  (i-A)  =  Tx  T2  say,  the  quantity  -log 
T2  or  -log  (i-A)  is  proportional  to  thickness. 

2.  Partly  Specular  Diffusion. — Any  reflection  or  transmission  of 
light  in  which  a  distinct  image  of  the  source  may  be  seen  is 
classed  as  partly  specular.  A  dusty  mirror  or  a  sheet  of  glass  over- 


0        10      20      30     40      50      60     70     80      90° 
Fig.  i. — Types  of  partly  specular  reflection  and  transmission. 

lying  paper  exhibits  typical  semi-diffuse  reflection.  Correspond- 
ing examples  of  transmission  are  given  by  atmospheric  haze  and 
by  glass  or  ice  filled  with  bubbles.  Of  the  original  incident  beam 
a  fraction  is  absorbed,  another  specularly  reflected  or  trans- 
mitted, and  a  third  scattered  in  all  directions  in  various  propor- 
tions. 

In  Fig.  i  are  plotted  distribution  curves  typical  of  reflected  or 
transmitted  beams  of  light  in  which  some  specular  remains.  The 
projecting  knobs  represent  the  residual  specular  light,  their  width 
being  the  angular  width  of  the  source  and  their  heights  propor- 
tional to  the  coefficient  of  specular  reflection.  Their  area  rela- 
tive to  the  total  area  is  the  fraction  of  the  reflected  or  transmitted 


OPTICAL   PROPERTIES   OF   DIFFUSING    MEDIA 


355 


beam  that  is  specular.  The  various  types  of  semi-specular  dif- 
fusion differ  in  ratio  of  diffuse  to  specular  light  and  in  distribu- 
tion of  diffuse  light.  Each  curve  is  from  actual  data.  In  colored 
materials  these  curves  vary  greatly  with  the  quality  of  the  illum- 
ination. 

3.  Nearly  Diffuse. — Reflection  and  transmission  are  classed  as 
nearly  diffuse  when  the  specular  image  is  completely  broken  up, 
yet  the  diffusion  is  far  from  complete.  The  reflection  from  calen- 
dered papers  and  other  wavy  surfaces  and  the  transmission 
through  ribbed  and  chipped  glass  and  oiled  paper  are  of  this 
class.     Typical  distributions  are  illustrated  in  Fig.  2. 

Diffusion  varies  from  high  and  nearly  uniform  to  that  which  is 
nearly  all  confined  to  very  near  the  specular  angle. 


10      20      30     40      50     60      70     80     90" 


Fig.  2. — Types  of  semi-diffused  reflection  and  transmission. 

With  this  class  of  diffusion  any  quantitative  definition  of 
glossiness  or  of  glare  must  be  arbitrary  for  there  is  no  truly  spec- 
ular reflected  or  transmitted  light.  It  might  be  agreed,  for  ex- 
ample, to  take  the  ratio  of  the  light  within  io°  of  the  specular 
angle  to  the  total  in  certain  cases,  say  focusing  screens.  This 
would  doubtless  be  advantageous  in  comparing  materials  of  the 
same  class,  but  definitions  rational  and  useful  for  all  classes  of 
materials  seem  out  of  the  question. 

Probably  the  most  scientific  analysis  and  specification  of  non- 
specular  beams  would  be  to  treat  them  as  aggregates  of  miniature 
specular  or  semi-specular  beams.  An  analysis  of  the  beam  would 
thus  give  by  deduction  the  surface  of  internal  structure  of  the 
surface  producing  it.    For  a  wavy  surface  we  should  thus  derive 


356     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

a  mean  amplitude  and  period;  for  a  surface  composed  of  minute 
planes  we  should  be  led  to  a  probability  law  of  angular  distribu- 
tion. However  interesting  such  analyses,  they  would  be  of  little 
practical  value  compared  with  the  distribution  curve  itself.  An 
outline  of  the  theory  of  the  action  of  such  aggregates  is  given  at 
the  end  of  this  report. 

Both  reflecting  power  and  coefficient  of  transmission  vary  with 
both  the  angle  of  illumination  and  angle  of  reflection  or  trans- 
mission. Mean  reflecting  power  is  the  ratio  of  total  reflected  to 
total  incident  light  for  any  given  (say  perpendicular)  illumination. 
Absolute  reflecting  power  is  the  ratio  of  reflected  to  incident  light 
when  the  incident  light  is  perfectly  diffuse.  The  mean  and  ab- 
solute coefficients  of  transmission  are  similarly  defined. 

Certain  arbitrarily  defined  quantities  are  useful  in  comparing 
materials  of  the  same  class.  With  perpendicular  illumination, 
brightness  is  measured  at  angles  of  o°,  45 °  (reflected),  1350  and 
1800  (transmitted),  B450  :  Bo°  is  a  measure  of  entrant  scatter, 
B135   :  B180  of  exit  scatter  (v.  infra). 

4.  Diffuse  Reflection  and  Transmission. — When  a  surface  that 
is  uniformly  illuminated  appears  equally  bright  viewed  at  all 
angles  of  reflection  or  transmission,  the  reflection  or  transmission 
is  perfectly  diffuse.  Blotting  paper,  felt,  snow  and  other  masses 
of  fine  crystals  exhibit  nearly  perfect  diffuse  reflection.  Good 
opal  glass  and  a  few  other  materials  give  nearly  perfectly  dif- 
fuse transmission. 

The  reflecting  powers  of  some  diffusely  reflecting  surfaces  is 
independent  of  the  angle  of  incidence,  in  others  not.  The  dif- 
ference appears  to  be  due  to  the  shadows  cast  by  minute  pits  or 
projecting  particles.  When  these  are  present,  oblique  illumina- 
tion is  accompanied  by  a  decreased  brightness  on  the  side  away 
from  that  on  which  the  surface  is  illuminated.  Surfaces  of  crys- 
talline powders  formed  by  pressing  with  a  plate  of  glass  are  quite 
free  from  this  effect  and  also  from  specular  reflection. 

PROPERTIES  OF  MATERIALS. 
Granular  Glare. — Direct  sunlight  reflected  from  the  wavy  sur- 
face of  water  or  transmitted  through  ribbed  glass  gives  typical 
granular  glare.    The  brilliant  points  or  lines  are  such  as  reflect  or 
transmit  specularly  while  the  intervening  spaces  are  of  much 


OPTICAL   PROPERTIES   OP   DIFFUSING    MEDIA 


357 


lower  brightness  and  give  highly  diffused  light.  Intrinsic  bril- 
liancies and  contrasts  are  met  with  as  excessive  as  those  met  with 
in  filament  lamps  without  diffusing  screens  and  just  as  objection- 
able. 

The  size  of  grain  that  is  tolerable  depends  upon  the  degree  of 
contrast.  Halftone  dots  with  a  contrast  of  but  20  :  1  are  quite 
unobjectionable  but  brilliant  points  of  similar  angular  size  would 
be  intolerable.  Excessive  contrasts  are  tolerable  only  when  the 
angular  size  of  grain  is  below  the  resolving  power  of  the  eye  or 
about  half  a  minute  of  arc  in  angle. 

Measurements  may  be  made  upon  either  average  brightness 
or  brightness  of  detail  and  the  results  specified  either  as  a  glare, 
a  contrast  or  a  brightness  distribution.  An  image  of  the  surface 
is  either  magnified  or  diffused  if  required  for  measurement. 

Thickness  of  Diffusing  Layer. — Diffuse  reflecting  power  in- 
creases steadily  to  a  fixed  maximum  value  with  increasing  thick- 
ness of  diffusing  medium.  Diffuse  transmission  increases  rapidly 
to  a  maximum  then  decreases  to  zero  for  thick  layers. 


R    CB 

^tfLtcTToNT" 

T_MMt/ 

^ 

^^0^ 

'      THICKNESS 

Fig.  3. — Effect  of  thickness  on  diffusion. 

Fig.  3  indicates  graphically  the  variation  with  thickness  in  a 
typical  case.  Similar  curves  have  been  obtained  on  thin  wedges 
of  opal  glass  illuminated  perpendicularly  and  viewed  at  angles 
of  45  and  1350  from  the  normal. 

Reflecting  power  follows  closely  the  simple  exponential  law: 
R  =  Roo  (1  —  e  ~ki)  constant  k  being  a  measure  of  the  turbidity 
of  the  material  and  R^  the  maximum  reflecting  power  attained 
with  increasing  thickness  of  material.     The  diffuse  transmission 


358     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

also  appears  to  follow  an  exponential  law,  but  not  so  simple  a  one. 
In  the  theory  of  diffusion  given  below  these  exponential  laws  are 
deduced  from  simple  assumptions  as  to  the  nature  of  scatter. 

Suppose  a  light  flux  I0  is  incident  on  the  first  surface.  I0  R  is 
reflected  and  I0  —  I0  R  or  I0  (1  —  R)  enters  the  surface.  Of  this, 
I  =  TI„  (1  —  R)  is  transmitted  to  the  back  surface.  The 
transmission  T  is  computed  from  I.I^and  R,  all  three  of  which 
are  measured.     T  =  I/I0  (1  —  R) 

D  =  —  log  T  =  log  O,  O  =  i/T. 
Opacity  O  is  the  reciprocal  of  percentage  transmission.  Log  O 
=  -log  T  is  D  the  density,  a  quantity  proportional  to  thickness. 
Specific  density  is  the  density  divided  by  the  thickness  in  mm. 
Measurements  on  opal  glass,  piles  of  paper,  blocks  of  magnesium 
carbonate,  etc.,  show  that  the  density  law  holds  well. 

The  amount  that  print  on  the  back  of  a  sheet  of  paper  shows 
through  (contrast  ratio)  is  simply  related  to  the  above  constants. 

The  light  returned  to  the  front  surface  is  T2R(i  —  R)  where 
the  sheet  is  backed  by  a  similar  sheet,  T2RZ  (1  —  R)  where 
backed  by  ink  of  reflecting  power  R*  .  The  brightness  of  the 
front  surface  is  proportional  to  the  initial  reflecting  power  plus 
this  returned  light.     Back  contrast  Cb  is  then 

R  +  T2R   (1   -  R) 
*     ~  R  +  T2R,  (1  —  R)* 
If  R  is  large  and  R,-  is  small,  as  in  ordinary  cases,    d  =  1   -f- 
T2  (1  —  R)  to  a  very  close  approximation. 

Another  quantity  of  value  in  describing  the  diffusion  of  special 
materials  is  the  diffusion  efficiency,  the  relative  brightness  at  some 
assigned  angle  to  the  brightness  viewed  perpendicularly.  For 
example,  with  projection  screens  intended  to  be  viewed  at  angles 
up  to  300  from  the  normal,  relative  brightness  at  30  and  o°  is  a 
proper  measure  of  diffusion  efficiency.  With  focusing  screens 
B170  :  B180  may  be  used  as  a  criterion  of  efficiency. 

Angle  of  Illumination. — The  ratio  of  the  diffuse  to  the  specular 
brightness  of  a  surface  varies  with  the  solid  angle  subtended  by 
the  illuminant.  That  angle  may  in  practise  be  anything  from 
almost  a  point  (sun  or  Nernst  lamp  filament)  to  a  hemisphere 
like  an  overcast  sky.  The  simple  problems  may  be  treated  as 
follows : 


OPTICAL   PROPERTIES   OF   DIFFUSING    MEDIA 


359 


Specular  brightness  B*  is  equal  to  the  brightness  of  the  source 
B0  times  the  coefficient  of  specular  reflection  (Rs  )  or  transmission 
(  Ts  )  as  the  case  may  be.  Diffuse  brightness  B^  is  such  that  irBd 
=  B0  Rrfto  for  not  too  large  solid  angle  o>  (=  area/dist.*)  of  source 
and  nearly  perpendicular  illumination.  Both  Bd  and  B0  are  in 
light  units  per  unit  area,  say  in  lumens  per  square  cm.  B0  «»  = 
B0  X  Area/(dist.)2,  is  the  illumination  and  the  factor  it  converts 
this  into  brightness.  For  illumination  at  a  considerable  angle, 
a  correction  for  oblique  incidence  must  be  applied  (by  integration 
of  the  cosine  of  the  angle  of  illumination)  amounting  to  a  factor 
of  ^  for  illumination  from  a  complete  hemisphere.  In  Fig.  4  is 
plotted  the  ratio  of  diffuse  to  specular  brightness  with  increasing 
solid  angle  of  the  source  of  illumination. 


I  2  3TT  4  5  6     2TT 

Fig.  4.— Ratio  of  diffuse  to  specular  brightness. 

For  a  source  of  limited  extent  and  nearly  normal  illumination, 
therefore,  the  ratio  of  specular  to  diffuse  brightness  is 

p  Bj  Rj     ir 

Bd  Rd     0  * 

This  ratio  of  total  to  diffuse  brightness  is  a  logical  definition  of 
spot  glare.  Since  it  depends  upon  the  illumination  as  well  as  the 
material,  it  is  not  a  specific  property  of  a  surface  or  material,  but 
of  its  appearance  under  stated  conditions.  Glare  cannot  be  ex- 
pressed in  terms  of  reflecting  or  transmitting  power  alone.  For 
a  source  of  small  solid  angle  such  as  the  sun,  an  arc  or  a  lamp 
filament,  glare  may  have  very  large  values  unless  specular  re- 
flecting power  be  very  small. 

The  glare  from  large  angle  illumination  must  be  treated  by 
elements,  since  both  reflecting  powers  as  well  as  the  illumination 


360    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

varies  with  angle  of  incidence.  It  is  always  small  and  of  little 
practical  importance. 

Contrast  is  relative  total  brightness.     Call  this  C,  then 

p  Brf  H~  B5 

C  ~  B'd  +  B',  ' 
Bd  and  B5  being  diffuse  and  specular  brightness  of  one  part  of 
the  surface  and  B'd  and  B's  of  neighboring  portions  whose  con- 
trast with  the  first  is  to  be  specified.     For  rather  small  illumi- 
nants  we  may  put  as  above  Bs  =  B0R5  and  nBd  =  B0R^o),  hence 

_         0)Rrf  4-  ttR5 

_    <oR'd  +  7rR's  ■ 
For  ordinary  glossy  print  paper  and  ink  R^  is  about  0.6  for 
the  paper  and  0.04  for  the  ink.     R*  is  about  0.02  for  the  paper 
and  0.01  for  the  ink.     Hence 

„     _         0.6ft)     +     0.027T 

0.04ft)    ~T"    O.Ol7r" 

For  a  small  or  distinct  illuminant  <o  is  nearly  zero  and  C  =  2. 
For  lighting  from  a  single  window,  w  is  about  unity  and  C  =  9.4. 
For  a  hemispherical  illuminant  such  as  the  open  sky  C  =  6.7. 
In  other  words,  with  direct  lighting  from  a  bare  lamp  the  ink 
may  appear  half  as  bright  as  the  paper  but  with  open  sky  illumi- 
nation, the  paper  is  nearly  seven  times  as  bright  as  the  ink.  In 
extreme  cases  of  glossy  ink  or  paint  on  a  dark  matt  ground,  the 
print  may  appear  even  twenty  times  as  bright  as  the  background. 

THEORY  OF  DIFFUSION. 

Certain  cases  of  mixed  specular  and  diffuse  reflection  and 
transmission  yield  to  theoretical  treatment  by  which  certain  prop- 
erties may  be  deduced  from  known  data  or  insight  be  gained  into 
the  mechanism  of  diffusion. 

Specular  Surfaces. — Metals  reflect  high  (60  to  98  per  cent.) 
and  absorb  light  very  strongly  except  in  very  thin  layers.  The 
non-metals  such  as  glass,  varnish,  water  crystals  of  salts  and  the 
like,  reflect  weakly  (3  to  5  per  cent.)  but  transmit,  if  transparent, 
practically  all  the  light  incident  except  that  lost  by  reflection. 
Between  these  two  classes  of  materials  there  is  a  wide  gap 
in  which  only  a  few  solid  dyes  have  intermediate  properties. 
The  reflecting  power  of  a  metal  may  be  expressed  in  terms  of 
its   refractive  index,  its  absorptive  index  and  the  angle  of  in- 


OPTICAL   PROPERTIES   0F   DIFFUSING    MEDIA  361 

cidence.  The  reflecting  power  of  a  non-metal  depends  upon  re- 
fractive index  and  angle  of  incidence.  The  laws  of  reflection  and 
refraction  may  be  found  in  any  text  of  theoretical  optics  such  as 
Wood  or  Preston.  The  essential  characteristics  are  those  noted 
above  and  that  the  reflecting  powers  of  metals  decrease  while 
those  of  non-metals  increase  with  increasing  angle  of  incidence. 
The  cases  of  silver  and  glass  are  typical. 

Angle  of  incidence 


e-,  „  »  10  20  40  60  80 

Silver       R  =         0.98        0.75        0.70        0.70  0.70  0.70 

Glass  1.5  R=         0.04        0.04        0.04        0.045        0.085        0.20 

Reflection  from  an  interface  between  non-metals  depends  upon 
the  relative  refractive  indices  of  the  two  media  (say  varnish  and 
glass)  and  at  the  same  angle  is  equal  on  the  two  sides.  Between 
a  metal  and  non-metal  (silver  on  glass,  say)  the  laws  of  reflection 
are  not  yet  fully  developed  but  the  reflection  is  in  amount  much 
as  though  the  non-metal  were  not  present. 

The  reflection  from  a  rough  surface  such  as  a  powder,  a  mass 
of  crystals  or  a  scratched  surface  is  simply  an  aggregate  of  re- 
flections from  the  small  elementary  faces  according  to  the  laws 
for  large  plane  surfaces,  except  when  the  elementary  faces  are 
small  compared  with  the  length  of  a  light  wave.  In  the  latter 
case  the  reflected  waves  tend  to  fuse  together  as  though  reflected 
from  the  general  level. 

Partly  Specular  Diffusion.— In  case  part  of  the  incident  light  is 
specularly  reflected  or  transmitted,  the  remainder  may  be  highly 
or  but  slightly  diffused.  The  theoretical  treatment  of  this  case  is 
that  of  the  purely  specular  reflection  or  transmission  together 
with  that  of  complete  or  partial  diffusion  given  below.  It  may 
be  noted,  however,  that  actual  distribution  curves  always  show 
some  shading  off  from  specular  to  diffuse.  This  behavior  is 
hardly  to  be  expected  in  the  case  of  a  dusty  mirror,  a  hazy  atmos- 
phere or  of  a  glass  containing  bubbles. 

Partly  specular  diffusion  is  of  little  if  any  use  as  such  but  is 
made  use  of  in  studying  the  atmosphere  and  the  chemical  forma- 
tion of  slight  suspended  precipitates.  The  minimum  perceptible 
diffusion  is  extremely  small  if  sufficiently  powerful  illumination 
is  available.    The  brightness  of  the  diffused  light  is  proportional 


$62     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

both  to  the  size  and  to  the  number  per  unit  volume  of  particles  in 
suspension. 

Pure  and  Partial  Diffusion. — Diffusion  is  due  ultimately  to 
either  small  spherical  surfaces,  small  plane  surfaces,  spherical 
bubbles,  wavy  surfaces  or  small  opaque  particles  of  indifferent 
form  and  orientation.  Consider  first  the  problem  of  the  gradual 
scatter  of  light  in  entering  a  diffusing  medium.  At  any  plane 
element  of  the  medium  of  thickness  dx  let 

S  =  flux  density  of  specular  light  in  the  direction  of  x 
A  =  flux  density  of  diffused  light  in  the  direction  of  x 
B  =  flux  density  of  diffused  light  backward  against  x 
a  =  total  area  of  grains  in  unit  area  of  elementary  plane 
r  =  percentage  of  incident  light  reflected  by  each  grain  in  all 
directions. 

Then,  if  the  thickness  dx  of  an  element  is  of  the  same  order  as 

the  mean  diameter  of  grains 

dS  \dx  =  —  ks  — as  (k  =  absorptive  index) 

dAldx  =  y2  arS  —  %  arA  +  }4  arB 

dBjdx  =  —  y2  arS  +  y2  arB  —  y  arA. 
These  equations  readily  give 
S  =  S0e-"!X 

2A  =  —  (i  +  R)  RSoe-"1*  —  mRC.x  +  C,  +  C3 

2B  =  -f  (i  —  R)  RS„  e  -«*  —  wRC,*  —  Ct  +  C2 
R  being  an  abbreviation  for  ar\m  (m  =  s  +  k)  and  Q  and  C2 
being  integration  constants.  The  specular  component  falls  off 
according  to  the  simple  exponential  law.  The  integration  con- 
stants are  readily  determined  since  for  x  =:  o,  A  =  o  and  for 
x  =1  t,  the  total  thickness,  B  =  o. 

Diffuse  reflecting  power  (total)  is  then  given  by  the  ratio  of 
the  back  emergent  light  B  to  the  incident  light  S0  for  X  =  o  or 
B  mRt  +  (i  —  R)  ( i  —  e  —* ) 

—  is. 


So  2  +  mRt 

The  reflecting  power  increases  according  to  an  exponential  law 
from  o  up  to  a  maximum  value  B/S<?  =  R  =  ar\m  (=  r  if  k  =  o). 
Diffuse  transmission,  given  by  A/S0  for  X  =  /,  is  a  more  com- 
plicated exponential  which  is  equal  to  zero  both  for  /  =  o  and 
for  /  =  oo  and  has  a  maximum  value  for  an  intermediate  thick- 


OPTICAL   PROPERTIES   OF   DIFFUSING    MF.DIA  363 

ness  such  that  the  specular  transmission  ratio  is  reduced  to  about 
0.1. 

Of  the  light  incident  on  a  single  particle  approximately  half 
the  reflected  light  is  reflected  at  angles  greater  than  900  from 
the  direction  of  incidence,  hence  in  a  thin  layer  diffuse  reflection 
and  transmission  are  nearly  equal.  The  calculations  are  not  dif- 
ficult in  the  case  of  a  reflecting  opaque  sphere  such  as  a  mercury 
globule,  an  imbedded  bubble  or  a  tiny  crystal  or  opaque  particle, 
but  are  too  long  to  reproduce  here.  To  mention  but  one  instance : 
the  light  reflected  at  an  angle  of  900  from  a  polished  sphere  is  in- 
cident on  a  ring  R/j/~2~  in  diameter  and  the  projected  area  re- 
flecting light  lies  half  within  and  half  without  this  ring. 

The  distribution  of  the  light  reflected  or  transmitted  by  a  thin 
layer  is  to  a  first  approximation  uniform  within  the  hemisphere 
provided  the  scattering  particles  have  either  (a)  spherical 
symmetry  or  (b)  indifferent  orientation.  A  great  many  quanti- 
tative investigations  show  this.  For  example,  when  a  liquid  con- 
taining suspended  particles  is  illuminated  by  a  rectangular  beam, 
the  brightness  of  the  path  of  the  beam  is  closely  proportional  to 
the  reciprocal  cosine  of  the  angle  of  view ;  that  is,  to  the  number 
of  particles  in  the  line  of  vision  independently  of  the  angle  of 
reflection  from  their  surfaces. 

When  a  diffusing  layer  consists  of  minute  planes  not  indif- 
ferently oriented,  the  distribution  of  the  reflected  and  transmitted 
light  depends  upon  the  law  of  orientation  of  the  surfaces.  Let  p 
be  the  fraction  of  the  surface  covered  by  reflecting  planes  in- 
clined to  the  perpendicular  at  angles  lying  between  a  and  a  -(-  da. 
Then  p  will  be  the  fraction  of  the  light  reflected  at  angles  lying 
between  2a  and  2  (a -\-  da).  This  function,  times  the  reflecting 
power  of  the  surface  at  that  angle,  will  be  the  distribution  of  re- 
flected light.  In  other  words  the  light  distribution  ~L(a)  =  R  ( — ) 

X  P  ( — ),    reflecting   power    times    angular    distribution    but 

doubled  in  angle. 

The  transmitted  light  is  distributed  in  accordance  with  the  law 
of  refraction.    The  deviation  d  in  passing  through  a  thin  wedge 


364    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

of  angle  a  is  d  =  a  (n  —  /)  where  n  is  the  refractive  index  of  the 
material.    Hence  for  shallow  angles 

i,-w  =  (#_»)(±.)x>(.  +  5rin). 

This  law  applies  to  the  transmission  of  ribbed,  ground  or  frosted 
glass  or  glass  with  any  kind  of  wavy  surface.  Good  focusing 
glass  shows,  under  a  microscope,  shallow  spherical  depressions 
acting  like  weak  negative  lenses.  Such  glasses  scatter  transmitted 
light  nearly  uniformly  over  an  angle  of  only  a  few  degrees. 

In  this  report  certain  terms  relating  to  illumination  have  been 
used  that  have  not  yet  been  officially  sanctioned  by  the  society. 
These  are  tabulated  below  together  with  brief  definitions  of  each 
indicating  the  senses  in  which  each  has  been  used. 

Partly  specular  diffusion :  partly  diffuse  reflection  or  transmis- 
sion in  which  some  pure  specular  remains. 

Nearly  diffuse  reflection  or  transmission :  that  in  which  no  pure 
specular  remains  but  in  which  diffusion  is  incomplete. 

Reflecting  power  at  any  angle:  brightness  relative  to  that  of  a 
perfectly  diffusing  surface  reflecting  100  per  cent. 

Total  reflecting  power:  ratio  of  total  incident  to  total  reflected 
light. 

Mean  reflecting  power:  mean  of  angular  reflecting  powers  with 
normal  illumination. 

Transmission ;  angular,  mean,  total :  analogous  to  reflecting 
powers. 

Entrant  scatter:  brightness  at  450  /  brightness  at  o°. 

Exit  scatter:   brightness  at  1 35  °  /  brightness  at  1800. 

Diffusion  efficiency:  brightness  at  maximum  effective  angle  / 
Bo°  or  B1800. 

Turbidity:  constant  of  exponential  reflecting  power. 

Opacity:  reciprocal  of  transmission. 

Specific  density:  -log  opacity  /  thickness. 

Gloss :  ratio  of  total  to  diffuse  brightness  source  0.0 1  ster- 
adian. 

Contrast :  relative  total  brightness. 

The  terms  partly  specular  and  nearly  diffuse  are  used  only  be- 
cause none  more  fitting  have  been  suggested  and  are  not  recom- 


OPTICAL   PROPERTIES   OF  DIFFUSING   MEDIA  365 

mended  by  this  committee.  The  definitions  of  all  the  terms,  par- 
ticularly of  turbidity  and  glare,  are  to  be  considered  merely  tenta- 
tive. For  precise  definitions  of  glare  and  its  sub-classes  see  our 
general  report. 

For  nearly  all  of  the  new  matter  in  this  report  the  chair- 
man alone  is  responsible,  the  other  members  of  the  committee 
having  read  the  report  but  not  having  considered  it  in  sufficient 
detail  to  assume  full  responsibility  for  it. 

The  following  report  is  to  cover  the  practical  problems  of 
measuring  mixed  specular  and  diffuse  reflection  and  transmission 
and  of  specifying  the  distribution  of  diffused  light. 

Nelson  M.  Black, 

J.  R.  Cravath, 

F.  H.  Gilpin, 

M.  Luckiesh, 

F.  K.  Richtmyer, 

F.  A.  Vaughn, 

P.  G.  Nutting,  Chairman. 


366     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

THE  OPTICAL  PROPERTIES  OF  DIFFUSING 
MEDIA,  II* 


Synopsis:  This  report  deals  with  the  methods  of  measurement  and 
the  geometrical  theory  of  diffusion.  It  follows  a  report  under  the  same 
title  dealing  with  the  general  properties,  nomenclature  and  physical  theory 
of  diffusion  media.  The  following  reports  are  to  give  the  results  of 
extended  investigations  of  various  classes  of  diffusing  media  by  various 
methods.  The  numerous  methods  discussed  include  laboratory  methods 
of  investigation  and  practical  methods  for  quickly  determining  important 
constants,  methods  for  measuring  either  specular  or  diffuse  reflection  or 
transmission  separately,  in  the  presence  of  the  other  or  of  measuring  the 
two  combined.  'The  geometry  of  distribution  photometry  involved  in 
deducing  the  required  data  and  constants  from  observed  data  is  outlined. 


The  investigation  of  the  optical  properties  of  diffusing  media 
requires  means  for  determining  (a)  the  distribution  of  the  re- 
flected and  transmitted  light  with  any  desired  illumination  (b) 
the  total  amounts  of  light  reflected,  transmitted  and  absorbed  and 
(c)  the  relative  amounts  specularly  and  diffusely  reflected,  trans- 
mitted and  absorbed. 

THE  DETERMINATION  OF  DISTRIBUTION. 

There  is  but  one  general  method  for  determining  the  angular 
distribution  of  the  light  reflected  from  or  transmitted  through 
the  medium  studied  and  that  is  to  mount  the  specimen  at  the  axis 
of  some  form  of  spectrometer,  then  determine  its  brightness 
with  a  brightness  photometer  attached  to  the  observing  arm. 

Spectrometer. — The  crudest  form  of  spectrometer  will  serve 
since  the  sole  requirements  are  a  definite  axis  of  rotation  and  a 
coarsely  divided  circle  reading  only  to  single  degrees  of  angle. 
Projection  screens  are  often  investigated  in  situ  with  only  a 
board,  a  nail  and  a  tape  line  to  direct  the  photometer  and  deter- 
mine angles  of  reflection. 

The  Brightness  Photometer. — The  brightness  of  the  material 
is  best  determined  with  some  brightness  photometer  through 
which  the  surface  studied  is  viewed  directly.  If  an  illumino- 
meter  be  used,  that  surface  must  be  limited  to  a  definite  area  and 
the  illumination  from  this  on  the  test  screen  of  the  illuminometer 
at  a  convenient  distance  is  very  faint.     A  brightness  photometer 

*  Report  No  3  of  the  I.  E.  S.  Committee  on  Glare,  submitted  in  March,  1915. 


OPTICAL   PROPERTIES   OF  DIFFUSING    MEDIA  367 

is  preferable;  when  this  is  used,  it  should  be  light,  compact  and 
of  high  precision. 

Two  forms  of  these  have  found  favor  and  others  might  doubt- 
less be  devised.  No  entirely  suitable  brightness  photometer  is 
on  the  market.  The  Beck  "Lumeter"  is  perhaps  the  best  and  this 
requires  modification  to  free  it  from  serious  systematic  error. 
The  comparison  screen  is  in  the  photometer  box  while  the  surface 
whose  brightness  is  to  be  measured  is  viewed  through  a  hole  in  the 
comparison  screen.  The  eye  cannot  accommodate  to  the  near  com- 
parison screen  and  the  distant  surface  simultaneously,  and  lack  of 
perfect  accommodation  seriously  affects  the  brightness  of  retinal 
image  and  hence  the  reading  of  the  instrument.  This  failure  to 
provide  for  equal  accommodation  is  by  the  way  a  very  common 
and  very  serious  defect  in  brightness  photometers.  The  remedy  is 
simply  to  throw  an  image  of  the  distant  surface  into  the  plane  of 
the  comparison  screen  with  a  telescope  objective  or  simple  lens. 

Another  suitable  brightness  photometer  is  a  simple  reading 
telescope  with  comparison  strip  or  spot  fixed  in  the  focus  of  the 
ocular  and  illuminated  from  the  side.  Several  forms  of  illumin- 
ation and  illumination  control  have  been  used.  The  use  of  a 
miniature  lamp  filament  for  comparison  strip  is  objectionable  in 
that  it  requires  the  use  of  a  monochromatic  filter  for  precise 
work. 

The  Illumination. — The  distribution  curve  obtained  for  any 
surface  depends  of  course  upon  the  position  of  the  illuminant 
and  the  solid  angle  which  it  subtends  and  it  is  necessary  to  use 
some  definite  known  angular  size  and  position  of  illuminant. 
Those  most  useful  are  (a)  nearly  parallel  light  from  an  appproxi- 
mately  point  source  such  as  a  Xernst  filament  or  a  beam  colli- 
mated  with  slit  and  lens  and  (b)  a  uniformly  illuminated  plane 
area  such  as  a  plate  of  opal  glass  in  front  of  a  frosted  lamp.  If 
1 1.3  cm.  in  diameter,  or  10  cm.  square,  it  subtends  at  1  meter 
0.01  steradian. 

If  the  point  source  or  collimated  illuminant  be  used,  specular 
brightness  rises  to  a  high  value.  The  illumination  is  checked  by 
observing  the  brightness  of  a  magnesium  block  or  other  diffusing 
surface  of  known  reflecting  power.  When  the  plane  source  is 
used,  determinations  are  in  terms  of  relative  brightness  of  the 


368     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

illuminant  and  surface  studied.  Both  forms  of  source  are  about 
equally  useful.  The  collimated  beam  appears  to  have  no  advan- 
tage over  the  point  or  line  source  direct,  and  gives  the  same  dis- 
tribution curve.  The  rectangular  plane  source  is  to  be  preferred 
to  the  circular  since  the  data  obtained  with  it  are  more  easily- 
reduced. 

Fluctuation  in  the  illuminant  is,  of  course,  a  serious  source  of 
error  unless  counterbalanced  by  a  similar  variation  in  the  com- 
parison source.  This  is  easily  done  if  both  are  electric  lamps  by 
putting  both  on  the  same  circuit.  Differences  in  characteristic 
curves  of  the  two  lamps,  control  rheostats  and  the  like  do  not 
cause  serious  differential  variations  if  the  line  voltage  varies  not 
over  2  per  cent. 

The  Data. — The  brightness  of  a  surface  viewed  from  any  angle 
is  a  measure  of  the  light  per  unit  solid  angle  per  unit  projected 
area  of  surface  leaving  that  surface  in  that  direction.  With  the 
gonio  photometer  (angular  photometer)  above  discussed  and  a 
given  illumination,  brightness  is  measured  at  each  angle  in  a 
plane  through  the  incident  beam  and  perpendicular  to  the  sur- 
face. Brightness  as  a  function  of  angle,  B  (a)  say,  is  then 
plotted.  Light  emitted  per  unit  area  is  then  proportional  to  B 
(a)  cosa,  the  angle  being  measured  from  the  perpendicular  to 
the  surface.  If  at  the  point  observed,  the  illumination  is  all 
nearly  normal  to  the  surface  this  emitted  light  may  readily  be 
integrated  by  zonal  elements,  the  ratio  of  the  total  light  emitted 
to  the  light  incident  being  the  mean  reflecting  or  transmitting 
power.  The  geometry  of  this  process  is  discussed  toward  the  end 
of  this  report. 

INTEGRATING  INSTRUMENTS  AND  METHODS. 

While  the  distribution  curves  of  reflected  and  transmitted  light 
give  all  the  data  required,  their  determination  requires  a  skilled 
observer,  laboratory  instruments  and  considerable  time.  When 
only  integrated  reflecting  power,  absorption  or  transmission  are 
required,  much  simpler  instruments  and  methods  are  available. 

Anyone  or  all  of  these  classes  of  data  may  be  required  (1) 
mean  reflecting  power  or  transmission ;  i.  e.,  the  light  emitted 
through  a  hemisphere  relative  to  the  light  incident  in  a  normal 


OPTICAL   PROPERTIES   OF  DIFFUSING    MEDIA  369 

pencil;  (2)  illumination  hemispherical,  observing  light  a  pencil; 
and  (3)  both  illumination  and  observation  hemispherical  (total 
reflecting  power  or  transmission). 

Transmission. — Either  mean  or  total  transmission  may  be  de- 
termined by  several  different  methods.  By  far  the  most  con- 
venient is  to  use  the  Konig-Martens  polarization  photometer, 
really  a  brightness  comparator.  It  has  an  excellent  field  with  no 
apparent  dividing  line.  The  error  in  scale  zero  is  determined  by 
setting  in  both  first  and  fourth  or  second  and  third  quadrants. 
Possible  errors  due  to  plane  polarization  in  the  light  are  elimi- 
nated by  reading  with  the  instrument  direct  and  reversed.  When 
desirable  to  set  on  an  actual  image  of  the  object  viewed,  it  may 
be  provided  with  a  pair  of  the  small  lenses  used  as  objectives  on 
a  low  power  binocular  microscope. 

Uniform  diffuse  illumination  is  secured  by  placing  a  plate  of 
solid  opal  glass  ground  on  both  sides,  over  the  end  of  a  white 
paper  cylinder  within  which  is  an  ordinary  tungsten  lamp.  The 
sample  whose  transmission  is  desired  is  placed  over  half  the 
field.  With  this  arrangement  the  readings  of  the  instrument  give 
mean  percentage  transmissions.  If  total  transmission  is  desired, 
another  diffusing  medium  such  as  flashed  opal  glass  is  placed 
over  both  sample  and  comparison  field.  Mean  and  total  trans- 
mission will  be  the  same  when  the  material  is  highly  diffusing. 

Less  precise  determinations  may  be  made  with  any  brightness 
instrument  such  as  the  "Lumeter"  for  example.  A  highly  dif- 
fused uniform  illumination  is  provided  as  above,  and  the  sample 
placed  over  part  of  the  field.  The  relative  brightness  of  the  cov- 
ered and  uncovered  parts  of  the  field  give  at  once  the  trans- 
mission of  the  sample. 

To  use  an  ordinary  bench  photometer  to  measure  diffuse  trans- 
mission it  is  necessary  to  provide  a  highly  diffused  very  bright 
area  at  one  end  and  limit  it  to  a  definite  small  area.  After  meas- 
uring its  apparent  candlepower,  the  sample  is  placed  over  it  in 
close  contact  with  it  (to  avoid  side  light)  and  the  candlepower 
again  measured.  Great  care  must  be  exercised  in  avoiding  stray 
reflected  light. 

Transmission  with  illumination  by  a  direct  pencil  is  of  impor- 
tance in  diffusing  lamp  globes  and  shades  and  a  few  other  mate- 


370     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

rials.  This  may  readily  be  determined  by  illuminating  the  speci- 
men with  a  known  flux  and  determining  its  brightness  on  the  rear 
side  in  the  desired  direction.  If  the  integrated  light  emitted  in 
all  directions  be  desired,  then  a  highly  diffusing  sheet  of  known 
transmission  is  interposed  close  behind  the  specimen. 

Purely  specular  transmission  may  be  measured  with  practically 
any  sort  of  photometer  or  spectrophotometer  and  any  source  by 
simply  interposing  the  specimen  between  source  and  photometer. 
Large  errors  due  to  refraction  are  the  rule  unless  the  specimen 
is  very  thin  and  plane.  If  the  specimen  is  very  thick,  good  results 
can  be  obtained  only  by  having  end  faces  very  plane  and  by  using 
only  very  parallel  light. 

Reflection. — The  total  and  mean  reflecting  power  of  surfaces 
are  much  less  readily  determined  than  transmissions  on  account 
of  the  difficulty  in  avoiding  shadows.  The  only  instrument  of 
general  usefulness  available  for  the  purpose  is  the  ring  reflec- 
tometer  described  on  page  413  of  the  1912  (vol.  VII)  Transac- 
tions of  the  Illuminating  Engineering  Society.  This  instru- 
ment measures  the  relative  brightness  of  two  parallel  planes,  one 
of  which  is  the  specimen  surface  and  the  other  a  diffuse  illumina- 
tor. The  planes  are  limited  by  a  reflecting  ring  serving  to  return 
the  light  which  would  otherwise  escape  at  the  edges.  The  instru- 
ment gives  mean  reflecting  power  directly  except  when  the  reflect- 
ing power  is  either  very  high  or  very  low  and  at  the  same  time 
highly  specular.  The  reading  head  is  a  modified  form  of  the 
Konig-Martens  brightness  comparator  mentioned  above.  Read- 
ing the  head  in  direct  and  reversed  positions  gives  data  for  deter- 
mining the  percentage  of  light  specularly  reflected  and  for  cor- 
recting for  polarization.  By  a  slight  modification,  this  instrument 
may  be  used  on  wall  coverings  in  position. 

To  measure  total  reflecting  power,  perfectly  diffuse  illumina- 
tion and  observed  light  integrated  over  1800  are  required.  A 
small  receiving  disk  is  mounted  half  way  between  the  two  planes 
at  the  center  of  the  ring  and  the  photometer  sighted  on  the  two 
sides  of  this  by  means  of  two  small  reflecting  prisms. 

Purely  specular  reflecting  power  is  determined  with  a  bright- 
ness photometer  and  an  extended  plane  source.  The  reflecting 
power  of  a  mirror  is  the  ratio  of  the  brightness  of  the  image  to 


OPTICAL   PROPERTIES   OP  DIFFUSING    MEDIA  37 1 

that  of  the  source  at  any  desired  angle  of  incidence.  The  specu- 
lar component  in  partly  specular  reflection  may  be  determined  by 
the  same  method,  the  source  being  made  either  so  small  or  dis- 
tant or  weak  as  to  give  only  negligible  diffuse  brightness  or  else 
diffuse  brightness  is  measured  just  off  the  specular  angle  and 
allowed  for. 

Purely  diffuse  reflecting  power  may  be  determined  by  deter- 
mining the  brightness  under  a  given  illumination.  The  reflect- 
ing power  is  v  times  the  brightness  (in  candles  per  square  foot,, 
say)  divided  by  the  illumination  in  foot-candles.  This  method 
is  not  so  precise  as  that  in  which  the  brightness  comparator  is 
used. 

SELECTIVE  INSTRUMENTS  AND  METHODS. 

Specular  and  diffuse  reflection  and  transmission  may  in  most 
cases  be  determined  separately  with  sufficient  precision  for  prac- 
tical purposes  without  recourse  to  the  more  laborious  determina- 
tion of  distribution  curves.  The  three  classes  of  partial  diffusion 
of  importance  require  different  treatment.  These  are  (a)  a 
mixture  of  pure  specular  with  pure  or  nearly  pure  diffuse  light, 
(b)  a  very  slight  scatter  such  as  is  caused  by  dust  suspensions 
and  very  light  precipitates  from  a  solution  and  (c)  diffusion 
departing  widely  both  from  the  purely  specular  and  diffuse  types. 

Separable  Mixtures. — In  separating  specular  from  diffuse  light, 
one  may  either  measure  diffuse  and  total,  specular  and  total  or 
specular  and  diffuse  separately.  With  a  good  brightness  pho- 
tometer any  of  the  three  methods  may  be  used.  With  an  illumi- 
nation of  known  brightness  and  solid  angle,  the  specimen  is 
placed  at  a  known  distance  and  angle,  then  its  brightness  meas- 
ured at  the  angle  of  specular  reflection  or  transmission  and  at 
some  neighboring  angle,  arbitrarily  chosen  according  to  the  class 
of  the  material  and  the  purity  of  the  diffusion.  Such  materials 
as  glossy  paper,  polished  woods  and  opal  glasses  are  readily 
studied  by  these  methods. 

Another  good  practical  method  depends  upon  the  fact  that 
light  specularly  reflected  at  a  certain  angle  (about  6o°)  is  nearly 
completely  plane  polarized.  Hence  if  a  surface  be  illuminated 
and  viewed  through  a  nicol  prism  at  this  angle,  if  the  nicol  be 
properly  oriented,  the  specular  light  may  be  eliminated.     The 


XJ2     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

phenomenon  is  very  striking  in  the  case  of  materials  like  polished 
furniture  and  glossy  paper.  Ingersoll1  has  designed  a  practical 
instrument  for  measuring  glare  based  on  this  polarization  phe- 
nomenon. The  specimen  is  placed  on  the  bottom  of  a  box  and 
illuminated  at  the  proper  angle  by  an  opal  window  at  one  end. 
It  is  viewed  through  a  polarizing  ocular  at  the  other  end.  With 
this  instrument  either  relative  diffuse  and  total  brightness  or 
relative  specular  and  diffuse  reflecting  power  may  be  determined. 

Ingersoll's  instrument  or  some  modification  of  it  promises  to 
be  useful  for  practical  purposes  when  properly  used.  It  should 
be  noted,  however,  that  (a)  it  gives  a  'minimum,  value  of  the 
specular  reflection,  if  a  surface  is  quite  wavy  or  rough  a  crossed 
nicol  does  not  cut  out  all  the  specular  light;  (b)  it  does  not  apply 
to  metallic  surfaces,  these  not  reflecting  plane  polarized  light,  and 
(c)  it  is  committed  to  a  particular  angular  illumination;  namely, 
that  of  the  window  supplied.  Since  the  ratio  of  specular  to  total 
brightness  varies  wi,th  the  solid  angle  of  illumination,  different 
sizes  of  window  will  give  different  values  of  gloss. 

In  using  the  ring  reflectometer  (see  above)  the  readings  with 
the  instrument  in  direct  and  reversed  position  differ  by  double 
the  mean  percentage  polarization,  hence  give  a  measure  of  per- 
centage specular  reflection.  This  method  gives  fair  results  in 
practise.  Another  method  is  to  use  the  ring  reflectometer  to 
determine  total  reflecting  power  and  some  other  instrument  such 
as  the  modified  Bechstein2  to  determine  diffuse  alone. 

An  ordinary  bench  photometer  with  a  Lummer-Brodhun  head 
may  be  used  to  determine  diffuse  reflecting  power  at  perpen- 
dicular incidence  of  certain  materials3  such  as  paints  and  papers. 
The  photometer  screen  is  replaced  by  a  double  one,  half  of  which 
is  of  the  ordinary  material,  and  the  other  half  is  faced  with  the 
material  to  be  investigated. 

Slight  Turbidity. — The  amount  of  light  scattered  by  atmos- 
pheric haze,  photographic  negatives,  light  chemical  precipitates 
and  other  similar  agents  is  proportional  to  the  size,  number  and 
reflecting  power  of  the  reflecting  particles  and  to  the  intensity  of 
illumination.     The  brightness   of   a   slightly   scattered  beam  is 

1  Electrical  World,  March  21,  1914. 

2  Trans.  I.  E.  S.,  Vol.  IX,  p.  611,  1914. 

3  Louis  Bell,  Electrical  World,  Jan.,  1915. 


OPTICAL   PROPERTIES   OF   DIFFUSING    MEDIA  373 

determined  by  some  form  of  brightness  photometer  or  compara- 
tor. Precision,  of  course,  depends  primarily  upon  the  intensity 
and  constancy  of  the  illumination  and  the  thickness  of  the 
observing  path.  Direct  sunlight  is,  of  course,  by  far  the  best 
illumination.  In  photographic  negatives  the  scatter  is  so  great 
that  it  may  be  determined  by  measuring  specular  and  total  trans- 
mission by  ordinary  methods. 

P.  V.  Wells  of  the  Bureau  of  Standards4  has  designed  a  "tur- 
bidimeter" for  measuring  slight  diffusion  in  solids,  liquids  and 
gases.  Mecklenberg  and  Valentiner5  have  designed  a  somewhat 
similar  but  very  elaborate  instrument  primarily  for  liquids.  Both 
instruments  determine  the  relative  intensity  of  direct  and  scat- 
tered light.  T.  W.  Richards  has  designed  a  turbidity  comparator 
which  he  calls  a  "nephelometer."  The  liquids  are  contained  in  a 
pair  of  silvered  test  tubes  illuminated  from  the  side  through  slits 
in  the  silver.  Atmospheric  scatter  has  been  studied  by  Diercks,6 
the  photometer  being  pointed  at  various  angles  from  the  limb 
of  the  sun.  He  found  a  drop  to  nearly  pure  diffusion  at  about  4° 
from  the  sun,  the  brightness  at  that  point  being  on  moderately 
hazy  days,  about  one  ten-thousandth  that  of  that  solar  disk. 

Inseparable  Mixtures. — Very  rough  materials  in  which  there 
is  more  or  less  regularity  of  distribution  give  all  forms  of  dis- 
tribution curves  and  any  distinctions  between  specular  and  diffuse 
reflection  or  transmission  must  be  quite  arbitrary.  Nothing  but 
the  distribution  curve  itself  can  give  an  adequate  description  of 
the  effect  of  the  material  on  a  beam  of  light.  In  particular 
classes  of  materials,  brightness  observations  at  particular  angles 
give  sufficient  data  for  practical  purposes  as  shown  in  the  pre- 
ceding and  following  reports.  Some  form  of  good  brightness 
photometer,  means  of  illuminating  with  a  known  source  at  a 
known  angle  and  of  observing  at  a  known  angle  are  essential. 
THEORY  OF  DIFFUSION  PHOTOMETRY. 

Nomenclature. — In  dealing  with  the  theory  of  diffusion  meas- 
urements it  is  convenient  to  depart  somewhat  from  the  accepted 
nomenclature  of  engineering  photometry  and  define  flux  and 
brightness  in  the  simplest  physical  terms. 

4  Ph.  Rev.,  1914,  p.  396. 
6  Zeit  Inst.,  1914,  p.  209. 
6  Ph.  Zeit,  1912,  p.  562. 


374     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Physically,  light  quantity  is  radiant  energy  times  visibility. 
Flux  is  the  rate  in  ergs  per  second  (or  in  watts)  times  visibility 
at  which  light  streams  through  or  upon  a  given  area.  The 
density  of  this  light  stream,  as  it  passes  a  given  surface,  is  the 
flux  per  unit  area.  Its  concentration  is  the  flux  per  unit  solid 
angle.  A  beam  of  light  is  made  up  of  a  great  many  pencils  of 
light,  hence  the  density  of  light  on  a  given  surface  is  the  integral 
of  the  concentration  over  a  hemisphere. 

The  brightness  of  a  given  surface  to  the  eye,  when  viewed  in 
a  given  direction,  is  proportional  to  the  flux  within  a  cone  filling 
the  pupil  of  the  eye  at  one  end  and  coming  from  an  elementary 
projected  area  at  the  other  and  hence  proportional  to  the  light 
leaving  a  given  projected  area  in  a  given  direction.  Brightness 
is  then  measured  by  the  flux  per  unit  solid  angle  per  unit  pro- 
jected area  of  surface.  The  unit  of  brightness,  the  lambert  is  v 
candles  per  square  centimeter  of  projected  area. 

Distribution  Curves. — When  a  surface  is  illuminated  by  light 
of  a  known  density  and  concentration,  the  readings  of  a  bright- 
ness photometer  sighted  on  it  at  various  angles  may  be  plotted 
as  a  function  of  angle  B  (a)  giving  a  distribution  curve.  The 
scale  of  the  photometer  is  checked  by  sighting  it  on  a  surface  of 
known  brightness;  that  is,  a  surface  of  known  reflecting  power, 
diffusion  and  illumination.  The  brightness  photometer  will  then 
read  in  flux  per  unit  solid  angle  per  unit  projected  area  on  any 
surface  viewed  at  any  angle. 

In  practise  the  photometer  is  sighted  on  a  block  of  magnesium 
carbonate  whose  reflecting  power  (about  86  per  cent.)  has  been 
determined  with  an  absolute  reflectometer.  When  such  a  block 
is  illuminated  perpendicularly  with  a  flux  density  D,  the  total 
flux  outward  is  RD,  R  being  the  reflecting  power  of  the  surface. 
If  the  surface  is  perfectly  diffusing,  the  flux  density  in  a  direc- 
tion perpendicular  to  it  at  a  distance  r  from  it  will  be  RD/nT2 
for  each  unit  area  of  the  reflecting  surface.  Hence  the  flux  per 
steradian  will  be  RD/V  in  that  direction.  Therefore,  the  bright- 
ness of  the  comparison  block  so  illuminated  will  be  in  any  direc- 
tion RD/tt  flux  units  per  steradian  per  unit  projected  area, 
lamberts  for  short.  If,  then  the  brightness  photometer  sighted 
on  the  surface  measured  reads  B/R  times  as  bright  as  on  the 


OPTICAL   PROPERTIES   OF   DIFFUSING    MEDIA  375 

comparison  block,  the  brightness  of  the  surface  is  BD/rr  lamberts 
in  that  direction. 

The  angular  relations  involved  are  angle  of  view  (a)  and  solid 
angle  w.  In  Fig.  1  let  a  be  the  half  angle  of  a  cone  of  solid  angle 
w  intersecting  the  surface  of  a  sphere  of  radius  r.  The  area  of 
the  surface  intercept  is  2irr*  (1  —  cos  a)  hence  o>  =  in  ( 1  —  cos  a) 
and  dm  =  2v  sin  a  d  a. 


Fig.  1. — Solid  angle  and  angle  of  observation. 

Let  the  concentration  of  light  in  a  narrow  axial  pencil  be  C 
coming  from  a  small  plane  area  of  diffusing  surface.  Then  the 
flux  within  a  solid  angle  w  will  be 

F„  =  JC  cos  a  do>  =  C  (o  —  — ) 

the  element  of  flux  dV  within  an  element  of  solid  angle  du>  is 
therefore 

dF  =  27rC  sin  a  COS  a  da 


('  -  T> 


Our  data  then  consist  of  a  series  of  brightness  readings  B(a) 
at  various  angles  and  a  single  reading  B0  on  a  comparison  block, 
the  incident  normal  flux  density  F0  being  known.  B(a)  is  plotted 
as  a  function  of  angle  as  in  the  middle  curve  Fig.  2.  This  is  pro- 
portional to  the  emission  per  unit  projected  area,  multiplied  by 
cosa  it  gives  the  lower  curve,  of  which  the  ordinates  are  pro- 
portional to  emission  per  unit  area. 

Multiplying  further  by  27rsina  gives  the  upper  curve  the  ordi- 
nates of  which  is  proportional  to  the  light  emitted  in  a  cone 
element  of  which  da  is  a  section  and  2a  the  apex  angle.  This 
third  curve  is  then  2ttB  (a)  sin  a  cos  a,  which  by  the  above  equa- 
tion is  equal  to  dF/Cda  or  the  concentration  of  the  emitted  light 
divided  by  the  flux  density  of  the  incident  light. 


376     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

In  case  the  scatter  is  in  one  direction  only,  as  is  the  case  with 
ribbed  glass  for  example,  the  integration  is  carried  out  directly 
in  the  plane  angle  without  recourse  to  the  solid  angle.  When 
the  reflected  or  transmitted  light  is  symmetrical  about  neither 
the  axis  nor  a  plane,  integration  is  rarely  required  in  practise. 
Distribution  curves  may,  of  course,  be  determined  at  any  orienta- 
tion of  the  sample  and  mean  reflecting  power  found  with  the 
ring  reflectometer.  Should  further  data  be  required,  the  distri- 
bution curves  for  different  orientations  may  be  summed  by  plane 
angles. 


Fig.  2.— Brightness  and  angular  radiation. 

The  graphical  integration  of  the  brightness  curve  by  this  proc- 
ess is  perfectly  general,  applying  to  even  specular  reflection  and 
transmission.  Reflecting  power  or  transmission  coefficient  at  a 
particular  angle  is  a  meaningless  term  but  mean  reflecting  power 
and  mean  transmission  are  perfectly  definite  quantities.  The  in- 
tegration of  both  the  reflected  and  transmitted  light  gives  the  ab- 
sorption with  quite  satisfactory  precision  by  this  method.  Total 
reflection  and  transmission  require  further  integration  for  ex- 
tended sources. 

Extended  Sources. — Having  obtained  the  distribution  curve  for 
normal  illumination  (source  of  small  angular  extention),  the 
distribution  curve  for  a  more  extended  source  of  known  bright- 
ness is  easily  calculated.  If  the  brightness  of  the  source  in  the 
direction  of  the  sample  is  Bs  lamberts,  then  unit  area  of  the 
latter  receives  Bslir  light  units  per  unit  area  from  each  unit  area 
of  the  source.     Hence  the  distribution  curve  for  the  extended 


OPTICAL   PROPERTIES   OF   DIFFUSING    MEDIA 


377 


source  is  the  sum  of  distribution  curves  for  the  elements  of  the 
source. 

When  the  source  is  so  large  as  to  extend  quite  an  angle  from 
the  normal  to  the  specimen  and  that  is  not  highly  diffusing,  or  in 
case  the  specimen  reflects  unequally  in  different  directions  (ribbed 
glass  and  textiles  with  a  nap  are  examples)  then  several  distri- 
bution curves  must  be  determined  by  observation.  Data  on  a 
few  such  cases  will  be  given  in  the  following  report.  In  Fig.  3 
are  shown  for  illustration,  curves  obtained  on  glossy  paper  with 


Fig.  3. — Distribution  curves  with  extended  sources. 

wider  and  wider  sources. 

Letts  Systems. — The  intensity  and  distribution  of  light  in  image 
forming  optical  instruments  is  of  importance  in  many  practical 
problems.  There  are  two  principal  cases  to  be  considered  (1) 
object  self-luminous  or  illuminated  from  in  front  and  (2)  object 
illuminated  from  the  rear  by  a  condenser  system,  an  image  of  the 
light  source  being  formed  at  the  projecting  lens. 


Fig.  4. — Direct  and  projected  images. 

In  the  first  case  the  object  has  a  certain  brightness  in  the 
direction  of  the  first  lens.  The  light  flux  is  constant  through  all 
the  series  of  zone  pencils  through  the  system  except  for  light 
losses  in  the  lenses  themselves.  The  same  is  true  of  the  field 
pencils.     Hence  the  relative  flux  density  in  image  and  object  is 


378     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  percentage  transmission  of  the  system  times  the  solid  angle 
of  the  final  zone  pencil.  The  brightness  of  the  image  on  the  other 
hand  is  the  brightness  of  the  object,  as  viewed  from  the  first  lens, 
times  the  percentage  transmission  of  the  system. 

In  the  second  case  the  brightness  of  object  is  its  transmission 
coefficient  times  the  flux  per  unit  area  and  this  latter  is  the  angular 
flux  density  divided  by  the  square  of  the  distance  from  the 
source  to  the  Gauss  point  of  the  condenser  (roughly  the  focal 
length  of  the  condenser).  Given  the  brightness  of  object  found 
in  this  manner,  the  brightness  of  the  image  and  the  flux  density  in 
the  plane  of  the  image  are  found  as  in  case  one. 

Nelson  M.  Black, 

J.  R.  Cravath, 

F.  H.  Gilpin, 

M.  Luckiesh, 

F.  K.  RichtmyEr, 

F.  A.  Vaughn, 

P.  G.  Nutting,  Chairman. 


DIFFUSING    MEDIA  379 

DIFFUSING  MEDIA  III.     PAPERS  AND  INKS.* 


Synopsis:  This  report  covers  print  papers;  mat,  semi-glossy,  glossy; 
sizings,  fillers,  inks ;  writing  papers  and  inks ;  typewriter  papers,  inks  and 
carbons ;  drawing  papers  and  inks ;  tracing  papers  and  cloths ;  blue  print 
papers ;  photostat  papers.  Data  are  given  for  specular  and  diffuse  reflect- 
ing power  and  brightness,  diffuse  transmission  and  opacity,  contrast  ratio, 
back  reflection,  entrant  and  exit  scatter  and  other  properties. 


Print  Papers  and  Inks. — The  untinted  print  papers  differ 
chiefly  in  reflecting  power  (whiteness)  and  gloss.  The  reflecting 
powers  of  the  newspaper  papers,  unfilled  and  not  very  opaque, 
run  as  low  as  50  per  cent.;  medium  grade  papers,  just  perceptibly 
grayish,  reflect  60  to  70  per  cent.,  while  the  whitest,  finest 
grade  papers  reflect  as  high  as  83  per  cent.  Thin  papers  of  low 
opacity  often  reflect  much  less  than  50  per  cent. 

The  proportion  of  light  specularly  reflected  varies  from  prac- 
tically nothing  up  to  5  per  cent,  in  the  case  of  the  highly  glazed 
plate  papers.  There  is  a  wide  variety  of  half  gloss  papers. 
When  the  surface  is  dulled  by  putting  a  thin  mat  overcoat  on  a 
glossy  paper,  the  specular  angle  is  small  and  the  paper  has  a 
subdued  brilliancy  and  gives  but  slight  glare.  On  the  other  hand, 
paper  that  is  heavily  filled  and  calendered  but  unglazed  has  a 
wavy  surface  that  gives  a  bad  glare  on  account  of  the  wider 
angle  of  specular  reflection. 

Print  inks  vary  from  dead  mat  to  very  glossy.  The  mat  inks 
vary  in  reflecting  power  from  3  to  4  per  cent.  The  glossy  inks, 
if  coated  on  a  smooth  hard  surface  reflect  about  3  per  cent, 
specularly  and  0.8  diffusely.  If  used  on  a  rough  or  strongly 
absorbent  paper,  they  reflect  more  diffusely  and  may  even  appear 
quite  mat.  The  glare  from  glossy  ink  is  particularly  objection- 
able in  the  larger  cuts  usually  printed  on  glossy  plate  papers. 

Typical  distribution  curves  for  the  various  classes  of  print 
papers  are  shown  in  Fig.  1.  Curve  No.  1  is  from  a  mat  paper1 
of  63.6  per  cent,  reflecting  power ;  No.  2,  an  unglazed  book  paper 
of  good  quality;  No.  3,  a  heavily  calendered  glazed  paper,  while 
No.  4  is  a  glossy  plate  paper.     These  curves  are  taken  with  a 

*  Report  No.  4  of  the  I.  E.  S.  Committee  on  Glare. 
1  Warren's  cameo,  paper. 


380     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

disk  source  subtending  a  solid  angle  of  0.01  and  perpendicular 
illumination. 


10  0  10  20  30 

Fig.  1. — Distribution  curves  of  print  papers. 


Total  reflect- 
ing power 

No.  I.   Mat 0.636 

No.  2.  Slightly  glossy  •  0.575 

No.  3.  Semi-glossy 0.633 

No.  4.  Glossy    0.636 


Specular 
reflection 

0.002  Warren  "Cameo" 

0.016  Jour.  Wash.  Acad. 

0.031  Warren  "Cumberland" 

0.037  Kodak  park  plate. 


In  the  figure  only  the  portion  of  the  distribution  curves  near 
the  specular  angle  are  given.  The  reflecting  powers  given  are 
integrals  of  the  distribution  curves  obtained  as  outlined  in 
Report  No.  3.  The  specular  reflection  given  in  the  table  above 
was  obtained  by  integrating  the  excess  over  a  smoothed  cosine 
curve. 

In  the  table  below  are  listed  optical  data  on  a  number  of  print 
papers  ranging  from  newspaper  to  the  heaviest  plate  papers.  These 
data  are  given  by  way  of  illustration  of  the  desirable  properties 
and  as  means  of  drawing  comparisons  between  papers  more  or  less 
familiar  to  all  readers.  They  were  taken  with  a  spectrometer 
with  brightness  photometer  attachment. 

From  the  reader's  point  of  view,  print  paper  should  possess  a 
high  reflecting  power  and  but  little  gloss  and  the  print  or  cuts  on 
the  back  should  not  show  through.  In  the  first  column  marked 
R,f  is  given  the  diffuse  reflecting  power  oi  a  single  thickness  of  the 
paper;  in  the  following  column  (Rqq  )  that  of  a  pile  of  the  paper 


DIFFUSING    MEDIA  381 

so  thick  that  adding  more  would  not  increase  the  reflecting  power 
of  the  first  surface.  These  reflecting  powers  determine  the 
brightness  when  illuminated  with  a  given  source.  In  the  third 
column  Rj  is  given  the  specular  reflecting  power,  in  column  G 
following  the  gloss  or  ratio  of  specular  to  diffuse  brightness  with 
a  normal  illumination  subtending  0.01  steradian  (10  cm.  square 
at  1  meter). 

Paper                             Rrf  R^         R;          G          t           T              B  D          Di 

Weather  Review 055  0.63     0.000  0.02  0.109  0.178  0.0143  °-4°5  3-72 

Science  Abstracts 0.58  0.616  0.000  0.01  0.091  0.171  0.0120  0.394  4.32 

Science 0.62  0.640  0.001  0.03  0.118  o.m  0.0047  °-523  4-44 

Analen  der  Physik  ..   0.540  0.600  0.008  0.47  0.063  0.223  0.0023  °-328  5.21 

SitzungsberichteYVien  0.35  0.57     0.002  0.21  0.038  0.405  0.1070  0.208  5.47 

(index) 

SitzungsberichteWien  0.55  0.59    0.005  °-3°  0.061  0.194  0.0170  0.353  5.78 

(text) 

Industrial  Arts  Index  0.533  0566  0.003  0.15  0.53  0.24  0.027  0.290  5.48 
"Light,"    111.    Eng. 

Soc.  0.62  0.633  0.001  0.04  0.128  0.067  0.0017  0.760  5.65 

Brittanica,    India 

Paper    0.59  0.62     0.000  0.02  0.048  0.215  0.019  0.280  5.82 

Bible  Paper 0.575  °-6i     0.000  0.02  0.048  0.21     0.187  °-3°5  6.34 

Astrophysical  Jour.  . .   0.605  0.617  0.009  °-44  0.112  0.07     0.002  0.750  6.70 

Rochester  Herald 0.50  0.51     0.001  0.06  0.09    0.116  0.0067  0.644  7.14 

Shap  Shots 0.580  0.60     0.02     1.80  0.083  0.096  0.0039  0.628  7.56 

Amer.      Machinist  0.577  0585  0.019  °-9&  °-I25  °-°5     o.oon  0.956  7.65 

(cov. ) 

Amer.      Machinist  0.550  0.57     0.019  IO°  0.078  o.  10    0.0045  0.670  8.58 

(text) 
Photographic  Jour.  ..   0.57  0.5S3  0.013  o-11  °°95  0.081  0.0028  0.729  7.67 
"Cumberland"  (War- 
ren)     0.595  0.598  0.03     1.26  0.117  0.046  0.0009  0.946  8.08 

Inland  Printer  (text)  0.60  0.625  0.021   1. 12  0.083  0.0S1  0.0026  0.680  8.18 

Inland  Printer  (plate)  0.58  0.50     0.023   I22  0.119  0.042  0.007  0.988  8.30 

E.  K.  Co.  Bulletin  ...   0.590  0.60    0.037   1.89  0.123  0.038  00006  1.032  8.38 

Jour.  Wash.  Acad.  Sci.  0.57  0.50    0.016  0.50  0.088  0.75     0.0024  °-752  8.55 

Moving  Picture  World  0.555  °-565  0.015  °-78  0.073  0.113  0.0059  0.602  8.25 

Modern  Sanitation...  0.59  0.595  0037  1.89  0.101  0.056  0.0013  0.870  8.60 

Central  Zeitung 0.55  0.60    0.006  0.38  0.053  °-I7     o-OI3  0.414  7.80 

Engineering  World-.  0.575  °-592  0.01     0.52  0.074  0.115  0.0056  0.668  9.00 

The  thickness  of  the  samples  is  given  in  column  t  in  fractions 
of  a  millimeter,  the  percentage  transmission  in  column  T.  Most 
papers  absorb  from  75  to  95  per  cent,  of  the  incident  light  not 
reflected,  i  — T  being  the  absorption.  Column  B  is  T2(i  —  R). 
Of  the  incident  light,  the  fraction  R  is  reflected  and  1  —  R  enters 
5 


382     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  paper,  T(i — R)  reaches  the  back  face.  If  a  similar  sheet 
underlies  the  first  TR(i — R)  re-enters  the  back  of  the  first 
sheet  and  T2R(i  —  R)  emerges  from  its  front  face  (see  report 
Diffusing  Media  I).  The  brightness  of  the  front  face  depends 
upon  the  sum  of  the  light  reflected  from  this  face  and  the  light 
reflected  back  from  underlying  sheets  or  R-f-T2R(i —  R). 
Hence  if  T2  is  small  and  R  is  large,  1  -\-  B  is  the  relative  bright- 
ness of  plain  paper  and  paper  inked  on  the  back.  If  B,  the  back 
reflection,  is  greater  than  half  a  per  cent.  (0.005),  print  on  the 
back  will  show  through  quite  perceptibly.  No  paper  should  be 
used  except  for  special  purposes  for  which  B  is  greater  than 
0.02,  if  B  is  1  per  cent.  (0.01)  the  transparency  is  annoying. 

Density  D  =  — log  T,  in  the  next  column,  is  a  quantity  pro- 
portional to  the  thickness  and  a  proper  measure  of  the  opacity 
of  a  paper.  Dx  =  ( — log  T)/t,  the  specific  density  or  the  density 
per  unit  thickness,  is  a  measure  of  the  quality  of  the  paper  mate- 
rial. It  depends  largely  upon  the  quality  and  the  amount  of  filler 
used. 

Reflecting  powers  range  from  about  50  per  cent,  for  the  news- 
papers up  to  nearly  70  for  Nos.  4,  7,  8  and  16.  These  are 
slightly  cream  tinted  papers;  No.  6  is  by  far  the  whitest  paper 
of  any  but  has  a  lower  reflecting  power  probably  on  account  of 
blue  used  to  counteract  a  slight  yellow.  The  back  reflections 
vary  from  practically  nothing  (20)  up  to  0.12 1  in  No.  5,  a  very 
thin  transparent  paper.  Specific  densities  range  from  3.7  up  to 
a  fairly  definite  maximum  at  from  8.5  to  9.0. 

Fillers. — Fillers  are  used  to  give  the  paper  opacity  as  well  as 
to  give  it  certain  mechanical  properties.  Good  filler  should  then 
possess  high  specific  density  and  high  reflecting  power.  Kaolin 
is  largely  used  for  the  cheaper  and  medium  grade  paper,  baryta 
for  the  most  expensive  papers.  Both  reflecting  power  and  opacity 
increase  with  dryness  and  with  increasing  fineness  of  particle2 
until  the  particle  is  smaller  than  a  light  wave.  The  ideal  filler 
would  be  a  mass  of  non-hygroscopic  transparent  crystals  about 
0.0002  mm.  in  mean  diameter  and  free  from  smaller  and  larger 
particles  since  these  would  tend  to  lower  both  opacity  and  reflect- 
ing power. 

2  Trans.  I.  E.  S.,  1914,  p.  593. 


DIFFUSING    MEDIA  383 

The  reflecting  powers  of  fillers  vary  from  60  per  cent,  or  lower 
up  to  over  80  per  cent.  Their  specific  densities  are  approxi- 
mately: kaolin,  dry  powder,  1.96;  magnesium  carbonate  block 
0.35,  powder,  0.61 ;  barium  sulphate  powder,  2.30. 

G laces. — The  glazing  material  chiefly  used  is  an  inferior  grade 
of  gelatine  with  a  refractive  index  of  about  1.36  and  a  specular 
reflecting  power  of  2^2  per  cent.  Any  glazing  is  entirely  dele- 
terious optically,  but  it  is  considered  necessary  in  some  forms  of 
paper  to  give  a  smoother  surface  and  to  prevent  too  free  pene- 
tration of  the  ink. 

Inks. — Print  inks  differ  in  specular  and  diffuse  reflecting 
power.  All  are  so  opaque  that  the  twice  transmitted  light  reflected 
from  the  underlying  paper  is  quite  negligible  wherever  the  ink 
actually  covers  the  paper.  Glossy  inks  are  preferred  for  their 
somewhat  better  working  qualities.  Optically,  the  glossy  inks 
have  lower  diffuse  reflecting  powers  than  the  mat  inks,  hence  are 
blacker  and  present  a  greater  contrast  with  the  paper.  The  mat 
inks  are  preferable  only  in  the  complete  absence  of  glare.  The 
following  data  indicate  the  properties  of  some  characteristic 
printing  materials. 


1.  Ord.  print  paper  and  ink-  • 

2.  Jour.  Am.  Soc.  Mech.  Eng. 

3.  Snap  shots 

4.  Calender 0.59 

5.  "  Light,"  its  use  and  misuse  0.65 

The  relative  transmission,  fourth  column,  is  the  ratio  of  the 
light  transmitted  through  paper  and  printed  character  to  the 
light  through  the  paper  alone.  The  density  of  ink,  fifth  column, 
is  the  negative  logarithm  of  this  ratio.  The  density  per  milli- 
meter (specific  density)  of  print  inks  are  too  high  to  measure 
with  any  precision  (about  60)  and  of  little  interest.  The  back 
reflection,  last  column,  is  the  relative  brightness  of  paper  alone 
and  paper  printed  on  the  back,  the  quantity  computed  in  the 
table  on  print  papers,  above,  plus  unity. 

The  specular  reflection  of  an  ink  depends  upon  the  matness  of 
the  paper  upon  which  it  is  printed.  The  following  measurements 
were  taken  using  a  glossy  ordinary  ink  and  a  mat  ink  each  on 


Diffuse  ref. 

power 

Rel. 
trans. 

Dens, 
of  ink 

Back 
reflec- 
tion 

Paper 

Ink 

Contrast 

0.59 

O.025 

23.6 

0.03 

1-52 

I  05 

O.61 

O.043 

14.2 

O.13 

O.89 

I.03 

0.63 

0.047 

14.O 

O.I2 

O.92 

I.02 

0.59 

O.030 

I9.8 

O.04 

I.40 

I.08 

O.65 

0.037 

17-5 

O.IO 

I. OO 

I. OO 

384    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

three  supports;  photographic  film,  a  glossy  plate  paper  and  a 
mat  paper. 

Reflecting  power 

Diffuse  Specular  Gloss 

Glossy  ink  on  film 0.008  0.034  430 

Glossy  ink  on  glossy  paper 0.008  0.017  2I° 

Glossy  ink  on  mat  paper    0.012  0.006  51 

Mat  ink  on  film 0.036  0.0024  2-9 

Mat  ink  on  glossy  paper    0.036  0.0020  2.4 

Mat  ink  on  mat  paper    0.037  0.0015  2.2 

Specular  reflection  from  ink  is  unobjectionable  when  below  half 
a  per  cent.  (0.005)  and  even  glossy  ink  on  a  mat  paper,  not  too 
fine  grained,  will  not  give  serious  glare.  The  glossy  ink  of  the 
above  table  is  seen  to  be  about  four  times  as  black  as  the  mat; 
that  is,  the  diffuse  reflecting  power  is  only  a  quarter  of  that  of 
the  mat  ink. 

Writing  Papers  and  Inks. — Writing  papers  differ  from  print 
papers  as  a  class  chiefly  in  the  glaze  applied  to  render  it  non- 
absorbent  and  prevent  running  of  the  ink.  This  glazing  material 
(gelatin,  dextrin,  glue,  resin  or  soap)  being  of  low  index  (1.36 
about)  and  transparent,  has  the  effect  of  (a)  slightly  lowering 
diffuse  reflecting  power  and  (b)  considerably  increasing  specular 
reflecting  power.  In  other  words,  it  tends  to  render  the  paper 
slightly  grayer  and  much  more  glossy.  Many  writing  papers, 
however,  have  so  low  a  gloss  as  to  be  quite  unobjectionable. 

The  data  given  below  is  of  the  same  nature  as  that  given  above 
for  print  paper  and  is  to  be  interpreted  in  the  same  way. 

Kd      Roo  Ry  G  t  T  B  D        Dj 

Linen  finish  ordinary  0.61     0.64     0.0030    0.21     0.13   0.127   0.006  0.48   3.71 
Commercial  ordinary  0.57    0.63     0.0024    OI7     °-°7  o-^S  0.013   °-4°  5-72 

Writing  ink  was  tested  when  on  a  semi-glossy  paper  and  when 
on  a  specular  film  support.  The  inks  were  a  good  ordinary  pen  ink 
(Buffalo  Standard)  and  a  carbon  (Higgin's  "Eternal  Black"). 

Rrf  R5                   T                              D 

Ordinary  iron  ink  on  film 0.025  0.005       0.019-0. 18        0.74-1.74 

Ordinary  iron  ink  on  glossy  paper .   0.035  0.0000 

Ordinary  iron  ink  on  mat  paper  . . .   0.054  0.0001 

Carbon  writing  ink  on  film 0.005  0.085       0.096-0.44        0.35-1.58 

Carbon  writing  ink  on  glossy  paper  0.027  0.004 

Carbon  writing  ink  on  mat  paper..   0.045  0.0012 


DIFFUSING    MEDIA  385 

Typewriter  papers,  inks  and  carbons.  Typewriter  papers  are 
quite  similar  to  the  print  papers  of  medium  grade  with  but  little 
fillers  and  very  little  glazing. 

Rd  rot  R*        G  <          T          B         D  D, 

Ordinary  E.  K.  Co.  0.515  0.594  0.0006   0.05  o.  10  0.180  0.015  0.432  4.32 

Ordinary  I.  E.  S.  ••   0.50  0.565  0.0000  0.00  0.87  0.216  0.023  °-2^2>  4-2° 

Tissue  carbon  paper  0.36  0.552  o  005     0.64  0.038  0.366  0.085  °-243  6.38 

The  ink  impressions  vary  greatly  in  density.  The  data  given 
below  refer  to  what  was  considered  a  fair  average  density. 

Rd  Ry  G  T  D 

Ordinary  black  ribbon  ink 0.05  0.000  0.07  0.37  0.43 

Ordinary  blue  ribbon  ink 0.128  0.001  0.37  0.62  0.21 

Ordinary  red  ribbon  ink 0.160  0.002  0.25  0.55  0.26 

Carbon  paper 0.032  0.005  0.25  0.24  0.62 

Drafting  Paper  and  Ink. — Drafting  paper  contains  somewhat 
more  filler  and  sizing  than  print  paper  and  less  than  writing 
paper.  The  data  below  refer  to  a  good  ordinary  paper  and  to 
some  of  special  quality. 

Rs        Roo  Ry  G  t  T  B  D  D! 

Good  ordinary .   0.54     0.64     0.0005     °-°4     0.117     0.222     0.023     0.3182     2.72 
Special   quality  0.62     0.64     0.0012     0.09     0.19      0.078     0.002     0.684      3-6o 

The  India  ink  which  the  following  data  applies  is  of  the  or- 
dinary prepared  variety  (Higgins). 

Rd  Rs  G  T  D 

India  drafting  ink  on  film. . .  0.013      °-°37       2&4         0.017-0.47      0.33-1.82 
India  drafting  ink  on  paper  •  0.029       0.002  5.3 

Tracing  Cloth  and  Paper. — The  most  important  optical  prop- 
erty of  tracing  cloth  is  its  transparency.  Glare  and  reflecting 
power  are  of  less  consequence.  The  requirements  are  quite  sim- 
ilar to  those  for  window  envelopes  (Report  6)  and  the  reverse 
of  those  for  print  paper.  With  tracing  cloth,  the  most  distinct 
possible  view  of  the  underlying  layer  is  desired.  The  same  high 
transparency  is  desired  for  printing.  The  necessary  fabric  used 
as  a  body,  however,  scatters  light  to  a  considerable  degree.  Trac- 
ing paper  must  be  opaque  enough  to  show  well  a  drawing  made 
upon  it  but  so  thin  and  transparent  that  prints  may  be  made 
directly  through  it. 

Different  grades  of  tracing  paper  and  cloth  differ  widely  in 


386     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

properties.     Below  are  given  distribution  data  on  materials  of 
about  an  average  grade. 

Relative  Brightness. 

o°  5°                io°  150  300  450 

Tracing  cloth,  reflection 0.41  0.37  0.34  0.32  0.28  0.28 

Tracing  paper,  reflection 0.77  —  —  —  —  75 

1800  175  170  165  150  1350 

Tracing  cloth,  transmission. . .   6.3  5.3  3.6  2.1  0.82  0.53 

Tracing  paper,  transmission  • .   0.87  —  0.76  0.69  0.57  0.4b 

These  readings  were  taken  with  an  illumination  and  a 
photometer  scale  such  that  the  reading  on  a  100  per  cent,  per- 
fectly diffuse  reflector  would  have  been  1.56. 

With  the  same  constant  (1.56)  the  following  data  on  a  number 
of  tracing  cloths  were  obained. 

Cloths  over  black  R  Over 

, --' >        White     Contrast       B  45  B  135 

BO°  B  45  B  135  B  180  B  45  Ratio  BO  B  180 

15817 0.78        0.39        0.41        3.7  0.79        0.49        0.50        O.II 

P.    13 O.72  O.41  O.42  2.03  O.75  O.54  O.56  0.2I 

N.  T.  7 0.88        0.38        0.60        3.3  0.78        0.47        0.43        0.18 

15742 I.04  O.40  O.56  2.0  O.80  O.50  O.39  O.38 

12    O.72  O.44  O.46  2.4  O.Sl  O.54  O.61  0.I9 

S3 O.75  O.42  O.45  I.32  O.79  O.54  O.56  O.34 

Vi 0.55        0.29        0.41         2.00        0.74        0,52        0.71        0.21 

E.  K.   0.51         0.24        0.41         5.0  0.74        0.33        0.48        0.08 

The  first  four  column  give  the  observed  brightness  at  the  angles 
°>  45>  J35  aild  1800  from  the  (perpendicular)  direction  of  illum- 
ination in  a  black  walled  room  giving  very  little  stray  light.  "B 
45  over  White"  is  the  brightness  of  the  cloth  when  backed  by 
drafting  paper  of  64  per  cent,  reflecting  power.  The  contrast 
ratio  is  the  ratio  of  brightness  over  white  to  brightness  over 
black.  B45  :  Bo  is  entrant  scatter,  B135  :  B180  exit  scatter. 
(See  report  No.  2.) 

Blue  print  paper  is  of  medium  reflecting  power  and  weight, 
mat  and  very  absorbent.  The  equivalent  density  of  the  photo- 
graphic deposit  as  compared  with  inks  is  of  interest.  The  follow- 
ing data  were  taken  on  two  samples,  one  of  the  very  high  grade, 
the  other  of  inferior  quality. 

Rrf  Rs  B:W            T                 D^ 

High  grade,  white 0.58  0.0005  0.16         0.31 

High  grade,  blue 0.084  0.0004                        0.088        0.56 

Low  grade,  white 0.44  0.0010  0.13        0.35 

Low  grade,  blue    0.07  0.0009                        0.106        0.51 


DIFFUSING    MEDIA  387 

The  reflecting  powers  of  the  exposed  (blue)  parts  run  about 
7  or  8  per  cent.,  only  about  twice  that  of  mat  print  ink.  The 
maximum  blacks  of  the  regular  photographic  papers  run  from 
(glossy  solio)  0.6  per  cent,  up  to  the  4  per  cent,  on  the  mat 
papers. 

Photostat  paper  is  a  thin,  inexpensive  photographic  paper. 
Data  on  two  samples  are  given.  These  did  not  differ  greatly  in 
material  but  the  "special"  had  been  forced  by  a  professional 
photographer  to  give  maximum  contrast. 

Rrf  R5  B/W              T                 T)b 

Ordinary  white  (clean) 0.594  0.0014                          0.26 

Ordinary  black  (exposed) 0.056  0.0004  0.094         0.056        0.68 

Special  white  (clean)    0.594  0.0012                         0.33 

Special  black  (exposed)  0.03  0.0003  0.51           0.03           0.85 

The  blacks  are  nearly  as  black  as  print  ink  while  the  contrast 
ratio  of  black  to  white  runs  as  high  as  20  for  the  carefully  devel- 
oped sample. 

The  following  report  is  to  deal  with  the  regular  photographic 
papers. 

Nelson  M.  Black, 

J.  R.  Cravath, 

F.  H.  Gilpin, 

M.  Luckiesh, 

F.  K.  Richtmyer, 

F.  A.  Vaughn, 

P.  G.  Nutting,  Chairman. 


388     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

DIFFUSING  MEDIA  IV.— THE  OPTICAL  PROPERTIES 
OF  PHOTOGRAPHIC  PAPERS.* 


Synopsis:  Photographic  papers  vary  in  reflecting  power  from  pure 
white  to  dense  black  and  in  gloss  from  a  nearly  pure  mat  to  a  high  gloss. 
Practical  methods  of  measuring  and  specifying  reflection  densities  and 
sensitometric  data  are  outlined,  distribution  analyses  of  various  types  are 
given,  gloss  and  its  determination  are  discussed,  data  are  given  on  trans- 
mission densities  and  diffusion  in  photographic  plates  and  negatives. 


Aside  from  the  fact  that  nearly  every  one  is  more  or  less  of  a 
photographer  and  interested  in  photographic  prints,  the  investi- 
gation of  the  optical  properties  of  photographic  papers  is  of  great 
interest  because  in  this  product  is  prepared  a  wide  range  of  pre- 
cisely reproducible  gloss  and  because  in  each  paper  with  its 
particular  gloss,  a  wide  range  of  diffuse  reflecting  powers  may  be 
produced  by  the  photographic  process.  No  other  product  offers 
such  excellent  material  for  the  study  of  these  two  optical  prop- 
erties. 

REFLECTING  POWER. 

Photographic  papers  unexposed  or  fixed  without  exposure 
reflect  from  65  to  75  per  cent,  and  this,  of  course,  represents  the 
lightest  high  lights  possible  in  a  print.  A  print  reflecting  but  50 
per  cent,  is  just  noticeably  grayish,  30  per  cent,  a  medium  gray, 
3  to  8  per  cent,  a  muddy  black.  The  maximum  blacks  obtainable 
on  any  papers  reflect  diffusely  less  than  1  per  cent. — just  about 
as  much  as  the  blackest  printer's  ink. 

In  viewing  a  photographic  print  it  is  usually  held  nearly  per- 
pendicular to  the  line  of  sight.  The  practical  measurement  of 
reflecting  power  involves  illumination  at  an  angle  of  45  °  and  an 
observation  of  brightness  in  the  direction  normal  to  the  surface. 
A  print  may  be  comfortably  viewed  under  widely  different  angles 
of  illumination,  but  45  °  is  considered  a  fair  average  direction  for 
testing  purposes.  The  photometer  for  small  areas  described  by 
Jones  and  Nutting1  measures  reflecting  power  in  this  manner. 
This  photometer  has  been  used  chiefly  for  testing  photographic 
papers,  in  fact. 

A  set  of  readings  of  diffuse  reflecting  power  taken  on  un- 

*  Report  No.  5,  I.  E.  S.,  Committee  on  Glare,  1914-15. 
1  Trans.  I.  E.  S.,  p.  611.  vol.  IX,  (1914). 


DIFFUSING   MEDIA  389 

exposed  and  fully  exposed  papers  is  given  below  together  with  the 
maximum  contrast  ratio.  The  readings  are  relative  to  the  read- 
ing on  a  perfectly  diffusing  surface  of  109-  per  cent,  reflecting 
power  under  the  same  illumination. 

Max.  white        Max.  black    Max.  contrast 

Azo  A  (Mat)    0715  0.038  19 

C   (Glossy)    0.745  0.018  41 

D  (Semi-gloss)   0.65  0.029  22 

E  (Velvet)    0.70  0.023  30 

F  (Glossy)    0.70  0.013  54 

G  (Mat)   0.695  0.040  17 

Glossy  velox  (reg.) 0.70  0.010  70 

Solio    0.64  0.006  107 

The  maximum  blacks  are  of  about  the  same  reflecting  power 
as  printer's  ink  (Report  No.  4).  It  is  interesting  to  note  that 
while  the  whiteness  appears  to  bear  no  relation  to  gloss,  the 
maximum  blacks  are  always  deeper  in  the  glossy  than  on  the 
mat  papers.  Ordinary  glossy  printer's  ink  reflects  (1.  c.)  less 
than  a  third  as  much  diffusely  as  mat  ink — 3.6  against  0.8  per 
cent.  The  range  is  somewhat  less  than  in  the  papers  listed  above, 
namely,  4.0  to  0.6  per  cent. 

The  fact  that  the  deeper  blacks  are  obtained  on  the  glossy 
papers  and  inks  is  possibly  due  to  the  fact  that  the  light  absorbing 
particles  are  covered  with  a  coating  of  more  or  less  transparent 
substance  of  about  the  same  refractive  index  as  themselves,  hence 
there  is  little  reflection  at  the  interface.  With  mat  surfaces,  the 
absorption  within  the  particles  is  of  the  same  order  but  the  sur- 
face reflection  from  the  individual  particles  is  so  great  that  con- 
siderable light  is  scattered. 

In  a  series  of  grays  running  from  white  to  black  made  on 
photographic  paper,  the  specular  reflecting  power  remains  con- 
stant or  nearly  constant  while  the  diffuse  varies  by  a  factor  of 
20  to  100.  Gloss  then  varies  through  the  same  range  of  values, 
gloss  being  defined  as  the  ratio  of  specular  to  diffuse  brightness. 

In  the  sensitometry  of  photographic  paper  it  is  the  diffuse  re- 
flecting power  that  is  taken  as  a  measure  of  the  photographic 
effect.  A  series  of  about  20  exposures  are  made,  each  the  square 
root  of  two  times  the  preceding,  by  printing  through  carefully 
selected  neutral  gray  film  of  the  proper  series  of  densities.  After 
development   the    reflecting   powers    of    the   exposed    spots    are 


390     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

measured  relative  to  the  adjacent  white  paper,  the  paper  being 
illuminated  at  an  angle  of  45  °  and  read  perpendicularly.  Re- 
flection densities  are  taken  as  the  common  logarithm  of  relative 
reflecting  power.  This  is  not  proportional  to  the  mass  of  reduced 
silver  as  is  the  case  with  transmission  densities  (-log  transmis- 
sions) except  at  the  lowest  densities.  Specular  reflection  is  ig- 
nored as  it  does  not  affect  either  relative  exposure  nor  the  deposit 
of  silver.  A  typical  series  is  given  below.  It  is  a  test  of  the 
paper  known  as  Artura  Iris  A.  T  is  the  transmission  of  the 
series  of  printing  screens,  D*  (=  —  log  T)  the  corresponding 
printing  densities  (steps  roughly  0.15),  E  the  relative  exposures, 
R<f  the  relative  reflecting  power  of  the  print  spots  and  white  field 
adjacent,  and  Dr  the  reflection  densities  of  the  series. 


Step 

T 

»p 

E 

Rrf 

Dr 

I 

0.0025 

2.709 

I.O 

1.0 

0.0 

2 

0.0029 

2.551 

I.I6 

1.0 

0.0 

3 

O.OO45 

2.385 

I.80 

1.0 

0.0 

4 

O.OO54 

2.268 

2.l6 

1.0 

0.0 

5 

0.0077 

2.127 

3.08 

1.0 

0.0 

6 

0.0II2 

1-939 

4.48 

1.0 

0.0 

7 

O.OI57 

1.803 

6.28 

0.97 

0.015 

8 

0.0240 

1.643 

9.60 

0.86 

0.065 

9 

O.O308 

1.510 

12.32 

0.75 

0.125 

10 

O.O452 

1-345 

18.08 

0.48 

0.32 

11 

O.O434 

1.364 

17.36 

0.565 

0.25 

12 

0.0622 

1.206 

24.88 

0-354 

0.46 

13 

0.0912 

1.040 

36.48 

0.220 

0.66 

14 

0.1205 

0.922 

48.2 

0.164 

0.78 

15 

0.165 

0.782 

66.0 

0.1 1 1 

0.97 

16 

0.255 

0-594 

102.0 

0.055 

1.26 

17 

0-347 

0.462 

138.8 

0.041 

1.38 

18 

0.503 

0.298 

201.2 

0.039 

1.41 

19 

O.684 

0.165 

273.6 

0.038 

1.42 

20 

1.0 

0.0 

400.0 

0.038 

1.42 

The  sensitometer  curve  is  D,-  plotted  as  a  function  of  log  E. 
From  this,  speed,  gradation  and  maximum  gradient  are  read  off. 

GLOSS  AND  GLARE. 
The  distribution  of  the  light  reflected  from  four  selected  pho- 
tographic papers  is  shown  in  Fig.  1  to  illustrate  the  character  and 
range  of  diffusion  provided  for.     Curves  were  taken  with  illum- 
ination nearly  normal  and  0.01  in  angle.     The  curve  for  Azo  C  is 


DIFFUSING    MEDIA 


391 


plotted  with  half  the  ordinate  scale  of  the  others.  The  range  in 
gloss  is  from  an  almost  dead  mat  surface  (G)  to  the  extremely 
glossy  C.  Solio,  regular  glossy  Velox  and  Azo  F  are  of  the  same 
type  as  C  but  slightly  more  glossy.  The  specular  projections  on 
the  curves  for  C  and  D  are  of  the  ordinary  type  such  as  is  pro- 
duced by  varnish  or  by  the  calendering  of  print  paper.  E,  how- 
ever, shows  the  superposition  of  two  distinctly  different  types  of 
gloss,  one  of  the  ordinary  type  and  the  other  of  about  three  times 
the  angle  but  of  less  maximum  reflecting  power. 


amci.es  onuriicTioH 


Fig.  1.— Distribution  Curves  of  Azo  C,  D,  E  and  G. 


\  iewed  at  the  specular  angle  under  a  single  bare  lamp  or  other 
narrow  angle  illuminant,  papers  C  and  D  show  a  small  glare  spot 
of  about  the  same  size  but  C  brighter  than  D,  while  E  shows  a 
much  larger  spot.  It  is  desirable  to  distinguish  between  the 
effects  of  (a)  the  maximum  height  of  the  distribution  curve  (b) 
the  width  and  (c)  the  area  of  the  projecting  part  of  the  curve 
representing  specular  reflection.  The  maximum  height  depends 
upon  the  brightness  of  the  illuminating  source,  the  width  upon 


39-2     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  angular  width  of  the  source  and  the  area  upon  both.  Now, 
gloss  defined  as  the  ratio  of  specular  to  diffuse  brightness,  is  a 
measure  of  height  and  is  independent  of  width  or  area  of  distri- 
bution curve.  On  the  other  hand,  total  specular  reflection,  the 
area  of  the  projecting  area  on  the  corrected  distribution  curve,  is 
not  a  measure  of  either  gloss  or  glare.  For  practical  purposes 
it  might  be  desirable  in  some  cases  to  record  the  angular  spread  of 
light  in  the  glare  spot  when  a  narrow  source  is  used,  but  usually 
gloss  is  of  chief  or  sole  value  in  photographic  papers.  In  diffus- 
ing globes  it  is  the  maximum  spread  that  is  particularly  desired. 

PHOTOGRAPHIC  PLATES  AND  NEGATIVES. 

Undeveloped  photographic  plates  have  a  high  turbidity  and  for 
blue  light  a  high  opacity.  The  emulsion  with  which  the  plate  is 
coated  is  a  yellowish  white  in  color  and  roughly  0.02  mm.  thick. 
It  has  a  moderate  surface  gloss.  Distribution  curves  plotted  for 
Seed  23,  30  and  lantern  plates  with  white  light  gave  substantially 
the  same  results.  The  brightness  given  is  relative  to  that  of  a 
perfectly  diffusing  surface  reflecting  100  per  cent. 

Reflection  Transmission 


Angle 15   30   45   60   75     105   120   135   150   165 

Brightness...  0.69  0.56  0.54  0.52  0.42    0.27  0.33  0.35  0.37  0.37 

There  is  no  specular  transmission  but  a  specular  reflection  of 
about  5  per  cent.  The  density  is  about  0.2  in  the  yellow  and  very 
high  in  the  blue,  the  density  per  millimeter  is  about  10  in  the 
yellow. 

In  photographic  negatives  the  absorbing  silver  grains  are  in 
the  form  of  spongy  black  masses  imbedded  in  transparent  gela- 
tine. A  great  deal  of  light  is  scattered  in  addition  to  that  directly 
absorbed.  Diffuse  transmission  is  several  times  greater  than 
specular.  Diffuse  densities  deterrhine  exposures  in  contact  prints, 
specular  densities  in  projection  printing  and  enlarging.  Different 
plates  differ  in  ratio  of  diffuse  to  specular  densities.  Different 
exposures  on  the  same  plate  show  the  same  relative  densities  in 
some  plates  and  different  in  others,  the  variation  being  most 
marked  in  the  coarse  grained  high  speed  plates. 


DIFFUSING    MEDIA  393 

Diffuse  Specular  PJ 

Plate  density  density  Hd  R  45° 

Seed  lantern   0.47  0.77  1.64  0.050 

1.04  1.66  1.60  0.023 

1.69  2.67  1.57  0.022 

2.75  4.3  1. 6 1  0.021 

Seed  23   0.75  I-I3  1-5*  °-°3i 

1.68  2.51  1.49  0.021 

2.90  4.3  1.50  0.021 

Seed  30  0.50  0.89  1.78  0.052 

1. 12  1.85  1.65  0.025 

1.88  2.83  1.5 1  0.022 

Seed  graflex   0.55  1.17  2.18  0.051 

1.22  2.27  1.86  0.028 

1.78  3.12  1.67  0.028 

Cine  pos.  film 0.06-2.11  0.10-3.30  1.58  (mean)      — 

The  reflected  and  transmitted  light  is  not  uniformly  distributed. 
The  following  data  taken  on  a  medium  exposure  on  Seed  23  is 
typical : 

Angle 15         30        45        60        75        105        120      135       150      165 

Rel.  brightness     1.7     0.60    0.39    0.32     0.26    0.079     0.128     0.25     0.50     1.96 

The  sensitometry  of  plates  by  the  Hurter  and  Driffield  method 
is  described  in  treatises  on  photography  and  applied  optics. 

Considerable  data  of  related  interest  on  the  specular  and  diffuse 
reflecting  powers  of  ordinary  papers  is  contained  in  our  report 
No.  4  on  papers.  General  relations  and  definitions  are  given  in 
our  general  report,  No.  1,  and  in  report  No.  2  on  diffusing  media. 

Nelson  M.  Black, 

J.  R.  Cravath, 

F.  H.  Gilpin, 

M.  Luckiesh, 

F.  K.  Richtmyer, 

F.  A.  Vaughn, 

P.  G.  Nutting,  Chairman, 


394     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

WINDOW  ENVELOPES.* 


At  the  request  of  a  letter  carriers'  association  the  Committee 
on  Glare  of  the  Illuminating  Engineering  Society  has  undertaken 
an  investigation  of  the  optical  properties  of  the  various  kinds  of 
window  envelopes  now  in  use.  About  ioo  samples  of  used 
envelopes  were  submitted  by  the  letter  carriers'  association  for 
the  tests.  The  determinations  were  made  in  a  well  equipped 
optical  laboratory  under  the  personal  supervision  of  the  Chair- 
man of  the  Glare  Committee  on  about  25  carefully  selected 
samples.  A  classification  of  material,  the  conclusions  drawn  and 
the  more  important  data  obtained  are  given  below : 

In  the  window  envelopes  in  question  the  windows  are  of  the 
following  four  classes : 

1.  An  oblong  hole  without  any  covering. 

2.  A  window  covered  by  an  insertion  of  clear,  transpar- 

ent film  usually  of  gelatin. 

3.  A  window  covered  by  a  translucent  insertion  of  special 

oiled  paper. 

4.  The  window  is  merely  an  oiled  or  varnished  portion  of 

the  envelope  itself.     The  envelope  is   frequently  of 
heavy  blue  or  yellow  paper. 
The  essential  properties  of  these  four  forms  of  windows  are 
those  outlined  below: 

1.  The  open  window  is  visually  equivalent,  except  for  a  slight 
bordering  shadow,  to  viewing  the  address  directly.  The  slight 
bordering  shadow  occurring  sometimes  under  poor  illumination 
has  no  ill  effect  of  any  consequence  on  vision. 

2.  The  window  of  clear  film  causes : 

(a)  A  general  lowering  of  brightness  of  the  address  by  about 
10  per  cent.  This  is  equivalent  merely  to  a  lowering  of  illum- 
ination by  that  amount  for  any  angle  of  view  except  the  angle 
of  specular  reflection. 

(b)  Occasional  specular  glare,  very  bright  except  for  very 
diffuse  indirect  lighting.  This  glare  spot  is  about  one-hundredth  to 
one-tenth  as  bright  as  the  source  of  light  whose  image  is  re- 
flected.    It  is  very  bright  indeed  when  bare  lamps  are  used  as  il- 

*  Report  No.  6  of  the  Committee  on  Glare  of  the  Illuminating  Engineering  Society. 


WINDOW    ENVELOPES  395 

luminants.  The  diffuse  brightness  of  the  address  read  is  de- 
termined simply  by  the  illumination  at  that  point  and  the  diffuse 
reflecting  power  of  the  paper,  and  is  thus  very  nearly  independent 
of  diffuseness  of  the  illumination  and  the  angle  of  view. 

(c)  Clear  windows  produce  no  noticeable  decrease  in  con- 
trast or  in  definition  except  at  the  angle  of  glare. 

3  and  4.  Windows  of  translucent  materials  cause : 

(a)  A  slight  general  lowering  of  brightness  due  to  loss  of 
light  by  specular  reflection  from  their  surfaces  of  the  same  order 
as  that  caused  by  clear  windows.  (See  2a.) 

(b)  A  specular  glare  similar  to  2b. 

(c)  A  veiling  effect  (superposed  brightness)  due  to  light  dif- 
fusely reflected  from  the  material  of  the  window.  This  causes 
a  serious  lowering  of  contrast  to  about  1/10  its  value  in  the  un- 
covered address  (see  data  below). 

(d)  A  veiling  due  to  diffuse  transmission  through  the  win- 
dow. This  causes  at  best  a  serious  loss  of  definition  rendering 
the  address  quite  illegible  in  the  worst  cases  even  under  good 
illumination  and  with  the  window  pressed  close  to  the  address. 

We  have  made  the  following  measurements  on  selected  samples 
of  the  various  classes  of  window  envelopes.  A  strip  of  mat 
black  paper  was  placed  on  mat  white  paper  (except  in  tests 
Nos.  3  and  8)  and  the  reflecting  power  of  each  determined  be- 
hind each  window : 

Reflecting  power 

White  Black        Contrast 

per  cent.        per  cent.         ratio 

Test  No.  i.  Bare  test  pieces 68.0  2.1  32.4 

2.  Clear  gelatine  window 61.3  2.8  22.0 

3.  Ditto,  ink  on  brown  paper  . .  .   43.0  18.0  2.4 

4.  Oiled  tissue  paper  (class  3)  ••  •   61.0  15.0  4.1 

5.  Ditto,  another  sample 61.0  11. 5  5.3 

6.  Envelope,  oiled(white,  class 4)  49.0  14.0  3.5 

7.  Ditto,  blue  envelope 35.0  9.0  3.9 

8.  Ditto,  ink  on  bluish  paper  ••  •   18.5  9.0  2.1 

It  is  to  be  noted  that  the  oiled  and  varnished  paper  windows 
increased  the  apparent  brightness  of  the  black  strip  from  5  to  9 
times  and  decreased  the  contrast  by  from  8  to  10  times. 

The  diffusing  properties  of  these  window  materials  were 
further  determined  by  the  ordinary  methods.     Each  sample  is 


396     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

illuminated  perpendicularly  by  a  collimated  beam  of  light.  Then 
its  brightness  is  measured  at  angles  of  45,  135  and  1800  from 
the  incident  beam.  The  unit  of  brightness  is  that  of  a  diffuse 
reflector  reflecting  100  per  cent.,  magnesium  carbonate  reflecting 
88.0  per  cent. 

Material  Rel  bright- 

ness at  450 

Oiled  tissue  (c.  f.  No.  4) 0.45 

Oiled  env.  white  (No.  6) 0.52 

Ditto,  blue  (No.  7) 0.12 

The  specular  transmission  of  each  sample  was  zero.  No  light 
was  transmitted  directly  through.  The  scatter  is  from  ]/%  to  y2 
as  much  as  is  caused  by  a  perfectly  diffusing  surface. 

Nelson  M.  Black, 
J.  R.  Cravat h, 
F.  H.  Gilpin, 
M.  Luckiesh, 

F.  K.  RlCHTMYER, 

F.  A.  Vaughn, 

P.  G.  Nutting,  Chairman. 


135° 

1800 

B45 

Bi35 

Bi35 
B180 

O.62 

165 

0.73 

O.OO26 

O.74 

38 

O.70 

O.OO51 

O.40 

6l 

0.30 

O.OOI5 

DIFFUSING    MEDIA  397 

DIFFUSING   MEDIA   VI.— INTERIOR   FURNISHINGS.* 


Synopsis:  In  this  report  are  discussed  the  optical  properties  of  walls, 
woodwork,  ceilings,  floors,  fixtures,  shades,  draperies  and  furniture  as 
dependent  upon  the  raw  material,  the  finish  and  the  covering.  Attention 
is  given  largely  to  the  general  properties  necessary  to  minimize  glare  con- 
sistently with  good  illumination.  The  relation  of  illumination  to  the 
properties  of  furnishings  is  considered  in  each  case. 


The  proper  choice  of  surfaces  for  house  and  office  furnishings 
to  provide  a  maximum  of  eye  comfort  involves  not  only  the  sur- 
faces themselves  but  their  positions  relative  to  illuminant  and 
inhabitant  and  the  character  of  the  illuminant.  The  condition 
desired  is  not  necessarily  the  elimination  of  all  glossy  surfaces 
but  an  arrangement  such  that  no  glossy  surfaces  are  in  a  position 
to  cause  objectionable  glare.  In  other  words,  the  desired  condi- 
tion is  one  of  no  glare  rather  than  of  no  gloss.  A  gloss  that 
would  be  intolerable  in  a  table  top  is  of  no  consequence  in  a 
baseboard,  fireplace  or  ceiling,  since  from  plane  surfaces  placed 
as  these  are,  under  ordinary  conditions,  no  specularly  reflected 
light  can  enter  the  eye. 

Limits  of  tolerance  are  discussed  in  the  general  report  (Report 
No.  1)  on  classes  of  glare  and  means  of  suppression.  The 
classes  of  glare  involved  in  houses  and  offices  are : 

(1)  Brightness  Glare. — Excessive  brightness  such  as  occurs 
with  sun  shining  directly  on  snow,  white  paper  or  a  white  window 
shade.  The  limit  of  tolerance  depends  upon  (a)  the  state  of 
brightness  accommodation  of  the  eye  due  to  the  general  bright- 
ness of  the  surroundings  and  (b)  upon  the  angular  area  of 
the  bright  surface  viewed.  Some  measurements  indicate  that  the 
product  of  brightness  and  area,  that  is  the  total  candlepower  of  the 
bright  object  viewed,  would  be  a  better  measure  of  brightness 
glare  than  mere  brightness  alone.  Possibly  some  simple  function 
of  both  brightness  and  area  will  ultimately  be  chosen  as  a  measure 
of  this  kind  of  glare. 

(2)  Contrast  Glare. — Contiguous  bright  and  dark  objects 
cause  disturbance  of    vision  if  their  relative  brightness  is  exces- 

*  Report  No.  7,  I.  E.  S.,  Committee  on  Glare,  1914-15. 

6 


398     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

sive.  A  bright  illuminant  viewed  against  its  background,  a  dark 
window  frame  against  sky  or  a  bright  landscape  and  a  glare  spot 
on  a  glossy  surface  are  familiar  examples. 

At  moderate  and  high  intensities  a  relative  brightness  of  100:1 
or  over  is  uncomfortable  and  is  to  be  avoided.  Ordinary  print 
on  white  paper  presents  a  contrast  of  about  20:1.  When  the 
darker  part  of  the  field  of  view  is  but  little  lighter  than  complete 
darkness  (a  hole  in  a  black  lined  box,  say)  then  relative  bright- 
ness may  be  very  high  without  producing  an  objectionable  effect. 
This  begins  when  the  brightness  of  the  brighter  area  is  over  a 
fixed  value,  considerably  less  than  the  limit  in  case  the  whole 
visual  field  is  bright  (case  1  above)  or  is  free  from  excessive 
contrasts. 

The  limit  of  tolerance  in  contrast  glare  is  somewhat  lower  the 
shorter  the  line  of  contact  between  the  neighboring  surfaces  show- 
ing excessive  contrast.  In  specifying  contrast  glare  it  is,  of 
course,  total  brightness  (specular  plus  diffuse)  which  is  to  be 
considered. 

(3)  Veiling  Glare. — By  veiling  glare  is  meant  that  condition  in 
which  the  surface  to  be  observed  appears  covered  with  a  light 
or  dark  veil  of  a  different  or  imperceptible  pattern.  A  picture  or 
polished  wood  viewed  from  near  the  specular  angle,  a  landscape 
viewed  through  a  window  screen  or  dirty  window  are  familiar 
examples.  Bright  veiling  is  measured  by  relative  contrast ;  that 
is,  by  the  ratio  of  contrast  with  veiling  to  contrast  without  veiling. 

Walls  and  Wall  Coverings. — Walls  of  rooms  may  vary  widely 
in  reflecting  power,  hue,  shade  or  gloss.  A  low  diffuse  reflecting 
power  means,  of  course,  a  dead  loss  in  illumination,  but  white 
walls  highly  illuminated  lead  to  mild  visual  discomfort.  Gloss  in 
the  middle  levels  may  lead  to  a  highly  objectionable  glare,  but 
if  near  the  floor  margins  or  ceiling  no  specularly  reflecting  light 
can  reach  the  eye.  With  totally  indirect  illumination  consider- 
ably more  gloss  may  be  tolerated,  since  the  light  specularly  re- 
flected from  glossy  walls  is  reflected  downward  at  a  much  larger 
angle  than  under  direct  or  semi-indirect   illumination. 

But  little  data  on  wall  coverings  of  general  value  can  be  given 
on  account  of  their  widely  varying  nature. 


DIFFUSING    MEDIA  399 

Reflecting  power 

Diffuse  Specular 

Raw  plaster 0.40-0.50  0.0 

Finished  plaster 0.60-0.70  0.005-0.020 

Fine  white  washes 0.70-0.84  0.0 

White  tile,  marble 0.50-0.70  0.0    -0.05 

White  paint 0.40-0.60  0.05 

Finished  wood — light 012  0.04 

Finished  wood — dark 0.06  0.04 

Aside  from  esthetic  considerations,  perhaps  the  ideal  wall  cover- 
ing from  the  standpoint  of  economy  and  eye  comfort  would  be  one 
free  from  gloss  throughout  and  varying  in  diffuse  reflecting  power 
from  30  per  cent,  near  the  floor  to  80  per  cent,  near  the  ceil- 
ing. The  high  reflecting  power  above  saves  light  and  does  not 
greatly  affect  vision,  the  low  reflecting  power  below  avoids  eye 
fatigue.  A  reflecting  power  as  low  as  10  per  cent,  or  less  on  the 
lower  part  of  a  wall  would  not  only  waste  light  but  be  slightly 
uncomfortable  to  an  eye  accommodated  to  the  brightness  of  white 
paper. 

Ceilings. — That  ceilings  should  be  white  and  of  high  total  re- 
flecting power  is  widely  recognized  in  practise.  In  all  ordinary 
cases  the  sole  consideration  is  economy  of  light  since  they  are 
above  the  ordinary  level  of  vision.  In  very  large  rooms  a  glossy 
surface  is  to  be  avoided  since  in  such  cases  troublesome  glare 
within  the  line  of  vision  may  occur.  Diffuse  reflecting  powers  of 
70  to  80  per  cent,  are  readily  available  in  papers,  washes  and 
paints. 

Floors. — Floors  are  constantly  within  the  range  of  vision  and  a 
moderate  to  low  reflecting  power  is  preferable.  Near  the  walls, 
gloss  on  a  floor  is  quite  unobjectionable  since  no  specularly  re- 
flected light  can  reach  the  eye.  Near  the  center  of  the  room 
uncovered,  glossy  floors  are  intolerable.  The  common  practise 
of  covering  the  centers  of  floors  with  rugs  is  an  excellent  one, 
since  rugs  are  usually  very  mat  and  of  but  moderate  reflecting 
power. 

But  little  reflection  data  on  floor  materials,  finishes  or  coverings 
can  be  given  on  account  of  their  variability.  The  following  data 
refer  to  oak  of  about  an  average  tint: 

Reflecting  power 

Red  Green  Blue  White 

Oak  oiled  diffuse 0.074        0.046         0.012         0.053 

Oak  oiled  specular 0.036         0.042         0.032         0.039 


400     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Maple  has  about  the  same  reflecting  power  as  oak,  perhaps  a  little 
higher  on  an  average.  A  fresh  surface  on  soft  pine  reflects  15 
to  40  per  cent.,  white  tiling  and  marble  reflect  about  60  per  cent. 
Furniture  and  Fixtures. — In  the  finishing  of  furniture  and 
fixtures,  common  practise  is  bad,  in  that  glossy  surfaces  and  un- 
comfortable glare  are  commonly  met  with.  Varnished  and 
polished  tables  and  chairs  near  the  center  of  a  room  can  hardly 
fail  to  present  bad  glare  spots  to  anyone  in  a  room  unless  the 
illumination  be  totally  indirect  and  in  this  case  much  of  the 
beauty  of  the  wood  is  lost  in  the  overlying  gray  veil.  Metal  or 
metal  painted  fixtures  and  gilded  picture  frames  are  quite  as 
bad,  or  worse,  since  their  reflecting  powers  are  higher  than  that  of 
varnish.  A  little  dull  finished  furniture  is  on  the  market  and  it 
is  to  be  hoped  that  it  will  meet  with  increasing  favor.  Metal 
coverings  of  low  gloss  are  not  common  but  could  no  doubt  be 
developed.  The  relative  specular  and  diffuse  reflecting  powers 
of  metals  run  about  as  follows : 

Reflecting-  power 

Diffuse  Specular 

Brass  polished 0.018  0.46 

Copper  polished 0.03  0.21 

Nickel  polished 0.003  o.  70 

Aluminum  paint 0.29  0.22 

The  amount  by  which  the  reflecting  powers  of  brass  are  spec- 
trally selective  is  shown  by  the  following  table: 

White  Red  Yellow  Blue 

Diffuse 0.018        0.017        0.023        0.014 

Specular 0.46  0.45  0.45  0.39 

The  reflecting  powers  of  finished  mahogany  surfaces  average 
about  4  per  cent,  diffuse  and  5  per  cent,  specular.  The  diffusely 
reflected  light  is  practically  all  red,  while  the  specular  is  non- 
selective. 

Window  Shades,  Curtains  and  Draperies. — The  requirements 
for  window  coverings  are  similar  to  those  for  wall  coverings  on 
north  exposures.  Where  exposed  to  direct  sunlight  only  very 
opaque  shades,  and  curtains  and  draperies  of  very  low  reflect- 
ing power  should  be  used,  otherwise  they  become  at  times  in- 
tense sources  of  light  directly  at  the  level  of  vision.  A  double 
coated  shade,  black  outside  and  of  a  color  harmonious  with  the 
prevailing  tones  of  the  room  inside,  is  to  be  chosen. 


DIFFUSING    MEDIA  4OI 

General  Remarks  on  Furnishings. — Considered  from  the  stand- 
point of  gloss  and  glare,  ideal  furnishings  should  show  ( i )  a 
general  decrease  in  diffuse  reflecting  power  from  80  per  cent,  on 
the  ceiling  down  to  about  20  or  30  per  cent,  on  the  floor  and  (2) 
no  gloss  anywhere  except  (if  desired)  above  the  eye  level  on  the 
ceiling  and  near  the  angle  of  floor  and  wall,  a  location  from 
which  no  glare,  under  ordinary  conditions,  can  reach  the  eye. 

Common  practise  is  good  in  regard  to  the  first  of  these  condi- 
tions but  very  bad  in  regard  to  the  elimination  of  specular  reflec- 
tion. In  dwellings  there  is  wide  latitude  for  improvement;  in 
auditoriums,  stores,  factories  and  machine  shops  conditions  are 
much  more  difficult  to  deal  with,  but  general  practise  is  better 
developed. 

Illuminants. — From  the  standpoint  of  glare  alone,  the  rule  to 
be  observed  is  to  keep  intense  sources  of  light  well  above  the 
visual  level.  The  fault  commonly  met  with  is  not  insufficient 
light  so  much  as  improperly  placed  sources  of  light. 

Artificial  light  sources  are  easily  dealt  with,  thanks  to  the 
variety  of  lighting  units  and  fixtures  available.  The  subject  is 
discussed  at  length  in  the  illumination  primer1  published  by  this 
society.  On  the  other  hand,  common  practise  in  day  illumination 
is  bad  and  the  proper  arrangement  of  window  lighting  quite  dif- 
ficult in  most  cases.  Ordinary  window  lighting  is  bad,  in  that  it 
is  largely  at  the  level  of  vision  and  that  it  is  surrounded  by  rela- 
tively deep  shadow.  The  remedy  for  these  conditions  would  be 
to  cut  off  the  light  entirely  at  the  level  of  vision  and  illuminate 
the  room  solely  by  light  from  the  upper  part  of  the  window. 
However,  the  loss  of  view  involved  would  hardly  be  tolerated. 
The  light  from  the  sky  quadrant  available  passing  the  upper  sash 
is  easily  thrown  on  the  ceiling  and  used  to  illuminate  the  room 
in  an  ideal  manner  by  the  use  of  an  inclined  mirror  or  a  plain 
white  surface.  To  partly  avoid  excess  illumination  at  eye  level 
without  cutting  off  the  view,  a  sill  shade  may  be  drawn  up  when 
conditions  are  worst  or  the  window  may  be  supplied  with  yellow 
or  amber  glass.  This  is  quite  effective  in  suppressing  sky  glare 
and  actually  brightens  rather  than  dims  a  landscape. 

The  nature  and  definitions  of  the  various  classes  of  glare  are 

1  "  Light  :  Its  Use  and  Misuse  ".  (7th  ed.  April,  1915). 


402     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

dealt  with  at  greater  length  in  the  Report  No.  I.  The  general 
properties  of  diffusing  media  are  dealt  with  in  the  first  report 
on  diffusing  media,  while  considerable  data  on  the  reflecting 
power  and  gloss  of  papers  is  contained  in  Report  No.  4  on  papers. 

Nelson  M.  Black, 
J.  R.  Cravath, 
F.  H.  Gilpin, 
M.  Luckiesh, 
F.  K.  Richtmyer, 
F.  A.  Vaughn, 
P.  G.  Nutting,  Chairman. 


SUBMARINE    PHOTOGRAPHY 

SUBMARINE  PHOTOGRAPHY.* 


403 


BY  J.  E.  WILLIAMSON. 


The  taking  of  pictures  under  and  through  water  has  been 
attempted  by  several  investigators — notably,  M.  Louis  Boutan, 
Mr.  Jaques  Reighard  of  the  University  of  Michigan,  Mr.  Etienne 
Peau  and  Dr.  Francis  Ward  of  Eipswich,  England.  Of  these,. 
Dr.  Ward  had  the  best  results.    On  his  estate  in  England  he  con- 


Fig.  1. — A  tube  used  in  submarine  photography. 

structed  an  artificial  pond,  having  a  cement  well  with  a  large  plate 
glass  window  at  one  side  of  the  pond.  As  a  result  of  his  experi- 
ments he  stated  that  he  believed  under  the  most  favorable  condi- 
tions it  would  be  possible  to  photograph  through  3  feet  (0.91  m.) 
of  water. 

The  actual  taking  of  the  pictures  is  not  difficult.     The  main 

*  Abstract  of  a  paper  read  at  a  meeting  of  the  New  York  Section  of  the  Illuminating 
Engineering  Society,  January  14,  1915. 

The  Illuminating  Engineering  Society  is  not  responsible   for  the  statements  or 
opinions  advanced  bv  contributors. 


404     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

requisite  is  to  get  beneath  the  water  and  be  able  to  remain  there 
in  comfort  under  normal  atmospheric  conditions.  The  author 
and  his  associates1  have  accomplished  this  by  means  of  the 
Williamson  submarine  tube  (Fig.  i).  This  consists  of  a  water- 
tight collapsible  tube,  containing  a  chamber  at  its  lower  end  of 
sufficient  size  to  hold  a  man  and  a  camera.  The  tube  is  lowered 
through  an  opening  in  the  center  of  a  boat  specially  constructed 
for  this  purpose.  The  chamber  has  a  heavy  glass  plate  to  with- 
stand the  water  pressure.  Through  this  plate  photographs  can 
be  taken.  In  the  West  Indies,  where  the  water  is  very  clear, 
both  day  and  night  pictures  have  been  taken  at  considerable 
depths,  which  show  objects  clearly  at  distances  of  ioo  feet 
(30.5  m.)  from  the  camera.  Daylight  illumination,  coming  down 
through  the  water,  is  supplemented  by  the  light  from  a  bank  of 
quartz-tube,  mercury-vapor,  arc  lamps,  which  are  placed  in  special 
water-tight  housings  and  lowered  over  the  stern  of  the  ship. 
Fig.  1  shows  a  diagrammatic  sketch  of  the  apparatus  in  service. 

1  Williamson  Submarine  Film  Corporation. 


hurley:    street  lighting  405 

STREET  LIGHTING  WITH  MODERN  ARC  LAMPS.* 


BY  W.  P.   HURLEY. 


Arc  Lamp  Development. — The  original  commercial  arc  lamp 
system  used  for  street  lighting  in  America  was  of  the  open  arc 
type,  which  came  into  commercial  use  about  1880.  This  lamp 
was  usually  operated  in  series  on  a  direct  current  from  special 
arc  lighting  generators.  These  lamps  gave  a  very  unsteady  light 
with  relatively  high  maintenance  cost,  due  to  the  short  carbon  life 
and  frequent  trimming. 

The  enclosed  carbon  arc  lamps  for  both  alternating  current  and 
direct  current  came  on  the  market  about  1890  and  were  very 
popular  in  America  because  they  were  much  steadier  than  the 
open  arcs;  and,  owing  to  a  carbon  life  of  from  100  to  150  hours, 
requiring  less  labor,  were  much  more  economical  to  maintain. 
Their  efficiency,  however,  was  slightly  less  than  the  open  arc. 

The  metallic  flame  or  magnetite  arc  lamp  was  developed  about 
1906;  it  was  essentially  a  low  current,  long-burning  lamp  of  com- 
paratively high  efficiency.  Owing  to  the  nature  of  the  electrodes, 
however,  it  could  be  made  only  for  direct  current.  By  reason  of  its 
very  economical  maintenance  and  good  efficiency,  many  thousands 
of  the  previous  types  of  arc  lamps  were  superseded  by  this 
lamp,  and  it  remained  as  the  highest  type  of  arc  lamp  development 
for  the  lighting  of  residence  streets. 

Flame  carbon  arc  lamps  were  first  developed  in  Europe  and 
marketed  about  1906.  These  lamps  were  very  expensive,  burning 
from  10  to  17  hours  with  comparatively  expensive  carbons,  so 
that  their  use  for  street  lighting  in  America  was  never  very 
popular. 

In  191 1  a  long-burning  flame  carbon  arc  lamp  was  developed, 
this  being  more  in  the  nature  of  an  enclosed  arc  lamp  to  burn  im- 
pregnated carbons,  with  special  devices  for  steadying  the  arc 
and  keeping  the  globes  clear  of  deposit  from  the  arc.  The  long- 
burning  flame  carbon  arc  lamp  is  inherently  of  very  high  effi- 
ciency and,  as  the  energy  cost  in  any  street  lighting  system  is 

*  Abstract  of  a  paper  read  before  the  Pittsburgh  Section  of  the  Illuminating  Engi- 
neering Society,  May  7,  1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  bv  contributors. 


406     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

approximately  50  per  cent,  of  the  total  cost,  including  interest  and 
depreciation  on  the  equipment,  it  can  be  readily  seen  that  where 
this  unit  is  adapted  its  extremely  high  efficiency  makes  it  superior 
to  any  other  type.  The  lamp  is  inherently  of  high  candlepower 
and  cannot  be  practically  applied  where  low  intensity  is  required. 
It  is  suitable  for  either  alternating  or  direct  current  and  admits 
of  a  wide  application. 

For  residence  street  lighting,  the  metallic  flame  lamp  is  recom- 
mended, as  the  intensity  and  color  are  most  suitable  for  the  usual 
requirements.  Where  very  small  lamps  are  required,  as  in  out- 
lying districts  or  alleys,  small  incandescent  lamps  should  be 
operated  in  series  with  the  arc  lamps. 

For  business  streets  or  "white  way"  lighting  where  relatively 
high  intensities  are  required  and  the  limitations  of  economy  per 
unit  are  not  so  essential,  as  in  residence  districts,  because  the 
population  per  square  foot  of  street  area  to  be  illuminated  is 
higher,  the  flame  carbon  arc  lamp  is  excellently  adapted.  It 
can  be  supplied  in  either  a  pendent  or  an  ornamental  post  or 
bracket  lamp,  the  mechanism  being  comparatively  simple  and 
practically  the  same  in  the  two  types. 

For  "white  way"  lighting,  appearance  of  the  street  is  the  most 
essential.  The  arc  lamp  with  its  clear,  white  light  contrasting 
favorably  with  the  store  window  lighting  always  causes  favorable 
comments.  The  intensity  of  the  light  is  relatively  high,  so  that 
large  units  can  be  employed  profitably,  thus  reducing  the  number 
of  poles  and  the  first  cost  of  the  installation — at  the  same  time 
taking  advantage  of  the  highest  efficiency  and  economy  in  the  use 
of  energy. 

Further  developments  in  the  way  of  luminous  efficiency  are 
most  favorable  to  arc  lamp  development,  as  chemical  limitations 
rather  than  physical  are  preeminent  in  this  line,  and  the  field  of 
selective  radiation  of  light  has  been  as  yet  but  slightly  touched 
upon. 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 

Vol.  X  AUGUST  30,  1915  NO.  6 

THE  EFFICIENCY  OF  THE  EYE  UNDER  DIFFERENT 

CONDITIONS    OF    LIGHTING:     THE    EFFECT 

OF    VARYING    THE     DISTRIBUTION 

FACTORS  AND  INTENSITY.* 


BY  C.   E.   EERREE  AND  GERTRUDE  RAND, 
BRYN    MAWR   COLLEGE. 


Synopsis:     In  a  previous  paper**  a  plan  of  work  was  outlined  by  one 
of  the  writers  for  the  study  of  the  effect  of  different  kinds  of  lighting 
conditions  on  the  eye.    The  problem  was  divided  into  three  parts:    (i)  the 
determination  of  the  conditions  that  give  in  general  the  highest  level  or 
scale  of  visual  efficiency;    (2)   the  conditions  that  give  the  least  loss  of 
efficiency  for  continued  work;  and  (3)  the  determination  of  the  conditions 
that  cause  the  least  discomfort.     Tests  were  described  especially  designed 
to  meet  the   requirements   of   each   of   these   divisions   of  the   work   and 
results  were  given  to  show  in  a  general  way  the  sensitivity  of  the  tests 
employed.    The  work  of  the  present  paper  is  confined  to  the  second  divi- 
sion of  the  problem  and  should  be  considered  as  an  explorative  investiga- 
tion for  the  determination  of   factors.     Six  aspects  of  lighting  are  con- 
sidered provisionally  as  sustaining  an  important  relation  to  the  eye:    the 
evenness  of  the  illumination,  the  diffuseness  of  light,  the  angle  at  which 
ght  falls  on  the  object  viewed,  the  evenness  of  surface  brightness, 
intensity  and  quality.     Only  the  first  five  of  these  are  dealt  with  in  this 
paper.    The  first  four  are  called,  for  convenience  of  reference,  distribution 
factors.     In   order   to  produce   the   variation   in   the   distribution   factors 
needed  for  the  purposes  of  the  test,  three  types  of  reflectors  in  common  use 
were  employed — a  direct,  a  semi-indirect,  and  an  indirect.  These  reflec- 
s  were  selected  with  reference  to  the  object  of  the  investigation  rather 
than  as  representative  in  every  case  of  any  particular  principle  of  lighting. 
The  illumination  effects  produced  in  each  case  were  specified  in  the  fol- 
lowing ways  :     ( 1 )  A  determination  was  made  of  the  average  illumination 
the  room  under  each  of  the  three  installations.     (2)  The  brightness  of 
prominent  objects  in  the  room,  such  as  the  test  card,  the  reflectors  for  the 
emi-indirect  installation,  the  reading  page,  specular  reflection  from  sur- 
aces,  etc.,  was  given.     (3)    Photographs  were  made  of  the  room   from 
hree  positions  under  each  kind  of  installation.     These  effects  were  then 
correlated  with  the  results  obtained  with  the  eye  test. 

In  order  to  determine  the  effect  of  varying  intensity  with  a  certain 
grouping  of  distribution  factors,  lamps  of  different  wattage  were  used 
with  each  type  of  reflector  employed  in  the  distribution  series.  The 
writ.*™  ^'ef  rNP°rt  uf  the  work  described  »n  this  paper  was  read  by  one  of  the 
*££  he.edrr:tV^sbhuergh:VSererLC^V^30n  *  *°  IUumin»tin«  Engineering 
oPi„ionhs\dvr«daby!om"fbXlng  ^^  ^  ^  reSP°nsible  for  the  statements  or 
**  Trans.  I.  E.  S..  p.  40,  vol.  VIII  (1913). 


408     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

illumination  effects  produced  were  specified  by  illumination  and  brightness 
measurements  in  the  way  described  above,  and  the  effects  were  again 
correlated  with  the  results  of  the  eye  tests  conducted  at  each  intensity  of 
illumination. 


I.    INTRODUCTION. 

In  a  paper1  presented  to  the  annual  convention  of  this  society 
last  year,  a  plan  of  work  was  outlined  by  one  of  the  writers  for 
the  study  of  the  effect  of  different  kinds  of  lighting  conditions 
on  the  eye.  The  problem  was  divided  into  three  parts  :  ( i )  the 
determination  of  the  conditions  that  give  in  general  the  highest 
level  or  scale  of  visual  efficiency,  (2)  the  determination  of  the 
conditions  that  give  the  least  loss  of  efficiency  for  continued 
work,  and  (3)  the  determination  of  the  conditions  that  cause  the 
least  discomfort.  Tests  were  described  which  seemed  to  the 
writer  after  six  months  of  trial  to  be  adequate  for  the  require- 
ments of  each  of  these  three  divisions  of  work,  and  results  were 
given  to  show  in  a  general  way  the  sensitivity  of  the  tests  em- 
ployed. With  the  beginning  of  the  present  year  work  on  the 
problem  proper  was  begun.  This  work  has  been  confined  to  the 
second  division  of  the  problem,  namely,  the  determination  of 
the  conditions  that  give  the  least  loss  of  efficiency  as  the  result 
of  a  period  of  work.  It  has  been  thought  best  to  conduct  this 
investigation  at  first  along  broad  lines  in  order  to  determine  in  a 
general  way  the  conditions  that  affect  the  eye's  ability  to  maintain 
its  efficiency  for  continuous  work.  Later  a  more  detailed  ex- 
amination will  be  made  of  the  ways  in  which  these  conditions 
have  been  worked  out  in  the  various  types  of  lighting  systems  in 
existence  at  this  time. 

The  following  aspects  of  lighting  sustain  an  important  relation 
to  the  eye :  the  evenness  of  the  illumination,  the  diffuseness  of 
light,  the  angle  at  which  the  light  falls  on  the  object  viewed,  the 
evenness  of  surface  brightness,  intensity,  and  quality.  The  first 
four  of  these  aspects  are  very  closely  interrelated,  and  are  apt 
to  vary  together  in  a  concrete  lighting  situation,  although  not  in 
a  1  :  1  ratio.  For  the  purposes  of  this  paper,  therefore,  which 
is  the  report  of  an  investigation  primarily  explorative,  it  will  be 
convenient  to  group  these  aspects  together  and  refer  to  them  as 

1  Ferree,  C.  E.,  Tests  for  the  Efficiency  of  the  Eye  under  Different  Systems  of 
Illumination  and  a  Preliminary  Study  of  the  Causes  of  Discomfort;  Trans.  I.  E-  S., 
1913,  Vol.   VIII,  pp.  40-61. 


FEKREE  AND  RAM):     EFFICIENCY   OF   THE   EYE  409 

the  distribution  of  light  and  surface  brightness  in  the  field  of 
vision,  or  still  more  generally  as  distribution.  In  later  work  an 
attempt  will  be  made  to  study  the  effect  of  varying  each  in  separ- 
ation, but  in  the  work  here  reported  upon,  no  especial  attempt  has 
been  made  to  do  this.  The  ideal  condition  with  regard  to  dis- 
tribution is  to  have  the  field  of  vision  uniformly  illuminated  with 
light  well  diffused  and  no  extremes  of  surface  brightness.  When 
this  condition  is  attained  the  illumination  of  the  retina  will  shade 
off  more  or  less  gradually  from  center  to  periphery,  which  grad- 
ation is  necessary  for  accurate  and  comfortable  fixation  and  ac- 
commodation. Up  to  the  present  time,  we  have  been  able  to  finish 
in  as  complete  a  way  as  we  wish  for  the  installations  used  the 
work  on  distribution  and  part  of  the  work  on  intensity.  The 
remainder  of  the  work  will  be  completed  early  in  the  course  of 
the  present  year. 

The  factors  we  have  grouped  under  the  heading  distribution 
can  most  conveniently  be  discussed  with  reference  to  four  types 
of  lighting  in  common  use  to-day:  illumination  by  daylight, 
illumination  by  direct  lighting  systems,  by  indirect  lighting  sys- 
tems, and  by  semi-indirect  systems.  In  the  proper  illumination 
of  a  room  by  daylight  we  have  been  able  thus  far  to  get  the  best 
conditions  of  distribution.  Before  it  reaches  our  windows  or 
skylights,  daylight  has  been  rendered  widely  diffuse  by  innumer- 
able reflections,  and  the  windows  and  skylights  themselves  acting 
as  sources  have  a  broad  area  and  a  low  intrinsic  brilliancy,  all  of 
which  features  contribute  towards  giving  the  ideal  condition  of 
distribution  stated  above,  namely,  that  the  field  of  vision  shall 
be  uniformly  illuminated  with  light  well  diffused  and  that  there 
shall  be  no  extremes  of  surface  brightness.  Of  the  systems  of 
artificial  lighting,  the  best  distribution  effects  from  the  standpoint 
of  the  comfort  and  efficiency  of  the  eye  are,  speaking  in  general 
terms,  given  perhaps  by  the  indirect  systems.  In  this  type  of 
system  the  source  is  concealed  from  the  eye  and  the  light  is  thrown 
against  the  ceiling  or  some  other  diffusely  reflecting  surface  in 
such  a  way  that  it  suffers  one  or  more  reflections  before  it  reaches 
the  eye.  The  direct  lighting  systems  are  designed  to  send  the 
light  directly  to  the  plane  of  work.  There  is  in  the  use  of  these 
systems  a  tendency  to  concentrate  the  light  on  the  plane  of  work 
or  object  viewed  rather  than  to  diffuse  it,  and,  therefore,  a  ten- 


4IO     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

dency  to  emphasize  brightness  extremes  in  the  field  of  vision 
rather  than  to  level  them  down.  Too  often,  too,  the  eye  is  not 
properly  shielded  from  the  primary  source  of  light,  and  fre- 
quently no  attempt  at  all  is  made  to  do  this.  The  semi-indirect 
systems  are  intended  to  represent  a  compromise  between  the 
direct  and  the  indirect  systems.  A  part  of  the  light  is  transmitted 
directly  to  the  plane  of  work  through  the  translucent  reflectors 
placed  beneath,  and  a  part  is  reflected  to  the  ceiling.  Thus,  de- 
pending upon  the  density  of  the  reflector,  this  type  of  system  may 
vary  between  the  totally  direct  and  totally  indirect  as  extremes  and 
share  in  the  relative  merits  and  demerits  of  each  in  proportion  to 
its  place  in  the  scale.  It  is  not  our  purpose,  however,  at  this  time 
to  attempt  a  final  rating  of  the  comparative  merits  of  types  of 
lighting  systems.  For  that  our  work  is  still  too  young.  More- 
over, there  are  relatively  good  and  bad  fixtures  of  each  type,  and 
good  and  bad  installations  may  be  made  of  any  system.  What 
we  hope  to  do  is  by  the  appropriate  selection  and  variation  of 
conditions  to  find  out  what  the  factors  are  that  are  of  importance 
to  the  eye  in  lighting,  and  from  this  knowledge  as  a  starting  point 
to  work  towards  reconstruction. 

It  was  stated  also  in  our  former  paper  that  the  problem  dealing 
with  loss  of  efficiency  presents  two  phases.  We  may  investigate 
(a)  whether  the  eye  shows  a  loss  of  efficiency  after  three  or  four 
hours  of  work  under  a  given  lighting  system,  and  (b)  whether 
there  is  progressive  loss  of  efficiency  in  working  several  months 
or  years  under  a  given  system.  We  have  confined  and  purpose  to 
confine  our  work  for  the  present  to  the  former  aspect  of  the 
problem,  because  it  alone  falls  within  the  scope  of  laboratory 
studies  and  because  we  believe  that  the  problem  should  be  worked 
out  first  in  miniature  with  all  the  conveniences  of  manipulation 
and  possibilities  of  precision  obtaining  under  laboratory  con- 
ditions. 

II.  THE  EFFECT  OF  VARIATION  IN  THE  DISTRIBUTION  OF 
LIGHT  AND  SURFACE  BRIGHTNESS  ON  THE  EFFI- 
CIENCY OF  THE  EYE  FOR  A  PERIOD  OF  WORK. 

In  order  better  to  understand  the  data  given  in  the  tables  of 
results,  the  nature  of  the  tests  used  in  this  part  of  the  work  will 
again  be  briefly  called  to  mind.  It  will  be  remembered  that  the 
conventional  tests  for  the  eye's  responsiveness  to  its  stimulus, 


FERREE   AND   RAND:     EFFICIENCY   OF   THE    EYE  411 

namely,  tests  for  brightness  sensitivity,  color  sensitivity,  and 
visual  acuity,  were  found  to  be  practically  useless  for  this  work. 
Modified  and  rendered  sensitive  in  the  ways  described  in  the 
previous  paper,  they  were  found  to  serve  as  a  measure  of  the 
general  level  of  efficiency  of  the  un fatigued  eye  under  different 
conditions  of  lighting;  but  they  failed  to  show  loss  of  efficiency 
as  the  result  of  a  period  of  work.  This  is  clue  to  the  following 
reasons,  (a)  There  is  doubtless  very  little,  if  any,  loss  of 
sensitivity  to  brightness  and  color  during  this  length  of  time.2 
It  is  commonly  believed,  in  fact,  that  the  brightness  and  color 
processes  are  compensating  in  nature.  And  (b)  the  visual  acuity 
test,  in  spite  of  the  fact  that  its  results  may  be  ascribed  prac- 
tically entirely  to  changes  in  the  muscular  control  of  the  eye, 
is  not  adapted  to  show  loss  in  muscular  efficiency,  because 
the  muscles  of  the  eye,  while  they  may  have  fallen  off  enormously 
in  efficiency,  can  under  the  spur  of  the  will  be  whipped  up  to 
their  normal  power  long  enough  to  make  the  judgment  required 
by  the  test.  But  they  can  not  long  sustain  this  extra  effort.  This 
consideration,  it  will  be  remembered,  led  us  to  continue  the  test 
through  an  interval  of  time.  After  considerable  experimenta- 
tion an  interval  of  three  minutes  was  chosen  as  best  suited  for 
our  purpose.  When  the  observer  is  required  to  look  at  the  test 
card  for  three  minutes,  the  test  objects,  even  when  the  eyes  are 
fresh,  are  not  seen  clearly  for  the  whole  time.  They  are  seen 
alternately  as  clear  and  blurred.  The  time  they  are  seen  clear  and 
blurred  is  recorded  on  a  rotating  drum  upon  which  a  line  regis- 
tering seconds  is  also  run.  From  this  record  the  ratio  of  time 
seen  clear  to  time  seen  blurred  is  determined.  This  ratio  may 
be  fairly  taken  as  a  measure  of  the  efficiency  of  the  eye  for  three 
minutes  of  clear  seeing  at  the  time  the  test  is  taken.  In  applying 
the  test  to  our  problem,  a  record  is  taken  at  the  beginning  and  at 
the  close  of  work,  and  the  ratios  of  the  time  clear  and  the  time 

2  That  there  is  practically  no  loss  of  sensitivity  to  brightness  and  color  for  this 
period  of  time  was  shown  in  our  former  paper  by  the  results  of  our  tests  for  bright- 
ness and  color  sensitivity  with   and  without   the  time  element  as  an   aid  to  the  test. 

(See  also  in  connection  with  tests  for  brightness  and  color  sensitivity,  Ferree 
and  Rand:  A  Note  on  the  Determination  of  the  Retina's  Sensitivity  to  Colored 
Light  in  Terms  of  Radiometric  Units,  Amer.  Jour,  of  Psychol.,  1912,  Vol.  XXIII, 
PP-  328-332;  An  Optics-Room  and  a  Method  of  Standardizing  its  Illumination, 
Psychol.  Rev.,  191 2,  Vol.  XIX,  pp.  364-373;  Colored  After-Image  and  Contrast 
Sensations  from  Stimuli  in  which  no  Color  is  Sensed,  ibid,  pp.  195-239;  Rand: 
The  Factors  that  Influence  the  Sensitivity  of  the  Retina  to  Color:  A  Quantitative 
Study  and  Methods  of  Standardizing,  Psychol.  Rev.  Monog.,  1913,  r66  pp.;  The 
Effect  of  Changes  in  the  General  Illumination  of  the  Retina  upon  its  Sensitivity  to 
Color,  Psychol.   Rev.,    1912,   Vol.    XIX,    pp.    463-490. 


412     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

blurred  are  compared  for  the  two  cases  to  determine  how  much 
the  eye  has  lost  in  efficiency  as  the  result  of  work.  Two  values 
were  used  for  the  distance  at  which  the  test  card  was  placed 
from  the  eye:  (a)  the  maximal  distance  at  which  the  test  objects 
could  be  seen  clearly  in  the  momentary  judgment,  and  (b)  a 
distance  less  than  this.  The  latter  distance  was  finally  chosen  be- 
cause for  the  maximal  distance,  towards  the  close  of  the  test  even 
when  the  eyes  were  fresh,  the  value  of  the  time  blurred  became 
too  high,  it  was  found,  to  make  the  most  effective  comparison 
of  the  ratios  obtaining  at  the  beginning  and  at  the  close  of  work. 
In  order  to  eliminate  the  memory  and  fatigue  factors  which 
make  it  impossible  to  reproduce  results  in  a  series  of  tests  with 
the  same  observer  when  the  conventional  Snellen  test  of  visual 
acuity  is  employed,  it  will  be  remembered  that  the  test  card  was 
made  to  consist  of  one  or  more  simple  objects,  and  the  type  of 
judgment  was  changed  so  that  results  were  rendered  in  terms 
of  clearness  of  vision  instead  of  in  terms  of  the  ability  to  recog- 
nize a  series  of  letters  or  characters.3  That  is,  in  this  type  of 
test  the  observer  knows  what  the  objects  are,  and  he  records  the 
time  during  which  he  sees  them  clear  and  the  time  he  sees  them 
blurred.  A  number  of  test  objects  were  used  in  the  work  of  last 
year :   two  vertical  parallel  lines  stamped  i  mm.  apart  on  a  white 

I 
card  ;  the  letters  li  printed  in  small  type,  the  figures    •  , 

I 

I 
—  •  — ,  etc.     To  these  was  added  this  year  the  figure         ^ 

This  form  of  test  object  was  suggested  by  the  one  used  in  Dr. 
Ives'  visual   acuity  apparatus.4     While   apparently   it  gives   ex- 

s  For  a  further  explanation  of  this  point  see  Tests  for  the  Efficiency  of  the 
Eye  under  Different  Systems  of  Lighting  and  a  Preliminary  Study  of  the  Causes 
of  Discomfort,   Trans.   I.   E.    S.,   Vol.   VIII,   1913,  pp.   43-45. 

4  The  writers  wish  to  state  that  the  test  object  used  by  them  was  similar  to 
that  employed  by  Dr.  Ives  only  with  regard  to  form.  One  of  the  prominent  features 
of  the  apparatus  used  by  Dr.  Ives,  for  example,  is  a  device  for  the  control  of  the 
width  of  the  parallel  lines  and  the  interspaces,  while  the  figure  used  by  us  was 
printed  on  a  white  card  with  a  fixed  width  of  line  and  interspace.  All  that  the 
writers  wish  to  point  out  here  is  that  a  figure  made  up  of  parallel  lines  and  inter- 
spaces is  not,  they  believe,  the  most  suitable  for  work  of  the  kind  we  are  doing 
because  of  the  comparatively  large  mean  variation  it  gives  in  the  ratio,  time  clear 
to  time   blurred. 

The  figure  was  at  first  made  7  mm.  in  diameter;  but  this  figure  was  found  to 
be  too  large.  It  would  blur  irregularly  over  its  surface,  i.  e.,  the  edges  would 
become  indistinct  when  the  center  was  clear  and  vice  versa.  The  figure  finally 
adopted  was  3.5  mm.  in  diameter.  This  size  was  found  to  be  more  satisfactory  for 
our  work. 


FERREE   AND   RAND:     EFFICIENCY   OF   THE   EYE  4!  3 

cellcnt  results  for  the  purpose  for  which  it  was  adopted  by 
Dr.  Ives,  it  gives  too  large  a  mean  variation  of  ratio,  time 
clear  to  time  blurred,  when  the  element  of  time  is  introduced 
into  the  visual  acuity  test  to  be  of  maximal  service  in  our 
work.  This  is  probably  because  a  figure  of  this  form  is  more 
influenced  by  adaptation,  the  streaming  phenomenon,5  and  other 
variable  physiological  conditions  of  the  retina  than  are.  for 
example,  the  letters  li.  This  latter  object  was  found  to  be  far 
the  most  satisfactory  for  our  purpose.  When  used  as  test  object 
the  mean  variation  of  the  ratio,  time  clear  to  time  blurred,  for 
the  same  observer  working  under  conditions  as  nearly  constant  as 
possible,  is  very  small  indeed.6  Results  will  be  given,  therefore, 
in  this  report  only  for  the  work  in  which  the  letters  li  were  used 
as  test  object. 

In  our  work  on  distribution  the  tests  were  made  in  a  room 
30.5  ft.  (9.29  m.)  long,  22.3  ft.  (6.797  m0  wide,  and  9.5  ft. 
(2.895  m-)  high.  The  artificial  lighting  was  accomplished  by 
means  of  two  rows  of  fixtures  of  four  fixtures  each.  Each  row 
was  6  ft.  (1.828  m.)  from  the  side  wall,  and  the  fixtures  were 
6  ft.  apart.  The  reflectors  were  29  in.  from  the  ceiling  for  the 
direct  system,  and  16  in.  for  the  indirect  and  semi-indirect.  Clear 
tungsten  lamps  were  used  as  source.  The  voltage  was  kept 
constant  by  means  of  a  voltmeter  and  a  finely  graduated  wall 
rheostat  placed  in  series  with  the  lighting  circuit. 

In  order  to  get  the  desired  variation  in  the  distribution  of  light 
and  surface  brightness  in  the  field  of  vision  required  for  the 
purposes  of  the  test,  four  types  of  lighting  were  selected.  One 
may  be  called  a  direct  system ;  one  an  indirect  system ;  one  a 
semi-indirect  system ;  and  one  was  the  illumination  of  a  room  by 
daylight.  In  case  of  the  direct  system,  two  bulbs  making  an 
angle  of  180  deg.  were  used  for  each  fixture.    Directly  above  the 

5  Ferree,  C.  E.,  The  Streaming  Phenomenon,  Amer.  Jour,  of  Psychol..  1908, 
19.  PP-  484-503;  also  The  Intermittence  of  Minimal  Visual  Sensation,  Amcr.  Jour,  of 
Psychol..    1908,    Vol.    XIX,    pp.    112-730. 

*  The  order  of  magnitude  of  the  mean  variation  of  the  test  for  the  fresh  eye 
was  obtained  as  follows.  Beginning  at  9  a.  m.,  five  three-minute  records  were  run 
with  a  rest  period  of  20  minutes  between  each  test.  This  was  done  with  all  ob- 
servers on  several  days  under  each  system  of  lighting  employed.  The  rest  period 
was  taken  in  each  case  in  a  room  lighted  by  daylight  facing  a  wall  with  an  evenly 
lighted  mat  surface.  For  a  single  series  of  five  tests,  the  variations  of  the  time 
seen  clear  in  the  three-minute  period  have  always  fallen  within  1  per  cent,  for  all 
of  the  observers  we  have  used  and  all  systems  of  lighting. 


414     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

lights  was  fastened  a  slightly  concaved  porcelain  reflector  16  in. 
in  diameter.  This  type  of  fixture  was  not  chosen  with  an  especial 
reference  to  its  representative  character  in  any  system  of  com- 
mercial classification.  It  was  chosen  rather  with  reference  to 
the  purpose  of  the  test.  It  may  be  said,  however,  that  it  was  the 
one  in  use  throughout  the  building  in  which  the  tests  were  made 
and  gives  effects  very  similar  to  much  of  the  lighting  in  actual 
use  at  the  present  time.  In  case  of  the  indirect  system,  corrugated 
mirror  reflectors  were  used  enclosed  in  a  brass  bowl.  For  the 
semi-indirect  system  inverted  alba  reflectors  11  in.  in  diameter 
were  employed.  The  daylight  illumination  came  from  three  win- 
dows all  on  one  side  of  the  room.  These  windows  were  so  shel- 
tered that  it  was  never  possible  for  them  to  receive  light  directly 
from  the  sun  or  from  a  brilliantly  illuminated  sky.  Moreover, 
the  light  from  one  of  them,  the  one  nearest  the  observer,  was 
further  diffused  by  passing  through  a  diffusion  sash  made  of 
double  thick  glass  ground  on  one  side. 

In  order  to  get  the  effect  of  the  distribution  factors  on  the  eye's 
loss  of  efficiency  as  the  result  of  a  period  of  work,  the  tests  should 
be  conducted  with  the  quality  and  intensity  of  light  made  as  nearly 
equal  as  possible.  The  quality  of  light  was  made  approximately 
the  same  for  the  three  installations  of  artificial  light  by  using 
clear  tungsten  lamps  in  each  case.  It  was  decided  to  make  the 
intensity  of  light  as  nearly  equal  as  possible  at  the  point  of  test, 
and  to  give  a  supplementary  specification  of  the  lighting  effects 
in  the  remainder  of  the  room  for  the  three  installations  of  arti- 
ficial light.7  At  the  point  of  test  the  light  was  photometered  in 
several  directions.  It  was  made  approximately  equal  in  the  plane 
of  the  test  card  and  as  nearly  as  possible  equal  in  the  other  direc- 
tions. 

The  specification  of  the  lighting  effects  in  the  remainder  of  the 
room  has  been  accomplished  as  follows.       (1)  A  determination 

7  We  have  not  as  yet  made  the  fuller  photometric  specification  of  the  room 
lighted  by  daylight  with  our  present  arrangement  of  windows,  curtains,  etc.  We  hope 
to  make  the  effect  of  varying  the  distribution  factors  in  daylight  illumination 
(employing  windows,  skylights,  etc.)  the  study  of  a  future  study.  In  this  study  a 
photometric  analysis  of  the  illumination  effects  produced  will  be  made  an  especial 
feature. 


ferree  and  rand:   efficiency  of  the  eye  415 

has  been  made  of  the  average  illumination  of  the  room  under 
each  of  the  three  installations.  The  room  was  laid  out  in  3-ft. 
squares,  and  illumination  measurements  were  made  at  66  of  the 
intersections  of  the  sides  of  these  squares.  Readings  were  made 
in  a  plane  122  cm.  above  the  floor  with  the  receiving  test-plate  of 
the  illuminometer  in  the  horizontal,  45  deg.  and  90  deg.  positions, 
measuring  respectively  the  vertical,  45  deg.,  and  horizontal  com- 
ponents. The  122  cm.  plane  was  chosen  because  that  was  the 
height  of  the  test  object.  (2)  A  determination  was  made  of  the 
brightness  of  prominent  objects  in  the  room,  such  as  the  test  card, 
the  reflectors  for  the  semi-indirect  installation,  book  of  the  ob- 
server, specular  reflection  from  surfaces,  etc.  The  brightness 
measurements  were  made  by  means  of  a  Sharp-Millar  illumino- 
meter with  the  receiving  test  plate  removed.  The  instrument  was 
calibrated  against  a  magnesium  oxide  surface  obtained  by  de- 
positing the  oxide  from  the  burning  metal  on  a  white  card.  By 
this  method  the  reflecting  surfaces  were  used  as  detached  test 
plates.  The  readings  were  converted  into  candlepower  per  sq.  in. 
by  the  following  formula :  Brightness  =  Foot-candles/V  X  144- 
(3)  Photographs  were  made  of  the  room  from  three  positions 
under  each  system  of  illumination. 

In  Fig.  1  (see  "Further  Experiments  on  the  Efficiency  of  the 
Eye  under  Different  Conditions  of  Lighting,"  Trans,  of  the  111. 
Eng.  Soc,  1915,  X,  p.  452a)8  the  test  room  is  drawn  to  scale :  Plan 
of  room,  north,  south,  east,  and  west  elevations.9  In  the  drawing- 
plan  of  room,  are  shown  the  66  stations  at  which  the  illumination 
measurements  were  made  and  the  position  of  the  outlets  for  the 
lighting  fixtures  A,  B,  C,  D,  E,  F,  G,  H.  In  the  drawing,  east 
elevation,  the  position  of  the  observer  at  one  of  the  points  at 

8  The  present  paper  is  the  second  one  in  a  series  of  three  on  the  efficiency  of 
the  eye  under  different  conditions  of  lighting.  Before  it  was  printed  the  third 
paper  had  been  read  at  the  eighth  annual  convention  of  the  Illuminating  Engineering 
Society  and  printed  in  the  papers  for  that  convention.  In  this  paper  it  had  been 
found  necessary  to  repeat  some  of  the  data  of  the  second  paper  for  reference.  Since 
both  the  second  and  third  papers  are  now  appearing  simultaneously,  the  data  that 
was  repeated  in  the  third  paper  has  been  omitted  from  the  second.  Wherever  this 
has  been   done   a  cross  reference  is   given   to  the  third  paper. 

•  For  the  scale  drawing  of  the  test-room,  for  the  measurements  for  the  direct 
and  semi-indirect  systems  given  in  Table  II,  and  for  the  photographs  of  the  test- 
room,   we  are  indebted  to  Mr.   C.   W.   Jordan  of  the  United   Gas  Improvement  Co. 


416     TRANSACTIONS  01?  ILLUMINATING  ENGINEERING  SOCIETY 

which  the  tests  were  taken  is  represented.10  The  other  three 
positions  are  indicated  by  X. 

Table  I  (see  Table  I,  op.  cit.,  p.  454)  shows  the  number  and 
wattage  of  the  lamps  used  at  outlets  A,  B,  C,  D,  E,  F,  G,  H ;  and 
Table  IT  (see  Table  II,  op.  cit.,  454-455)  gives  the  illumination 
measurements  for  each  of  the  66  stations  represented  in  Fig.  1, 
made  with  the  receiving  test  plate  of  the  photometer  in  the  hori- 
zontal, vertical,  and  45  deg.  planes. 

Table  III  has  been  compiled  as  a  supplement  to  Table  II  for  the 
purpose  of  making  a  comparative  showing  of  the  evenness  of  il- 
lumination at  the  122  cm.  level  given  by  the  three  systems  of  light- 
ing. Two  cases  may  be  made  of  this  :  ( I )  A  comparison  may  be 
made  of  a  given  component  from  station  to  station;  or  (2)  the 
difference  between  the  components  may  be  compared.  To  facil- 
itate the  comparisons,  (a)  the  mean  variation  from  the  average 
of  each  of  the  components  has  been  computed;  and  (b)  the  dif- 
ference in  the  averages  of  the  three  components  has  been  deter- 
mined. Results  for  the  first  of  these  points  are  shown  in  Division 
A  of  the  table;  for  the  second  in  Division  B.11 

10  The  track  along  which  the  test  card  was  moved  was  parallel  to  the  east  and  west 
walls  of  the  room.  During  the  three  hours  of  reading  which  intervened  between 
the  two  tests  the  observer  moved  just  far  enough  back  from  the  upright  supporting 
the  mouthboard  to  give  room  for  the  book  to  be  held  and  to  permit  of  a  comfortable 
reading  position.  The  book  was  elevated  and  held  approximately  at  an  angle  of  45  deg. 
When  taking  the  test,  the  observer  faced  the  north  wall  of  the  room,  in  such  a 
position  that  with  the  eyes  in  the  primary  position,  the  lines  of  regard  were  para'lel 
with  the  east  and  west  walls  of  the  room.  Care  was  taken  to  have  print  of  uniform 
size  and  distinctness  for  use  with  the  three  systems,  and  to  have  a  page  which 
gave  a  comparatively  small  amount  of  specular  reflection.  The  brightness  values  of 
the  page  in  the  horizontal  and  45  deg.  positions  for  the  three  systems,  are  given  in 
the   legends    for   Figs.    8,   9,    and    10. 

11  It  would  be  interesting  to  make  this  comparison  for  other  levels  in  the  room 
and  for  a  greater  number  of  components.  But  unfortunately  we  have  not  been  able 
to  make  the  number  of  measurements  needed  for  this  comparison.  The  evenness  of 
the  illumination,  it  will  be  remembered,  is  not  only  of  importance  to  the  efficiency 
of  the  eye  with  reference  to  the  object  directly  viewed,  but  also  in  its  influence  on 
the  distribution  of  surface  brightness.  The  evenness  of  surface  brightness  depends 
in  general  upon  two  sets  of  factors:  (a)  the  nature  and  position  of  the  reflecting 
surfaces  in  the  room;  and   (b)   the  type  of  delivery  of  light  to  these  surfaces. 

We  realize  that  the  evenness  of  the  illumination  on  the  I22_  cm.  plane  given  by 
the  indirect  and  semi-indirect  units  was  somewhat  interfered  with  by  the  reflectors 
of  the  direct  system  which  were  beneath  and  a  little  to  the  right  of  these  units 
when  in  position  for  the  test.  Also  the  evenness  of  surface  brightness  on  the 
ceiling  for  the  direct  system  was  interfered  with  by  the  indirect  and  semi-indirect 
reflectors,  which  were  above  and  a  little  to  the  side  of  the  direct  units.  The  in- 
fluence of  this  "dead  apparatus"  will  be  eliminated  in  the  next  series  of  installa- 
tions. Moreover,  the  installation  in  each  case  was  not  such  as  to  give  the  best 
effects  obtainable  from  the  type  of  reflector  used.  For  example,  the  indirect  re- 
flectors were  too  close  to  the  ceiling  to  give  the  maximum  evenness  of  illumination 
and  of  surface  brightness  for  the  type  of  reflector  used.  The  above  analysis  of 
effects  is,  therefore,  not  made  for  the  purpose  of  drawing  general  conclusions  with 
retrard  to  the  type  of  reflector  employed.  It  is  made  solely  for  the  sake  of  the 
comparison  of  the  illuminating  effects  obtained  with  the  corresponding  results  for 
loss    of    efficiency. 


TABLE  III.1-'— (Distribution  Series). 
Compiled  from  Table  II  to  show  a  comparison  of  the  evenness  of  the  illu- 
mination at  the  122  cm.  level  given  by  the  direct,  semi-indirect,  and  indirect 
systems.  Division  A  shows  the  mean  variation  from  the  average  for  each  of 
the  three  components  of  illumination  ;  Division  B,  the  difference  in  the 
average  value  of  the  three  components. 

Division  A. 


Direct    

Semi-indirect 
Indirect  


Mean  variation  of  the  components    Percentage  of  mean  variation  of 

components 


Vertical     Horizontal 


1.88 
1.68 
i.i 


1.09 
0.66 
0.4 


i-53 
1.32 
0.61 


Vertical    Horizontal 


3«% 
39% 
30  # 


47% 
42% 
37% 


32% 
36', 
19% 


System 


Division  B. 


Difference  between  components 


Vertical 

and 

Horizontal 


Vertical  450 

and  and 

45°  Horizontal 


Direct   2.68 

Semi-indirect..        2.68 
Indirect 2.13 


0.23 
0.64 
031 


2-45 
2.04 
1.82 


Percentage  of  difference  between 
components 


Vertical 

and 

Horizontal 


54  ^ 
63% 

59% 


Vertical 
and 

45° 


5% 

15% 

9% 


45° 

and 

Horizontal 


51% 
56% 
55% 


■  For    Tables    I    and    II,    see    Tables    I    and    II,    Further    Experiments    on    the 
Efficiency  of  the  Eye,  etc.,  Trans.  I.  E.  S.,   1915,  Vol.  X,  pp.  454-455. 


Fig.  2. — Showing  the  test  room  illuminated  by  the  direct  system.     The  photograph  was 
taken  from  the  south  end  of  the  room  at  a  point  4  ft.  from  the  west  wall. 


Fig.  3. — Showing  the  test  room  illuminated  by  the  semi-indirect  system.     The  photograph 
was  taken  from  the  south  end  of  the  room  at  a  point  4  ft.  from  the  west  wall. 


Fig.  4.— Showing  the  test  room  illuminated  by  the  indirect  system.    The  photograph 
was  taken  from  the  south  end  of  the  room  at  a  point  4  ft.  from  the  west  wall. 


Fig.  5.— Showing  the  illumination  effects  for  the  west  wall  of  the  room,  direct  system. 


Fig,  6.— Showing  the  illumination  for  the  west  wall  of  the  room,  semi-indirect  system. 


Fig.  7.*— Showing  the  illumination  effects  for  the  west  wall  of  the  room,  indirect  system. 
*  For  Figs.  8,  9,  and  10,  see  Figs.  2,  3,  and  4,   "  Further  Experiments  on  the  Efficiency  of 
the  Eye,  etc."    Trans,  of  the  I.  E.  S.,  1915,  Vol.  X,  pp.  4528-4520. 


FERRFE    AND    RAND:     EFFICIENCY   OF   THE    EYE  41/ 

In  Figs.  2  to  10  are  given  photographs  showing  the  illumination 
of  the  room  and  the  distribution  of  surface  brightness  for  the 
three  systems.  Figs.  2,  3  and  4  are  taken  from  the  south  end  of 
the  room  at  a  point  4  ft.  from  the  west  wall.  These  photographs 
were  taken  so  as  to  comprehend  as  much  of  the  room  as  was  pos- 
sible in  one  view.  They  include  the  greater  part  of  the  ceiling, 
floor,  and  north  wall ;  six  of  the  fixtures ;  and  about  one-half  of 
the  east  wall.  The  difference  in  surface  brightness  for  the  various 
points  of  the  room  (including  the  lighting  units)  is,  it  will  be 
noted,  greatest  for  the  direct  system,  next  greatest  for  the  semi- 
indirect  system,  and  least  for  the  indirect  system.  The  indirect 
and  semi-indirect  reflectors  were  attached  to  arms  of  approxi- 
mately equal  length  which  could  be  revolved  about  the  fixture 
stem  as  an  axis.  When  the  tests  were  taken,  these  reflectors  were 
turned  in  each  case  to  the  inside  position  indicated  in  the  photo- 
graph, the  object  being  to  have  the  two  types  of  reflectors  as 
nearly  as  possible  in  the  same  position  in  the  field  of  vision  for  the 
comparative  tests.  The  direct  fixtures,  it  will  be  noted,  were  below 
and  slightly  outside  this  position.  In  our  next  series  of  experi- 
ments, arrangements  have  been  made  such  that  the  reflectors  can 
be  placed  in  exactly  the  same  position  for  each  type  of  installation 
when  it  suits  the  needs  of  the  experiment  to  have  it  so.  The 
slight  deviation  from  exact  coincidence  found  in  these  experi- 
ments is.  however,  perhaps  of  no  great  consequence  for  the  pur- 
pose of  the  present  work  especially  in  the  case  of  the  indirect  and 
semi-indirect  reflectors.  In  Figs.  5.  6  and  7,  are  represented  the 
illumination  effects  for  the  west  half  of  the  room.  These  photo- 
graphs show  the  distribution  of  light  and  shade  on  the  greater  part 
of  the  west  wall,  and  the  adjacent  ceiling,  and  include  two  of  the 
fixtures.  In  Figs.  8,  9  and  10  (see  Figs.  2-4.  op.  cit.  pp.  452a-452b  ) 
are  shown  the  brightness  measurements  of  all  surfaces  having 
very  high  or  very  low  brilliancy.  The  spot  measured  is  indicated 
by  a  cross,  and  the  numerical  value  of  the  brightness  measurement 
in  candlepower  per  square  inch  is  printed  nearby.  These  spots 
are  also  lettered  for  convenience  of  reference  in  the  intensity 
series.  That  is.  since  several  installations  were  used  in  the  in- 
tensity series  it  was  found  convenient  to  express  these  values  in 
tabular  form  and  to  identify  them  with  the  surfaces  measured 


418     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

by  means  of  letters.  These  photographs  were  taken  from  a  point 
in  the  line  with  the  four  positions  of  the  observer  as  near  to  the 
south  wall  of  the  room  as  was  possible,  but  owing  to  the  narrow 
field  of  the  camera  as  compared  with  the  binocular  field,  these 
views  include,  for  example,  only  about  one-half  of  the  field  of 
vision  of  the  observer  at  the  test  station  nearest  to  this  end  of 
the  room.  The  camera's  field  in  this  position  corresponds  in  fact 
very  closely  to  the  field  presented  to  the  observer  seated  at  the 
center  of  the  room.  While,  therefore,  not  all  of  his  field  of 
view  for  all  the  positions  at  which  tests  were  made  is  covered  by 
the  brightness  measurements  shown  in  the  photographs,  still  the 
order  of  magnitude  of  brightness  differences  present  in  the  field 
of  vision  for  the  different  systems  is  well  represented  by  these 
measurements,  as  can  be  seen  by  an  inspection  of  the  preceding 
photographs  and  from  the  descriptions  of  the  installations  used. 

In  order  to  facilitate  certain  features  of  comparison  such  as, 
for  example,  of  the  evenness  of  surface  brightness  for  each  sys- 
tem for  all  of  the  room,  for  all  but  the  sources  or  the  sources  and 
spots  above  the  sources,  the  brightness  measurements  shown  in 
Figs.  8,  9  and  10  are  also  given  in  tabular  form.  These  measure- 
ments and  the  letters  identifying  them  with  the  surfaces  measured 
are  given  in  Table  IV  and  V.  (see  Table  III  and  IV,  op.  cit., 
p.  457).  In  making  a  comparison  it  should  be  noted  that  the  spots 
measured  are  not  in  all  cases  identical  for  the  three  systems. 
That  is,  owing  to  the  different  effects  produced  by  the  different 
reflectors,  the  same  spot  was  not  always  conspicuously  light  or 
dark  for  the  three  systems.  The  letters  E,  F,  G,  etc.  may  refer, 
then,  to  entirely  different  spots  in  case  of  the  three  systems. 

In  Tables  VI  and  VII  (see  Table  V  and  VI,  op.  cit.,  pp.  463- 
464)  are  shown  some  prominent  ratios  of  surface  brightness  for 
the  three  systems.13    In  representing  these  ratios  it  has  been  consid- 

13  In  attempting  to  make  comparisons  of  the  effect  of  the  different  magnitudes 
of  brightness  ratios,  one  obviously  must  bear  in  mind  that  the  surfaces  between 
which  the  ratios  are  established  are  not  in  all  cases  in  the  same  position  in  the 
field  of  vision  for  the  three  systems.  For  example,  the  brightest  surfaces  in  case 
of  the  indirect  system,  namely,  the  spots  on  the  ceiling  directly  above  the  reflectors 
are  farther  removed  from  the  direct  line  of  vision  of  the  observer  when  in  the 
working  position  than  were  the  brightest  surfaces  in  case  of  the  direct  and  semi- 
indirect  systems.  The  position  of  the  Surface  in  the  field  of  vision  would  come  into 
question,  for  example,  in  making  a  determination  of  the  maximum  value  of  bright- 
ness difference  that  the  eye  is  adapted  to  stand.  While  we  have  done  a  great  deal 
[Continued  on  next  page.) 


1-KKkKK    AND    RAND:     I'.FF  Id  l-.NCV    OF    Till".    I'.YK  419 

ered  important  to  make  a  comparative  showing  for  the  three  sys- 
tems (a)  of  the  extremes  of  surface  brightness;  and  (b)  of  the 
relation  of  the  brilliancy  of  objects  in  the  surrounding  field  to  the 
surface  brightness  at  the  point  of  work.  The  extremes  of  sur- 
face brightness  are  shown  by  giving  the  ratios  between  surfaces 
of  the  first,  second,  third,  etc.,  order  of  brilliancy  and  the  sur- 
face of  the  lowest  order  of  brilliancy ;  and  the  comparison  of  the 
brilliancy  of  objects  in  the  surrounding  field  to  the  brightness  at 
the  point  of  work  by  giving  the  ratios  of  the  surfaces  of  the  first, 
second,  and  third  order  of  brilliancy  to  the  brightness  of  the  test 
card  and  the  reading  page  in  the  working  position.  The  follow- 
ing points  may  be  noted.  ( 1 )  The  illumination  effects  produced 
by  the  direct  system  are  characterized  by  great  extremes  of  sur- 
face brightness  and  a  high  ratio  of  brilliancy  of  objects  in  the 
surrounding  field  to  the  surface  brightness  at  the  point  of  work. 
These  effects  are  much  less  pronounced  for  the  semi-indirect 
system,  and  still  less  for  the  indirect.  (2)  A  comparison  of  this 
table  with  the  tables  showing  loss  of  efficiency  as  the  result  of 
work  shows  that  while  the  extremes  of  brightness  are  enormously 
larger  for  the  direct  than  for  the  semi-indirect  system,  the  eye 
loses  almost  as  much  in  efficiency  for  three  hours  of  work  under 
the  semi-indirect  system  as  under  the  direct.  That  is,  the  great- 
est ratio  of  brightness  for  the  direct  system  is  over  1,000  times 
as  much  as  the  greatest  ratio  for  the  semi-indirect,  while  the 
difference  in  loss  of  efficiency  for  the  two  systems  is  compar- 
atively insignificant.  On  the  other  hand  the  greatest  ratio  of 
brightness  for  the  semi-indirect  system  is  only  about  five  times 
as  much  as  for  the  indirect  and  the  difference  in  loss  of  efficiency 
for  three  hours  of  work  is  very  large,  this  loss  of  efficiency  for 
three  hours  of  work  for  the  indirect  system  being,  it  will  be  noted, 

of  work  on  the  effect  of  position  of  the  brilliant  surface  in  the  field  of  vision  in  our 
investigation  of  the  causes  of  discomfort,  we  have  made  no  especial  investigation  of 
this  point  in  relation  to  loss  of  efficiency.  Doubtless  what  we  shall  all  have  to  bear 
in  mind  is  that  even  in  the  end  we  can  not  hope  to  specify  narrowly  what  is  most  fav- 
orable, etc.  in  lighting  conditions.  The  factors  that  enter  into  the  concrete  lighting  situ- 
ation are  so  complex,  or  rather  are  so  variable  and  so  rarely  duplicated  that  we  can 
hope  to  make  general  specifications  with  regard  to  what  is  most  favorable,  for  ex- 
ample, only  within  very  broad  limits.  If  one  wishes  to  work  the  conditions  down 
to  a  finer  point  than  this,  the  particular  installation  must  itself  be  tested  in  situ.  We 
are  at  present  working  on  a  shorter  test  which  we  hope  will  serve  this  purpose 
better  than  the  test  which  has  been  used  in  the  work  described  in  this  paper. 
2 


420   Transactions  of  illuminating  engineering  society 

very  small  indeed.  This  seems  to  indicate  (a)  that  for  the  scale 
of  magnitudes  present  in  this  series  of  experiments,  the  gradation 
of  surface  brightness  for  the  indirect  system  is  very  close  to  what 
the  eye  is  prepared  to  stand  without  loss  of  efficiency;  and  (b) 
that  an  increase  in  differences  in  brightness  above  this  point  is 
followed  at  first  by  a  rapid  increase  in  loss  of  efficiency  and 
later  by  a  much  slower  increase.  In  the  intensity  series  the 
following  points  also  come  out.  (i)  The  effect  of  size  of  ratio 
on  loss  of  efficiency  is  different  for  different  orders  of  magnitude 
of  brightness.  That  is,  for  the  range  of  scale  of  magnitudes  we 
have  used,  the  lower  is  the  order  of  magnitude,  the  greater  is  the 
ratio  that  is  permissible.  And  (2)  the  size  of  the  brilliant  object 
as  well  as  its  brilliancy  is  of  importance.  That  is,  within  certain 
limits,  as  yet  undefined,  an  increase  in  the  area  of  the  brilliant 
surface  causes  an  increase  in  loss  of  efficiency. 

Supplementary  to  Tables  IY-VII  we  have  computed  for  the 
three  systems  the  mean  variation  of  the  several  brightness  values 
from  their  average  values.  While  important  from  the  standpoint 
of  showing  the  variation  from  the  mean  for  the  different  systems, 
such  a  comparison  is,  however,  probably  not  so  important  from 
the  standpoint  of  the  eye  as  are  the  comparisons  given  in  Tables 
IV-VII.  That  is,  from  the  standpoint  of  effect  on  the  eye  it  is 
probably  more  important  to  give  a  representation  of  the  bright- 
ness of  individual  surfaces,  more  especially  of  surfaces  showing 
extremes  of  brightness,  than  it  is  the  mean  variation  from  the 
average  brightness  of  all  the  surfaces.  In  order  to  make  possible 
the  comparison  with  and  without  the  source  and  the  spot  above 
the  source,  the  table  is  made  to  show  separately  the  mean  varia- 
tion for  the  following  measurements:  (a)  for  all;  (b)  for  all 
but  the  source;  and  (c)  for  all  but  the  source  and  the  spot  above 
the  source.     Results  are  given  in  Table  VIII. 

Obviously  the  effect  of  these  installations  on  the  eye's  ability 
to  maintain  its  efficiency  for  a  period  of  work  will  vary  with 
the  position  of  the  observer  in  the  room.  The  tests  have  been 
made,  therefore,  at  four  positions :  one  in  which  six  fixtures  were 
in  the  field  of  view,  one  in  which  four  were  in  the  field  of  view, 
one  in  which  two  were  in  the  field  of  view,  and  one  in  which 
none  were  in  the  field  of  view.     This  variation  of  position  at 


FKKREE    AND   RAND:     EFFICIENCY    OF    THE    EYE 


421 


which  the  observation  was  made  accomplishes  two  purposes. 
(  1)  It  gives  us  a  more  representative  idea  of  the  difference  in 
the  effect  on  the  eye  of  the  four  types  of  lighting.  And  (2)  it 
shows  the  effect  of  varying  the  number  of  surfaces  showing 
brightness  differences,  particularly  the  number  of  primary 
sources  in  the  field  of  view. 

TABLE  VIII. "—(Distribution  Series). 
Compiled  from  Table  IV  to  show  the  mean  variations  in   surface  bright- 
ness for  the  direct,  semi-indirect,  and  indirect  systems.15 


Mean  variation  for  the  three 
systems 

Percentage  of  mean  variation  for 
the  three  systems 

Measurements 
considered 

Direct 

Semi- 
indirect 

Indirect 

Direct 

Semi- 
indirect 

Indirect 

All    

All   but   the 

All   but   the 
source  and  the 
spot  above  the 

94-977 
O.OOlS 

0.0016 

0.075 
0.01817 

0.0013 

O.0235 
O.0235 

O.OOI2 

189% 

33% 

32% 

145% 
120% 

30% 

135% 
135% 

35% 

"  For  Tables  IV-VII,  see  Tables  III- VI,  Further  Experiments  on  the  Ef- 
ficiency of  the  Eye,  etc.,  Trans.   I,   E.   S.(   1915?  Vol.  X,  pp.  457,  463-464. 

15  It  is  scarcely  necessary  to  point  out  that  the  above  results  seem  to  indicate 
that  the  great  advantage  of  the  indirect  over  the  other  systems  of  lighting  we  have 
used  with  regard  to  the  factor:  evenness  of  surface  brightness,  comes  primarily  at 
least  from  its  provision  for  shielding  the  eye  from  the  light  source  rather  than 
from  any  conspicuously  greater  evenness  of  illumination  given  by  it  to  the  objects 
in  the  field  of  view.  In  fact  all  of  the  systems  give  a  fairly  even  distribution  of 
surface  brightness  outside  of  the  source  and  the  surfaces  immediately  surrounding 
it. 

The  need  of  keeping  the  surface  brightness  within  certain  limits  and  the 
primary  importance  of  properly  shielding  the  eye  from  the  source  to  the  accom- 
plishment of  this  desideratum  are  both  obvious  Doubtless  many  ways  will  be  de- 
vised in  course  of  time  for  cutting  down  useless  and  harmful  brightness  differences  in 
lighting  effects.  For  example,  the  possibility  is  here  suggested  of  producing  a  still 
smaller  brightness  difference  than  is  given  by  the  indirect  reflectors  of  the  type  we 
have  employed,  by  using  semi-indirect  reflectors  of  such  a  density  as  to  give  a 
surface  brilliancy  equal  to  that  of  the  spot  of  light  cast  upon  the  ceiling.  The 
value  of  this  brilliancy,  because  of  the  larger  area  of  luminous  surface  presented, 
could  then  be  made  smaller  than  that  of  the  ceiling  spot  cast  by  the  indirect 
reflector  and  still  give  the  same  amount  of  light  to  the  room.  A  similar  effect 
may  be  obtained  with  the  indirect  reflector  by  using  lamps  of  lower  wattage  and 
adding  the  light  needed  to  make  up  the  deficiency  by  installing  directly  beneath  the 
reflector  lamps  of  low  wattage  in  translucent  enclosures  of  a  density  that  will 
give  a  surface  brilliancy  equal  to  that  of  the  ceiling  spots.  The  eTfect  of  both 
of  these  devices  would  be  to  lower  the  surface  brilliancy  for  a  given  light  flux 
by  increasing  the  area  of  the  luminous  surface.  Whether  either  would  be  advisable 
from  other  standpoints   we  are  not  at  present  prepared   to  say. 


422     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Results  will  be  given  in  this  paper  only  for  the  position  with 
six  fixtures  in  the  field  of  view.  The  results  for  the  other  posi- 
tions will  be  given  in  a  later  paper.  When  working  at  the  posi- 
tion with  six  fixtures  in  the  field  of  view,  our  tests  show  that  the 
eye  loses  practically  nothing  in  efficiency  as  the  result  of  three  to 
four  hours  of  work  under  daylight,  it  loses  enormously  for  the 
same  period  of  work  under  the  direct  installation,  and  almost  as 
much  under  the  semi-indirect  installation.  Under  the  indirect 
installation  the  eye  loses  a  little  more  than  under  daylight,  but 
not  nearly  so  much  as  under  the  other  installations. 

The  results  of  the  work  on  distribution  are  given  in  Tables 
IX  and  X.  Early  in  the  work  it  was  found  that  nearly  as 
much  difference  in  result  was  gotten  for  two  as  for  three  hours 
of  work.  In  Table  IX  is  shown  the  loss  in  efficiency  for  Ob- 
server R  for  three  hours  of  work  under  the  four  systems ;  and 
in  Table  X,  the  loss  in  efficiency  for  Observer  G  for  two  hours 
of  work.  These  tables  are  typical  of  the  results  obtained  from 
all  of  our  observers  for  these  periods  of  work.16  Column  i  of 
these  tables  gives  the  type  of  lighting  system.  Column  2  gives 
the  total  wattage  of  the  lamps  used,  and  Column  3  the  voltage  at 
which  these  lamps  were  operated.  Columns  4,  5,  and  6  give  the 
foot-candles  of  illumination  at  the  point  of  work  measured  re- 
spectively in  the  horizontal,  vertical,  and  45  deg.  planes.  Column 
7  gives  the  maximal  distance  at  which  the  test  object  could  be 
seen  clearly,  and  Column  8  the  distance  chosen  at  which  to  con- 
duct the  test  for  loss  of  efficiency.  Care  was  taken  in  every  case 
to  choose  this  working  distance  of  such  a  value  that  the  ratio  it 
sustained  to  the  maximum  distance  was  always  approximately 
the  same.  Column  9  gives  the  total  time  the  test  object  was  seen 
clear  in  the  three  minutes  of  observation  and  Column  10  the  total 
time  it  was  seen  blurred.  Column  11  gives  the  ratio  of  the  total 
time  seen  clear  to  the  total  time  seen  blurred,  and  Column  12 
gives  the  comparative  values  of  these  ratios  in  terms  of  a  com- 
mon standard.  These  ratios  were  reduced  to  a  common  scale  or 
standard  in  order  to  make  the  comparison  of  the  amounts  of 

16  Obviously  in  the  consideration  of  the  effect  of  a  given  lighting  system  on 
the  ability  of  the  eye  to  hold  its  efficiency  for  a  period  of  work,  the  age  of  the 
observer  and  the  condition  of  his  eyes  should  be  taken  into  account.  For  a  full 
clinic  report  of  the  eyes  of  the  observers  employed,  see  op.  cit.,  foot-note  14,  p.  460. 


FKRREE   AND   RAND:     EFFICIENCY    OF    THE    BYE  423 

change  in  their  ratios  easier.  They  express  the  comparative 
ability  of  the  eye  to  sustain  its  power  of  clear  seeing  for  three 
minutes  before  and  after  work  for  the  four  conditions  of  light- 
ing used. 

It  will  also  be  noted  from  Column  8  of  the  above  tables  that 
the  visual  acuity  tests  show  that  acuity  of  vision  as  determined  by 
the  momentary  judgment  is  higher  for  the  same  foot-candles  of 
illumination  under  daylight  than  under  artificial  light,  and  of  the 
artificial  lights  it  is  very  slightly  highest  for  the  indirect  system, 
next  highest  for  the  semi-indirect  system,  and  slightly  lowest  for 
the  direct.  It  will  thus  be  seen  that  for  all  the  purposes  of  clear 
seeing,  whether  the  criterion  be  maximal  acuity  or  the  ability  of 
the  eye  to  hold  its  efficiency  for  a  period  of  work,  the  best  re- 
sults are  given  in  order  by  the  systems  that  give  the  best  distri- 
bution. The  effect  of  distribution,  however,  on  the  ability  of  the 
fresh  eye  to  see  clearly,  is  not  nearly  so  great  as  it  is  on  its  power 
to  hold  its  efficiency  for  a  period  of  work. 

In  order  to  give  a  typical  representation  in  graphic  form  of 
the  effect  on  the  efficiency  of  the  eye  of  a  period  of  work  under 
these  four  conditions  of  lighting,  the  results  of  the  above  tables 
will  also  be  given  in  the  form  of  a  chart  made  up  of  straight 
lines  showing  in  each  case  the  loss  of  efficiency  from  beginning 
to  close  of  work.  In  constructing  these  charts,  the  length  of  time 
of  work  is  plotted  along  the  abscissa,  and  the  ratio  of  the  time 
the  test  object  is  seen  clear  to  the  time  it  is  seen  blurred  is 
plotted  along  the  ordinate.  Each  one  of  the  large  squares  along 
the  abscissa  represents  one  hour  of  work  and  along  the  ordinate 
an  integer  of  the  ratio.  Chart  A  shows  the  results  for  Table  IX, 
and  Chart  B  for  Table  X.  An  inspection  of  these  charts  will 
show  how  widely  different  in  amount  is  the  loss  in  efficiency 
under  the  specified  conditions  for  the  direct  and  semi-indirect 
systems  as  compared  with  the  indirect  system  and  daylight,  and 
how  close  is  the  correspondence  between  the  results  for  the 
direct  and  semi-indirect  system,  and  between  the  results  for  the 
indirect  system  and  daylight. 

The  loss  in  efficiency  found  in  the  above  work  seems  to  be 
predominantly,  if  not  entirely,  muscular,  for  the  tests  for  the 
sensitivity  of  the  retina  show  practically  no  loss  in  sensitivity 


424     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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FERKEE    AND    RAND:     EFFICIENCY    OF    THE    EVE 


425 


Chart  A  (Observer  R). — Showing  the  eye's  loss  in  efficiency  as  the 
ICStllt  of  three  hours  of  work  under  the  systems  of  indirect,  semi-indirect 
and  direct  lighting  employed  as  compared  with  daylight. 


Lighting  system  Watts 

A— Daylight  — 

B— Indirect 800 

C — Semi-indirect  .  ..   760 
D— Direct S80 


Foot-candles 

(folta 

Horizontal 

Vertical 

45° 

— 

5-5 

1-32 

4.2 

107 

5-2 

1.36 

3-5 

107 

5-3 

1-45 

4.0 

107 

4.2 

1.41 

2.6 

8 

D 

1  I 

Chart  A. 


Chart  B  (Observer  G). — Shows  the  eye's  loss  in  efficiency  as  the  result 
of  two  hours  of  work  under  the  systems  of  indirect,  semi-indirect  and  direct 
lighting  employed  as  compared  with  daylight. 


lighting  system  Watts 

A— Daylight — 

B — Indirect 800 

C — Semi-indirect  .  . .   760 
D— Direct 880 


Foot- 

candles 

'olts 

Horizontal 

Vertical 

45° 

— 

5-5 

'•32 

4-2 

107 

52 

1.36 

3-5 

107 

5-S 

1-45 

4.0 

107 

4.2 

I-4I 

2.6 

3 
1 


Chart  B. 


426     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

as  the  result  of  work  under  any  of  the  installations  employed.17 
The  following  reasons  are  suggested  why  the  muscles  of  the  eye 
giving  both  fixation  and  accommodation  should  be  subjected  to 
a  greater  strain  by  the  direct  and  semi-indirect  installations  than 
by  the  indirect  installation  or  daylight.  (1)  The  bright  images 
of  the  sources  falling  on  the  peripheral  retina,  which  is  in  a 
perpetual  state  of  darkness-adaptation  as  compared  with  the 
central  retina,  and  is,  therefore,  extremely  sensitive  in  its  re- 
action to  such  intensive  stimuli,  set  up  a  reflex  tendency  for  the 
eye  to  fixate  them  instead  of,  for  example,  the  letters  which  the 
observer  is  required  to  read.  (2)  Likewise  a  strong  reflex  tend- 
ency to  accommodate  for  these  brilliant  sources  of  light,  all  at 
different  distances  from  each  other  and  the  lettered  page,  is  set 
up.  (3)  These  brilliant  images,  falling  on  a  part  of  the  retina 
that  is  not  adapted  to  them,  causing  as  they  do  acute  discomfort 
in  a  very  short  period  of  time,  doubtless  induce  spasmodic  con- 
tractions of  the  muscles  which  both  disturb  the  clearness  of 
vision  and  greatly  accentuate  the  fatiguing  of  the  muscles.  The 
net  result  of  all  these  causes  is  excessive  strain  which  shows 
itself  in  a  loss  of  power  to  do  work.  In  the  illumination  of  a 
room  by  daylight,  however,  with  a  proper  distribution  of  win- 
dows, the  situation  is  quite  different.  The  field  of  vision  con- 
tains no  bright  sources  of  light  to  disturb  fixation  and  accommo- 
dation and  to  cause  spasmodic  muscular  disturbances  due  to  the 
action  of  the  intensive  light  sources  on  the  dark-adapted  and 
sensitive  peripheral  retina.  As  we  have  already  pointed  out, 
the  light  waves  have  suffered  innumerable  reflections  and  the 
light  has  become  diffuse.  The  field  of  vision  is,  comparatively 
speaking,  uniformly  illuminated,  and  there  are  no  extremes  of 
surface  brightness.  The  illumination  of  the  retina,  therefore, 
falls  off  more  or  less  gradually  from  center  to  periphery,  as  it 
should  to  permit  of  fixation  and  accommodation  for  a  given 
object  with  a  minimum  amount  of  strain. 

11  In  the  next  paper  of  the  series  it  is  shown  (see  op.  cit.  pp.  484-490)  that  the 
loss  in  muscular  efficiency  is  confined  largely  to  the  accommodation  muscles.  The 
fixation  muscles  apparently  suffer  little  loss  for  the  period  of  work  we  have  used. 


FERREE   AND   RAND:     EFFICIENCY  OF   THE    BYE  427 

III.  THE  EFFECT  OF  VARIATION  IN  THE  INTENSITY  OF 
LIGHT  ON  THE  EFFICIENCY  OF  THE  EYE  FOR  A 
PERIOD  OF  WORK. 

It  is  not  our  purpose,  however,  to  contend  that  distribution 
of  light  and  surface  brightness  in  the  field  of  vision  is  the  only 
factor  of  importance  in  the  illumination  of  a  room.  The  in- 
tensity and  quality  of  light  must  also  be  taken  into  account.  For 
example,  one  of  the  most  persistent  questions  asked  by  the  il- 
luminating engineer  is :  "How  much  light  should  be  used  with  a 
given  lighting  installation  to  give  the  best  results  for  seeing?" 

We  have  undertaken,  therefore,  to  determine  the  most  favor- 
able range  of  intensity  for  the  four  types  of  lighting  we  have 
used.     Our  work   shows   in  general   the   following   results.     A 
very  wide  range  of  intensity  is  permissible  for  daylight,  and  a 
comparatively    wide    range    for   the    indirect    installation.      For 
the  semi-indirect  installation  the  eye  fell  off  heavily  in  efficiency 
for  all  intensities  with  exception  of  a  narrow  range  on  either 
side  of  2.2  foot-candles  measured  at  the  level  of  the  eye  at  the 
point  of  work  with  the  receiving  surface  of  the  photometer  in 
the   horizontal  plane.     For  the   direct   installation   no   intensity 
could  be  found  for  which  the  eye  did  not  lose  a  very  great  deal 
in  efficiency  as  the  result  of  work.    Thus  it  seems  that  the  factors 
we   have   grouped   under   the   heading    distribution    are    funda- 
mental.    That  is,  if  the  light  is  well  distributed  and  diffuse,  as  it 
was  in  case  of  the  daylight  and  indirect  installations  we  used, 
and  there  are  no  extremes  of  surface  brightness,  the  ability  of 
the  eye  to  hold  its   efficiency  is,   within  limits,  independent   of 
intensity.     In   short,  the   retina  is  itself  highly  accommodative 
or  adaptive  to  intensity,  and  if  there  is  the  proper  distribution 
and  diffuseness  of  light  and  the  proper  gradation   of   surface 
brightness  in  the  field  of  vision,  the  conditions  are  not  present 
which  cause  strain  and  consequent  loss  in  efficiency  in  the  ad- 
justment of  the  eye.     The  results  of  this  series  of  tests,  then, 
accomplish  two  purposes,     (i)   They  show  that  when  the  dis- 
tribution and  diffuseness  of  light  and  the  distribution  of  surface 
brightness  in  the  field  of  view  are  properly  taken  care  of,  the 
eye,  so  far  as  the  problem  of  lighting  is  concerned,  is  practically 
independent  of  intensity.     And  (2)  they  show  the  effect  on  the 
efficiency  of  the  eye  of  the  variations  in  surface  brightness  pro- 


428     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

duced  by  varying  intensity  in  case  of  the  direct  and  semi-indirect 
installations  we  have  used. 

The  tests  were  made  in  the  same  room,  with  the  same  fixtures, 
and  in  general  with  the  same  conditions  of  installation  and  meth- 
ods of  working  as  were  described  in  the  work  on  distribution. 
To  secure  the  various  degrees  of  intensity  needed,  lamps  of 
different  wattage  were  used.  These  were  selected  from  a  series 
of  tungsten  lamps  ranging  from  15-100  watts.  In  order  to  keep 
the  distribution  factor  as  nearly  constant  as  possible  for  a  given 
type  of  system,  the  lamps  used  in  making  the  test  for  that  type 
of  system  were  all  of  one  wattage,  i.  e.,  all  15's,  25's,  40's,  6o's, 
or  ioo's. 

For  the  semi-indirect  system  the  total  range  of  intensity  of 
illumination  employed  is  shown  by  the  following  figures.  The 
series  was  begun  with  25-watt  lamps18  and  consisted  of  25,  40, 
60,  and  100-watt  lamps.19  For  the  25-watt  lamps  the  photometer 
reading  at  the  point  of  work  with  the  receiving  test  plate  of 
the  photometer  in  the  horizontal  plane,  showed  1.6  foot-candles; 
with  the  test  plate  in  the  vertical  position  0.45  foot-candle;  in 
the  45  deg.  position  1.15  foot-candles.  For  the  100-watt  lamps. 
6.8  foot-candles  were  obtained  with  the  test  plate  horizontal ; 
1.82  foot-candles  with  the  test  plate  vertical;  and  4.5  foot-candles 
with  it  in  the  45  deg.  position.  The  tests  for  loss  in  efficiency20 
showed  that  the  intensity  most  favorable  to  the  eye  was  secured 

18  Since  the  most  favorable  intensity  was  given  by  the  40-watt  lamps  and  since 
the  15-watt  lamps  gave  so  little  light  as  to  be  extremely  trying  to  the  eyes,  it  was 
thought  best  to  begin  the  series  with  the  25-watt  lamps  instead  of  the  15  as  was 
done  in  case  of  the   direct   system. 

19  Owing  to  their  smaller  size,  socket  extenders  had  to  be  used  for  the  25  and 
40-watt  lamps.  That  is,  without  the  extenders  these  lamps  came  so  low  in  the  re- 
flector  as   to   change   the   distribution   effects    given    by   the   reflector. 

20  In  conducting  these  tests  it  was  found  necessary  to  allow  a  period  of 
adaptation  without  work  to  the  illumination  of  the  room  before  the  first  test  was  taken. 
If  this  were  not  done,  especially  in  case  of  the  lower  intensities  of  light  used,  the 
changing  sensitivity  of  the  eye  to  the  intensity  of  light  employed  produced  a  notice- 
able change  in  the  visual  acuity  between  the  times  the  tests  before  and  after  work  were 
taken.  Since  the  distance  of  the  test  card  was  kept  the  same  for  the  two  tests,  this 
change  in  the  visual  acuity  tended  to  influence  the  ratio:  time  clear  to  time  blurred. 
To  determine  the  length  of  time  needed  with  a  given  intensity  of  light  to  insure  a  con- 
stant acuity  so  far  as  adaptation  is  concerned,  preliminary  tests  were  made  as  follows. 
The  acuity  of  the  observer  was  taken  every  three  minutes  until  no  noticeable 
change  was  found.  This  length  of  time  was  then  always  allowed  for  that  observer 
as  an  adaptation  period  prior  to  the  loss  of  efficiency  test  conducted  for  the  intensity 
of  illumination. 


FERREE   AND   RAND:     EFFICIENCY   OF    THE    EYE  4-"J 

when  the  photometric  reading  with  the  test  plate  in  the  horizontal 
plane  showed  2.2  foot-candles ;  in  the  vertical  plane,  0.58  foot- 
candle;  and  in  the  45  deg.  plane,  1.52  foot-candles.  The  total 
wattage  in  this  case  was  only  320.  At  this  intensity  of  illumin- 
ation the  semi-indirect  installation,  so  far  as  its  effect  on  the  eye 
is  concerned,  compares  very  favorably  with  the  indirect  installa- 
tion at  such  ranges  of  intensity  as  we  have  employed.  At  in- 
tensities appreciable  higher  than  this  most  favorable  value, 
however,  or  appreciably  lower,  the  loss  in  efficiency  is  very  great. 
At  the  intensity  commonly  recommended  in  lighting  practise,  this 
semi-indirect  installation  is  almost,  if  not  quite  as  damaging  as 
the  direct  installation.  The  intensity  recommended  by  the  Il- 
luminating Engineering  Society,  for  example,  in  its  primer  issued 
in  1912,  ranges  from  2-3  to  7-10  foot-candles,  depending  upon 
the  kind  of  work ;  5  foot-candles  is  taken  as  a  medium  value. 
This  medium  value  is  more  than  double  the  amount  we  have 
found  to  give  the  least  loss  in  efficiency  for  the  type  and  installa- 
tion of  semi-indirect  lighting  we  have  used.  The  intensity  we 
have  found  to  give  the  least  loss  in  efficiency  for  this  type  of 
lighting  does  not,  however,  give  maximal  acuity  of  vision  as 
determined  by  the  momentary  judgment.  At  an  intensity  that 
does  give  maximal  acuity  of  vision  as  determined  by  the  momen- 
tary judgment,  the  eye  runs  down  rapidly  in  efficiency.  That 
is,  in  this  type  of  lighting  one  or  the  other  of  these  features  must 
be  sacrificed.  High  acuity  and  little  loss  in  efficiency  can  not 
both  be  had  at  the  same  intensity.  These  features  can  both  be 
had  only  under  daylight  and,  in  case  of  the  installations,  we  used, 
with  the  indirect  system.  However,  the  amount  of  light  we 
find  to  give  the  least  loss  in  efficiency  seems  to  be  sufficient  for 
much  of  the  work  ordinarily  done  in  the  office  or  home.  It  is 
not  enough,  though,  for  drafting  or  other  work  requiring  great 
clearness  of  detail.  By  giving  better  distribution  effects  this  sys- 
tem is  supposed  also  to  be  a  concession  to  the  welfare  of  the  eye, 
but  our  tests  show  that  this  concession  is  not  so  great  as  it  is 
supposed  to  be.  In  fact,  installed  at  the  intensity  of  illumination 
ordinarily  used,  or  at  an  intensity  great  enough  for  all  kinds  of 
work,  little  advantage  is  gained  for  the  eye  in  this  type  of  light- 
ing with  reflectors  of  low  or  medium  densities ;  for  with  these 


430     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

intensities  of  light  and  densities  of  reflector,  the  brightness  of  the 
source  has  not  been  sufficiently  reduced  to  give  much  relief  to  the 
suffering  eye.  Until  this  is  done  in  home,  office,  and  public 
lighting,  we  can  not  hope  to  get  rid  of  eye  strain  with  its  complex 
train  of  mental  and  physical  disturbances.  If  the  semi-indirect 
principle  of  lighting  is  to  be  used  with  benefit  to  the  eye,  a  density 
of  reflector  and  type  of  installation  must  be  employed  that  will 
give  a  gradation  of  brightness  in  the  field  of  view  in  conformity 
with  the  limits  of  difference  that  the  eye  can  stand  without  loss  in 
efficiency  or  comfort. 

In  case  of  the  direct  system  of  lighting,  we  were  able  to  im- 
prove the  conditions  so  far  as  loss  of  efficiency  of  the  eye  is 
concerned,  by  reducing  the  intensity  ;  but  this  system  never  proved 
to  be  so  favorable  in  this  regard  as  even  the  semi-indirect  system. 
In  the  tests  made  under  the  direct  system  care  was  taken  to  have 
the  fixtures  as  nearly  as  possible  in  the  same  position  as  they 
were  for  the  semi-indirect  system.  Our  fixtures  for  the  direct 
system  were  so  installed  that  either  one  or  two  lamps  could  be 
used  in  each  fixture,  totalling  respectively  8  and  16.  In  order 
to  get  a  wider  range  of  intensity  both  numbers  of  lamps  were 
used,  i.  e.,  one  series  was  made  with  8  lamps  and  aonther  with 
16.  Four  intensities  of  light  were  used  in  each  case.  These 
intensities  were  secured  in  the  8-lamp  system  by  using  lamps 
totalling  120,  200,  320,  and  480  watts.  The  foot-candles  at  the 
point  of  work  ranged  from  0.64  with  the  receiving  test  plate  of 
the  photometer  in  the  horizontal,  0.32  in  the  vertical,  and  0.49 
in  the  45  deg.  position  with  the  lamps  totalling  120  watts,  to  2.6 
with  the  test  plate  in  the  horizontal,  1.02  in  the  vertical,  and  2.0  in 
the  45  deg.  position  with  the  lamps  totalling  480  watts.  The  four 
intensities  were  secured  in  the  16-lamp  system  by  using  lamps 
totalling  240,  365,  400,  and  880  watts.  The  foot-candles  at  the 
point  of  work  with  the  16-lamp  system  ranged  from  1.23  with 
the  test  plate  in  the  horizontal,  0.54  in  the  vertical,  and  0.935  m 
the  45  deg.  position  with  the  lamps  totalling  240  wattts,  to  4.2 
with  the  test  plate  in  the  horizontal,  1.41  in  the  vertical,  and  2.6 
in  the  45  deg.  position  with  the  lamps  totalling  880  watts.  The 
most  favorable  intensity  was  secured  by  an  installation  that  gave 
1. 16  foot-candles  with  the  test  plate  in  the  horizontal,  0.45  in  the 


FERREE  and  rand:    EFFICIENCY  OF  THE  EYE  431 

vertical,  and  0.85  in  the  45  deg.  position.  This  intensity  was 
given  by  the  8-lamp  system  with  a  total  wattage  of  200.  At  this 
intensity,  however,  the  loss  in  the  efficiency  of  the  eye  for  three 
hours  of  work  was  almost  four  and  one-half  times  as  great  as 
for  the  most  favorable  intensity  for  the  semi-indirect  system ;  and 
more  than  four  and  one-half  times  as  great  as  for  a  wide  range 
of  intensities  for  either  the  indirect  system  or  daylight. 

The  following  specification  was  made  of  the  illumination  effects 
for  the  intensity  series.  (1)  Illumination  measurements  were 
made  for  the  highest  intensity  employed  at  the  66  stations  in 
the  test  room.  These  measurements  were  made  in  the  way  de- 
scribed in  the  preceding  section.  For  the  other  intensities  em- 
ployed, measurements  were  made  at  9  representative  stations  to 
show  in  a  general  way  the  order  of  magnitude  of  reduction 
produced  by  using  the  lamps  of  lower  wattages.  (2)  Brightness 
measurements  were  made  of  prominent  objects  in  the  room,  such 
as  the  test  card,  the  book  of  the  observer,  and  all  surfaces  show- 
ing very  high  or  very  low  brilliancy,  for  all  intensities  for  all 
systems. 

In  Table  XI  are  given  the  illumination  measurements  for  the 
highest  wattages  used  made  with  the  receiving  test  plate  of  the 
photometer  in  the  horizontal,  vertical,  and  45  deg.  planes.  Tables 
XII,  XIII  and  XIV  show  the  illumination  measurements  for 
the  other  wattages  employed  in  the  series  at  nine  representative 
stations.  These  measurements  are  intended  to  show  the  order 
of  magnitude  of  reduction  of  the  illumination  of  the  room  pro- 
duced by  using  the  lamps  of  lower  wattage.  They  conform  in 
each  case  pretty  closely,  it  will  be  noted,  to  the  simple  ratio 
of  the  wattages  employed.  Tables  XV,  XVI  and  XVII  give 
the  brightness  measurements  for  these  installations  for  the  dif- 
ferent intensities  used.  The  points  at  which  the  measurements 
were  taken  are  indicated  by  the  letters  A,  B,  C,  D,  E,  F,  etc., 
see  Figs.  8  and  9.  In  Tables  XVIII,  XIX  and  XX  are  given  the 
prominent  brightness  ratios  for  the  different  intensities  used. 
It  was  stated  in  the  preceding  section  that  the  order  of  magnitude 
of  the  brightness  scale  exerts  an  influence  on  the  effect  of  bright- 
ness ratio  on  the  eye's  loss  of  efficiency.  This  influence  is  readily 
seen  on  comparing  the  results  of  Table  XVIII  with  those  of 


432     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Table  XXI.  That  is,  while  the  various  brightness  ratios  remain 
pretty  much  the  same  for  the  different  intensities  of  light  em- 
ployed, the  least  loss  of  efficiency  was  given  by  the  40-watt  lamps. 
This  loss  was,  for  example,  very  much  less  than  was  given  by  the 
100-watt  lamps,  not  quite  so  much  less  than  was  given  by  the 
60-watt  lamps,  and  very  little  less  than  was  given  by  the  25  watt 
lamps.  The  loss  in  efficiency  for  the  25-watt  lamps  can  also 
doubtless  be  attributed  in  part  to  an  insufficient  amount  of  light. 
At  least  the  testimony  of  the  various  observers  was  that  not 
enough  light  was  given  by  these  lamps  for  ease  and  comfort 
in  reading.  The  results  of  these  experiments  seem  to  show,  then, 
that  a  given  order  of  magnitude  of  brightness  difference  in  the 
field  of  view  has  more  effect  on  the  efficiency  of  the  eye  when 
the  general  scale  of  brightness  values  is  higher  than  when  it  is 
low. 

A  comparison  of  Tables  XIX  and  XX  with  Tables  XXII  and 
XXIII  shows  the  influence  of  the  area  of  the  bright  surface  on 
the  ability  of  the  eye  to  hold  its  efficiency  for  a  period  of  work. 
For  example,  although  it  is  shown  in  Table  XIX  that  the  ratios : 
lightest  surface  to  darkest  surface,  and  lightest  surface  to  test 
card  and  reading  page,  are  greater  in  the  16-lamp  system  for  the 
15  than  for  the  25-watt  lamps,  Table  XXII  shows  that  greater 
loss  of  efficiency  is  caused  by  the  25-watt  lamps.  Similarly, 
Table  XX  shows  that  in  the  8-lamp  system  these  ratios  are 
greater  for  the  25  and  40  than  for  the  60-watt  lamps,  while 
Table  XXIII  shows  that  the  60-watt  lamps  cause  the  greater  loss 
in  efficiency.  This  may  be  explained  as  follows.  The  brightest 
surfaces  in  the  field  of  vision  for  the  direct  system  are  the  fila- 
ments of  the  lamps.  The  brightness  measurements  given  in  the 
table  are  in  terms  of  candlepower  per  square  inch.  The  candle- 
power  per  square  inch  is  the  same,  for  example,  for  the  filaments 
of  the  15  as  for  those  of  the  25-watt  lamps.  But  since  the  darkest 
surfaces,  the  test  card,  and  the  reading  page,  are  darker  for  the 
15-watt  than  for  the  25-watt  system,  the  ratios:  lightest  to 
darkest  surface,  lightest  surface  to  test  card,  and  lightest  sur- 
face to  reading  page,  are  greater  for  the  15  than  for  the  25-watt 
system.  While,  however,  the  candlepower  per  square  inch  is  the 
same  for  the  15  as  for  the  25-watt  filaments,  the  actual  candle- 


FERREE    AND    RAND:     EFFICIENCY    OF    THE    EYE  433 

power  is  less  for  the  15-watt  filaments  because  of  their  smaller 
area  of  surface.  That  is,  the  area  of  the  brilliant  surface  or 
in  terms  of  luminous  effects,  its  actual  candlepower  must  be 
taken  into  account  in  estimating  the  effect  on  the  eye  as  well  as 
the  candlepower  per  square  inch.  The  effect  of  area  on  sensa- 
tion is  well  known  in  physiological  optics  (for  example,  see 
Abney,  Philos.  Trans.,  1897,  CXC,  A,  p.  169),  and  is  expressed 
in  the  law  that  within  limits  an  increase  of  area  of  the  stimulus 
functions  as  an  increase  of  intensity,  although  not  in  a  simple 
ratio.  Apparently,  too,  in  its  effect  on  the  eye's  power  to  main- 
tain its  efficiency  for  a  period  of  work,  an  increase  of  area  of 
the  brilliant  surface  also  functions  within  limits  as  an  increase 
in  intensity.21  Ratios  expressed  in  candlepower  per  square  inch 
do  not  seem  therefore,  in  all  cases  to  be  an  adequate  specification 
of  surface  brightness,  so  far  as  its  effect  on  the  efficiency  of  the 
eye  is  concerned,  unless  the  areas  compared  be  the  same. 

21  The  above  explanation  is,  however,  not  complete.  It  shows  only  that  the 
ratios:  lightest  to  darkest  surface,  and  lightest  surface  to  test  card  and  reading 
page,  are  greater  for  the  is  than  for  the  25-watt  lamps  because  the  candlepower 
per   square   inch   not  the   actual   candlepower   was   used   in  computing  the   ratios. 

We  are  not  at  present  able  to  give  the  ratio  of  actual  candlepower  of  lightest  to 
darkest,  lightest  to  reading  page,  etc.,  because  we  did  not  measure  the  actual  candle- 
power  of  the  darkest  surface,  the  reading  page,  etc.,  only  the  candlepower  per 
square  inch.  However,  since  the  test  card  and  the  reading  page  were  of  the  same  area 
in  case  of  the  different  intensities,  and  the  darkest  surface  of  approximately  the  same 
area,  ratios  based  on  the  total  candlepower  of  the  lightest  surface  (the  lamp 
filament)  and  the  candlepower  per  square  inch  of  the  darkest  surface,  test  card,  and 
reading  page  have  comparative  values.  These  ratios  are  very  little  different  for  the 
15-  and  25-watt  lamps.  That  is,  the  ratio  lightest  to  darkest  for  the  15-watt 
lamps  zzz  28,698,  for  the  25-watt  lamps  =3  28,933;  lightest  to  test  card  for  the 
15-watt  lamps  =r  11,828,  for  the  25-watt  lamps  zzs  12,616;  lightest  to  reading  page 
for  the  15-watt  lamps  z=z  7,352;  for  the  25-watt  lamps  zzz.  7,483. 

A  complete  explanation  of  the  result  will  doubtless  involve  two  factors  (1)  the 
ratio  of  the  actual  candlepower  of  the  lightest  and  darkest  surfaces;  and  (2)  the 
point  brought  out  in  connection  with  Tables  XVIII  and  XXI,  namely  that  a  given 
order  of  magnitude  of  brightness  difference  in  the  field  of  view  has  more  effect  on 
the  loss  of  efficiency  of  the  eye  when  the  general  scale  of  brightness  values  is  high 
than  when  it  is  low.  From  this  we  would  expect,  for  example,  that  if  the  ratio 
lightest  to  darkest  surface  and  lightest  surface  to  test  card  and  reading  page  were 
equal  or  approximately  so  for  the  25-  and  15-watt  lamps,  for  example,  the  greater 
loss  of  efficiency  should  come  with  the  lamps  of  higher  wattage.  Similarly  for  the 
8-lamp  system,  the  60-  and  40-watt  lamps  should  cause  a  greater  loss  of  efficiency 
than  the  25-watt  lamps.  The  15-watt  lamps  with  this  system  gave  too  little  light  to 
read    with    ease    and   comfort    hence    are    ruled    out   of  count   in   the   comparison. 

For  investigating  in  detail  the  effect  of  area  of  the  brilliant  surface  on  the  eye's 
loss  of  efficiency,  the  campimeter  may  prove  of  convenience  and  of  service.  This  is 
one  of  the  instances  where  the  abstract  may  be  used  to  advantage  to  supplement  the 
concrete  method  of  investigation.  (See  Memorandum  on  the  Report  of  the  Research 
Committee,  Trans.  I.   E.   S.,   1914,  Vol.  IX,   No.   4.  p.   358.) 

The  great  difficulty  with  the  abstract  type  of  investigation,  as  the  writers  see  the 
case  at  this  time,  is  that  a  determination  of  what  is  permissible  with  regard  to  one 
factor  in  isolation  may  not  be  at  all  permissible  in  conjunction  with  other  factors. 
A  more  feasible  plan  seems  to  us  to  be  to  vary  the  factor  over  a  certain  practical 
range  in  an  actual  concrete  situation.  By  a  proper  selection  of  the  concrete  situations 
employed  the  ground  of  all  that  is  practicable  in  lighting'  can  be  covered,  and  the 
results  obtained  can   have   a   safe   application. 


434     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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FERREE   AND   RAND:     EFFICIENCY   OF   THE    EYE 


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436     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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FERREE    AND    RAND:     EFFICIENCY   OF   THE    BYE 


437 


TABLE  XII.  — (Intensity  Series.) 
Showing  the  illumination  measurements  in  foot-candles  at  nine  representa- 
tive stations  for  the  different  intensities  used  for  the  semi-indirect  system. 


Horizontal 

Vertical 

45° 

Station 

800 
watts 

480 
watts 

320 
watts 

200 
watts 

800 

watts 

480 

watts 

320 
watts 

200 
watts 

800        480        320 
watts  watts ;  watts 

200 
watts 

Card  .... 

12 

16 

3i 

34 

39 

45 

54 

58 

Average . 

6.8 
2.9 
6.8 

7-4 
4.6 

4-4 
6.8 
2.47 

5-2 

4-44 

3-3 
1.79 

3-2 

3-6 

2.1 

1.79 

3-3 

1.31 

2.82 

2.66 

2.2 
I.O 
2.0 
2.2 

1-45 
1. 17 
2.2 
O.87 

r-9 

I.78 

1.6 

o.75 

1.32 

1.6 

o.95 

o-93 

1.4 

0.7 

1.44 
1. 11 

I.82 

0.55 
0.69 
2.2 
1.76 

1-95 
2.65 

1.77 
2.6 

i-93 

O.94 

0.35 

0.44 

O.94 

0.9 

0.86 

i-3 

1. 15 
i-35 

1. 16 

O.58 
O.22 
O.23 
O.58 
O.58 

0-54 
0.82 
O.62 
O.87 
O.77 

0.45 
0.17 

O.I5 
O.44 

0.43 
O.41 
0.58 
0.48 
0.63 
0.48 

4-5 
I.49 
36 
5-2 

3-4 

3.68 

5-6 

2.65 

5.28 

4-°3 

2.4 

0.76 

1-75 

2.4 

1.68 

1-52 

2.7 

1.47 
2.68 

2.42 

1-52 
0.51 

1.03 

i-53 
1. 12 

o-95 

1-7 
o-95 
1.8 
1. 61 

115 

0.4 

0.68 

115 
0.74 

0.73 
1. 19 
0.76 

1-3 

1. 01 

TABLE  XIII.— (Intensity  Series.) 
Showing  the  illumination  measurements  in  foot-candles  at  nine  representa- 
tive stations  for  the  different  intensities  used  for  the  direct  system  (16  lamps). 


Station 


Card  •  •  - 

12 

16 

3i 

34 

39 

45 

54 

58 

Average 


Horizontal 


400 
watts 


1.86 

2.6 

4.0 

2.1 

2-35 

2-7 

2.2 

4.0 

4-3 

2.14 


365        240 
watts     watts 


2.1 
1-45 
4-4 
2.1 

2-3 
2.6 

i-75 
1.6 

2-3 


1.23 

1-43 
2.6 

i-45 
1.84 

i-5 

1-45 

1-34 

2-5 

1.26 


Vertical 


400 
watts 


0.8 

O.44 

O.47 

O.81 

1. 41 

1.44 

1.27 

2.1 

1.88 
1. 12 


365 
watts 


240 
watts 


0.6 

0.275 

0.34 

0.735 

I.49 

i-55 

i-3 

I.I3 

1-25 


o.54 
0.265 

0.385 
o-575 
1.08 
0.825 

o.77 
0.78 
1.02 
0.67 


400        365 

watts      watts 


I.46 

I.42 

2.4 

1.6 

2.1 

2.2 

2.1 

3-2 

3-35 

2.06 


1-33 
0.68 

2.4 
1.68 

2-5 

2.4 

1-95 

1.64 

2.1 


240 
watts 


o-935 
0.85 

1-55 
1.1 
1-57 
1. 19 
1.23 
1.38 
2.1 
1. 21 


43§     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


TABLE  XIV.— (Intensity  Series.) 
Showing  the  illumination  measurements  in  foot-candles  at  nine  representa- 
tive stations  for  the  different  intensities  used  for  the  direct  system  (8  lamps). 


Horizontal 

Vertical 

45° 

Station 

4  So 

WilttS 

320  |    200 
watts  j  watts 

120 

watts 

480 
watts 

320 

watts 

200 
watts 

120 
watis 

480 

watts 

320 
watts 

200 
watts 

120 
watts 

Card 

12 

16 

3i 

34 

39 

45 

54 

53 

Average. 

2.6 
2.8 

4-4 

2.95 

2.65 

3-o 

3-6 
3-o 
4.4 
2.72 

I.97 

I.94 

2.8 

2.1 

I.76 

2.2 

2.1 

2.2 

3-1 
I.8l 

16 
36 

2.4 

i-34 

1-3 

1-25 

1.2 

1.22 

2.1 

'•13 

O.64 

O.69 

1.22 

O.7I 

O.76 

O.7 

O.69 

0.6S 

1.3 

0.68 

I.02 

0.45 
O.4I 
I.06 

i-35 

i-5 

i-54 

■•54 

1.69 

1.48 

O.65 

O.4I 

O.36 

O.7I 

I. OI 

I.O 

I.07 

I.I 

1.22 

O.99 

0.45 

0.2I 

0.2 

0.2S 

0.92 

O.66 

0.72 

o-59 

o.77 

0.62 

0.32 
0.15 

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0.32 

0.4 

0.44 

0.46 

0.4 

0.52 

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1-7 
2.4 

2-35 

2.2 

2.6 

2-35 
3-* 
3-6 
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1-39 

1. 12 

1  88 

1-45 

1-45 

1.8 

1.84 

2.4 

2-5 

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O.85 
O.76 

1.44 
I.03 
I.24 
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1-  '5 
1. 18 
1.6S 
0.47 

0  45 

O.41 

0.66 

0.6 

0.56 

O.65 

0.65 

I.63 

O.96 

0.28 

TABLE  XV.— (Intensity  Series.) 
Showing  the  brightness  measurements  in  candlepower  per  square  inch  for 
the  different  intensities  used  for  the  semi-indirect  system  at  points  indicated 
by  the  letters  A,  B,  C,  D,  etc.,  see  Fig.  3,  Further  Experiments  on  the  Effi- 
ciency of  the  Eye,  etc.,  Trans.  I.  E.  S.  (1915),  vol.  X,  p.  452b. 


A 

B    

C    

D   

E  

F    

G   

H 

I 

J 

K 

L 

M 

N   

O 

P      

X  

Reading  page  horizontal  . 
Reading  page  450  position 


800  watts 


0.6S7 

0.0461 

0.0858 

0.0461 

0.00264 

0.0034 

0.0058 

0.00662 

0.00638 

0.00149 

0.00462 

0.00255 

0.00572 

O.002S6 

0.00704 

0.00616 

0.003432 

0.0107 

0.00654 


480  watts 


0.370 

0.0219 

0.0504 

0.0219 

0.00177 

0.001S7 

0.00242 

0.00259 

0.00237 

0.00076 

0.00189 

0.00173 

0.00224 

0.00173 

0.00462 

0.003196 

0.00176 

0.00462 

0.00316 


320  watts 


O.180 

o  01402 

0.0346 

0.0163 

o  0008 

0.001034 

0.00187 

0.00162 

0.00187 

O.C004S4 

0.0014 

0.0OI0S5 

0.001408 

0.001085 

0.00264 

0.00 1 9S 

0.00105 

0.0029 

0.00193 


o.  142S 

0.01008 

0.02414 

0.0100S 

0.00061 

0.000792 

0.00123 

O.COI44 

0.00123 

0.000325 

0.000902 

0.00063 

O.OOII 

0.00063 

0.00176 

0.00154 

0.000814 

0.002024 

0.00176 


TABLE  XVI.— (Intensity  Series.) 
Showing  the  brightness  measurements  in  candlepower  per  square  inch  for 
the  different  intensities  used  for  the  direct  system  (16  lamps)  at  points  indi- 
cated by  ihe  letters  A,  B,  C,  D,  etc.,  see  Fig.  2,  Further  Experiments  on  the 
Efficiency  of  the  Eye,  etc.,  Trans,  of  the  I.  E.  S.,  1915,  X.  p.  452a. 


B    

C    

D   

E 

F   

G  

H 

I 

J 

K   

L   

M 

N  

O 

P    

Q  

x 

Reading  page  horizontal  .  . 
Reading  page  450  position 


400  watts 


A 1000.00000 

o.  rSoj 

0.002.53 

0.00277 

0.00097 

0.00277 

0.00303 

0.00303 

0.00316 

0.00075 

0.00252 

0.00191 

0.00273 

0.00176 

0.0026 

0.00215 

0.00184 

0.00172 

0.00396 

0.0029 


3*5  watts 


IOOO.OOOOO 
O.1232 
0.00/51 
o  oor45 
0.00067 
0.00185 
0.00246 
0.00229 
0.00216 
0.0004 
0.00167 
0.00149 
0.00198 
0.00145 
0.00242 
0.00167 
0.00103 
0.00132 
o  00405 
0.00273 


240  waits 


IOOO.OOOOO 
O.  1232 
0.0015  I 
O.OOII9 
O.OOO545 
O.OOI56 
O.OOI72 
O.OOI74 
O.OOI8 
O.OO0453 
O.OOI76 
O.OOI54 
O.OOI94 
O.OOI36 
0.00143 
o. 001 19 
0.00103 
0001 
0.00211 
0.00176 


TABLE  XVII. —(Intensity  Series). 
Showing  the  brightness  measurements  in  candlepower  per  square  inch  for 
the  different  intensities  used  for  the  direct  system  (8  lamps)  at  points  indi" 
cated  by  the  letters  A,  B,  C,  D.  etc.,  see  Fig.  2,  Further  Tests  for    the   Effr 
ciencv  of  the  Eve,  etc.,  Trans,  of  the  I.  E.  S.,  1915,  X,  p.  452a. 


A 

B 

C 

D 

E 

F 

G 

H    

I    

J    

K    

L 

M    

N 

O 

P 

Q 

X  •• 

Reading  page  hori 
zontal  

Reading  page  45' 
position 


4S0  watts 


IOOO.OOOOO 

0.2953 

0.00317 

0.00454 

o.  00 1 848 

0.00198 

0^0347 

0.00391 

0.00405 

0.00069 

o  00308 

0.00229 

0.00387 

0.00192 

0.00246 

o  00192 

0.00325 

0.002376 

0.00528 

0.003696 


320  watts 


IOOO.OOOOO 

0.2398 

0.00299 

0.0033 

0.00118 
0.00272 
0.00361 

0.00334 

0.0029 

0.00046 

0.00167 

0.00141 

0.00229 

0.00128 

0.00252 

0.00185 

0.00222 

0.00141 

0.00334 

0.0022 


1000.00000 

0.1657 

0.00154 
0.00185 
0.00059 
0.00145 
0.00 r 89 
0.00122 
0.00167 
0.00037 
0.00122 
0.00103 
0.00141 
0.00096 
0.00101 
0.00083 
0.00136 
0.000924 

0.OJ229 

0.00149 


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0.0S998 
0.00097 
0.000704 
0.0003 
o.  00063 
0.00074 
0.001 1 
0.00092 
0.00023 
0.00073 
0.00056 
0.00068 
0.00054 
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0.00051 
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0.00077 


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FERREE    AND   RAND:     EFFICIENCY   OF   THE    EYE 


445 


Chart  P.—  Showing  the  effect  on  the  efficiency  of  the  eye  of  varying  the 
intensity  of  light  for  the  semi-indirect  system  of  lighting.  Foot-candles  at 
the  point  of  the  test  card  are  plotted  along  the  abscissa;  loss  of  efficiency 
along  the  ordinate.  X  =  points  where  the  change  in  intensity  was  pro- 
duced by  changing  the  voltage  (see  Table  XXI). 


2  3  4  5  6  7 


Chart  F. 


Chart  G.— Showing  the  effect  on  the  efficiency  of  the  eye  of  varying  the 
intensity  of  light  for  the  direct  system  of  lighting.  Foot-candles  at  the 
point  of  the  test  card  are  plotted  along  the  abscissa;  and  loss  of  efficiency 
along  the  ordinate.     A  =  curve  for  16  lamps;  B,  for  8  lamps. 


i 

' — i 

z 

A, 

3 

c 

> 

I 

i 

i 

y 

5 

Chart  G. 


446     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  results  of  the  tests  for  the  intensity  series  are  shown 
in  Tables  XXI-XXIII.  Three  hours  was  ^elected  as  the  period 
of  work  in  all  of  these  experiments.  Briefly  stated  the  procedure 
was  as  follows.  First  the  most  favorable  intensity  was  deter- 
mined and  then  variations  were  made  on  either  side  of  this 
intensity  until  it  was  certain  that  the  characteristic  effect  of 
increase  and  decrease  of  illumination  was  obtained.  Table  XXI 
gives  the  results  for  Observer  R  under  the  semi-indirect  system. 
Seven  variations  of  intensity  were  used.  These  results  are  typical 
of  the  effect  of  variations  of  intensities  for  this  system.  Tables 
XXII  and  XXIII  show  the  results  for  the  direct  system  for  the 
same  observer.  For  the  direct  system  the  most  favorable  inten- 
sity, it  will  be  noted,  was  secured  with  the  8-lamp  system  with 
a  total  wattage  lower  than  could  be  gotten  with  the  16-lamp 
system,  i.  e.,  a  system  totalling  200  watts  caused  the  least  loss  of 
efficiency  to  the  eye,  while  240  was  the  smallest  total  of  wattage 
that  could  be  secured  with  the  16-lamp  system. 

Charts  have  been  constructed  also  to  give  a  graphic  representa- 
tion of  these  tables.  Chart  C  shows  the  results  of  Table  XXI ; 
Chart  D,  of  Table  XXII ;  and  Chart  E,  of  Table  XXIII. 

In  these  charts  loss  of  efficiency  was  plotted  against  time  of 
work.  In  Charts  F  and  G  loss  of  efficiency  is  plotted  against 
intensity  of  light  in  foot-candles  at  the  point  of  the  test  card. 
Chart  F  shows  the  results  for  Table  XXI ;  Chart  G  for  Tables 
XXII  and  XXIII. 

IV.  CONCLUSION. 
Two  facts  may  be  emphasized  at  this  point.  ( 1 )  Of  the  light- 
ing factors  that  influence  the  welfare  of  the  eye,  those  we  have 
grouped  under  the  heading  distribution  are  apparently  funda- 
mental. They  seem  to  be  the  most  important  we  have  yet  to  deal 
with  in  our  search  for  the  conditions  that  give  us  the  minimum 
loss  of  efficiency  and  the  maximum  comfort  in  seeing.  If,  for 
example,  the  light  is  well  distributed  in  the  field  of  vision  and 
there  are  no  extremes  of  surface  brightness,  our  tests  seem  to 
indicate  that  the  eye,  so  far  as  the  problem  of  lighting  is  con- 
cerned, is  practically  independent  of  intensity.  That  is,  when  the 
proper  distribution  effects  are  obtained,  intensities  high  enough 
to   give   maximum    discrimination   of   detail   may   be   employed 


FERREE  and  rand:    EFFICIENCY  OF  THE  EYE  447 

without  causing  appreciable  damage  or  discomfort  to  the  eye. 
(2)  For  the  kind  of  distribution  effects  given  by  reflectors  of 
the  type  employed  in  our  direct  and  semi-indirect  installations, 
our  results  show  that  unquestionably  too  much  light  is  being  used 
for  the  welfare  of  the  eye. 

Before  concluding  cur  paper  we  wish  again  to  state  that  the 
units  we  have  employed  were  not  selected  as  fully  representative 
of  the  classes  direct,  semi-indirect,  and  indirect.  Agreement  in 
fact  has  not  yet  been  reached  with  regard  to  what  falls  within 
each  of  these  classes.  The  units  employed  were  chosen  rather 
to  show  the  effect  on  the  ability  of  the  eye  to  maintain  its  ef- 
ficiency for  a  period  of  work  of  varying  the  factors  we  have 
grouped  under  the  heading  distribution.  We  hope  ultimately  to 
determine  the  limits  between  which  each  of  these  factors  may  vary 
without  damage  to  the  eye  in  a  selected  range  of  lighting  situa- 
tions, especially  the  factor  surface  brightness.  These  most  fav- 
orable conditions  will  then  serve  as  a  goal  to  be  attained  what- 
ever principle  of  lighting  is  employed. 

Our  next  step  in  this  division  of  the  work  will  be  to  determine 
the  effect  on  loss  in  efficiency  of  using  reflectors  of  different 
degrees  of  opacity  when  the  light  is  distributed  to  the  plane  of 
work  both  by  the  direct  and  indirect  principles  of  lighting. 
That  is,  reflectors  of  different  densities:  prismatic,  alba,  opalux, 
totally  opaque,  etc.,  will  be  used  turned  up  and  down.  In  each 
case  the  installation  will  be  made  with  special  reference  to  giving 
the  best  results  obtainable  for  the  particular  type  of  unit  em- 
ployed; and  the  factors:  evenness  of  illumination,  diffuseness  of 
light,  the  angle  at  which  the  light  falls  on  the  work,  and  the 
evenness  of  surface  brightness  will  be  varied  separately  in  turn, 
and  the  effect  on  loss  of  efficiency  will  be  determined.  More- 
over, if  it  is  found  that  the  factors  in  question  can  not  be  studied 
in  sufficient  detail  in  the  concrete  lighting  situation,  the  work 
will  be  supplemented  by  more  abstract  investigations.  The  re- 
sults of  this  series  of  tests  should  give  us  among  other  things, 
for  example,  a  still  better  idea  of  what  amount  of  brightness  dif- 
ference the  eye  is  adapted  to  stand,  and  the  comparative  effect  of 
different  ratios  of  surface  brightness  on  loss  of  efficiency. 


448     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

FURTHER  EXPERIMENTS  ON  THE  EFFICIENCY  OF 

THE   EYE  UNDER  DIFFERENT  CONDITIONS 

OF  LIGHTING.* 


BY  C.  E.  FERREE  AND  G.  RAND. 


Synopsis:  This  paper  is  a  continuation  of  the  papers  presented  to 
the  Society  in  1912  and  1913.  It  describes  the  completion  of  the  plan  of 
work  outlined  in  the  preceding  papers  for  one  set  of  lighting  conditions 
for  three  of  the  tests  thus  far  devised  by  one  of  the  writers  (Ferree)  — 
namely,  a  test  of  the  ability  of  the  eye  to  hold  its  efficiency  for  a  period 
of  work ;  a  test  for  loss  of  efficiency  of  the  fixation  muscles ;  and  a  test 
for  the  comparative  tendency  of  different  conditions  of  lighting  to  produce 
discomfort.  A  report  is  also  given  of  some  miscellaneous  experiments 
related  to  the  hygienic  employment  of  the  eye  in  which  the  following 
points  are  taken  up :  the  effect  of  varying  the  area  and  conversely  the 
intrinsic  brightness  of  the  ceiling  spots  above  the  reflectors  of  an  indirect 
system  of  lighting;  the  effect  of  varying  the  angle  at  which  the  light 
falls  on  the  work  in  a  given  lighting  situation ;  the  effect  of  using  an 
opaque  eye  shade  with  dark  and  light  linings  with  each  of  the  installations 
of  artificial  lighting  employed  in  this  and  the  previous  work;  the  effect 
on  the  efficiency  of  the  fixation  muscles  of  three  hours  of  work  under 
these  installations ;  the  effect  of  motion  pictures  on  the  eye  for  different 
distances  of  the  observer  from  the  projection  screen;  a  determination  of 
the  tendency  of  different  conditions  of  lighting  to  produce  discomfort, 
and  a  comparison  of  the  tendency  of  these  conditions  to  produce  dis- 
comfort and  to  cause  loss  of  efficiency. 


INTRODUCTION. 
The  present  paper  is  the  third  in  a  series  of  papers  presented 
to  this  Society  on  the  subject  of  lighting  in  its  relation  to  the 
eye.  In  the  first  paper  of  this  series1  it  was  pointed  out  that  if 
we  are  to  make  a  comparative  study  of  the  effect  of  different 
conditions  of  lighting  on  the  eye,  we  must  have  a  means  of 
estimating  effects.     Work  was  described  in  this  paper  in  which 

*  A  paper  read  at  the  eighth  annual  convention  of  the  Illuminating  Engineering 
Society,  Cleveland,  O.,  September  21-24,  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  oj 
opinions  advanced  by  contributors. 

1  Tests  for  the  Efficiency  of  the  Eye  Under  Different  Systems  of  Illumination  and 
a  Preliminary  Study  of  the  Causes  of  Discomfort,  Trans.  I.  E.  S.,  vol.  VIII,  1913,  pp.  40-60. 


FERREE   AND   HAND:     EFFICIENCY    OF   TIIK    EYE  449 

the  tests  already  known  to  physiological  optics  had  been  applied 
to  the  problem  with  negative  results.  New  tests  were  proposed 
and  brief  results  were  given  to  show  their  feasibility  for  the 
problem  in  hand  and  to  some  extent  their  sensitivity.  The  sug- 
gestion was  made  that  a  systematic  investigation  of  the  effect  of 
different  conditions  of  lighting  on  the  eye  should  include  a  study 
of  the  following  points:  (1)  the  efficiency  of  the  fresh  eye,  (2) 
the  loss  of  efficiency  as  the  result  of  a  period  of  work,  and  (3) 
the  tendency  to  produce  discomfort.  In  the  second  paper  of 
the  series,2  presented  to  the  Society  last  year,  a  plan  of  work  was 
outlined  and  in  part  carried  out  in  which  the  first  two  of  the 
above  points  were  covered  for  a  given  set  of  lighting  conditions. 
The  following  factors  of  importance  to  the  eye  were  enumerated : 
the  evenness  of  illumination,  the  diffuseness  of  light,  the  angle 
at  which  the  light  falls  on  the  object  viewed,  the  evenness  of 
surface  brightness,  intensity  and  quality.  The  first  four  of  these 
factors  are  very  closely  interrelated  and  are  apt  to  vary  together 
in  a  concrete  lighting  situation,  although  not  in  a  1  :  1  ratio.  It 
was  convenient,  therefore,  for  the  purpose  of  this  first  investiga- 
tion, which  was  primarily  explorative  in  character,  to  group  them 
together  under  one  heading  and  to  refer  to  them  as  distribution 
factors.  In  order  to  investigate  the  effect  of  certain  wide  varia- 
tions in  these  factors,  tests  were  conducted  under  four  types  of 
lighting  in  common  use:  one  was  the  lighting  of  a  room  by  day- 
light from  windows ;  the  others  were  the  lighting  of  the  same 
room  by  units  commonly  called  direct,  semi-indirect,  and  indirect, 
selected  to  serve  the  purposes  of  the  test.3 

2  "The  Efficiency  of  the  Eye  Under  Different  Conditions  of  Lighting — The  Effect 
of  Varying  the  Distribution  Factors  and  Intensity."  Trans,  of  the  111.  Eng.  Soc, 
1915,  vol.   X,  pp.  407-447. 

■  According  to  the  plan  as  the  investigation  proceeds,  the  effect  of  varying  each 
of  these  factors  separately  will  be  studied.  Xo  especial  attempt  was  made  to  do 
this  in  the  previous  study.  In  making  the  experimental  variations  necessary  to  the 
investigation,  it  was  stated  as  our  purpose  to  keep  as  close  as  possible  to  actual 
lighting  situations.  More  abstract  investigations  will  be  resorted  to  only  when  it 
becomes  necessary  to  supplement  the  results  by  details  that  cannot  be  gotten  from 
the  concrete  investigation.  The  objection  to  the  abstract  type  of  investigation,  as 
the  writers  see  the  case  at  the  present  time,  is  that  its  results  are  very  apt  to  be 
misleading.  That  is,  what  is  permissible  with  regard  to  one  factor  in  isolation,  may 
not  be  at  all  permissible  in  conjunction  with  other  factors.  A  more  feasible  plan 
seems  to  us  to  be  to  vary  the  factor  over  a  certain  practical  range  in  actual  concrete 
situations.  By  a  proper  selection  of  the  proper  situations  employed,  the  ground  of 
all  that  is  practicable  in  lighting  may  be  covered,  and  the  results  obtained  can  have 
a  safe  application. 


450    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

For  the  systems  of  artificial  lighting  the  tests  were  made  at 
four  positions  in  the  room ;  one  at  which  six  of  the  eight  lighting 
units  employed  were  in  the  field  of  view,  one  at  which  four  were 
in  the  field  of  view,  one  at  which  two  were  in  the  field  of  view, 
and  one  at  which  none  was  in  the  field  of  view.  This  variation 
of  position  at  which  the  observation  was  made  accomplishes,  it 
was  pointed  out,  two  purposes.  ( i )  It  gives  a  more  representa- 
tive idea  of  the  difference  in  the  effect  on  the  eye  of  the  four 
types  of  lighting  employed.  And  (2)  it  shows  the  effect  of 
varying  the  number  of  surfaces  in  the  field  of  view  presenting 
brightness  differences,  more  particularly  the  number  of  primary 
sources.  The  effect  of  varying  intensity  under  each  of  the  above 
conditions  of  distribution  was  also  tested.  The  two  sets  of  ex- 
periments were  called  respectively  the  distribution  and  intensity 
series.  Results  were  given  in  the  preceding  paper  for  only  one 
of  the  above  positions  in  the  distribution  series,  and  for  only  the 
direct  and  semi-indirect  systems  for  the  intensity  series.  The  re- 
sults of  the  remainder  of  these  two  series  of  experiments,  to- 
gether with  the  report  of  some  miscellaneous  experiments  will 
constitute  the  subject  matter  of  the  present  paper.  In  these 
miscellaneous  experiments,  the  following  points  have  been  taken 
up :  the  effect  of  varying  the  area  and  conversely  the  intrinsic 
brightness  of  the  ceiling  spots  above  the  reflectors  for  the  indirect 
system ;  the  effect  of  varying  the  angle  at  which  the  light  falls  on 
the  work ;  the  effect  of  using  an  eye  shade  with  dark  and  light  lin- 
ings with  each  of  the  three  installations  of  artificial  lighting;  the 
effect  on  the  efficiency  of  the  fixation  muscles  of  the  eye  of  three 
hours  of  work  under  each  of  the  conditions  of  lighting  described 
in  the  distribution  and  intensity  series ;  the  effect  of  motion 
pictures  on  the  eye  for  different  distances  of  the  observer  from 
the  projection  screen;  a  determination  of  the  tendency  of  each 
of  the  conditions  of  lighting  that  have  been  used  in  these  ex- 
periments to  produce  discomfort,  and  a  comparison  of  the  tend- 
ency to  produce  discomfort  and  to  cause  loss  of  efficiency.  Be- 
sides including  some  additional  matter,  these  experiments,  in 
connection  with  those  of  the  preceding  paper,  complete  the 
plan  of  work  we  had  outlined  for  one  set  of  lighting  conditions 
for  three  of  the  tests  we  have  thus  far  devised,  namely,  a  test 


FERREE   AND   RAND:     EFFICIENCY    Of    THE    EYE  451 

for  the  ability  of  the  eye  to  hold  its  efficiency  for  clear  seeing 
for  a  period  of  work,  a  test  for  loss  of  efficiency  of  the  fixation 
muscles,  and  a  test  for  the  comparative  tendency  of  the  different 
conditions  of  lighting  to  produce  discomfort,  with  the  exception 
that  in  a  further  analysis  of  the  loss  of  efficiency  caused  by 
these  lighting  conditions,  which  will  be  carried  out  in  part  by 
means  of  these  tests,  data  will  be  added  later  to  show  still  more 
clearly  the  relative  amounts  of  loss  that  are  sustained  by  the  dif- 
ferent functions  of  the  visual  apparatus. 

DISTRIBUTION  SERIES. 

As  was  pointed  out  in  the  former  paper,  in  order  to  get  the 
effect  of  variation  in  the  distribution  factors  on  the  eye's  loss  of 
efficiency  as  the  result  of  a  period  of  work,  the  test  should  be 
conducted  with  the  quality  and  intensity  of  light  made  as  nearly 
equal  as  possible.  The  quality  of  light  was  made  approximately 
the  same  for  the  three  installations  of  artificial  lighting  employed 
by  using  clear  tungsten  lamps  in  each  case.  It  was  decided  to 
make  the  intensity  of  light  as  nearly  equal4  as  possible  at  the 
point  of  test,  and  to  give  a  supplementary  specification  of  the 
lighting  effects  in  the  remainder  of  the  room  for  the  three  in- 
stallations of  artificial  light. 

At  the  point  of  test  the  light  was  photometered5  in  several 
directions.  It  was  made  approximately  equal  in  the  plane  of  the 
test  card  and  as  nearly  as  possible  equal  in  the  other  directions. 
The  specification  of  the  lighting  effects  in  the  remainder  of  the 
room  was  accomplished  as  follows :  ( I )  A  determination  was 
made  of  the  average  illumination  of  the  room  under  each  of  the 
three  installations.     The  room  was  laid  out  in  3-ft.    (0.0  m.) 

4  This  equalization  was  made  at  the  point  of  test  for  the  position  of  the  observer  with 
six  of  the  fixtures  in  the  field  of  view.  For  the  other  positions  illumination  measure- 
ments were  made  in  several  directions  at  the  test  card,  and  brightness  measurements 
were  made  of  the  surface  of  the  test  card  and  of  the  observer's  book  held  in  the  horizontal 
and  45  deg.  positions.  Equalization  could  not  have  been  made  at  all  of  these  poinls  with- 
out having  changed  the  relation  and  magnitude  of  the  distribution  factors,  which  would 
not  have  been  in  accord  with  the  purpose  of  the  test,  namely,  to  determine  the  effect  of  a 
certain  grouping  or  relation  of  these  factors  for  the  four  positions  in  the  room. 

6  We  have  not  as  yet  made  the  fuller  photometric  specifications  of  the  room  lighted  by 
daylight  with  our  present  arrangement  of  windows,  curtains,  etc.  We  hope  to  make  the 
effect  of  distribution  factors  in  daylight  illumination  (employing  windows,  skylights, 
etc.)  the  subject  of  a  future  study.  In  this  study  a  photometric  analysis  of  the  illumina- 
tion effects  produced  will  be  made  an  especial  feature. 

4 


452     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

squares  and  illumination  measurements  were  made  at  66  of  the 
intersections  of  the  sides  of  these  squares.  Readings  were  taken 
in  a  plane  122  cm.  above  the  floor  with  the  receiving  test  plate 
of  the  illuminometer  in  the  horizontal,  the  45  deg.  and  90  deg. 
positions  measuring  respectively  the  vertical,  the  45  deg.,  and 
horizontal  components  of  illumination.  The  122  cm.  plane  was 
chosen  because  that  was  the  height  of  the  test  object.  (2)  A 
determination  was  made  of  the  brightness  of  prominent  objects 
in  the  room,  such  as  the  test  card,  the  reflectors  for  the  semi- 
indirect  installation,  the  reading  page,  the  specular  reflection 
from  surfaces,  etc.  The  brightness  measurements  were  made  by 
means  of  a  Sharp-Millar  illuminometer  with  the  receiving  test 
plate  removed.  The  instrument  was  calibrated  against  a  mag- 
nesium oxide  surface  obtained  by  depositing  the  oxide  from  the 
burning  metal  on  a  white  card.  By  this  method  the  reflecting 
surfaces  were  used  as  detached  test  plates.  The  readings  were 
converted  into  candle-power  per  sq.  in.  by  the  following  formula : 

Brightness  =  Foot-candles/7r  X  144- 

(3)  Photographs  were  made  of  the  room  from  three  positions 
under  each  system  of  illumination. 

A  complete  specification  of  the  test  room,  the  types  of  installa- 
tion used,  and  the  illumination  effects  produced  for  the  systems 
of  lighting,  is  given  in  the  previous  paper  which  appears  else- 
where in  this  number  of  the  Transactions  (pp.  413-422).  Only 
such  data  will  be  repeated  here  as  are  necessary  for  reference.7 

In  Fig.  1  the  test  room  is  shown  drawn  to  scale:  plan  of 
room,  north,  south,  east  and  west  elevations.  In  the  draw- 
ing, plan  of  room,  are  shown  the  66  stations  at  which  the 
illumination  measurements  were  made,  and  the  positions  of 
the  outlets  for  the  lighting  fixtures,  A,  B,  C,  D,  E,  F,  G,  and  H. 
In  the  drawing,  east  elevation,  the  observer  in  position  at  one 
of  the  points  (Position  I)  at  which  the  tests  were  taken  is  repre- 

T  For  a  description  of  the  test  see  the  previous  article  referred  to  above 
(pp.  410-413);  also  Tests  for  the  Efficiency  of  the  Eye  Under  Different  Systems  of 
Illumination  and  a  Preliminary  Study  of  the  Causes  of  Discomfort,  Trans.  I.  E.  S., 
vol.  VIII   (1913).  PP-  41-51- 


ruw  a  udom 


Fig.  i. — Plan  of  test  room. 


Fig.  2.— Showing  brightness  measurements  of  all  surfaces  having  very  high  or  very 
low  brilliancj-,  direct  system.  The  brightness  of  the  printed  page  from  which  the 
observer  read  was,  when  held  in  the  horizontal  position,  0.0057  cp.  per  sq.  in.;  in 
the  45  deg.  position,  0.004  cp.  per  sq.  in.'; 

6  The  bright  spots  on  the  doors  of  the  apparatus  case  rated  at  100  cp.  persq.  in.,  shown 
in  Fig.  2.  were  not  in  the  field  of  view  when  the  tests  were  taken.  That  is,  when  the  tests 
were  taken,  the  doors  were  thrown  open,  and  all  of  the  apparatus  which  might  give 
specular  reflection  was  removed. 


Fig.  3. — Showing  brightness  measurements  of  all  surfaces  having  very  high  or  very 
low  brilliancy,  semi-indirect  system.  The  brightness  of  the  printed  page  from 
which  the  observer  read  was,  when  held  in  the  horizontal  position,  0.005S  cp.  per 
sq.  in.:  in  the  45  deg.  position,  0.0039  CP-  Per  scl-  in- 


Fig.  4.— Showing  brightness  measurements  of  all  surfaces  having  very  high  or  very 
low  brilliancy,  indirect  system.  The  brightness  of  the  printed  page  from  which 
the  observer  read  was.  when  held  in  the  horizontal  position,  0.00SS  cp.  per  sq.  in.: 
in  the  45  deg.  position,  0.0043  cp.  per  sq.  in. 


FERREE   AND   RAND:     EFFICIENCY   OF   THE   EYE  453 

sented.8  The  other  three  positions  are  indicated  in  the  photo- 
graphs by  (x).  They  will  be  referred  to  in  the  tables  and  charts, 
in  order,  by  the  numerals  II,  III,  and  IV. 

Table  I  shows  the  number  and  wattage  of  the  lamps  used  at 
the  outlets  A,  B,  C,  D,  E,  F,  G,  and  H ;  and  Table  II  shows  the 
illumination  measurements  for  each  of  the  66  stations  repre- 
sented in  Fig.  I.  These  measurements  were  made  with  the  re- 
ceiving test  plate  of  the  photometer  in  the  horizontal,  vertical 
and  45  deg.  planes.9 

8  The  track  along  which  the  test  card  was  moved  was  parallel  to  the  east  and 
west  walls  of  the  room.  During  the  three  hours  of  reading  which  intervened  be- 
tween the  two  tests,  the  observer  moved  just  far  enough  back  from  the  upright  sup- 
porting the  mouth-board  to  give  room  for  the  book  to  be  held  and  to  permit  of  a 
comfortable  reading  position.  The  book  was  elevated  and  held  approximately  at  an 
angle  of  45  deg.  When  taking  the  test,  the  observer  faced  the  north  wall  of  the 
room,  in  such  a  position  that  with  the  eyes  in  the  primary  position,  the  lines  of 
regard  were  parallel  with  the  east  and  west  walls  of  the  room.  Care  was  taken  to 
have  print  of  uniform  size  and  distinctness  for  use  with  the  three  systems  and  to 
have  a  page  which   gave  a  comparatively  small   amount  of  specular   reflection. 

8  See  also  Table  III,  The  Efficiency  of  the  Eye  Under  Different  Conditions  of 
Lighting,  etc.,  Trans.  I.  E.  S.,  vol.  X,  1915,  p.  416a.  This  table  was  compiled  as  a 
supplement  to  Table  II  for  the  purpose  of  making  a  comparative  showing  of  the 
evenness  of  illumination  at  the  122  cm.  level  given  by  the  three  systems  of  lighting. 
Two  cases  were  made  of  this.  (1)  Comparisons  were  made  of  each  component  from 
station  to  station;  (2)  the  difference  between  the  components  was  compared.  To 
facilitate  these  comparisons  (a)  the  mean  variation  from  the  average  of  each  of  the 
components  was  computed;  and  (b)  the  difference  between  the  averages  of  the  three 
components  was  determined.  The  evenness  of  the  illumination,  it  will  be  remembered, 
is  not  only  of  importance  to  the  efficiency  of  the  eye  with  reference  to  the  object 
directly  viewed;  but  also  in  its  influence  on  the  distribution  of  surface  brightness. 
The  evenness  of  surface  brightness  depends  in  general  upon  two  sets  of  factors;  (1) 
the  nature  and  position  of  the  reflecting  surfaces  in  the  room;  and  (2)  the  type  of 
delivery    of   light   to   these   surfaces. 

We  realize  that  the  evenness  of  the  illumination  on  the  122  cm.  plane  given  by 
the  indirect  and  semi-indirect  units  was  somewhat  interfered  with  by  the  reflectors  of 
the  direct  system  which  were  beneath  and  a  little  to  the  right  of  these  units  when  in 
position  for  the  test.  Also  the  evenness  of  surface  brightness  on  the  ceiling  for  the 
direct  system  was  interfered  with  by  the  indirect  and  semi-indirect  reflectors  which 
were  above  and  a  little  to  the  side  of  the  direct  units.  The  influence  of  this  "dead 
apparatus"  will  be  eliminated  in  the  next  series  of  installations.  Moreover,  the  in- 
stallation in  each  case  was  not  such  as  to  give  the  best  effects  obtainable  from  the 
type  of  reflector  used.  For  example,  the  indirect  reflectors  were  too  close  to  the 
ceiling  to  give  the  maximum  evenness  of  illumination  and  surface  brightness  for 
the  type  of  reflector  employed.  The  analysis  of  the  effects  given  in  the  former  paper 
was  not  made,  therefore,  for  the  purpose  of  drawing  general  conclusions  with  regard 
to  the  type  of  reflector  used.  It  was  made  solely  for  the  sake  of  the  comparison  of 
the  illumination  effects  obtained  with  the  corresponding  results  for  loss  of  efficiency. 


454     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


TABLE  I. 

Showing  the  number  and  wattage  of  the  lamps  used  at  outlets 

A,  B,  C,  D,  E,  F,  Gand  H. 

Outlet                                                   Direct  Semi-indirect  Indirect 

Watts  Watts  Watts 

A     2-6o  I-IOO  I-IOO 

B 2-60  1-100  1-100 

C 2-60  1-100  1-100 

D    2-40  1-100  i-loo 

E 2-60  1-100  1-100 

F 2-60  1-100  1-100 

G    2-60  1-100  1-100 

H 2-40  1-60  1-100 

TABLE  11.— Distribution  Series.10 
Showing  the  illumination  measurements  in  foot-candles  for  each  of  the  66 
stations  represented  in   Fig.    1   for  the  direct,   semi-indirect,   and  indirect 
systems  used. 

Horizontal  Vertical  45° 

Semi-  Semi-  Semi- 

Station      Direct  indirect.  Indirect     Direct     indirect  Indirect    Direct     indiiect  Indirect 

1  1. 41    I.44    1.22 

2  I.32  I.47  I.26 

3  I. IO  I.40  I.32 

4  1.37  i. 10  1.47 

5  2.03  2.58  2.20 

6  2.50  3.20  2.95 

7  2.51  3.60  2.90 

3  3-3°  3-75  3-oo 

9  2.78  2.53  2.20 

10  1.50  1.59  1.35 

11  2.12  1.64  1.66 

12  4.20  2.65  2.70  0.47  0.48  0.47  2.40  1.25  1.43 

13  6.10  5.25  4.10  0.47  0.48  0.42  3.30  2.25  1.96 

14  3.70  4.95  4.40  0.48  0.47  0.47  2.00  2.40  2.30 

15  3.00  4.S5  4.50  0.44  0.48  0.47  i-97  1.8S  2.30 

16  6.60  4.25  4.10  0.70  0.37  0.48  3.58  1.60  2.10 

17  4.65  2.35  3.15  0.48  0.24  0.46  1.80  0.69  1.60 

18  2.15  1.69  2.20  0.49  0.38  0.47  1. 10  0.66  1.63 

19  2.95  2.10  2.50 

20  5.30  3.20  3.40  1.62  0.53  0.86  3.00  2.30  2.20 

21  6.60  4.80  4.60  2.00  0.71  0.94  3.60  1.85  3.00 

22  2.25  4.40  4.80  0.61  0.69  1.07  1. 15  1.80  2.90 

23  4.50  6.00  5.10  1.20  1. 14  1. 10  2.18  3.30  2.90 

24  6.95  5.40  5.00  1.76  1.30  1.04  3.60  3.10  3.00 

25  4-85  3-72  3-5o  1-33  o-78  0.75  2.75  1.85  2.10 

26  2.50  1.82  2.20 

27  2.81  2.05  2.40 

28  6.50  3.28  3.70  1.30  1. 11  1. 12  4.40  2.10  2.50 

29  9.00  6.40  5.20  1.45  1.50  1.48  6.30  3.60  3.40 

30  4-95  6.95  5.40  1.36  1.46  1.40  3.15  4.15  3.60 

31  4.80  6.20  5.20  0.77  1.20  1.24  2.78  3.85  3.60 


FERREE    AND   RAND '.     EFFICIENCY   OF   THE    EYE 


455 


TABLE  II.— Distribution  Series.  —  (C 

ontinue 

d.) 

Horizont 

al 

Vertical 

45° 

Semi- 

Semi- 

Semi- 

Station 

Direct 

indirect 

Indirect 

Direct 

indirect 

Indirect 

Direct 

indirect 

Indirect 

32 

9.20 

5-50 

5.00 

O.47 

0.2S 

1-33 

5.20 

2.25 

3-40 

33 

6.20 

3-iS 

3-70 

1-54 

0.75 

1.22 

4.60 

I.83 

2.6o 

34 

5-75 

4-30 

4.00 

2.S5 

I.20 

1.46 

4-3° 

2.92 

3.IO 

35 

8.00 

6.90 

5-4o 

3-70 

I.70 

r-65 

6.00 

4.40 

4.90 

36 

5.60 

7-25 

5-3o 

2-35 

1. 91 

1.65 

4.20 

4.68 

4.00 

37 

5-45 

7.00 

5.80 

2.18 

2-15 

1.82 

3-78 

4-55 

4.00 

38 

8.25 

6.  So 

5-4o 

3.60 

2.20 

1.72 

6.00 

4.60 

3.8o 

39 

6-35 

3-7o 

4.00 

2.8o 

1.40 

i-43 

4.60 

2.80 

3.00 

40 

3.00 

2.05 

2.30 

4i 

2.70 

i-73 

2.10 

42 

7-3o 

3-65 

3-5o 

2.50 

1.64 

1.36 

5-4o 

2-93 

2.80 

43 

9.80 

6.90 

5.  CO 

2.70 

2.0S 

1.7S 

7.20 

4-50 

3-9° 

44 

5-5o 

7.10 

5.20 

2.42 

2.IS 

1. 88 

4-35 

.5.10 

4-3° 

45 

5-45 

8.00 

5.20 

2.60 

2.00 

i-93 

4.80 

5-30 

4.20 

46 

10.00 

7.70 

5.20 

2-75 

1.90 

1.86 

8.00 

5-4o 

4.10 

47 

6.60 

4.20 

3.60 

2-45 

1.56 

i-33 

5-3° 

3-05 

2.90 

48 

5-8o 

4-35 

3-70 

3.20 

1.69 

1.74 

5.00 

3.60 

3-30 

49 

8.40 

7.20 

4.80 

4-3° 

2.55 

2. 10 

7  20 

5-8o 

4.00 

50 

5-5o 

7.70 

4.90 

3-35 

2.42 

2.10 

8.50 

5 -So 

4.10 

5i 

5-4o 

6.80 

5.00 

3-05 

2.68 

2.15 

4.60 

5-35 

4-35 

52 

8.00 

6.40 

4.70 

4.20 

2-55 

i-93 

6.50 

4.82 

4.00 

53 

6.60 

3S5 

3.60 

3.00 

1-77 

1.41 

5-°J 

3.20 

3.00 

54 

6.95 

2.88 

2. So 

2.62 

1.80 

1.50 

5.80 

3.00 

2.90 

55 

9.00 

5-9o 

390 

3-15 

2.40 

1.94 

S.00 

5.20 

3-75 

56 

4-95 

5-9° 

4.60 

3.15 

2.50 

2.10 

5-30 

5-So 

4.40 

57 

4-65 

6.10 

450 

3.00 

2.60 

2.20 

4-65 

5-So 

4.40 

58 

9-75 

6-35 

4.00 

3-35 

2.58 

2.00 

8.50 

5-8o 

4.00 

59 

5.85 

3.20 

2.90 

2.98 

1.90 

1.76 

5.60 

3-62 

3.10 

60 

3-85 

2-57 

2.60 

1.66 

2.90 

61 

5.20 

4.20 

3.10 

4-45 

2.60 

1.90 

7. So 

5-4o 

3-5° 

62 

3-3o 

4.20 

3.20 

3-3° 

2-95 

2.10 

4-95 

5-7o 

3-70 

63 

3-52 

4.20 

3.00 

3.60 

2.80 

2.20 

5.60 

5.00 

3-5o 

64 

5-4o 

3-7o 

3.10 

4.60 

2-45 

i-93 

7-65 

4.60 

3-4o 

65 

4-15 

2.40 

2.25 

4.00 

1.79 

i-54 

5-50 

2.82 

2.60 

66 

2.10 

1.42 

i-35 

Average  5.0        4.27       3 .61 


1.59       1.48  4.77       3.63       3.30 


'"  Reduced  to  equal  wattages  (Soo  watts)  these  installations  give  the  following  average 
illumination  values  in  foot-caudles  for  the  receiving  test  pbite  111  the  positions  specified 
above  :  Direct  system:  horizontal,  4.54;  vertical,  2.2;  450.  433.  Semi-indirect  system: 
horizontal,  4.49;  vertical,  1.67;  450,  3.S2.     Indirect  :  horizontal,  3.61;  vertical,  1.4S;  450,  3.3. 

It  may  not  be  out  of  place  to  suggest  here  that  a  careful  study  of  the  illuminating  effi- 
ciencv  of  different  types  uf  lighting  units  should  be  made  under  conditions  that  are  strict- 
ly comparable  for  a  wide  range  of  variation.  Such  tests  should  be  made  under  common 
supervision  in  a  model  room  so  constructed  as  readily  to  permit  of  the  kind  of  variations 
needed;  and  should  be,  if  possible,  paralleled  by  tests  for  the  efficiency  of  the  eye.  In 
working  towards  a  reconstruction  of  lighting  conditions,  it  is  obvious  that  tests  for  the 
efficiency  of  the  eye  and  for  illuminating  efficiency  should  go  haud  in  hand. 


456     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Figs.  2,  3  and  4  are  taken  from  the  series  of  9  photographs  (see 
Figs.  2-10,  op.  cit.,  pp.  4i6b-4i6d)  showing  the  illumination  effects 
produced  by  the  three  systems  of  lighting.  In  these  figures  are 
given  the  brightness  measurements  of  all  surfaces  having  very 
high  or  very  low  brilliancy.  The  spot  measured  is  indicated  by  a 
cross  and  the  numerical  value  of  the  brightness  measurement  in 
candlepower  per  square  inch  is  printed  nearby.  These  spots  are 
also  lettered  for  convenience  of  reference  in  the  intensity  series. 
That  is,  since  several  installations  were  used  in  the  intensity 
series,  it  was  found  convenient  to  express  these  values  in  tabular 
form  and  to  identify  them  with  the  surfaces  measured  by  means 
of  letters.  These  photographs  were  taken  from  a  point  in  line 
with  the  four  positions  of  the  observer  as  near  to  the  south  wall 
of  the  room  as  was  possible ;  but  owing  to  the  narrow  field  of  the 
camera  as  compared  with  the  binocular  field,  these  views  include, 
for  example,  only  about  one-half  of  the  field  of  vision  of  the 
observer  at  the  test  station  nearest  to  this  wall  of  the  room.  The 
camera's  field  in  this  position  corresponds  in  fact  very  closely  to 
the  field  presented  to  the  observer  seated  at  the  center  of  the 
room.  While,  therefore,  not  all  of  his  field  of  view  for  all  of  the 
positions  at  which  tests  were  made  is  covered  by  the  brightness 
measurements  shown  in  the  photographs,  still  the  order  of  bright- 
ness difference  present  in  the  field  of  view  for  the  different  sys- 
tems is  well  represented  by  these  measurements,  as  can  be  seen  by 
an  inspection  of  the  preceding  photographs  (see  also  Figs.  2-10, 
op.  cit.,  pp.  4i6b-4i6d)  and  from  the  descriptions  of  the  installa- 
tions used.  In  order  to  facilitate  certain  features  of  comparison 
such  as,  for  example,  the  evenness  of  surface  brightness  for  each 
system  for  all  of  the  room;  for  all  of  the  room  but  the  sources  of 
light;  and  for  all  of  the  room  but  the  sources  and  the  spots 
above  the  sources,  the  brightness  measurements  shown  in  Figs. 
2,  3  and  4  are  also  given  in  tabular  form.  These  measurements 
and  the  letters  identifying  them  with  the  surfaces  measured,  are 
given  in  Table  III.  In  making  the  comparison  it  should  be  noted 
that  the  spots  mentioned  are  not  in  all  cases  identical  for  the 
three  systems.  That  is,  owing  to  the  different  effects  produced 
by  the  different  reflectors,  the  same  spots  were  not  always  con- 
spicuously light  or  dark  for  the  three  systems.     The  letters,  E, 


FERREE    AND    RAND:     EFFICIENCY   OF   THE    EVE 


457 


F,  G,  etc.,  may  then  refer  to  entirely  different  spots  in  case  of 
the  three  systems. 

TABLE  III.— Distribution  Series. 

Showing  the  brightness  measurements  in  candlepower  per  square  inch  for 

the  surfaces  A,  B,  C,  D.,  etc.,  see  Figs.  2,  3  and  4. 

Surface  Direct  Semi-indirect  Indirect 

measured  system  system  system 

A  1000.0000  O.710  0.138 

B  0.3816  0.057  0.0715 

C  0.517  0.093  0.066 

D  0.010  °-°59  0.0022 

E  0.00296  0.0029  0.0030 

F  0.0044  0.0033  0.00123 

G  0.0078  0.0053  0.0049 

H  0.0077  0.006  0.0040 

I  0.0075  0.0062  0.0042 

J  0.0014  0.0010  0.00095 

K  0.0063  0.0046  0.00255 

L  0.0042  0.0027  0.00246 

M  0.0065  0.0051  0.00352 

N  0.0047  0.0027  0.00272 

O  0.0074  0.0066  0.00343 

P  0.006  0.00484  0.0030S 

Q  0.00396      • 

TABLE  IV.— Distribution  Series. 
Showing  the  brightness  measurements  in  candlepower  persq.  in.  of  the  test 
card,  reading  page  horizontal,  and  reading  page  in  the  45  deg.  position  for 
Positions  I,  II,  III,  and  IV,  for  the  direct,  semi-indirect,  and  indirect  systems. 

Position  Direct       Semi-indirect      Indirect 

of  observer  Surface  measured  system  system  system 

I         Test  card 0.00308  0.0030  0.00299 

Reading  page  horizontal 0.0057  0.0058  0.0088 

Reading  page  450  position- . .  0.004  0.0039  0.00431 

II         Test  card 0.00506  0.00453  0.0046 

Reading  page  horizontal 0.0088  0.0107  0.0088 

Reading  page  45°  position- .  •  0.0068  0.00726  0.00792 

III  Test  card 0.0055  0.00462  0.00453 

Reading  page  horizontal 0.0092  0.0087  0.00814 

Reading  page  450  position...  0.00704  0.0077  0.00594 

IV  Test  card 0.0066  0.00475  0.00453 

Reading  page  horizontal 0.00814  0.00572  0.00572 

Reading  page  450  position  •• .  0.0063  0.00484  0.00484 

In  Table  IV  are  given  the  brightness  measurements  in  candle- 
power  per  square  inch  for  the  test  card  and  the  reading  page  for 
the  four  positions  of  the  observer :  I,  II,  III  and  IV,  for  the 
direct,  semi-indirect  and  indirect  systems.  The  measurements  of 
the  reading  page  were  taken  at  the  point  of  work  for  the  four 
positions  of  the  observer  with  the  book  in  the  horizontal  and  45 
deg.  position.  During  work  the  book  was  held  in  the  45  deg. 
position. 

In  Tables  V  and  VI  are  shown  some  prominent  ratios  of  sur- 


458     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

face  brightness  for  the  three  systems.11     (See  also  Table  VIII, 
op.  cit.,  p.  421. )12 

In  compiling  these  ratios  it  has  been  considered  important  to 
make  a  comparative  showine  for  the  three  systems  (a)  of  the 
extremes  of  surface  brightness ;  and  (b)  of  the  relation  of  the 
brilliancy  of  objects  in  the  surrounding  field  to  the  surface  bright- 
ness at  the  point  of  work.     The  extremes  of  surface  brightness 

11  In  attempting  to  make  comparisons  of  the  effect  of  the  different  magnitudes  of 
brightness  ratios,  one  obviously  must  bear  in  mind  that  the  surfaces  between  which 
the  ratios  are  established  are  not  in  all  cases  in  the  same  position  in  the  field  of 
vision  for  the  three  systems.  For  example,  the  brightest  surfaces  in  case  of  the 
indirect  system,  namely,  the  spots  on  the  ceiling  directly  above  the  reflectors,  are 
farther  removed  from  the  direct  line  of  vision  of  the  observer  in  the  working  position 
than  were  the  brightest  surfaces  in  case  of  the  direct  and  semi-indirect  systems. 
The  position  of  the  surface  in  the  field  of  vision  would  come  into  question,  for  ex- 
ample, in  making  a  determination  of  the  maximum  va'ue  of  brightness  difference  the 
eye  is  adapted  to  stand.  While  we  have  done  a  great  deal  of  work  on  the  effect  nf 
position  of  the  brilliant  surface  in  the  field  of  vision  in  our  investigation  of  the 
causes  of  discomfort,  we  have  made  no  especial  investigation  of  this  point  in  re'ation 
to  loss  of  efficiency.  Doubtless  what  we  shall  all  have  to  bear  in  mind  is  that,  even 
in  the  end,  we  cannot  hope  to  specify  narrowly  what  is  most  favorable,  etc.  In 
lighting  conditions.  The  factors  that  enter  into  the  concrete  lighting  situation  are  so 
complex  or  rather  are  so  variable  and  so  rarely  duplicated  that  we  can  hope  to  make 
general  specifications  with  regard  to  what  is  most  favorable,  for  example,  only  within 
very  broad  limits.  If  one  wishes  to  work  the  conditions  down  to  a  finer  point  than 
this,  the  particular  installation  must  be  tested  in  situ.  We  are  at  present  working 
on  a  test  which  we  hope  will  serve  this  purpose  better  than  the  test  which  has  been 
used   in    the   work   described   in   the   preceding   papers. 

12  Table  VIII,  (op.  cit.,  p.  421)  was  compiled  from  Tables  IV-VII  of  that 
paper  to  show  the  mean  variation  in  surface  brightness  for  all  the  surfaces  measured 
for  the  direct,  semi-indirect,  and  indirect  systems.  In  referring  back  to  that  paper 
it  may  not  be  out  of  place  to  call  to  mind  again  that  the  percentages  given  in  Table 
VIII  seem  to  indicate  that  the  great  advantage  of  the  indirect  over  the  other  systems 
of  lighting  we  have  used  with  regard  to  the  factor,  evenness  of  surface  brightness, 
comes,  primarily  at  least,  from  its  provisions  for  shielding  the  eye  from  the  light 
source  rather  than  from  any  conspicuously  greater  evenness  of  illumination  given 
by  it  to  the  objects  in  the  field  of  view.  In  fact,  as  may  be  seen  from  that  table,  all 
the  systems  give  a  fairly  even  distribution  of  surface  brightness  outside  of  the 
source   and    the    surfaces    immediately   surrounding   it. 

The  need  of  keeping  surface  brightness  within  certain  limits  and  the  primary  im- 
portance of  properly  shielding  the  eye  from  the  source,  to  the  accomplishment  of  this 
desideratum,  are  obvious.  Doubt' ess  many  ways  will  be  devised  in  course  of  time  for 
cutting  down  useless  and  harmful  brightness  differences  in  lighting  effects.  For  exam- 
ple, the  possibility  is  here  suggested  of  producing  a  still  smaller  brightness  difference 
than  is  given  by  the  indirect  reflectors  of  the  type  we  have  employed,  by  using  semi- 
iidirect  reflectors  of  such  a  density  as  to  give  a  surface  brilliancy  equal  to  that  of 
the  spot  of  light  cast  upon  the  ceiling.  The  value  of  this  brilliancy,  because  of  the 
larger  area  of  luminous  surface  presented,  could  then  be  made  smaller  than  that  of 
the  ceiling  spot  cast  by  the  indirect  reflector  and  still  give  the  same  amount  of  light 
to  the  room.  A  similar  effect  may  be  obtained  with  the  indirect  reflector  by  using 
lamps  of  lesser  wattage  and  adding  the  light  needed  to  make  up  the  deficiency  by 
installing  directly  beneath  the  reflector  lamps  of  low  wattage  in  trans'ueent  en- 
closures of  a  density  that  gives  a  surface  brilliancy  equal  to  that  of  the  ceiling  spots. 
The  effect  of  both  of  these  devices  would  be  to  lower  the  surface  brilliancy  for  a 
given  light  flux  by  increasing  the  area  of  the  luminous  surface.  Whether  either  de- 
vice would  be  advisable  from  other  standpoints  we  are  not  at  present  prepared  to 
say. 


i-KKRiiE  and  rand:    EFFICIENCY  of  the  EYE  459 

are  shown  by  giving  the  ratios  between  surfaces  of  the  first, 
second,  third,  etc.,  order  of  brilliancy  and  the  surface  of  the 
lowest  order  of  brilliancy ;  and  the  comparison  of  the  brilliancy 
of  objects  in  the  surrounding  field  to  the  brightness  at  the  point 
of  work  by  giving  the  ratios  of  the  surfaces  of  the  first,  second, 
and  third  order  of  brilliancy  to  the  brightness  of  the  test  card 
and  the  reading  page  in  the  working  position.  The  following 
points  may  be  noted,  (i)  The  illumination  effects  produced  by 
the  direct  system  are  characterized  by  great  extremes  of  surface 
brightness,  and  a  high  ratio  of  brilliancy  of  objects  in  the  sur- 
rounding field  to  the  surface  brightness  at  the  point  of  work. 
These  effects  are  much  less  pronounced  for  the  semi-indirect  sys- 
tem and  still  less  for  the  indirect.  (2)  A  comparison  of  this 
table  with  the  tables  giving  loss  of  efficiency  as  the  result  of  work 
shows  that  while  the  extremes  of  surface  brightness  are  enor- 
mously larger  for  the  direct  than  for  the  semi-indirect  system, 
the  eye  loses  almost  as  much  in  efficiency  for  three  hours  of  work 
under  the  semi-indirect  as  under  the  direct  system.  That  is,  the 
greatest  ratio  of  brightness  for  the  direct  system  is  over  one 
thousand  times  as  much  as  the  greatest  ratio  for  the  semi-indirect, 
while  the  difference  in  loss  of  efficiency  for  the  two  systems  is 
comparatively  insignificant.  On  the  other  hand,  the  greatest 
ratio  of  brightness  for  the  semi-indirect  system  is  only  about  five 
times  as  much  as  for  the  indirect;  while  the  difference  in  loss  of 
efficiency  for  three  hours  of  work  is  very  large,  this  loss  of  effi- 
ciency for  three  hours  of  work  for  the  indirect  system  being,  it 
will  be  noted,  very  small  indeed.  This  seems  to  indicate  (a)  that 
for  the  scale  of  brightness  magnitudes  and  the  illumina- 
tion effects  present  in  this  series  of  experiments  the  gradation 
of  surface  brightness  for  the  indirect  system  is  very  close 
to  what  the  eye  is  adapted  to  stand  without  loss  of  efficiency ; 
and  (b)  that  an  increase  in  difference  in  brightness  above 
this  point  is  followed  at  first  by  a  rapid  increase  in  loss  of 
efficiency  and  later  by  a  much  slower  increase.  In  the  intensity 
series,  in  the  work  of  the  former  paper,  it  wrill  be  remembered, 
the  following  points  also  came  out.  (1)  The  effect  of  size  of 
ratio  on  loss  of  efficiency  is  different  for  different  orders  of  mag- 
nitude of  brightness.     And  (2)  the  size  of  the  brilliant  object,  as 


460     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

well  as  its  brilliancy,  is  of  importance.  That  is,  within  certain 
limits,  as  yet  undefined,  an  increase  in  the  area  of  the  brilliant 
surface  causes  an  increase  in  loss  of  efficiency. 

In  Table  V  the  ratios  were  compiled  from  measurements  show- 
ing the  extremes  of  brightness  of  prominent  surfaces  in  the  room. 
In  Table  VI  they  were  compiled  to  show  the  relation  of  the 
brilliancy  of  objects  in  the  surrounding  field  to  the  surface  bright- 
ness at  the  point  of  work  for  the  positions  of  the  observer,  I,  II, 
III  and  IV13  (see  Fig.  i,  p.  452a).  In  general  a  falling  off  in 
the  magnitude  of  brightness  differences  in  the  field  of  view 
will  be  noted  in  order  from  the  Positions  I  to  IV.  This 
falling  off  is  greatest  for  the  direct  system,  next  greatest  for  the 
semi-indirect,  and  least  for  the  indirect.  Thus  there  is  not  only 
a  decrease  in  the  number  of  surfaces  in  the  field  of  view  show- 
ing a  high  brilliancy  from  Positions  I  to  IV,  but  also  a  decrease 
in  the  magnitude  of  brightness  difference  between  the  surfaces 
of  high  brilliancy  and  the  test  card,  between  these  surfaces  and 
the  reading  page,  etc.,  especially  for  the  direct  and  semi-indirect 
systems.  An  inspection  of  the  table  for  loss  of  efficiency  shows, 
roughly  speaking,  a  correspondingly  marked  decrease  in  loss  of 
efficiency  from  Positions  I  to  IV  for  the  systems  which  show  the 
marked  decrease  in  brightness  difference,  that  is,  for  the  direct 
and  semi-indirect  systems.  The  decrease  in  loss  of  efficiency, 
it  will  be  noted,  is  practically  nothing  for  the  indirect  system. 
Thus  not  only  much  less  loss  of  efficiency  is  sustained  by  the 
eye  for  the  indirect  units  used,  but  the  results  are  much  more 
independent  of  the  position  of  the  observer  in  the  room. 

The  loss  of  efficiency  for  the  Positions  I,  II,  III  and  IV  for  the 
three  systems  is  shown  in  Table  VII.14 

13  It  may  also  be  of  interest  to  the  reader  to  work  out  for  these  four  positions  the 
ratios:    lightest   to   darkest,    darkest   to   test  card,    darkest   to   reading   page,    etc. 

14  Obviously  in  the  consideration  of  the  effect  of  a  given  lighting  situation  on 
the  ability  of  the  eye  to  hold  its  efficiency  for  a  period  of  work,  the  age  of  the  ob- 
server and  the  condition  of  his  eyes  should  be  taken  into  account.  All  the  observers 
that  have  been  employed  by  us  in  this  work  were  .under  26  years  of  age.  Following 
is  a  clinic  report  of  the  eyes  of  the  observer  whose  results  are  given  in  the  following 
table,   made  by  Dr.   Wm.    Campbell   Posey  of   Philadelphia. 

Observer   R. 

With  glasses. — Vision  of  right  eye  =  20/25.     Par  muscle  test  =  Q  14  esophoria. 

Vision  of  left   eye  =  2o'2o.  Near  muscle  test  =  orthophoria. 
Ophthalmoscopic   examination.- — Right  eye    =    mixed   astigmatism,    Yi    diopter. 

Left    eye    =    hyperopic    astigmatism,    1  Yi    diopters. 
( Conthi  ued  on  next  page. ) 


FERREE   AND   RAND:     EFFICIENCY   OF   THE   EVE  461 

Chart  I  gives  a  graphic  representation  of  the  results  of  this 
table.  Loss  of  efficiency  is  plotted  along  the  ordinate  and  time 
of  work  along  the  abscissa.  Each  of  the  large  squares  along  the 
abscissa  represents  an  hour  of  work  and  along  the  ordinate  an 
integer  of  the  ratio,  time  clear  to  time  blurred.  The  effect  on 
loss  of  efficiency  of  the  number  and  magnitude  of  brightness  of 
surfaces  of  high  brilliancy,  especially  of  primary  sources,  in  the 
field  of  view  is  obvious  from  these  charts.  The  chart  for  position 
IV,  however,  shows  that  there  is  still  a  considerable  difference  in 
the  loss  of  efficiency  produced  by  the  three  systems,  even  when 
there  are  no  sources  or  other  surfaces  of  high  brilliancy  in  the  field 
of  view.  The  indirect  system  still  gives  the  least  loss  of  efficiency, 
the  semi-indirect  next,  and  the  direct  the  most.  As  may  be  seen 
in  Figs.  2,  3,  and  4,  and  in  Tables  III  and  VI  there  was  little  dif- 
ference in  the  evenness  of  surface  brightness  in  the  field  of  view 
presented  to  the  observer  in  this  position,  certainly  none  that  could 
be  considered  of  consequence  in  favor  of  the  indirect  system.  The 
above  results  seem  to  indicate,  therefore,  that  while  the  evenness  of 
surface  brightness  is  an  important  factor  it  is  not  the  only  factor 
in  a  lighting  situation  which  may  influence  the  amount  of  loss  of 
efficiency  sustained  by  the  eye  as  the  result  of  a  period  of  work 

We  wish  to  repeat  in  this  paper  what  was  very  strongly  empha- 
sized in  our  former  paper,  namely,  that  the  units  we  have  em- 
ployed were  not  selected  as  fully  representative  of  the  classes 
direct,  semi-indirect,  and  indirect.  Agreement  in  fact  has  not  yet 
been  reached  with   regard  to  what   falls  within  each   of  these 

Externa!    condition. — Adduction    good;    eyes    slightly    divergent    under    cover;    cornea 
clear;     pupils,    2^    mm.;    irides    respond    equally    and    freely    to 
light,    accommodation,    and   convergence    stimuli. 
Glasses  worn   during  test. — Right  eye  =  — S.,   0.50   D. ; — C,   0.37D.,   x    ieo* 
Left  eye   =  — C,    0.50   D.,   x    1800 
Lest  the  former  paper   has  not  appeared  in   print  before  this  one  is  presented  it 
may  be   well   to  make   some   mention   here   also   of   the   reproducibility   of   results  that 
may  be  obtained  for  our  test  for  loss  of  efficiency.     The  mean  variation  of  the  ratio, 
time  clear  to  time  blurred  for  the  same  observer  working  under  conditions  as  nearly 
constant   as   possible,    is   very    small    indeed.      The    order    of    magnitude   of   the    mean 
variation  of  the  test  for  the  fresh  eye  was  obtained  as  follows.     Beginning  at  9  a.  m. 
five    3    minute   tests   were    run    with    a    rest    period   of   20   minutes   between    each    test 
This   was   done   with   all   observers   on   several   days   under   each   system   of  lighting  em- 
ployed.    The  rest  period  was  taken   in  each  case  in  a  room  lighted  by  daylight,   with 
the  observer  facing  a  wall   with   an   evenly  lighted  matt  surface.     For  a  single  series 
of    five    tests    the    variation    in    the    time    seen    clear    in    the    3    minute    periods    have 
always   fallen   within    1    per  cent,    for   all   of  the   observers   we  have   used   and   for  all 
systems   of   lighting. 


462     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


classes.  The  units  employed  were  chosen  rather  to  show  the 
effect  of  varying  the  factors  we  have  grouped  under  the  heading 
of  distribution  on  the  ability  of  the  eye  to  maintain  its  efficiency 
for  a  period  of  work.       We  hope  ultimately  to  determine  the 

CHART  I.—  Distribution-  Series. 
Showing  the  effect  on  loss  of  efficiency  of  varying  the  observer's  position  in 
the  room,  or  the  number  of  bright  sources,  primary  and  secondary,  in  the 
field  of  vision. 


POSITION    I 


^liUSHi  FIXTURES  IN  FIELD  Of  m!0« 


POSITION    II 


POSITION    III 


POSITION    IV 


limits  between  which  each  of  these  factors  may  vary  in  a  se- 
lected range  of  lighting  situations,  without  damage  to  the  eye,  es- 
pecially the  factor  surface  brightness.  These  most  favorable 
conditions  will  then  serve  as  a  goal  to  be  attained  whatever  prin- 
cipal of  lighting  is  employed. 


FERREE   AND   RAND:     EFFICIENCY   OF   THE    EYE 


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FERREE   AND   RAND:     EFFICIENCY   OF   THE   EYE 


465 


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466     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

As  was  also  stated  in  our  former  paper  our  next  step  in  this 
division  of  the  work  will  be  to  determine  by  using  reflectors  of 
different  degrees  of  opacity  the  effect  on  loss  of  efficiency  when 
the  light  is  distributed  to  the  plane  of  work  both  by  the  direct 
and  indirect  principles  of  lighting.  That  is,  reflectors  of  differ- 
ent densities :  prismatic,  alba,  opal  lux,  totally  opaque,  etc.,  will  be 
used  turned  up  and  down.  In  each  case  the  installation  will  be 
made  with  special  reference  to  giving  the  best  results  obtainable 
for  the  particular  type  of  unit  employed ;  and  the  factors :  even- 
ness of  illumination,  diffuseness  of  light,  the  angle  at  which  the 
light  falls  on  the  work,  and  the  evenness  of  surface  brightness, 
will  be  varied  separately  in  turn  and  the  effect  on  loss  of  effi- 
ciency will  be  determined.  Moreover,  if  it  is  found  that  the 
factors  in  question  cannot  be  studied  in  sufficient  detail  in  the 
concrete  lighting  situation,  the  work  will  be  supplemented  by 
more  abstract  investigations.  The  results  of  this  series  of  tests 
should  give  us  among  other  things,  for  example,  a  still  better 
idea  of  what  amount  of  brightness  difference  the  eye  is  adapted 
to  stand,  and  the  comparative  effect  of  different  ratios  of  surface 
brightness  on  loss  of  efficiency. 

INTENSITY  SERIES. 

In  the  work  of  the  preceding  paper  we  had  undertaken  to 
determine  the  most  favorable  intensities  for  the  three  types  of 
artificial  lighting  we  had  used  in  the  distribution  series,  and  the 
effect  of  varying  intensity  with  the  particular  grouping  of  distri- 
bution factors  represented  in  each  case.  As  was  stated  in  the 
introduction  of  the  present  paper,  this  work  was  completed  for 
the  direct  and  semi-indirect  systems  but  not  for  the  indirect.  For 
the  semi-indirect  installation  it  will  be  remembered  that  the  eye 
fell  off  heavily  in  efficiency  for  all  intensities  with  the  exception 
of  a  very  narrow  range  on  either  side  of  2.2  foot-candles,  meas- 
ured at  the  point  of  work  with  the  receiving  test  plate  of  the 
photometer  in  the  horizontal  plane.  For  the  direct  installation 
no  intensity  could  be  found  for  which  the  eye  did  not  lose  a  great 
deal  in  efficiency  as  the  result  of  work.  For  the  indirect  installa- 
tion, however,  as  the  following  data  will  show,  a  comparatively 
wide  range  of  intensity  may  be  used  without  the  eye  suffering 


FERREE   AND   RAND:     EFFICIENCY   OF   THE    KYI-  467 

any  considerable  loss  of  efficiency  as  the  result  of  three  hours  of 
continuous  work. 

The  tests  were  made  in  the  same  room,  with  the  same  fixtures, 
and  in  general,  with  the  same  conditions  of  installation  and 
methods  of  working  as  were  described  in  the  work  on  the  distri- 
bution factors.  To  secure  the  various  degrees  of  intensity  needed, 
lamps  of  different  wattage  were  employed.  These  were  selected 
from  a  series  of  tungsten  lamps  ranging  from  15  to  100  watts.  In 
order  to  keep  the  distribution  factors  as  nearly  constant  as  pos- 
sible for  a  given  type  of  system,  the  lamps  used  in  making  the 
test  for  that  type  of  system  were  all  of  one  wattage,  *.  e.,  were 
all  15's,  25's,  40's,  6o's  or  ioo's. 

For  the  indirect  system  the  total  range  of  intensity  employed 
is  shown  by  the  following  figures.  The  series  was  begun  with 
25-watt  lamps,  and  consisted  of  25,  40,  60,  and  100-watt  lamps. 
For  the  25  watt  lamps  the  photometer  reading  at  the  point  of 
work  with  the  receiving  test  plate  in  the  horizontal  plane  showed 
1.33  foot-candles  of  light;  with  the  receiving  test  plate  in  the 
vertical  plane,  0.39  foot-candle ;  and  with  the  receiving  test  plate 
in  the  45  deg.  plane,  0.87  foot-candle.  For  the  100-watt  lamps  5.2 
foot-candles  were  obtained  with  the  receiving  test  plate  in  the 
horizontal  plane;  1.36  foot-candles  with  the  test  plate  vertical; 
and  3.5  foot-candles  with  the  test  plate  inclined  45  deg.  The  tests 
for  loss  of  efficiency15  showed  probably  a  slight  advantage  for  the 
25-watt  lamps,  although  the  difference  in  result  for  the  different 
intensities  is  sufficiently  near  in  value  to  the  mean  variation  of 
the  test  as  to  be  scarcely  worthy  of  consideration. 

As  was  the  case  for  the  direct  and  semi-indirect  installations, 
the  following  specification  was  made  of  the  illumination  effects 
produced  by  the  indirect  installation.     ( 1 )   Illumination  measure- 

15  In  conducting  these  tests  it  was  found  necessary  to  allow  a  period  of  adaptation 
without  work,  to  the  illumination  of  the  room  before  the  first  test  was  taken.  If  this 
were  not  done,  especially  in  case  of  the  lower  intensities  of  lights  used,  the  changing 
sensitivity  of  the  eye  to  the  intensity  of  light  employed,  produced  a  noticeable  change 
in  the  visual  acuity  between  the  times  the  tests  before  and  after  work  were  taken. 
Since  the  distance  of  the  test  card  was  kept  the  same  for  the  two  tests,  this  change  in 
the  visual  acuity  tended  to  influence  the  ratio,  time  clear  to  time  blurred.  To  deter- 
mine the  length  of  time  needed  under  a  given  intensity  of  light  to  insure  a  constant 
acuity,  so  far  as  adaptation  is  concerned,  preliminary  tests  were  made  as  follows. 
The  acuity  of  the  observer  was  taken  every  3  minutes  until  no  noticeable  change 
was  found.  This  length  of  time  was  then  always  allowed  for  that  observer  as  an 
adaptation  period  prior  to  the  loss  of  efficiency  test  conducted  for  the  given  intensity 
of  illumination. 
5 


468     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY' 

ments  were  made  for  the  highest  intensity  employed  at  the  66 
stations  in  the  test  room.  These  measurements  were  made  in 
the  way  described  in  the  preceding  section.  For  the  other  in- 
tensities used,  measurements  were  made  at  nine  representative 
stations  to  show  in  a  general  way  the  order  of  magnitude  of 
reduction  produced  by  using  the  lamps  of  lower  wattage.  (2) 
Brightness  measurements  were  made  of  the  prominent  objects 
in  the  room,  such  as  :he  test  card,  the  book  of  the  observer,  and 
all  surfaces  showing  very  high  or  very  low  brilliancy  for  all  of 
the  intensities. 

In  Table  VIII  are  given  the  illumination  measurements  at  the 
66  stations  for  the  highest  wattages  used,  made  with  the  re- 
ceiving test  plate  of  the  photometer  in  the  horizontal,  vertical, 
and  45  deg.  planes.  Tables  IX  and  X  show  the  illumination  meas- 
urements at  the  nine  representative  stations  for  the  other  watt- 
ages  employed  in  the  series.  The  order  of  magnitude  of  reduc- 
tion of  the  illumination  of  the  room  produced  by  using  the  lamps 
of  lower  wattage  conforms  pretty  closely  in  each  case,  it  will  be 
observed,  to  the  simple  ratio  of  the  wattages  employed.  (See 
foot-note  to  Table  XII,  p.  472.)  As  was  the  case  for  the  semi- 
indirect  system,  noted  in  the  preceding  paper,  socket  extenders 
had  to  be  used  with  the  25  and  40-watt  lamps.  That  is,  without 
the  extenders  these  lamps,  owing  to  their  smaller  size,  came  so  low 
in  the  reflector  as  to  change  the  distribution  effects  given  by 
reflectors.  For  example,  without  the  socket  extenders  for  these 
shorter  lamps,  the  spot  of  light  on  the  ceiling  was  made  smaller 
and  correspondingly  more  brilliant.  It  was  thought  advisable  to 
determine  whether  this  comparatively  small  change  in  illumina- 
tion effects  would  cause  any  difference  in  the  eye's  ability  to  hold 
its  efficiency  for  a  period  of  work.  In  the  specification  of  illumi- 
nating effects,  therefore,  measurements  have  been  made  for  the 
25  and  40-watt  lamps  both  with  and  without  socket  extenders. 
In  Table  IX  illumination  measurements  for  the  25  and  40-watt 
lamps  are  given  with  socket  extenders,  and  in  Table  X  illumina- 
tion measurements  for  these  lamps  are  given  without  socket 
extenders.  In  Table  XI  are  given  the  brightness  measurements 
for  the  indirect  installation  for  the  different  intensities  used,  both 
with  and  without  socket  extenders  for  the  25  and  40-watt  lamps. 


FERREE    AND   RAND:     EFFICIENCY   OF   THE    EYE 


469 


The  points  at  which  the  measurements  were  taken  are  indicated 
by  the  letters  A,  B,  C,  D,  E,  F,  etc.,  see  Fig.  4,  p.  452b.  In  Table 
XII  are  given  the  prominent  brightness  ratios  for  the  different 
intensities  used.  Obviously  an  important  point  of  comparison 
for  the  purposes  of  this  investigation  is  the  ratios  with  and  with- 
out socket  extenders  for  the  25  and  40-watt  lamps. 


TABLE  VIII.— Intensity  Series. 
Showing  the  illumination  measurements  in  foot-candles  for  each  of  the  66 
stations  represented  in  Fig.  1  for  the  indirect  system  used. 


tatiot 

»   Horizontal 

Vertical 

45° 

Station 

Horizontal 

Vertical 

45° 

I 

1.22 

— 

— 

34 

4.0 

I.46 

3-i 

2 

1.26 

— 

— 

35 

5-4 

1-65 

4-9 

3 

1-32 

— 

— 

36 

5-3 

I.65 

4.0 

4 

1.47 

— 

— 

37 

5-8 

I.82 

4.0 

5 

2.2 

— 

38 

5-4 

I.72 

3-8 

6 

2-95 

— 

— 

39 

4.0 

1-43 

3-o 

7 

2.9 

— 

— 

40 

2-3 

— 

— 

8 

3-0 

— 

— 

4i 

2.1 

— 

— 

9 

2.2 

— 

— 

42 

3-5 

1.36 

2.8 

10 

1-35 

— 

— 

43 

5-o 

1.78 

3-9 

11 

1.66 

— 

— 

44 

5-2 

1.88 

4-3 

12 

2.7 

O.47 

1-43 

45 

5-2 

i-93 

4.2 

13 

4-1 

O.42 

1.96 

46 

5-2 

1.86 

4-i 

14 

4-4 

0.47 

2-3 

47 

3-6 

1-33 

2-9 

15 

4-5 

O.47 

2-3 

48 

3-7 

1.74 

3-3 

16 

4-1 

O.48 

2.1 

49 

4-8 

2.1 

4.0 

17 

3-15 

O.46 

1.6 

50 

4-9 

2.1 

4.1 

18 

2.2 

O.47 

1.63 

5i 

5o 

2.15 

4-35 

19 

2.5 

— 

— 

52 

4-7 

i-93 

4.0 

20 

3-4 

O.86 

2.2 

53 

3-6 

1.41 

3° 

21 

4.6 

0.94 

3-° 

54 

2.8 

i-5 

2.9 

22 

4-8 

I.07 

2.9 

55 

3-9 

1.94 

3-75 

23 

5-i 

1. 1 

2.9 

56 

4.6 

2.1 

4.4 

24 

5-o 

I.04 

3-o 

57 

4-5 

2.2 

4.4 

25 

3-5 

0-75 

2.1 

58 

4.0 

2.0 

4.0 

26 

2.2 

— 

— 

59 

2-9 

1.76 

3-i 

27 

2.4 

— 

— 

60 

2.6 

1.66 

2.9 

28 

3-7 

1. 12 

2.5 

61 

3-i 

i-9 

3-5 

29 

5-2 

I.48 

3-4 

62 

3-2 

2.1 

3-7 

30 

5-4 

i-4 

3-6 

63 

3-o 

2.2 

3-5 

3i 

5-2 

1.24 

3-6 

64 

3-1 

i-93 

3-4 

32 

5-o 

i-33 

3-4 

65 

2.25 

i-54 

2.6 

33 

3-7 

1.22 

2.6 

66 

i-35 

— 

— 

Average  3.61 

1.48 

3-3 

4/0     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

TABLE  IX. — Intensity  Series. 
Showing   the  illumination  measurements  in  foot-candles  at  nine  repre- 
sentative stations  for  the  different  intensities  used  for  the  indirect  system. 
Socket  extenders  used  with  the  40  and  25-watt  lamps. 


Station 

Horizontal 

Vertical 

45° 

800 

4S0         320 

200 

800 

480 

320 

200 

800 

480 

320 

200 

Card 

5-2 

3.0      1.7 

1-33 

1.36 

O.765 

O.49 

039 

3-5 

i-97 

1.08 

0.87 

12 

2.7 

I.63  O.97 

0.65 

0.47 

0.265 

0.18 

O.I2 

1-43 

0.83 

0.48 

0.44 

16 

4.1 

2.2       I.32 

1. 11 

0.52 

0-33 

O.24 

O.14 

2. 1 

1.22 

0.66 

0.6 

3t 

5-2 

2.7       I.84 

i-45 

1.24 

0.77 

O.51 

0.47 

3-6 

1-95 

1. 16 

1. 01 

34 

4.0 

2.25    1. 21 

1.0 

1.46 

0.79 

O.52 

O.49 

3-1 

1.63 

0.89 

0.78 

39 

4.0 

2.2       1.6 

0.83 

1-43 

O.725 

O.51 

0.37 

30 

1-57 

1.04 

0.64 

45 

5-2 

2-75  i-94 

1.28 

i-93 

O.99 

O.58 

0.53 

4.2 

2.18 

1-43 

1.0 

54 

2.8 

1.48  I. 16 

0.68 

i-5 

0.82 

0.63 

O.41 

2.9 

I.5I 

1.23 

0.68 

58 

4.0 

2.1       I.3 

1.09 

2.0 

O.94 

O.64 

O.52 

4.0 

2.2 

i-3 

0.98 

Ave. 

3.61 

2.l6    I.44 

0.9 

1.32 

0.S9 

0.59 

0.37 

3-3 

1.98 

1.32 

0.83 

TABLE  X.— Intensity  Series. 
Showing  the  illumination  measurements  in  foot-candles  at  nine  represen- 
tative stations  for  the  different  intensities  used  for  the  indirect  system.     No 
socket  extenders  used  with  the  40  and  25-watt  lamps. 


Station 

Horizontal 

Vertical 

45° 
*  ■ 

800 

480         320 

200 

800 

480 

320 

200 

800 

480 

320 

200 

Card 

5-2 

3.0      I.48 

I. 16 

1.36 

O.765 

0.407 

0.37 

3-5 

1.97 

o.95 

0.76 

12 

2.7 

I.63  O.84 

0.5 

0.47 

0.265 

O.I39 

O.99 

1-43 

0.83 

o.44 

0.282 

16 

4.1 

2.2       I. OI 

O.96 

0.52 

0.33 

O.143 

O.14 

2.1 

1.22 

0.5 

0.48 

3i 

5-2 

2.7       I.48 

1-3 

1.24 

0.77 

O.462 

0-39 

3-6 

1-95 

1.0 

0.86 

34 

4.0 

2.25    O.99 

1.0 

1.46 

0.79 

0.5 

0.45 

3-i 

I.63 

0.84 

0.8 

39 

4.0 

2.2       I.63 

0.78 

1-43 

o.725 

0.44 

O.36 

3-o 

1-57 

0.98 

0.6 

45 

5-2 

2.75    1.62 

1. 18 

i-93 

0.99 

O.52 

0.48 

4.2 

2.18 

i-3i 

0.98 

54 

2.8 

I.48    I.03 

0.63 

i-5 

0.82 

0.61 

O.41 

2-9 

I.5I 

1. 18 

0.65 

58 

4.0 

2.1       I. II 

0.87 

2.0 

O.94 

0.54 

0.42 

4.0 

2.2 

1. 11 

0.83 

The  results  of  the  tests  for  the  intensity  series  for  the  indirect 
system  are  given  in  Table  XIII.  Three  hours  was  selected  as  the 
period  of  work  in  all  of  these  experiments.  The  tests  were  taken 
only  as  Position  I  (see  Fig.  1,  p.  452a),  the  position,  it  will  be  re- 
membered, at  which  six  of  the  fixtures  were  in  the  field  of  view. 
It  will  be  noted  that  there  is  practically  no  difference  in  the  loss 
of  efficiency  of  the  eye  for  the  different  intensities  of  illumination 
when  socket  extenders  were  used  for  the  shorter  lamps.  When 
socket  extenders  were  not  used  for  these  lamps,  quite  a  little  loss 
of  efficiency  was  experienced.  This  loss,  moreover,  was  consider- 
ably greater  for  the  shorter  25-watt  lamps  than  for  the  40-watt 


FERREE   AND   RAND:     EFFICIENCY   OF   THE   EYE 


471 


lamps.  Since  the  prominent  variable  in  this  case  was  intrinsic 
brilliancy  of  the  ceiling  spot  above  the  reflector,  the  increased  loss 
of  efficiency  can  probably  be  ascribed  primarily  to  this  cause;  or 
more  comprehensively  stated  perhaps,  to  the  change  in  the  magni- 
tude of  the  brightness  differences  that  were  present  in  the  field  of 
vision.  For  example,  the  ratio,  lightest  to  darkest  for  the  100- 
watt  lamps  was  145;  it  was  133  for  the  60-watt  lamps;  142  for 
the  40- watt  lamps  with  socket  extenders;  and  135  for  the  25- 
watt  lamps  with  socket  extenders.  For  the  40-watt  lamps  with- 
out socket  extenders,  however,  this  ratio  was  raised  to  326,  and 
for  the  25-watt  lamps  without  socket  extenders  it  was  raised  to 
374.  Similar  changes  were  also  made  in  the  other  ratios :  lightest 
to  test  card,  lightest  to  reading  page,  etc.,  as  may  be  seen  by  in- 
specting Table  XII. 


TABLE  XI.— Intensity  Series. 

Showing  the  brightness  measurements  in  candlepower  per  square  inch 
for  the  different  intensities  used  for  the  indirect  system  at  points  indicated 
by  the  letters  A,  B,  C,  D,  etc.,  see  Fig.  4. 

320  watts  200  watts 

With         Without  With  Without 
Surface                    800                   480           socket  ex-    socket  ex-  socket  ex-  socket  ex- 
measured              watts              watts             tenders        tenders  tenders  tenders 

A O.138            0.0704          O.0539          O.088  O.0352  0.0748 

B 0.0715          0.0385          O.0252          0.0231  0.0165  0.0187 

C 0.066           0.0352         0.0244         0.022  0.0159  0.0165 

D 0.0022          0.00097       0.00079       0.00059  0.00064  0.0004 

E 0.0030         0.000163     o. 001 19       0.0007  0.000S4  0.00057 

F 0.00123       0.000401     0.00035       0.00022  0.00032  0.00018 

G 0.0049         0.00169       0.00145       0.00101  0.00128  0.00084 

H 0.0040        0.00163      0.00129      0.00092  0.0011  0.00072 

I   0.0042         0.00158      0.00127       0.0009  0.0011  0.00068 

J  0.00095       0.00053       0.00038       0.00027  0.00026  0.0002 

K o.  00255       0.00123       0.00088       0.00088  0.00074  0.00064 

L 0.00246      0.0012 1       0.00085      0.00079  0.00066  0.00046 

M 0.00352      0.00158      0.00106      0.00097  0.00052  0.0007 

N 0.00272       0.00101       0.00076      0.00061  0.00066  0.00044 

0 0.00343       0.00128      0.00076      0.00028  0.00055  0.00019 

P    j. 00308,     o. 001 19      0.00067       0.00027  0.00041  0.00018 

X 0.00299       0.00154       0.00109      0.0008  0.00074  0.00059 

Reading  page 

horizontal  ..0.008S        0.00405      0.00281       0.0022  0.00198  0.0016 
Reading  page 

450  position  0.00431       0.00273      0.00167      0.00154  0.00117  0.0009 


472     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


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FERREE    AND   RAND:     EFFICIENCY   OF   THE   EYE 


475 


A  graphic  representation  of  the  results  for  the  indirect  sys- 
tem with  socket  extenders  is  given  in  Chart  II.  In  this  chart 
loss  of  efficiency  is  plotted  against  time  of  work  in  the  manner 
described  in  the  preceding  section.  For  the  sake  of  comparison 
results  are  shown  also  on  this  chart  for  the  direct  and  semi- 
indirect  systems.  A  graphic  representation  has  further  been 
made  of  the  results  for  the  indirect  system  with  and  without 
socket  extenders.     This  is  shown  in  Chart  III. 

CHART  III.  -Intensity  Series. 
Showing  the  effect  on  loss  of  efficiency  of  changing  the  height  of  the  light 
source  in  the  reflector  of  the  indirect  lighting  fixtures.  The  effect  on  surface 
brightness  is  primarily  to  change  the  area  and  surface  brilliancy  of  the  spot  of 
light  thrown  on  the  ceiling.  Chart  A  shows  the  results  when  height  of 
source  in  the  reflector  is  changed;  Chart  B,  the  results  when  the  height  is 
kept  approximately  constant. 


CHART  A 


CHARTB 


1,25  WATTS 

j^——            t  en      . 

/ 

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0 

J 

3                4 

EYE  SHADE  SERIES. 
This  series  of  experiments  has  been  conducted  for  the  follow- 
ing reasons,  (i)  In  general  two  methods  are  used  to  protect 
the  eye  from  the  source  of  light,  eye  shades  and  lamp  shades. 
It  is  desirable  to  know  whether  the  eye  is  protected  equally  well 
by  both;  and  if  the  eye  shade  can  be  substituted  for  the  lamp 
shade,  what  type  of  shade  would  best  serve  the  purpose.  (2) 
And  the  statement  has  been  made  to  us  many  times  that  with  an 
eye  shade  the  three  systems  of  artificial  lighting  we  have  used 
should  give  equally  good  results :  and  results,  moreover,  as  good 


4/6     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

as  those  given  by  the  indirect  system  without  an  eye  shade. 
There  are  in  general  two  classes  of  eye  shades,  the  translucent 
and  opaque.  Up  to  this  time  we  have  confined  our  work  to  the 
opaque  shade.  So  far  as  we  know  it  is  customary  to  make  the 
opaque  shade  with  a  dark  lining.  This  kind  of  lining  is  em- 
ployed probably  because  of  some  notion  that  it  is  restful  to  the 
eye  to  darken  as  much  of  the  field  of  vision  as  is  possible.18 

The  tests  were  begun  with  the  opaque  shade  with  the  dark 
lining.  What  we  found  as  the  result  of  these  tests  was  somewhat 
in  contradiction  to  the  predictions  that  had  been  made.  The 
shade  did  give  pretty  nearly  the  same  results  for  the  three  sys- 
tems ;  but  it  did  this,  contrary  to  prediction,  by  improving  the 
direct  and  semi-indirect  systems  and  making  worse  by  almost 
an  equal  amount  the  indirect  system.  That  is,  protected  by  the 
opaque  shade,  the  eye  lost  in  efficiency  for  the  three  systems  by 
an  amount  somewhere  near  the  mean  of  the  losses  experienced 
by  it  for  the  three  systems  without  a  shade.  Nor  is  this  result 
surprising  when  one  reflects  upon  the  conditions  imposed  upon 
the  eye  by  an  opaque  shade  with  a  dark  lining.  While  it  pro- 
tects the  eye  from  the  sources  of  light,  such  a  shade  does  not  by 
any  means  eliminate  harmful  brightness  differences  in  the  field 
of  vision.  It  in  fact  creates  for  the  eye  a  very  unnatural  bright- 
ness relation,  i.  e.,  it  renders  the  whole  upper  half  of  the  field  of 
vision  dark  in  sharp  contrast  with  the  brightly  lighted  lower 
half.  The  direct  effect  of  this  is  a  strong  brightness  induction 
C physiological)  over  the  lower  half  of  the  field  of  vision  which 
manifests  itself  to  the  observer  by  causing  glare  in  surfaces  that 
have  no  glare,  and  by  increasing  the  glare  in  surfaces  in  which 
glare  is  already  present.  This,  it  is  scarcely  necessary  to  point 
out,  operates  against  the  discrimination  of  detail  and  puts  the 
eye  under  strain  to  see  its  objects  clearly.  Moreover,  the  unusual 
and  strongly  irregular  character  of  the  image  formed  on  the  ret- 
ina probably  also  sets  up  a  warfare  in  the  incentives  given  to 
the  muscles  which  adjust  the  eye.  That  is,  the  upper  half  of 
the  field  of  vision  is  dark  and  presents  no  detail.  The  effect  of 
this  is  probably  to  exert  a  tendency  to  cause  the  muscular  relax- 

18  Another  popular  view  might  be,  so  far  as  protection  to  the  eye  is  concerned,  to  re- 
gard the  opaque  eye  shade  as  the  analogue  of  the  opaque  or  perhaps  the  indirect  lamp 
reflector  and  the  translucent  shade  as  the  analogue  of  the  semi-indirect  reflector. 


FERREE   AND   RAND:     EFFICIENCY    OF    THE    EVE  4/7 

ation  characteristic  of  the  darkened  field  of  vision.  The  lower 
half  of  the  field  is  light  and  filled  with  detail.  The  incentive 
here  is  towards  the  best  possible  adjustment  of  the  eye  for  the 
discrimination  of  detail  in  the  objects  viewed,  while  the  rim 
of  the  shade,  the  sharply  marked  boundary  between  the  dark  and 
light  halves  of  the  field  of  vision  and  much  nearer  to  the  eye 
than  the  objects  viewed,19  serves  as  a  constant  and  consciously 
annoying  distraction  to  fixation  and  accommodation.  These 
complex  and  somewhat  contradictory  impulses  given  to  the  mus- 
cles of  the  eye  might  very  well,  and  doubtless  do  cause  an  exces- 
sive and  unnatural  loss  of  energy  and  efficiency  in  case  of  the 
prolonged  adjustment  of  the  eye  needed  for  a  period  of  work. 

Early  in  the  course  of  the  tests  it  occurred  to  us  that  we  might 
render  the  brightness  distribution  in  the  field  of  view  presented 
to  the  eye  wearing  a  shade  more  natural,  and  thereby  improve 
the  effect  of  the  shade  on  the  eye,  by  employing  a  white  instead 
of  a  dark  lining.  By  using  a  matt  white  paper20  with  a  reflection 
coefficient  of  about  75  per  cent,  for  this  lining,  the  following 
effects  were  produced.  The  two  halves  of  the  field  of  vision 
were  rendered  much  more  nearly  of  equal  brightness ;  the  glare 
in  the  lower  half  of  the  field  of  vision  was  very  noticeably 
lessened  and  the  discrimination  of  detail  was  correspondingly 
improved;  the  upper  half  of  the  field  of  view  no  longer  tended 
to  give  to  the  eye  the  reflexes  of  the  darkened  field  of  vision; 
and  the  rim  of  the  shade  did  not  stand  out  nearly  so  distinctly 
in  the  field  of  view  to  distract  accommodation  and  fixation.  The 
results  of  the  test  for  loss  of  efficiency  show,  moreover,  that  our 
surmise  with  regard  to  the  effect  of  this  change  on  the  eye  was 
correct.  The  action  of  the  white  lining  was  greatly  to  improve 
the  ability  of  the  eye  to  maintain  its  efficiency  for  a  period  of 
work.  As  good  results  were  not  gotten,  however,  with  the  shade 
for  any  of  the  systems  as  were  given  by  the  indirect  system 
without  the  shade.  Since  there  was  a  still  greater  evenness  of 
surface  brightness  in  the  field  of  view  in  case  of  the  indirect 
system  with  the  eye  shade  than  without,  the  question  arises  why 

19  This  rim  is  about  three  inches  in  front  of  the  observer's  eye  when  the  shade  is  in 
position. 

■  Hering  standard  white  paper  was  used  for  this  lining.    The  reflection  coefficient 
of  the  dark  lining  was  about  6-8  per  cent. 


4/8     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

at  least  as  good  results  were  not  obtained  with  the  shade  as 
without.  The  answer,  we  believe,  is  to  be  found  in  terms  of 
the  distraction  to  fixation  and  accommodation  caused  by  the  eye 
shade  even  when  a  light  lining  was  used.  For  the  effect  of  a 
shade  on  the  eye  even  when  the  most  favorable  lining  is  em- 
ployed is  that  of  a  constantly  present  distracting  object  with 
its  lower  margin  not  far  removed  from  the  center  of  the  field  of 
vision,  and  much  nearer  to  the  eye  than  are  the  objects  which 
the  observer  is  called  upon  to  discriminate.  It  will  be  noticed 
also  in  Table  XVII  that  the  results  were  never  so  good  for  either 
kind  of  shade  for  the  direct  and  semi-indirect  systems  as  for  the 
indirect.  Since  the  evenness  of  surface  brightness  in  the  field 
of  view  was  not  very  different  for  the  three  systems  in  both 
cases,  this  again  probably  indicates  that  the  evenness  of  surface 
brightness  is  not  the  only  one  of  the  distribution  factors  that  has 
to  be  taken  into  account  in  studying  the  effect  of  different  con- 
ditions of  lighting  on  the  eye. 

These  tests  were  made  for  the  same  installations  that  were  used 
in  the  distribution  series.  Since  the  use  of  the  eye  shade  did  not 
affect  the  illumination  of  the  room  the  reader  is  referred  for  the 
illumination  measurements  to  the  tables  of  the  distribution  series. 
The  distribution  of  surface  brightness  in  the  field  of  vision,  how- 
ever, was  strongly  affected.  New  measurements  were  made, 
therefore,  of  the  brightness  of  the  prominent  surfaces  in  the  field 
of  vision.  The  tests  were  taken  at  Position  I,  see  Fig.  i,  p.  452a 
The  prominent  surfaces  in  the  observer's  field  of  vision  working 
in  this  position  were  J,  K,  and  L  (see  Fig.  4,  p.  452b)  ;  the  top 
of  the  table  carrying  test  and  recording  apparatus,  immediately 
in  front  of  the  observer  and  below  the  level  of  his  eyes;  the  test 
card ;  the  reading  page  in  the  45  deg.  position ;  and  the  white  and 
dark  lining  of  the  eye  shade  as  seen  by  the  observer  when  the 
shade  was  in  position  over  his  eyes.  The  measurements  of  the 
brightness  of  the  lining  of  the  eye  shades  as  seen  by  the  observer 
when  the  shades  were  in  position  were  made  as  follows.  A  sur- 
face in  front  of  the  observer  was  made  to  match  in  brightness  the 
lining  of  the  shade  as  it  was  seen  by  him.  The  brightness  of  this 
surface  was  then  measured  by  the '  method  described  on  page 
452.    In  procuring  the  match  between  the  comparison  surface  and 


FERREE   AND    RAND:     EFFICIENCY   OF   THE   EVE  479 

the  lining  of  the  shade  the  series  of  Hering  matt  gray  papers  was 
employed.  This  series  consists  of  50  shades  ranging  from  a  white 
with  a  reflection  coefficient  of  75  per  cent,  to  black.  Sheets  of 
these  differing  in  brightness  were  placed  in  a  vertical  position  at 
a  given  distance  in  front  of  the  observer  until  an  approximate 
match  was  made  with  the  lining  of  the  shade.  The  gradations 
needed  to  get  the  final  match  were  secured  by  moving  the  sur- 
face to  and  from  the  observer  and  by  tilting  it  at  different  angles 
with  the  line  of  sight.  The  former  adjustment  carried  it  into 
parts  of  the  room  having  different  intensities  of  illumination  and 
the  latter  turned  it  so  as  to  receive  a  greater  or  less  amount  of 
light.  In  making  the  brightness  measurements,  care  was  taken 
to  have  the  receiving  surface  of  the  photometer  arm  normal  at 
its  central  point  to  the  line  of  sight  taken  by  the  observer  when 
the  match  was  made.  The  results  of  these  measurements  are 
shown  in  Table  XIV.  In  Table  XV  are  given  some  of  the  prom- 
inent ratios  of  surface  brightness  in  the  field  of  vision  for  the 
shade  with  the  dark  lining ;  and  in  Table  XVI,  some  of  the  prom- 
inent ratios  for  the  shade  with  the  white  lining.  In  Table  XVII 
are  shown  the  results  for  the  test  for  loss  of  efficiency  for  the 
shade  with  the  dark  lining;  and  in  Table  XVIII  for  the  shade 
with  the  white  lining.  For  purposes  of  comparison  the  results 
of  the  three  systems  without  a  shade  are  repeated.  These  are 
given  in  Table  XIX.  A  graphic  representation  results  of  all 
three  tables  is  given  in  Chart  IV. 

TABLE  XIV.— Eye  Shade  Series. 

Showing  the  brightness  measurements  in  candlepower  per  square  inch 
for  the  various  surfaces  in  the  field  of  vision  for  the  direct,  semi-indirect  and 
indirect  systems  used  when  the  eyes  were  shielded  in  turn  by  an  opaque 
eye  shade  with  a  dark  lining,  and  an  opaque  eye  shade  with  a  white  lining. 

Surface  Direct  Semi-indi-  Indirect 

measured  system  rect  system  system 

J 0.0014  O.OOI  0.00095 

K 0.0063  0.0046  0.00255 

L 0.0042  0.0027  0.00246 

Table 0.0029  0.00255  0-00233 

Test  card 0.00308  0.003  0.00299 

Reading  page  450  position 0.004  0.0039  0.00431 

White  lining  of  eye  shade 0.00197  0.00204  0.00207 

Dark  lining  of  eye  shade 0.000091  0.00011  0.000126 


480     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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482     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


TABLE  XIX.— Eye-Shade  Series. 

Showing   the  eye's  loss  in  efficiency  as  the  result  of  3    hours   of    work 

under  the  direct,  semi-indirect,  and  indirect  systems  of  lighting  employed 

(No  eye  shade.) 

Maximal 

distance  at 

Foot-candles  which  test 

, ■ ,  object  can 

Lighting  Hori-  Verti-  be  seen 

system  Watts  zontal  cal  45°  Time  clear 

Indirect 800            5.2             1.36             3.5               9  A.M.  84.5 

12  M.  84.5 

Semi-indirect.  760            5.8            1.45            4.0              9A.M.  80.5 

12  m.  79.5 

Direct 880            4.2             1.41             2.6               9  A.M.  S1.0 

12  M.  78.0 

Total 
time 
clear 
Work-  -5-  Ratios 

ing  Total  Total  total  reduced 

dis-  time  time  time  to  common 

tance  clear  blurred  blurred  standard 

Indirect 67.5  135  45  3-°°  3-5 

67.5  132  48  2.75  3.2 

Semi-indirect 68.5  142  38  3.73  3.5 

68.5  92  88  1.64  0.97 

Direct    68.0  139  41  3.39  3.5 

68.0  771  109  0.69  0.671 

As  yet  we  have  not  determined  the  effect  of  translucent  shades 
on  the  eye.  In  attempting  to  deal  in  a  general  way  with  this 
class  of  shades  we  have  the  same  type  of  difficulty  to  face  that  we 
have  in  case  of  the  semi-indirect  reflector.  That  is,  we  may  have 
shades  varying  from  transparent  to  opaque,  and  sharing  in  the 
merits  and  demerits  of  each  extreme.  Our  judgment  would  be, 
however,  that  it  would  be  very  difficult  to  get  a  translucent  shade 
that  would  give  as  good  results  as  an  opaque  shade  with  a  light 
lining;  for  the  translucent  shade  when  made  sufficiently  opaque 
to  give  the  needed  reduction  to  the  image  of  the  source  will 
darken  too  much  the  upper  half  of  the  field  of  vision  and  thereby 
simulate  too  much  the  condition  given  by  the  opaque  shade  with 
the  dark  lining  to  give  the  best  results  for  comfortable  and  effi- 
cient seeing.  Moreover,  from  the  results  that  have  already  been 
obtained  with  the  opaque  shade  and  from  the  principles  it  seems 
fair  to  infer  from  these  results,  it  seems  very  probable  to  us  that 
as  good  effects  for  seeing  should  not  be  expected  from  the  use  of 


FERREE   AND   RAND:     EFFICIENCY   OF   THE    KVE 


483 


any  kind  of  eye  shade  as  may  be  gotten  from  lamp-shades.  That 
is.  if  we  are  to  secure  the  best  results  for  seeing,  the  shade  should 
be  put  on  the  lamp,  not  on  the  eye. 

THE  ANGLE  AT  WHICH  THE  LIGHT  FALLS  ON 
THE  WORK. 

The  object  of  these  experiments  was  to  find  out  whether  the 
CHART  IV.— Eye  Shade  Series. 
Showing  the  effect  on  loss  of  efficiency  of  opaque  eye  shades  with  dark  and 
with  white  lining  for  the  installations  direct,  semi-indirect,  and  indirect 
with  the  same  intensity  of  light  at  the  point  of  work.  Chart  A  shows 
results  without  shade  ;  Chart  B,  with  shade  having  dark  lining;  Chart  C" 
with  shade  having  white  lining. 


CHART  A 

— INC 

M£I±_ 

\Nm*-, 

• 

s 

5S 

cr 

SEMI -INDIRECT 


difference  in  the  angle  at  which  the  light  falls  on  the  work  pro- 
duces an  effect  on  the  eye  that  can  be  detected  by  the  test  we 
have  used  for  loss  of  efficiency.  For  the  purpose  of  this  pre- 
liminary investigation  it  was  decided  to  make  the  general  illumi- 
nation of  the  room  such  as  to  cause  the  eye  little  loss  of  effi- 
6 


484     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ciency  as  the  result  of  the  period  of  work ;  and  to  add  to  that 
at  the  point  of  work  a  component  of  light  which  was  less  diffuse 
in  order  that  the  amount  of  light  entering  the  eye  would  be  more 
dependent  upon  the  angle  at  which  the  reading  page  was  held. 

The  general  illumination  was  obtained  from  the  indirect  system 
used  in  the  work  of  the  preceding  sections  with  lamps  totalling 
800  watts.  The  less  diffuse  component  at  the  point  of  work 
was  obtained  from  a  60-watt  lamp  with  a  porcelain  reflector  of 
the  desk  lamp  type.  This  lamp  was  turned  into  the  horizontal 
position  and  was  placed  behind  the  observer  and  to  the  left  so 
that  the  light  came  over  the  left  shoulder.  When  in  the  position 
for  which  the  test  was  taken  the  tip  of  the  lamp  was  slightly 
above  the  level  of  the  observer's  eye,  at  a  distance  of  1  meter 
from  the  left  eye. 

The  illumination  and  brightness  measurements  for  the  test 
room  illuminated  by  the  indirect  system,  800  watts,  are  given  on 
pp.  469  and  471.  These  measurements  were  not  greatly  changed 
by  the  addition  of  the  60-watt  lamp  behind  the  observer.  Because 
of  the  presence  of  this  lamp,  however,  the  following  measurements 
were  added  to  those  given  on  pp.  469  and  471  :  the  horizontal, 
vertical,  and  45  deg.  components  of  light  at  the  point  of  work ;  the 
brightness  of  the  test  card  in  place  for  the  test ;  and  the  brightness 
of  the  reading  page  when  held  respectively  in  the  positions  which 
gave  the  least  and  the  greatest  amounts  of  specular  reflection. 
The  illumination  measurements  at  the  point  of  work  are  given  in 
Table  XX.  The  brightness  of  the  test  card  was  0.00365  cp.  per 
sq.  in. ;  of  the  reading  page  in  the  position  that  gave  the  least 
amount  of  specular  reflection,  0.0059  cp.  per  sq.  in. ;  and  in  the 
position  that  gave  the  greatest  amount  of  specular  reflection, 
0.0077  CP-  Per  S{1-  m-  A  mirror  surface  was  used  as  an  aid  in 
locating  the  position  of  least  and  greatest  specular  reflection. 
The  results  of  the  test  for  three  hours  of  work  done  with  the 
reading  page  in  these  two  positions  are  also  given  in  Table  XX. 
A  graphic  representation  of  the  results  of  this  table  is  shown  in 
Chart  V. 

THE  EFFECT  OF  DIFFERENT  CONDITIONS  OF  LIGHTING 
ON  THE  FIXATION  MUSCLES  OF  THE  EYE. 

The  test  we  have  employed  thus  far  in  the  conduct  of  our 


FERREE    AND   RAND:     EFFICIENCY   OF   THE   EYE 


485 


work  is  one  designed  to  show  the  effect  of  different  conditions  of 
lighting  on  the  ability  of  the  eye  to  hold  its  efficiency  for  clear 
seeing  for  a  period  of  three  minutes.  In  itself  this  test  is  not 
TABLE  XX.— The  Angle  at  Which  the  Light  Falls  on  the  Work. 
Showing  the  effect  on  loss  of  efficiency  of  the  angle  at  which  the  light 
falls  on  the  work. 


Kind  of 
reflection 
from  read- 
ing page 
during 
work  period 


Foot-candles  at 
test-card 


Hori- 
zon- 
tal 


Diffuse    5.3 

Specular 5.3 


Work- 
ing 
dis- 
tance 

Diffuse 73 

73 
Specular 73 

73 


Verti- 
cal 


I.84 


Total 
time 
clear 

139 

137 

137 

132 


45° 

3-9 
3-9 


Total 

time 

blurred 


41 
43 
43 


Time 
9  A.M. 

12  M. 
9  AM. 

12  M. 

Total 
time 
clear 

total 

time 

blurred 

3-39 
3.18 
3.18 

2.73 


Maximal 
distance 
at  which 
test  ob- 
ject can 
be  seen 
clear 


89 
89 
89 


Ratios 
reduced 
to  com- 
mon 
standard 

3-5 

3-27 

3-5 

3-o 


analytical  in  principle.  The  results,  as  is  stated  above,  are  ex- 
pressed in  terms  of  an  aggregate  loss  of  function.  The  con- 
tributive  factors  may  be  inferred  from  the  nature  of  the  test,  but 

CHART  V.— The  Angle  at  Which  the  Light 

Falls  on  the  Work. 

Showing  the  effect  on  loss  of  efficiency  of  the  angle 

at  which  the  light  falls  on  the  work. 


1  ~3~ 

the  test  is  not  in  itself  designed  to  separate  them  out.  And 
indeed  it  is  a  question  whether  any  practical  good  can  accrue  to 
the  practise  of  lighting  from  a  knowledge  of  just  what  part  of 


486     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  visual  apparatus  it  is  that  falls  off  in  function  as  the  result 
of  an  unfavorable  condition  of  lighting.  Obviously  the  chief 
need  is  to  find  out  what  are  the  conditions  that  cause  the  eye  to 
lose  its  ability  to  see  clearly  and  to  avoid  these  conditions  in 
planning  and  installing  a  lighting  system.  From  the  beginning 
we  have  had  in  mind,  however,  an  analysis  of  effect.  Our  tests 
for  the  sensitivity  of  the  retina  showed,  for  example,  that  very 
little,  if  any,  of  the  difference  in  results  we  have  gotten  for  the 
four  types  of  lighting  we  have  employed  can  be  ascribed  to  a 
loss  in  the  efficiency  of  the  retina,  or  the  light  sensitive  part  of 
the  visual  apparatus.  Three  sets  of  factors  are  involved  in  clear 
seeing :  ( 1 )  the  sensitivity  of  the  eye  to  colored  and  white  light ; 
(2)  the  ability  to  make  fine  space  discriminations  which  is  in 
part  dependent  upon  our  third  factor;  and  (3)  accurate  fixation 
and  accommodation.  Both  fixation  and  accommodation  are  the 
result  of  muscular  action.  When  the  muscles  lose  in  tone  because 
of  excessive  use  or  by  sharing  in  a  general  condition  or  state  of 
the  body,  the  eye  loses  correspondingly  in  its  power  to  sustain 
clear  seeing.  If,  for  example,  the  muscles  of  accommodation 
have  fallen  off  in  efficiency  the  lens  is  no  longer  held  in  the 
adjustment  needed  to  bring  the  light  to  a  sharp  focus  on  the 
retina  and  loss  of  detail  and  blurring  result ;  or,  if  it  be  the  fixa- 
tion muscles  that  have  suffered  the  loss,  the  eyes  cannot  be  con- 
tinuously held  in  such  a  position  that  the  images  of  the  object 
viewed  fall  symmetrically  on  the  fovea  of  each.  When  this  latter 
condition  is  present  loss  of  detail  results  from  two  causes.  (1) 
The  fovea  and  region  immediately  surrounding  it  are  the  most 
highly  developed  parts  of  the  retina  and  the  best  fitted  for  the  light 
and  space  discriminations  needed  for  clear  seeing.  Moreover,  the 
refracting  media  of  the  eye  give  the  clearest  images  when  the 
axis  of  the  cone  of  rays  from  the  object  viewed  deviates  as  little 
as  possible,  consistent  with  the  mechanism  of  the  eye,  from  the 
optic  axis.  And  (2)  if  the  images  in  the  two  eyes  do  not  fall 
more  or  less  symmetrically  upon  the  fovea  of  each  they  are  not 
accurately  combined  into  one,  and  blurring  and  loss  of  detail 
results  from  the  doubling  of  the  objects  seen.  It  is  our  purpose 
as  fast  as  possible  to  isolate  the  effect  of  the  three  systems  of 
lighting  we  have  used  on  each  of  the  above  named  factors.     In 


FERREE    AND   RAND:     EFFICIENCY   OF   THE    EYE  487 

the  work  of  the  present  section  the  effect  of  these  systems  on 
the  fixation  muscles  has  been  studied. 

The  doubling  of  the  image  seen  when  the  fixation  muscles  lose 
their  power  of  co-ordinated  action  furnishes  us  with  our  clue 
for  a  test  for  the  loss  of  efficiency  of  these  muscles.  That  is, 
just  as  blurring  and  the  loss  of  ability  to  discriminate  detail  is 
taken  as  the  criterion  of  the  loss  of  acuity  of  vision,  so  will  the 
doubling  of  the  image  seen  be  taken  as  our  index  of  the  loss  of 
the  co-ordinated  action  of  the  fixation  muscles.  If  one  were  to 
stare  continuously  for  an  interval  of  time  with  natural  vision  at 
a  simple  test  object,  as,  for  example,  a  vertical  line,  doubling 
might  be  detected  especially  if  there  had  been  protracted  strain 
or  considerable  loss  of  power  to  co-ordinate.  For  the  purpose  of 
our  work,  however,  greater  sensitivity  than  this  would  be 
needed.  Obviously  sensitivity  can  be  added  by  putting  the  eyes 
under  strain  to  combine  their  images.  When  this  is  done,  even 
when  the  muscles  are  fresh,  if  the  object  is  looked  at  or  fixated 
for  an  interval  of  time  it  will  be  seen  alternately  a.s  one  and  as 
two.  The  proportion  or  ratio  of  the  time  seen  as  one  to  the 
time  seen  as  two  can  be  regulated  by  the  amount  of  initial  strain 
under  which  the  eyes  are  put  to  combine  their  images.  The  regu- 
lation of  this  ratio  is  empirical  and  of  importance;  for  as  is  the 
case  with  the  test  for  loss  of  efficiency  for  clear  seeing,  the  sen- 
sitivity of  the  test  depends  to  a  considerable  extent  upon  the 
initial  value  that  is  given  to  this  ratio.  The  eyes  may  be  put 
under  strain  to  combine  their  images  by  interposing  between 
them  and  the  object  viewed  weak  prisms  and  so  adjusting  them 
and  regulating  the  distance  of  the  object  from  the  eye  that  with  the 
maximum  of  effort  to  see  it  as  one  it  is  seen  alternately  as  one  and 
as  two  in  the  proportion  desired.21     This  result  can  be  accom- 

21  It  would  seem  that  the  above  principle  might  be  utilized  to  advantage  by  the 
opthalmologist  in  testing  the  extrinsic  muscles  of  the  eye.  The  abduction  and  adduc- 
tion tests,  for  example,  determine  only  what  the  muscles  are  able  to  do  by  momen- 
tary effort.  Obviously,  however,  it  is  not  what  the  muscles  are  able  to  do  by  a 
momentary  effort  or  jerk  that  measures  their  ability  to  hold  the  eyes  continuously 
adjusted  for  work.  It  is  rather  their  endurance  or  what  they  are  able  to  accomplish 
in  an  interval  of  time.  An  expression  may  be  had  for  this  either  for  the  eyes  con- 
jointly or  separately  by  the  method  described  above.  That  is,  the  prisms  may  be  put 
in  front  of  either  one  or  both  eyes  and  the  ratio  be  determined  of  the  time  the 
object  is  seen  as  one  or  as  two  for  whatever  interval  of  time  the  operator  may  select. 
Similarly,  it  seems  to  the  writers  that  the  time  element  might  be  introduced  to  ad- 
( Continued  on  next  page. ) 


488    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

plished  still  more  conveniently,  however,  by  using  an  adaptation 
of  the  Brewster  stereoscope.  In  this  case  a  stereograph  consisting 
of  two  vertical  lines  exactly  alike  may  be  used  as  the  test  object. 
In  the  stereograph  employed  in  our  test  the  vertical  lines  were 
2.5  cm.  long  and  were  printed  on  the  card  4.5  cm.  apart  or  at 
2.25  cm.  from  the  center  of  the  card.  When  this  was  put  in  a 
sliding  carrier  and  was  made  to  approach  the  eyes,  a  position 
was  reached  at  which  with  the  maximum  of  effort  the  observer 
was  no  longer  able  to  see  the  two  vertical  lines  as  one.  They 
were  seen  alternately  as  one  and  as  two.  In  making  the  test  the 
hood  was  removed  from  the  stereoscope  so  that  the  eyes  were 
fully  exposed  to  the  conditions  of  illumination  that  were  being 
tested.  The  stereoscope  was  mounted  in  front  of  the  eyes  of 
the  observer  in  position  at  the  point  of  work.  The  distance  of 
the  carrier  containing  the  test  object  from  the  observer's  eyes 
was  adjusted  until  the  proper  ratio  of  time  seen  as  one  and  time 
seen  as  two  was  obtained.  Having  determined  this  position  a 
record  was  made  of  the  time  seen  as  one  and  the  time  seen  as 
two  for  three  minutes  at  the  beginning  and  the  close  of  work.  The 
ratio  of  the  sum  of  these  intervals  may  in  either  case  be  taken 
as  a  measure  at  that  time  of  the  power  of  the  fixation  muscles 
to  act  in  co-ordination  for  three  minutes  of  continuous  effort; 
and  the  decrease  in  this  ratio  from  the  beginning  to  the  close  of 
work  may  be  taken  as  a  measure  of  the  loss  in  that  power,  sus- 
tained as  the  result  of  work.  In  making  this  test  the  same  re- 
cording apparatus  was  used  as  was  employed  in  the  test  for  loss 
of  efficiency  for  clear  seeing.  That  is,  the  record  was  traced 
on  a  kymograph  by  means  of  an  electro-magnetic  marker  and  a 

vantage  into  the  visual  acuity  test  used  by  the  ophthalmologist  when  the  cycloplegic 
is  not  employed  or  in  cases  of  post-cycloplegic  refraction.  Is  it,  for  example,  enough 
to  know  that  the  eye  has  20/20  acuity  or  can  discriminate  a  certain  standard  visual 
angle  by  momentary  effort?  Would  it  not  give  a  more  complete  repreentation  of 
the  functional  condition  of  the  eye  to  know  what  it  can  discriminate  clearly  through 
an  interval  of  time;  or  better  still  perhaps,  for  what  proportion  of  an  interval  of 
time  it  can  discriminate  a  certain  detail  or  standard  visual  angle  clearly?  For  ex- 
ample, just  as  a  fatigued  eye  may  for  the  moment  under  the  spur  of  the  test  over- 
come the  functional  results  of  fatigue,  so  might  small  errors  of  refraction  be  overcome 
for  the  moment  by  muscular  effort,  especially  in  the  cases  in  which  fhe  muscles  of 
the  eye  are  unusually  strong.  But  just  as  the  fatigued  muscle  can  not  do  this  through 
an  interval  of  time,  so  it  would  seem  that  a  residual  error  of  refraction  might  not 
be  so  easily  masked  through  an  interval  of  time  by  means  of  muscular  effort.  In 
short,  this  form  of  test  is  suggested  as  affording  possibly  a  closer  approximation  to 
the  conditions  and  demands  imposed  upon  the  eye  during  a  period  of  work  than  is 
afforded  by  the   acuity  test  based  upon   the   momentary  judgment. 


FERREE   AND   RAND:     EFFICIENCY   OF   THE   EYE 


489 


telegraph  key,  and  a  time  line  was  run  beneath  the  record  by 
means  of  a  Jacquet  chronograph  registering  seconds. 

The  test  for  the  effect  on  the  fixation  muscles  of  a  period  of 
work  was  made  under  the  same  installations,  conditions  of 
work,  and  with  the  same  observers  that  were  used  in  the  dis- 
tribution series.  The  test,  however,  was  made  at  only  one  of  the 
positions  used  in  that  series,  namely,  the  position  at  which  the 
greatest  loss  of  efficiency  was  obtained.  (See  Position  I,  Fig.  1, 
p.  452a.)    At  this  point,  it  will  be  remembered,  six  of  the  lighting 

TABLE  XXI.— Fixation  Muscles  Series. 

Showing  the  loss  of  efficiency  of  the  fixation  muscles  as  the  result  of  3 

hours  of  work  under  the  direct,  semi-indirect,  and  indirect 

systems  of  lighting  employed. 


Watts 

Foot-candli 

ss 

Time 

Distance 
at  which 
test  ob- 
ject is 
normally 
seen  single 

Lighting  S3'stem 

Hori- 
zon- 

1        tal 

Verti- 
cal 

45° 

800 

4.2 

0.99 

2-5 

9  A.M. 
12  M. 

18 
18 

Semi-indirect 

760 

4.8 

0.98 

2.6 

9  A.M. 
12  M. 

18 
18 

880 

3-9 

I.o 

I.99 

9  A.M. 
12  M. 

18 
18 

Work- 
ing 
dis- 
tance 

Total 

time 

single 

Total 

time 

double 

Total 
time 
single 

total 

time 

double 

Ratios 
reduced  to 
common 
standard 

22 

142 

38 

3-7 

3-5 

22 

140 

40 

3-5 

3-3i 

22 

141 

39 

3-6 

3-5 

22 

138 

42 

3.28 

3-24 

20 

153 
151 

27 
29 

5-66 

5-21 

3-5 

3-21 

20 

units  were  in  the  field  of  view.  The  specification  of  the  lighting 
effects  produced  by  these  installations  are  given  on  pp.  452a-459 
Nothing  need  be  added  at  this  point  to  these  specifications  but 
the  brightness  of  the  stereograph  or  the  test  object  in  position 
for  the  three  systems  of  lighting,  and  the  illumination  meas- 
urements at  the  test  card.  The  brightness  measurements  are  as 
follows.  The  brightness  of  the  card,  corrected  for  the  ab- 
sorption of  the  prisms  of  the  stereoscope  was  for  the  direct 
system  0.00172   cp.   per  sq.   in.;    for   the   semi-indirect   system, 


490     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


0.00163  cp.  per  sq.  in.;  and  for  the  indirect  system,  0.00167  cp. 
per  sq.  in.  New  illumination  measurements  were  needed  at  the 
test  card  because  the  card  had  to  be  moved  closer  to  the  eyes 
than  was  the  case  in  the  tests  for  loss  of  efficiency  for  clear 
seeing,  which  brought  it  into  a  region  of  different  illumination. 
These  measurements  are  given  in  Table  XXI.  The  results  of 
our  tests  for  loss  of  efficiency  of  the  fixation  muscles  for  the 
three  systems  of  lighting  are  given  also  in  this  table.  These  re- 
sults show  (a)  that  very  little  loss  of  co-ordination  is  suffered  by 
the  fixation  muscles  as  the  result  of  three  hours  of  work  under  the 
systems  selected;  and  (b)  that  there  is  very  little  difference  in 

CHART  VI.— Fixation  Muscle  Series. 
Showing  the  loss  of  efficiency  of  the  fixation  muscles 
as  the  result  of  3  hours  of  work  under  the  direct, 
semi-indirect,  and  iudirect  systems  of  lighting  em- 
ployed. 

Foot-candles 


Lighting  system    Watts 

Indirect 800 

Semi-indirect  .  •   760 
Direct 880 


Horizontal 
4.2 
4.8 

3-9 


Vertical 
0.99 
O.98 
1.0 


45° 
2-5 
2.6 
I.99 


INDIRECT    i 
SEMI-  INDIRECT 
"-DIRECT 


the  effect  for  the  three  systems.  Since  there  is  no  reason  for  think- 
ing that  the  test  has  not  as  great  sensitivity  as  the  test  for  loss  of 
efficiency  for  clear  seeing,  and  since  the  same  observers,  condi- 
tions of  lighting  and  working  were  used  as  in  the  former  tests,  it 
does  not  seem  to  us  at  this  time  that  the  loss  of  efficiency  for  clear 
seeing  that  is  sustained  under  these  conditions,  shown  by  the 
former  tests,  can  be  ascribed  to  any  great  extent  to  an  effect  on 
the  muscles  of  fixation.  In  a  later  report  experiments  will  be 
described  in  which  the  effect  on  the  muscles  of  accommodation 
has  been  studied. 

A  graphic  representation  of  the  results  of  Table  XXI  is  shown 
in  Chart  VI. 


I'KKREE    AND   RAND:     EFFICIENCY   OF   THE   EYE  491 

THE  EFFECT  OF  MOTION  PICTURES  ON  THE  EFFICIENCY 
OF  THE  EYE. 

The  belief  that  motion  pictures  subject  the  eyes  to  undue 
strain  is  too  prevalent  to  need  more  than  mention  in  passing. 
All  are  familiar  with  the  conditions, — the  initially  dark-adapted 
and  highly  sensitized  eye,  the  comparatively  brilliant  screen  with 
its  dark  surrounding  field,  the  flickering  light,  and  the  shifting 
and  very  often  unsteady  pictures.  We  have  already  seen  that 
differences  in  surface  brightness  of  considerable  magnitude  in 
the  field  of  vision  cause  loss  of  efficiency  and  produce  discom- 
fort, and  we  have  discussed  the  causes  for  these  effects.  We  have 
nothing  further  to  add  to  that  discussion  here.  We  are,  how- 
ever, facing  for  the  first  time  in  our  work  the  question  of  the 
effect  upon  the  eye  of  a  flickering  light  and  lack  of  steadiness  in 
the  object  viewed.  The  following  reason  is  suggested  why  a 
flickering  or  unsteady  picture  may  cause  loss  of  efficiency.  The 
eye  is  so  constituted  that  when  its  images  lose  in  clearness  or 
distinctness  it  is  incited  to  a  muscular  readjustment  to  bring 
about  the  clearness  needed.  Ordinarily  in  seeing,  the  conditions 
for  loss  in  clearness  come  about  primarily  through  the  difference 
in  the  distance  or  direction  from  the  eye  of  the  objects  which 
are  successively  viewed.  In  motion  pictures,  however,  the  chang- 
ing clearness  of  the  objects  viewed  is  not  due  to  any  change  in 
their  distance  or  direction  from  the  eye;  nor  to  anything  in  fact 
which  the  readjustment  of  the  eye  can  remedy  to  any  consider- 
able degree.  The  effort  expended,  therefore,  is  of  little  avail  for 
seeing,  if,  indeed,  the  new  setting  of  the  parts  is  not  a  detriment 
to  clear  seeing  and  a  condition  which  in  turn  must  be  corrected. 
This  should,  and  doubtless  does,  lead  to  muscular  strain  and 
loss  of  efficiency.  It  was  decided,  therefore,  to  make  an  explora- 
tive investigation  to  determine  whether  there  is  an  effect  of  motion 
pictures  on  the  eye  which  can  be  detected  by  our  test  for  loss  of 
efficiency.  The  tests  were  conducted  in  a  local  theater,  selected 
primarily  because  of  the  favorable  conditions  that  prevailed.  The 
definition  at  the  screen  was  good  and  the  pictures  were  unusually 
steady  and  free  from  flicker.  The  conditions  were,  we  think,  fairly 
representative  of  what  is  found  in  the  better  class  of  motion 
picture  houses. 


492     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  tests  were  taken  immediately  before  and  after  two  hours 
of  observation  of  the  pictures.  During  the  exhibition  the  ob- 
server sat  directly  in  front  of  the  center  of  the  screen.  The 
observation  was  made  at  successive  times  at  three  distances  from 
the  screen, — in  the  front,  middle,  and  the  back  of  the  house. 
These  positions  were  respectively  25,  48,  and  71  ft.  (7.62,  14.6, 
and  21.6  m.)  from  the  screen.  The  room  in  which  the  pictures 
were  shown  was  78  ft.  (23.7  m.)  long  and  48  ft.  (14.6  m.)  wide. 
The  tests  were  taken  in  a  room  14  ft.  (4.2  m.)  long,  9  ft.  (2.74 
m.)  wide,  11  ft.  (3.35  m.)  high,  adjoining  the  stage.  The  walls 
and  ceiling  of  this  room  were  of  rough  plaster,  painted  a  flat  white. 
When  taking  the  test  the  observer  sat  facing  one  of  the  side  walls 
of  the  room,  1.5  m.  distant.  The  room  was  lighted  for  the  pur- 
pose of  the  test  by  one  100-watt  and  one  60-watt  clear  tungsten 
lamp  suspended  behind  and  slightly  to  the  right  of  the  observer 
when  in  position  for  the  test,  at  about  2  ft.  (0.6  m.)  above  the 
level  of  his  eyes.  The  source  of  light  was  thus  entirely  out  of 
the  field  of  view  and  the  light  fell  evenly  and  without  shadow  on 
the  test  card  and  the  wall  in  front  of  the  observer.  At  the  point 
of  the  test  card,  the  illumination  measured  with  the  receiving  test 
plate  of  the  photometer  in  the  horizontal  plane  was  1.3  foot- 
candles;  in  the  vertical  plane,  1.9  foot-candles;  and  in  the  45  deg. 
plane,  2.3  foot-candles.  The  surface  brightness  of  the  test  card 
was  0.003256  cp.  per  sq.  in.,  and  that  of  the  wall  directly  behind 
the  card  was  0.002288  cp.  per  sq.  in.  The  distribution  of  surface 
brightness  on  the  wall  which  the  observer  faced  was  very  even. 
At  the  point  of  maximum  brightness  to  the  right  of  the  observer, 
as  nearly  as  that  point  could  be  located,  the  brilliancy  was  0.00308 
cp.  per  sq.  in. ;  and  to  the  left  of  the  observer,  0.002024  cp.  per 
sq.  in. 

In  order  that  there  might  be  no  intermission  between  the  pic- 
tures for  changing  the  films,  two  projection  machines  were  used. 
The  following  is  the  specification  of  the  apparatus  employed  as 
given  by  the  operator. 

Type  of  machine,  Powers  6 — A  Projector. 

Lens  equipment,  1  pair  pearl  white  condensers,  6l/>  in.  F.  L. 

1   Bausch  and  Lomb  objective  combination. 
4}i  in.  E.  F. 


FERREE   AND   RAND:     EFFICIENCY   OF   THE   EYE  493 

Lamp,  i  io,ooo-cp.  adjustable  arc. 

Carbons,  y%  in.  cored  bio's. 

Current,  22  volt  a.  c.  through  Halberg  transformer. 

Line  current,  28-30  amperes. 

Arc  voltage,  45-50  volts. 

Length  of  throw  or  distance  from  objective  to  screen,  J2  ft. 
(21.9  m.) 

Screen,  sheet  muslin  sized  and  coated  with  flat  white  alabastine. 

Speed  of  film  through  machine,  66  ft.  8  in.  (20.3  m.)  per  min. 

Number  of  pictures  per  1  ft.  (0.3  m.)  of  film,  16. 

Size  of  picture  on  film,  y^  in.  (1.9  cm.)  high  by  15/16  in-  (2.38 
cm.)  wide. 

Size  of  picture  on  screen,  11  ft.  (3.35  m.)  high  by  14  ft.  (4.26 
m.)  wide. 

Approximate  brightness  of  screen  with  film  removed  from  pro- 
jector, 3.47  cp.  per  sq.  in. 

Exceptional  steadiness,  it  may  be  said,  is  given  to  the  move- 
ment of  the  film  and,  therefore,  to  the  picture  in  this  type  of  pro- 
jector by  the  special  type  of  intermittent  movement  that  is  em- 
ployed. Details  of  this  movement  need  not  be  given  here.  As 
has  already  been  stated,  our  reason  for  making  the  test  in  this 
particular  theater  was  the  comparative  steadiness  of  the  pictures 
and  the  comparative  freedom  from  flicker,  that  was  obtained. 

The  results  of  the  tests  are  shown  in  Table  XXII.  Quite  a 
great  deal  of  loss  of  efficiency  is  shown  as  the  result  of  two 
hours  of  observation.  The  nearer  the  observer  was  to  the  screen, 
the  greater  was  this  loss  found  to  be.  The  loss,  however,  so  far 
as  we  can  tell,  is  no  greater  than  is  caused  by  steady  work  under 
the  direct  and  semi-indirect  installations  of  lighting  used  in  our 
distribution  series.  Unfortunately,  we  have  not  for  the  pur- 
poses of  comparison,  results  for  the  same  observer  for  the  same 
length  of  time  of  exposure  for  the  two  sets  of  condition.  The 
loss  for  observer  R  for  two  hours  observation  of  the  motion 
pictures  was  not  nearly  so  great  as  for  three  hours  of  reading 
from  good  print  and  paper,  under  the  direct  and  semi-indirect 
systems  of  lighting.  But  comparing  the  results  for  observer  G  for 
two  hours  of  reading  from  the  same  type  and  paper  with  those 
for  observer  R  for  two  hours  observation  of  the  pictures  the 


494     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


loss  seems  to  be  about  the  same.     That  is,  our  results  indicate 
that  while  the  eyes  are  strained  a  great  deal  by  the  observation 

TABLE  XXII.— Motion  Picture  Series. 

Showing  the  loss  of  efficiency  of  the  eye  caused  by  two  hours'  observation 

of  motion  pictures. 


Maximal 

Total 

distance 

time 

at  which 

clear 

Ratios 

test  ob- 

Work- 

-i- 

reduced 

ject  can 

ing 

Total 

Total 

total 

to  com- 

be seen 

dis- 

time 

time 

time 

mon 

Position 

Time 

clear 

tance 

clear 

blurred 

blurred 

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25  ft.  (7.62  m.) 

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70.5 

123 

57 

2.14 

3-5 

IO  P.M. 

86.1 

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95 

85 

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71.0 

128 

52 

2.46 

3-5 

IO  P.M. 

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108 

72 

1-5 

2.13 

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from    projec- 

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86.0 

69.0 

137 

43 

3-19 

3-5 

IO  P.M. 

86.0 

69.0 

124 

56 

2.2 

2.42 

CHART  VII.  Motion  Picture  Series. 

Showing  the  loss  of  efficiency  of  the  eye  caused  by  two 

hours  observation  of  motion  pictures. 

Position  A 25  ft.  from  projection  screen 

Position  B 48  ft.  from  projection  screen 

Position  C 71  ft.  from  projection  screen 


POSITION  C 
B 


of  moving  pictures,  even  in  the  better  moving  picture  houses,  they 
are  damaged  little  more  by  that  in  all  probability  than  they  are  by 


FERREE   AND   RAND:     EFFICIENCY   OF   THE   EYE 


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496     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

reading  steadily  the  same  length  of  time  under  the  greater  part  of 
the  lighting  that  is  now  in  actual  use. 

A  graphic  representation  of  the  results  of  Table  XXII  is  given 
in  Chart  VII.  For  the  sake  of  comparing  the  effect  of  motion 
pictures  on  the  eyes  with  the  effect  of  reading  steadily  under  the 
direct,  semi-indirect,  and  indirect  systems  of  lighting  we  have 
employed,  Chart  VIII  has  been  prepared. 

THE  TENDENCY  OF  DIFFERENT  LIGHTING  CONDITIONS  TO 

PRODUCE  DISCOMFORT,  AND  A  COMPARISON  OF  THE 

TENDENCY  OF  THESE  CONDITIONS  TO  CAUSE 

LOSS  OF  EFFICIENCY  AND  TO  PRODUCE 

DISCOMFORT. 

In  the  former  papers  we  have  held  that  the  general  level  or 
scale  of  efficiency  of  the  fresh  eye,  loss  of  efficiency  as  the  result 
of  work,  and  the  tendency  to  produce  discomfort  are  all  separate 
aspects  of  the  problem  of  lighting  in  its  relation  to  the  eye,  and 
that  our  knowledge  of  each  must  be  obtained  by  different  methods 
of  investigation.  A  correlation  between  these  three  moments  is 
doubtless  possible,  but  that  correlation  should  be  founded  upon 
the  results  of  careful  investigation ;  it  should  not  be  assumed. 
It  is  our  purpose  in  this  section  of  the  paper  to  show  the  relative 
tendency  of  the  different  conditions  of  lighting  we  have  used  to 
produce  discomfort,  and  to  make  a  rough  comparison  of  each  con- 
dition to  cause  loss  of  efficiency  and  to  produce  discomfort.  Any 
comparative  study  of  the  conditions  producing  discomfort  neces- 
sitates a  means  of  estimating  discomfort.  It  is  obvious  that  the 
core  of  the  experience  of  discomfort  is  either  a  sensation  or  a  com- 
plex of  sensations.  As  such  it  should  have  a  limen  or  threshold 
just  as  other  sensations  have ;  and  just  as  we  are  able  in  general  to 
estimate  sensitivity  in  terms  of  the  threshold  value  so  should  we  in 
this  case  be  able  to  use  the  threshold  value  in  estimating  the  eye's 
sensitivity  or  liability  to  discomfort  under  a  given  lighting  con- 
dition. Threshold  values  are  usually  determined  by  finding  how 
much  energy  or  intensity  of  a  given  stimulus,  applied  for  a  short 
interval  of  time,  is  required  to  arouse  a  just  noticeable  sensation. 
This  form  of  procedure,  however,  is  not  adapted  to  the  needs  of 
our  problem.  It  is  much  better  to  reverse  the  process  and  find 
how  long  the  eye  has  to  be  exposed  to  a  stimulus  of  a  given  in- 
tensity to  arouse  just  noticeable  discomfort.     Our  threshold  thus 


FERREE   AND   RAND:     EFFICIF.NCV   OF   THE    EVE  497 

becomes  a  time  threshold  and  is  measured  in  units  of  time  instead 
of  units  of  intensity.  In  order  to  determine  whether  the  judg- 
ment of  the  threshold  of  discomfort  can  be  made  with  certainty 
and  to  perfect  the  method  and  to  test  in  general  its  feasibility,  an 
abstract  investigation  was  undertaken  first,  running  through  an 
entire  year,  in  which  a  better  and  more  convenient  control  of 
conditions  could  be  secured  than  is  possible  in  the  investigation 
of  a  concrete  lighting  situation.  That  is,  we  undertook  to  de- 
termine the  comparative  sensitivity  of  the  eye  to  discomfort  when 
a  single  source  of  light  was  exposed  in  different  parts  of  the 
field  of  vision.  In  order  to  carry  out  this  investigation  a  lamp 
house  with  a  circular  opening  in  one  side  3  cm.  in  diameter  was 
attached  to  the  arm  of  a  perimeter  in  such  a  way  that  the  opening 
was  always  directed  towards  the  observer's  eye.  In  the  lamp 
house  could  be  placed  a  lamp  of  whatever  candlepower  was  de- 
sired. The  arm  of  the  perimeter  could  be  shifted  to  any  meridian 
in  which  it  was  desired  to  work  and  the  lamp  house  could  be 
moved  at  will  along  this  arm.  It  was  thus  possible  to  expose 
the  light  for  any  length  of  time  in  any  part  of  the  field  of  vision 
that  was  desired.  Working  in  this  way  we  have  not  only  investi- 
gated the  effect  of  many  types  of  variation  of  the  position  of  the 
light  in  the  field  of  view,  the  effect  of  intensity  of  light,  etc. ;  but 
we  have  studied  and  standardized  the  factors  that  influence  the 
sensitivity  and  reproducibility  of  the  judgment  and  have  given 
our  observers  the  training  that  was  needed  for  the  concrete  in- 
vestigation. In  making  the  concrete  investigation  we  have  used 
every  variation  of  the  conditions  of  lighting  described  in  this 
and  the  preceding  paper.  That  is,  the  tendency  to  produce  dis- 
comfort, measured  in  terms  of  the  value  of  the  time  threshold, 
has  been  determined  for  all  the  conditions  of  lighting  we  have 
used  in  the  tests  for  loss  of  efficiency.  Two  cases  may  be  made 
of  the  investigation, — a  determination  of  the  tendency  to  cause 
discomfort  when  the  eye  is  at  rest,  and  a  determination  of  this 
tendency  when  the  eye  is  at  work.  Both  of  these  cases  were 
included  in  our  investigation.  The  following  determinations  were 
made,  (a)  The  time  threshold  of  discomfort  was  gotten  when 
the  observer  was  sitting  with  the  accommodation  muscles  relaxed 
and  with  the  fixation  muscles  as  nearly  relaxed  as  was  practica- 


498     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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500     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ble  under  the  conditions.  That  is,  the  observer  sat  in  the  positions 
shown  in  Fig.  i,  p.  452a,  and  took  an  easy  fixation  of  an  area  at  the 
level  of  the  eye  on  the  opposite  wall  of  the  room.  The  fixation  dis- 
tance, for  example,  for  Position  I,  Fig.  1,  p.  452a,  was  22  ft.  Since 
blinking  was  found  to  be  one  of  the  variable  factors  which  influ- 

TABLE  XXV.— Eye  Shade  Series. 

Showing  a  comparison  of  the  tendency  of  the  direct,  semi-indirect,  and 
indirect  installations  of  lighting  used  in  the  distribution  series  to  cause  loss 
of  efficiency  and  to  produce  discomfort  when  the  eye  was  protected  by  an 
opaque  eye  shade  with  a  dark  lining  and  by  an  opaque  eye  shade  with  a 
white  lining.  The  loss  of  efficiency  is  the  result  of  three  hours  of  work. 
The  tendency  to  produce  discomfort  is  estimated  by  the  time  required  for 
just  noticeable  discomfort  to  be  set  up. 


Lining 

of  eye  Lighting 

shade  system  Watts 

White     Indirect 800 

Semi-indirect  .  760 

Direct 880 

Dark       Indirect 800 

Semi-indirect  •  760 

Direct 880 

TABLE  XXVI.— The  Angle  at  which  the  Light  Falls  on  the  Work. 

Showing  a  comparison  of  the  tendency  to  cause  loss  of  efficiency  and  to 
produce  discomfort  of  the  angle  at  which  the  light  falls  on  the  work.  The 
loss  of  efficiency  is  the  result  of  three  hours  of  work.  The  tendency  to  pro- 
duce discomfort  is  estimated  by  the  time  required  for  just  noticeable  dis- 
comfort to  be  set  up. 

Time 
limen  of 
discomfort 
Per  cent,  loss    in  seconds 
of  efficiency      (readiug) 

6.6  95 

14-3  SO 

ence  the  tendency  to  produce  discomfort,  the  amount  of  blinking 
was  made  constant  from  test  to  test.  This  was  accomplished  by 
having  the  observer  blink  at  equal  intervals  during  the  test,  timing 
himself  by  means  of  the  stroke  of  a  metronome.  The  interval 
most  natural  and  suitable  for  this  purpose  was  determined  for 


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FERREE   AND   RAND:     EFFICIENCY   OF   THE   EYE  501 

each  observer  separately.  In  the  results  given  in  the  follow- 
ing table  a  three-second  interval  was  used.  And  (b)  the  time 
threshold  of  discomfort  was  determined  when  the  observer  was 
reading  from  print  and  paper  similar  to  that  used  in  the  loss 
of  efficiency  tests.  In  these  tests  all  the  conditions  were  kept  as 
nearly  the  same  as  they  were  in  the  work  on  loss  of  efficiency  as 
was  possible.  The  results  of  both  of  these  sets  of  experiments 
on  the  tendency  to  produce  discomfort  are  shown  in  Tables 
XXIII-XXVI.  The  tendency  to  produce  discomfort  should  be 
estimated,  roughly  speaking,  probably  as  inversely  proportional 
to  the  time  it  was  required  for  discomfort  to  be  set  up.  The  time 
required  for  discomfort  to  be  set  up  is  given  in  the  tables.  In 
order  to  make  convenient  a  comparison  of  the  tendency  of  the 
various  conditions  of  lighting  to  cause  loss  of  efficiency  and  to 
produce  discomfort  the  percentage  loss  of  efficiency  caused  by 
the  given  lighting  conditions  is  given  in  a  parallel  column  in  each 
table.  The  percentage  loss  of  efficiency  was  computed  by  divid- 
ing the  loss  in  the  ratio  of  time  seen  clear  to  time  seen  blurred 
sustained  as  a  result  of  work  by  3.5,  the  standard  ratio  to  which 
all  the  ratios  at  the  beginning  of  work  were  reduced.  A  rough 
correspondence  of  the  tendency  to  produce  discomfort  and  to 
cause  loss  of  efficiency  will  be  noted  in  every  case.  This  cor- 
respondence by  no  means  amounts  to  a  1  :  1  correlation,  however. 
In  Table  XXIII  is  given  the  comparison  of  the  tendency  to  cause 
loss  of  efficiency  and  to  produce  discomfort  for  the  distribution 
series;  in  Table  XXIV,  for  the  intensity  series;  in  Table  XXV, 
for  the  eye  shade  series;  and  in  Table  XXVI,  for  the  series 
showing  the  effect  of  the  angle  at  which  the  light  falls  on  the 
work. 

In  conclusion  we  wish  to  state  that  in  this  work,  and  the  work 
reported  in  the  former  papers,  the  purpose  has  been  primarily 
to  procure  methods  of  working  and  to  find  out,  as  broadly  as 
one  may,  the  applicability  of  these  methods  to  the  problems  sur- 
rounding the  hygiene  of  the  eye.  While  in  many  places  attention 
has  been  called  to  results  that  seemed  to  have  general  significance, 
the  intention  has  been,  in  general,  to  limit  all  comments  and 
conclusions  strictly  to  the  conditions  under  which  the  work  was 
done. 


502     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

SOME  RECENT  EXPERIMENTS  ON  VISION  IN 
ANIMALS.* 


BY  H.  M.  JOHNSON. 


Synopsis:  The  Cebus  capuchin  monkey  has  visual  acuity  of  the  same 
order  as  that  of  man.  Under  the  same  experimental  conditions  the 
monkey  yielded  a  stimulus-threshold  of  57  seconds  of  visual  angle  as 
compared  with  an  average  of  49  seconds  with  a  mean  variation  of  3  per 
cent,  for  five  trained  photometrists.  Two  chicks  under  the  same  condi- 
tions gave  stimulus-thresholds  of  over  4  minutes,  while  similar  tests  on 
two  dogs  yielded  negative  results.  The  monkey's  difference-threshold 
for  size  of  visible  bands  is  as  low  as  3  per  cent,  under  optimal  conditions. 
One  chick  failed  to  acquire  discrimination  on  the  basis  of  difference  in 
size ;  another  individual  yielded  threshold  values  some  ten  times  greater 
than  those  obtained  for  the  monkey.  The  chick  may  be  trained  with 
difficulty  to  distinguish  large  differences  in  direction  between  two  systems 
of  striae  whose  members  are  respectively  equal  in  width.  The  monkey, 
after  similar  training  on  other  problems,  acquired  this  form  of  discrimi- 
nation and  perfected  it  during  the  first  day's  training.  Determinations 
were  made  by  the  discrimination  method,  the  stimuli  being  two  modified 
Ives-Cobb  visual  acuity  test  objects.  The  results  are  consistent  with  those 
obtained  by  other  experimenters  on  color  vision  and  discrimination  on 
the  basis  of  difference  in  size  and  form.  Detailed  reports  of  the  author's 
experiments  are  to  be  found  in  the  Journal  of  Animal  Behavior. 


Recent  experimentation  on  vision  in  vertebrate  animals  has 
bearing  on  certain  factors  considered  in  theories  of  evolution.  The 
Darwinian  theory  for  example  assumes  that  certain  animals  are 
capable  of  making  differential  responses  to  specific  differences  in 
visual  objects.  In  the  doctrine  of  sexual  selection  it  is  asserted 
that  certain  pattern-markings  of  hair  or  plumage  are  of  value  to 
the  animal  possessing  them,  in  that  they  enable-  their  possessor  to 
secure  a  desirable  mate.  The  doctrine  of  natural  selection  as- 
serts that  certain  animals  and  birds  are  "protectively"  colored  or 
marked,  the  patterns  in  question  being  hard  to  distinguish  from 
the  animals'  immediate  environment.  Conversely  it  is  implied 
that  if  the  coloring  or  marking  were  different  the  animals'  nat- 
ural enemies  could  find  him  more  readily.     Certain  experimen- 

*  A  paper  read  at  the  eighth  annual  convention  of  the  Illuminating  Engineering 
Society,  Cleveland,  O.,  September  21-24,  1914. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


JOHNSON:     EXPERIMENTS    ON    VISION    IN    ANIMALS  503 


ters  on  vision  in  animals  are  interested  in  the  question  whether 
these  theories  attribute  to  certain  animals  better  visual  discrim- 
inative ability  than  these  animals  can  be  experimentally  shown 


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to  possess.     This  is  one  of  several  questions  of  general  interest 
which  led  to  the  present  and  other  recent  work. 

The  problems  attacked  require  that  the  animal  be  placed  in  a 
situation  in  which  he  can  be  made  to  establish  a  discrimination- 
habit  ;  that  in  forming  and  in  maintaining  this  habit  other  sources 


504     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

of  help  than  visual  stimuli  be  excluded ;  and  that  the  visual  stimuli 
be  controllable  so  that  only  the  stimulus-characteristic  under  study 
(e.  g.,  difference  of  wave-length,  intensity,  extent,  form,  disposi- 
tion of  brightnesses,  etc.)  shall  be  effective.  The  most  successful 
method  which  has  been  utilized  in  this  country  is  one  which 
Professors  Robert  M.  Yerkes  and  John  B.  Watson  developed. 
The  method  is  based  on  the  fact  that  animals  seek  to  obtain  food 
and  to  avoid  punishment.  The  animal  under  study  is  required 
to  choose  one  feeding-place  and  to  avoid  another.  The  place  to 
be  chosen  is  indicated  solely  by  one  visual  object  (the  "positive 
stimulus")  and  the  place  to  be  avoided  is  indicated  by  another 
visual  object  (the  "negative  stimulus").  The  two  objects  which 
constitute  the  stimuli  to  be  discriminated  are  interchangeable. 
The  details  may  be  readily  seen  in  the  accompanying  diagram. 
Fig.  1.  This  represents  in  floor  plan  a  box  first  used  by  Pro- 
fessor Yerkes,  as  modified  for  the  author's  present  work.  The 
animal  is  placed  in  a  home-compartment  H,  from  which  he  is 
released  through  the  exit-door  at  the  end.  Food  is  already  present 
in  each  of  the  food-compartments,  Lfb  and  Rfb,  which  the  animal 
may  enter  by  passing  through  Alley  A1  or  A2,  as  the  case  may  be. 
The  test-objects,  G1,  G2,  are  presented  to  the  animal  at  the  win- 
dows W1,  W2,  at  the  end  of  the  respective  alleys  A1,  A2.  A  false 
floor  is  placed  in  each  alley,  hinged  at  the  end  next  the  window, 
and  supported  at  the  free  end  by  a  light  spring.  These  floors  are 
covered  with  brass  strips  which  serve  as  electrodes,  alternate 
members  being  connected  with  corresponding  poles  of  the  second- 
ary coil  of  an  inductorium.  A  double-throw  switch  determines 
which  of  these  "punishment  grills"  shall  receive  the  induced 
charge.  The  charge  is  always  placed  on  the  grill  under  the 
"negative"  stimulus.  When  the  animal  steps  into  the  alley  he 
depresses  the  punishment  grill,  and  in  so  doing  closes  the  circuit 
through  the  primary  coil  and  breaks  the  circuit  through  one  of 
the  signal  lamps.  In  this  way  the  choice  is  recorded  automatically, 
and  it  is  not  necessary  for  the  experimenter  to  watch  the  animal 
while  the  latter  is  in  the  act  of  choosing.  The  entrance  door  to 
the  food-box  to  be  chosen  is  not  opened  until  the  animal  has 
entered  the  alley  beneath  the  positive  test-object.  After  the 
animal  has  obtained  the  food,  and  the  experimenter  has  recorded 


JOHNSON:     EXPERIMENTS   ON    VISION    IN    ANIMALS  505 

the  choice  and  arranged  the  stimuli  for  the  next  trial,  the  animal 
is  readmitted  to  the  home  compartment  through  a  door  opening 
directly  into  it  from  the  food-box,  the  exit-door  of  the  latter 
having  been  closed  meantime.  It  should  be  remarked  that  certain 
experimenters  do  not  feed  the  animals  for  correct  choices,  but 
punish  them  for  incorrect  choices.  In  such  procedure  the  animal's 
incentive  is  to  escape  from  the  home-compartment  and  to  avoid 
punishment.  Other  experimenters  do  not  punish  the  animals  for 
incorrect  choices,  but  feed  them  for  correct  choices.  In  the 
present  work  the  experimenter  used  both  incentives  combined. 
The  stimuli  are  presented  in  a  right-left  order  predetermined  by 
the  use  of  a  well  shuffled  pack  of  cards.  In  20  presentations  the 
positive  stimulus  will  appear  ten  times  at  W1  and  ten  times  at 
W2,  and  the  negative  stimulus  vice  versa. 

The  first  step  in  work  of  this  kind  is  a  course  of  training  in 
which  the  difference  between  the  stimuli  is  quite  large.  The  ani- 
mal often  forms  a  "position-habit"  early  in  the  work — invariably 
choosing  a  certain  food-box  or  choosing  them  in  a  perfectly  reg- 
ular order,  regardless  of  the  stimuli.  These  "position-habits"  are 
often  persistent.  If  the  type  of  discrimination  is  not  difficult,  a 
bird  or  higher  mammal  can  usually  be  trained  to  discriminate 
perfectly  in  three  or  four  weeks  of  daily  training.  Ten  to  twenty 
trials  or  presentations  are  usually  given  in  one  daily  "series." 
After  the  animal  has  learned  to  attend  to  the  test-objects  the 
number  of  trials  may  be  increased — depending  on  the  ease  with 
which  the  animal  becomes  restless  or  fatigued  and  upon  his 
capacity  for  food.  The  adult  chick  can  be  given  from  50  to  60 
trials  in  a  single  daily  series  if  the  amount  of  food  given  after 
each  choice  is  small.  After  the  animal  has  learned  to  discrimi- 
nate, the  difference  between  the  stimuli  is  reduced  by  small  steps 
until  discrimination  breaks  down.  This  point  is  arbitrarily  called 
the  animal's  threshold.  Experience  has  demonstrated  this 
method  to  be  practicable  and  reliable  if  the  stimuli  are  carefully 
controlled. 

Some  experimenters  have  used  for  stimuli  spectral  bands, 
diffused  on  plaster  surfaces  placed  at  the  windows  of  the  experi- 
ment-box. They  have  prepared  their  stimuli  in  such  a  way  that 
the  latter  are  accurately  measurable  and  highly  controllable  as  to 


506     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

wave-length,  intensity  and  saturation.  They  have  obtained  defi- 
nite results,  both  positive  and  negative,  on  various  animals  as  to 
the  range  of  wave-lengths  to  which  the  latter  are  sensitive,  as 
well  as  the  degree  of  sensitiveness  to  difference  of  wave-length. 

Other  experimenters  have  used  test-objects  designed  to  test 
the  animals'  ability  or  inability  to  discriminate  similar  forms 
(e.g.,  circles)  of  varying  sizes,  and  equivalent  areas  of  varying 
form.  Some  of  these  experimenters  have  also  attached  the 
question  of  brightness-sensitivity  by  the  same  general  method. 
Some  of  these  results  will  be  mentioned  presently. 

The  work  of  the  author,  which  will  be  described  in  some  detail, 
grew  out  of  an  interest  in  some  earlier  work  by  Casteel  on  the 
painted  turtle.  Casteel  used  the  general  method  which  has  just 
been  described,  the  stimuli  being  alternate  "black  and  white"  striae 
on  cardboard  fastened  to  the  entrance  to  the  food-boxes.  In  the 
first  experiments  the  striae  on  the  positive  and  those  on  the  nega- 
tive field  were  respectively  equal  in  width  but  lay  in  different  direc- 
tions. The  animal  was  trained  to  choose  the  vertical  system  and 
to  reject  the  horizontal  system.  As  Casteel  was  seeking  to  dem- 
onstrate only  that  the  turtles  were  responding  to  the  striation  as 
such,  he  did  not  attempt  to  control  the  distance  of  test-objects 
from  the  animals'  eyes  at  which  choice  had  to  be  made.  He 
obtained  perfect  discrimination  with  some  animals  when  each 
member  of  the  two  systems  of  striae  was  only  2  mm.  wide.  He 
then  presented  the  animals  to  another  problem  in  which  the  striae 
in  the  two  systems  were  respectively  unequal  in  width,  but  lying 
in  the  same  direction.  He  obtained  perfect  discrimination  when 
the  width-difference  was  very  large,  and  highly  accurate  choices 
when  the  individual  striae  in  one  system  were  3  mm.  wide,  and 
in  the  other  system  2  mm.  wide.  He  did  not  attempt  to  find  the 
limits  of  the  animals'  stimulus-sensitivity  or  difference-sensitivity. 

The  writer  has  been  working  on  a  group  of  animals  whose 
retinal  developments  varies  widely :  the  dog  and  cat,  the  domestic 
chick,  the  Cebus  monkey  and  the  crow.  The  problem  attacked  is 
the  difference  in  pattern-vision  which  exists  among  these  animals 
under  given  conditions  of  illumination,  the  patterns  used  being 
alternate  dark  and  bright  bands  equal  in  width.  In  some  problems 
the  variable  factor  is  the  band-width  in  the  positive  and  negative 


JOHNSON:     EXPERIMENTS   ON    VISION    IN    ANIMALS  S°7 

systems,  respectively;  in  other  problems  the  variable  factor  is  the 
direction  in  which  the  two  systems  respectively  lie.  The  first 
question  to  be  settled  is,  how  wide  must  the  individual  members 
of  a  system  of  striae  be,  for  the  striate  field  to  be  discriminate 
at  a  given  distance  from  a  plain  field,  equal  to  the  former  in  form, 
area  and  mean  brightness?  For  investigating  this  question  the 
writer  used  as  stimuli  two  Ives-Cobb  visual  acuity  test-objects, 
indicated  as  G1,  G2,  in  Fig.  i.  A  diffusing  screen  of  opal  glass 
was  placed  close  behind  each  test-object.  The  latter  were  inde- 
pendently illuminated  and  equated  in  brightness  at  12.2  candles 
per  square  meter.  The  sources  used  were  60-watt  tungsten  lamps, 
connected  in  multiple,  operated  at  a  specific  consumption  of  1.25 
watts  per  candle,  the  source  of  current  being  a  25-ampere  storage 
cell,  and  the  current  kept  constant  by  the  use  of  a  voltmeter  and 
a  rheostat.  The  two  fields  thus  prepared  were  both  striate.  The 
individual  members  of  the  negative  system  were  about  0.1  mm. 
wide,  and  it  was  assumed  that  at  the  distance  given  they  were 
too  small  to  be  resolved  by  the  eye.  The  individual  striae  on  the 
positive  field  were  made  2.23  mm.  wide  at  the  beginning  of  the 
training,  but  this  value  was  found  too  small  for  the  dogs.  The 
mounting  of  the  test-gratings  used  by  Cobb  was  modified  so  as 
to  permit  instantaneous  change  from  a  given  band-width  to  an- 
other given  width,  the  gratings  being  rotated  over  each  other  by 
a  lever  mechanism  between  limits  determined  by  the  setting  of 
two  stops  controlled  by  a  micrometer  screw.  Thus  either  test- 
object  could  be  made  at  will  to  present  a  sensibly  uniform  field 
or  a  field  of  a  given  striation. 

A  set  of  movable  stops  was  constructed  to  fit  into  the  experi- 
ment-box in  front  of  the  entrance  to  alleys  A1,  A2.  A  different 
stop  was  used  for  each  animal,  so  as  to  make  it  impossible  for 
any  of  them  to  bring  the  eye  nearer  than  60  cm.  to  the  test- 
object  without  stepping  into  the  alley  and  registering  a  choice. 

The  results  obtained  on  the  first  dog — a  pure-bred  male  English 
bull-terrier — were  negative,  but  not  clearly  so.  He  learned  in 
18  days  to  choose  the  alley  under  the  positive  test-object  and 
maintained  discrimination  for  several  days  during  which  the 
width  of  striae  on  the  positive  field  was  being  reduced.  The 
experimenter  introduced  a  control  test,  however,  which  revealed 


508     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

that  the  animal  had  been  testing  the  two  punishment  grills  for 
electrical  charge,  and  maintaining  discrimination  on  that  basis. 
(Hitherto  the  circuit  through  the  primary  coil  of  the  inductorium 
had  been  kept  closed  throughout  the  daily  series  of  trials.)  The 
dog's  behavior — sniffing  violently  at  the  entrances  of  the  two 
alleys — suggested  that  in  this  part  of  the  work  he  may  have  been 
sniffing  for  ozone  or  for  some  gas  similarly  generated,  about  the 
charged  electrodes.  As  soon  as  this  source  of  help  was  removed 
the  dog  ceased  to  discriminate.  Very  doubtful  evidence  of  dis- 
crimination was  obtained  when  the  band-width  on  the  positive 
field  was  about  4  mm. — near  the  limit  of  the  instrument — but 
this  behavior  was  not  persistent.  A  second  dog — a  pure-bred 
female  beagle-hound — did  not  give  evidence  of  discrimination  in 
900  trials. 

The  two  chicks — Indian  gamecocks — learned  the  problem 
readily.  Chick  1  required  very  careful  handling  as  he  was  easily 
disturbed  by  punishment.  He  ceased  to  discriminate  when  the 
band-width  on  the  positive  field  was  reduced  to  0.71  mm.,  sub- 
tending a  visual  angle  of  4'  4"  at  the  distance  given.  Chick  2 — a 
more  satisfactory  subject — ceased  to  discriminate  when  the  band- 
width on  the  positive  field  was  reduced  to  0.74  mm.— subtending 
a  visual  angle  of  4'  14"  at  the  distance  given. 

Monkey  2 — an  adolescent  Cebus  capuchin — discriminated  until 
the  band-width  on  the  positive  field  was  reduced  to  0.163  mm. — 
subtending  a  visual  angle  of  57".  For  practical  purposes  these 
values  may  be  taken  as  thresholds.  Monkey  i,  a  cat  and  a  crow 
died  during  the  early  stages  of  experimentation. 

For  purposes  of  comparison  the  author  tested  by  the  method  of 
limits,  the  visual  acuity  of  five  members  of  the  staff  of  the  Nela 
Research  Laboratory,  using  the  same  stimuli  under  the  same 
visual  conditions  as  obtained  in  the  work  on  the  animals.  All  the 
observers  are  skilled  photometrists,  four  being  physicists  and  one 
a  physiologist.  J,  whose  values  are  shown  separately,  is  a  high 
school  student. 

The  results  were  as  follows  : 


JOHNSON:     EXPERIMENTS   ON   VISION    IN   ANIMALS  509 

Mean 
Observer  threshold  M.  V.  per  cent 

F 4S"  3 

Co 50"  3 

L 54"  3 

Ca 48"  2 

W 46"  4 

Average 4c/'  3 

J  54"  4 

Monkey  2 57"  Obtained  by  discrimination  method 

Chick  1 244//r  Obtained  by  discrimination  method 

Chick  II 254"  Obtained  by  discrimination  method 

It  should  be  stated  explicitly  that  results  obtained  by  the 
method  of  limits  are  not  directly  comparable  with  those  obtained 
on  a  different  subject  by  the  discrimination  method.  The  atti- 
tude of  the  observer  is  different  in  the  two  cases,  and  the  prob- 
lem is  somewhat  different.  It  is  believed  however  that  one  is  safe 
in  taking  these  results  as  showing  that  the  visual  acuity  of  the 
monkey  is  of  the  same  order  as  that  of  the  human  subject ;  that 
the  visual  acuity  of  the  chick  is  only  20  per  cent,  to  25  per  cent. 
that  of  the  monkey  and  man;  while  the  visual  acuity  of  dog  1 
(taking  somewhat  indefinite  records  as  those  of  discrimination) 
is  not  over  4  per  cent,  that  of  the  monkey  and  man.  The  author  is 
hesitant  regarding  the  assumption  in  the  case  of  the  dog;  for 
neither  of  these  animals  gave  clear  evidence  of  possessing  sen- 
sitivity to  visual  detail. 

The  second  question  taken  up  is,  how  great  a  difference  in 
band-width  in  two  systems  of  horizontal  striae  distinguishable  by 
the  animal  as  such,  is  necessary  to  enable  the  animal  to  discrimi- 
nate them?  This  problem  was  attacked  by  the  same  general 
method  as  described  above.  The  same  test-objects  were  used  as 
in  the  work  on  the  first  problem.  For  the  chicks  the  brightness 
was  the  same  as  before — 12  candles  per  square  meter.  The  work 
on  the  monkey  was  done  somewhat  later,  and  at  a  lower  bright- 
ness— 6.67  candles  per  square  meter.  The  animals  used  were  the 
ones  which  had  succeeded  in  learning  the  first  problem — chicks 
1  and  2  and  monkey  2.  Chick  1  failed  to  learn  this  problem. 
The  following  table  shows  the  difference-threshold  values  ob- 
tained for  chick  2  and  monkey  2.  The  values  taken  for  the  chick 
are  those  at  the  first  breakdown  of  discrimination.  Those  for 
the  monkey  are  the  values   at   which  the  average  accuracy  is 


5IO     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


greater  than  70  per  cent,  and  less  than  80  per  cent.  The  results 
are  therefore  not  closely  comparable,  but  the  uncertainty  is  no 
greater  than  other  uncertainties  inherent  in  the  method.  It  is 
impossible  to  work  the  chick  successfully  when  discrimination  is 
difficult  and  the  bird  is  receiving  frequent  punishment.  This  is 
not  true  in  the  case  of  the  monkey,  if  conditions  are  carefully 
controlled. 

The  results  are  shown  in  the  following  table : 

Chick  2. 


Width  of  striae  on 

Difference  in 

per  cent,  of 

standard  stimulus 

Positive  field 

Negative 

:  field 

♦2.23  mm. 

1.28  mm. 

42 

1.30     " 

♦0.91 

33 

♦2.60     " 

i-73 

" 

33 

*3.I2       " 

1.80 

42 

1.56  " 

♦1.04 

11 

33 

1.04     " 

♦0.74 

<  i 

40 

Monkey  2. 

1.772  mm. 

♦1.561  mm. 

14 

*i.56i     " 

1. 301 

1 1 

17 

0.8S7     " 

♦0.780 

i  i 

14 

*o.78o     " 

0.673 

" 

14 

0.610     " 

♦0.520 

(< 

17 

♦0.52O       " 

0.479 

" 

8  (See  remarks  below) 

0.413    " 

♦0.390 

" 

6 

♦0.390    " 

o.37i 

( t 

5 

0.321    " 

♦0.312 

11 

2.9 

♦0.312     " 

0.304 

" 

2.6 

0.232     " 

♦0.223 

11 

4 

♦0.223     " 

0.210 

t  < 

6 

♦0.19 1     " 

O.I73 

" 

9 

0.750   " 

♦0.780 

(i 

3-8 

♦0.780     " 

0.764 

" 

2-f-  (Greater  than  2  an 

*  Standard  stimulus. 


The  results  appear  in  the  table  in  the  chronological  order 
of  the  tests.  The  results  for  monkey  2  show  a  progressive 
diminution  from  the  first  step  (value  of  standard  stimulus 
1. 561  mm.)  to  the  fourth  (standard  =  0.312  mm.).  It  ap- 
peared necessary,  therefore,  to  determine  by  a  control  test  whether 
this    was    not    due    largely    to    effect    of    training.       This    test 


joiinson:    experiments  on  vision  in  animals        511 

was  made  at  standard  stimulus  =  0.780  mm.,  and  it  showed  that 
an  important  practise  effect  was  present.  The  daily  record 
sheets  suggest  that  during  the  work  at  the  third  step  (standard 
=  0.520  mm.)  the  animal  acquired  a  higher  standard  of  "atten- 
tion" or  a  new  criterion,  which  he  maintained  fairly  well  there- 
after. Taking  the  later  value  as  approximating  the  true  thres- 
hold, according  to  this  mode  of  reaction,  for  that  region,  the 
monkey's  values  in  the  different  regions  are  quite  close  to  those 
obtained  in  rough  tests  on  two  human  observers.  Their  optimal 
results  were  at  stimulus-values  near  his,  and  the  threshold-values 
where  the  standard  stimulus  was  smaller  than  0.3  mm.  tended  to 
increase  as  did  the  monkey's.  These  results  are  not  to  be  taken 
as  final,  however,  as  more  detailed  and  more  careful  work  may 
change  them  considerably. 

A  third  problem  is  that  of  the  least  difference  in  direction 
occupied  by  two  systems  of  striae  whose  members  are  respec- 
tively equal  in  width,  which  is  necessary  to  effect  discrimination. 
This  problem  also  was  attacked  by  the  same  method  and  with 
the  same  apparatus  as  the  two  preceding  problems.  The  animals 
used  were  chicks  1  and  2  and  monkey  2.  Chick  1  failed  to  learn 
the  problem,  although  he  acquired  perfect  discrimination  when  a 
large  difference  in  band-width  was  presented  together  with  a 
difference  in  direction  of  90°.  Discrimination  failed  when  the 
difference  in  band-width  was  reduced.  Chick  2  learned  the 
problem  in  400  trials — with  much  greater  difficulty  than  in  the 
problem  of  striate-plain  discrimination.  Monkey  2  learned  the 
problem  during  the  first  daily  series,  giving  90  per  cent,  accuracy 
for  the  twenty  trials,  and  100  per  cent,  accuracy  in  the  series 
given  the  following  day.  His  threshold  and  that  of  chick  2  have 
not  been  finally  determined  at  this  writing.  Dog  1  has  also  been 
introduced  to  the  problem,  in  order  to  ascertain  if  this  problem 
is  easier  for  him  than  the  first  one,  in  which  he  probably  failed. 

To  sum  up:  the  monkey  possesses  sensitivity  to  visual  detail 
rivaling  that  of  the  best  human  subjects.  His  visual  acuity  is 
four  to  five  times  as  good  as  that  shown  by  the  chicks,  and  his 
difference-sensitivity  for  size  is  proportionately  much  greater. 
The  factor  of  direction  of  striation  is  much  more  effective  for 
him  than  for  the  chicks. 


512     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

A  complete  and  satisfactory  explanation  of  these  results  is  not 
possible  at  present.  The  tests  were  made  in  dark  surroundings 
but  not  with  good  darkness-adaptation.  It  is  possible  that  the 
visual  conditions  were  more  favorable  for  the  monkey  than  for 
the  chicks  and  dogs:  or  the  converse  may  be  true.  Since  the 
original  presentation  of  this  report  my  colleague,  Dr.  P.  W.  Cobb, 
has  tested  the  eyes  of  the  animals  used  for  refractive  errors. 
His  report  will  be  published  shortly.  It  is  sufficient  to  say  here 
that  dog  i  and  chick  2  were  found  practically  free  from  refrac- 
tive error,  hence  the  disparity  between  their  results  and  those 
of  monkey  2  is  not  explanable  on  that  basis.  The  different 
degrees  of  retinal  development  seem  by  far  the  most  important 
factor  at  present.  The  dog  has  no  fovea  and  the  existence  of  a 
"sensitive  area"  in  the  paracentral  region  is  doubtful.  According 
to  Slonaker  the  chick  is  the  only  bird  with  the  exception  of  the 
guinea  fowl  which  has  not  a  well  defined  fovea.  The  monkey 
has  a  retina  almost  like  that  of  man.  The  crow  possesses  a  well 
developed  fovea,  nasal  to  the  nerve-entrance.  Many  birds,  espe- 
cially birds  of  prey,  have  two  foveas,  one  nasal  the  other  temporal 
to  the  entrance  of  the  optic  nerve.  The  nasal  fovea  is  used  in 
monocular  vision,  the  temporal  fovea  in  binocular  vision.  If  the 
crow  had  yielded  results  closely  comparable  with  those  obtained 
on  the  monkey,  and  the  cat  yielded  results  like  those  obtained  on 
the  dogs,  the  author  should  have  been  tempted  to  refer  the  dif- 
ferences in  results  to  the  differences  in  retinal  structure.  Such 
interpretation  might  have  to  be  modified  after  future  tests  on 
optimal  conditions  of  discrimination  for  the  various  animals. 

It  may  be  interesting  to  recall  some  results  which  other  experi- 
menters have  obtained  in  work  on  other  problems  of  vision  with 
the  same  species. 

The  dog  has  been  tested  for  color-vision  by  numerous  experi- 
menters, but  by  none  so  far  whose  stimuli  were  adequately  con- 
trolled. There  is  no  evidence  whatever  that  he  is  sensitive  to 
differences  of  wave-length.  There  is  good  evidence  that  rodents, 
whose  retinal  development  is  very  like  that  of  the  dog,  are  color- 
blind and  have  a  shortened  spectrum.  "Watson  has  investigated 
the  range  of  effective  wave-lengths  for  the  chick,  and  reports 
that  it  extends   from  A  =  400  up  to  A  =  715  pp,   the  maximum 


JOHNSON:     EXPERIMENTS   ON   VISION    IN    ANIMALS  513 

lying  near  A  =  500  fi/x,  and  the  luminosity-curve  being  roughly 
similar  to  that  for  the  experimenter's  eye  under  the  same  condi- 
tions. Lashley  and  Watson  have  demonstrated  the  Purkinje 
phenomenon  in  the  chick,  and  have  also  obtained  discrimination 
between  monochromatic  bands,  apparently  based  on  wave-length 
difference  alone. 

There  is  incomplete  evidence  that  the  Rhesus  monkey  dis- 
criminates between  monochromatic  bands  on  the  basis  of  wave- 
length and  that  the  wave-lengths  in  the  region  of  red  have  a  low 
stimulating  value.  No  reliable  work  on  color-vision  in  the  cat 
and  the  crow  has  been  published. 

The  dog  has  shown  no  evidence  of  ability  to  discriminate 
between  visual  objects  differing  only  in  form.  The  writer  once 
worked  on  a  single  dog,  using  a  circle  and  its  equivalent  square 
as  stimuli.  Discrimination  was  established  in  about  1,000  trials 
when  the  brightness  of  the  positive  stimulus  was  4  times  that  of 
the  negative  stimulus.  Discrimination  failed  when  the  stimuli 
were  equated  in  brightness,  and  it  was  not  re-established  in  600 
trials.  Breed  and  Bingham  have  shown  certain  individual  chicks 
to  be  sensitive  to  differences  of  about  40  per  cent,  in  luminous 
intensity  and  area.  They  also  trained  several  chicks  to  discrimi- 
nate between  visual  objects  differing  only  in  form — circles  from 
equivalent  triangles  and  squares.  Watson  also  obtained  positive 
results  with  the  Rhesus  monkey,  but  has  not  yet  published  them. 
Coburn,  in  some  rather  rough  preliminary  tests,  obtained  results 
on  the  crow  which  compare  very  favorably  with  those  obtained 
by  Breed  and  Bingham  on  the  chick. 

Nela  Research  Laboratory, 

National  Lamp  Works  of  General  Electric  Co., 

Nela  Park,  Cleveland  Ohio. 

BIBLIOGRAPHY. 

Yerkes,  R.  M.  and  Morguus,  S. 

The  method  of  Pavloff  in  comparative  psychology. 
Psychological  Bull.,  1909,  pp.  257,  ff. 

Yerkes,  R.  M.  and  Watson,  John  B. 

Methods  of  studying  vision  in  animals. 

No.  2   Behavior   Monographs,   Cambridge,   Mass.,   Henry  Holt, 
1911. 


514     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Yerkes,  R.  M. 

The  dancing  mouse. 

New  York  McMillans,  1907. 
Lashley,  K.  S. 

Visual  discrimination  of  size  and  form  in  the  albino  rat. 
Jour,  of  Animal  Behavior,  1912,  pp.  310,  ff. 
Breed,  F.  S. 

Development  of  certain  instincts  and  habits  in  chicks. 

No.  1  Behavior  Monographs. 
Reactions  of  chicks  to  optical  stimuli. 

Jour,  of  Animal  Behavior,  1912,  pp.  280,  ff. 
Bingham,  H.  C. 

Size  and   form  preception  in   gallus   domesticus. 
Jour,  of  Animal  Behavior,  1913,  pp.  65  ff. 
Coburn,  Chas.  B. 

The  behavior  of  the  crow. 

Jour,  of  Animal  Behavior,  1914,  pp.  185,  ff. 

Watson,  John  B. 

Some  experiments  bearing  upon  color  vision  in  monkeys. 

Jour,  of  Comparative  Neurology  and  Psychology,  1909,  pp.  I,  ff. 

Casteel,  D.  B. 

Discriminative  ability  of  the  painted  turtle. 
Jour,  of  Animal  Behavior,  191 1,  pp.  1,  ff. 
Watson,  John  B. 

Experiments  upon  the  chick's  spectrum. 
Psychological  Bulletin,  1913,  pp.  71,  f. 
Watson,  John  B.,  and  Watson,  M.  I. 

A  study  of  the  responses  of  rodents  to  monochromatic  light. 
Jour,  of  Animal  Behavior,  1913,  pp.  1,  ff. 
Watson,  John  B. 

Behavior — an  introduction  to  comparative  psychology. 
N.  Y.,  Henry  Holt,  1914. 
Johnson,  H.  M. 

Visual  pattern  discrimination  in  the  vertebrates. 
Jour,  of  Animal  Behavior,  vol.  4,  No.  5,  1914. 

SeonakER,  J.  R. 

A  comparative  study  of  the  area  of  acute  vision  in  vertebrates. 
Jour,  of  Morphology,  vol.  13,  No.  3,  1897. 
Vincent,  Stella  B. 

The  mammalian  eye. 

Jour,  of  Animal  Behavior,  vol.  2,  1912. 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 

Vol.  X  OCTOBER  lO.  1915  NO.  7 


REPORT  OF  THE  COMMITTEE  ON  PROGRESS.* 


Where  is  the  way  where  light  dwelleth?  and  as  for 
darkness,  where  is  the  place  thereof?     Job  38 :    19. 


To  the  Illuminating  Engineering  Society  : 

During  the  past  year  there  have  occurred  two  events  of  strik- 
ing significance,  which  may  be  symbolized  by  two  flaming  torches, 
one  signalizing  destruction  and  conflagration,  the  other  spreading 
its  glow  over  construction,  progress  and  enlightenment.  One 
heralds  animosity  and  antagonism;  the  other  discloses  amity  and 
friendly  relationship.  The  one  is  the  sign  of  war;  the  other  a 
proof  of  peace.  In  spite  of  the  one  progress  has  continued;  in 
conjunction  with  the  other  the  art  of  illumination  has  been 
extended.  The  European  war,  repellent  in  its  awful  carnage,  has 
afforded  grim  and  hitherto  undreamt  of  possibilities  in  the  use 
of  light.  The  Panama-Pacific  Exposition  welcomes  the  whole 
world  and  stands  as  a  magnificent  example  of  the  art  of  applied 
illumination. 

Illuminating  engineering  is  becoming  recognized  as  a  profes- 
sion as  attested  by  the  employment  of  an  illuminating  engineer 
to  take  care  of  the  lighting  of  the  Exposition  and  by  the  announce- 
ment by  the  United  States  Government  of  examinations  for  the 
position  of  illuminating  engineer  in  the  office  of  the  supervising 
architect  at  Washington. 

The  enormous  demand  for  all  sorts  of  material  required  by 
the  nations  at  war  has  necessitated  night  work  in  a  large  number 
of  foreign  factories.  This  has  stimulated  interest  abroad  in 
satisfactory  and  efficient  systems  of  interior  illumination. 

It  will  be  noted  that  the  list  of  subjects  covered  by  this  year's 

*  A  report  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing Society,  Washington,   D.   C,    September  20-23,    1915. 

The   Illuminating   Engineering    Society   is   not    responsible    for   the   statements    or 
opinions  advanced  by  contributors. 


516     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

report  is  slightly  different  from  that  shown  in  the  report  of  last 
year.  Some  subjects  are  missing,  others  have  been  added.  This 
is  natural,  since  progress  is  continually  appearing  in  new 
directions. 

The  committee  again  desire  to  express  their  thanks  for  the 
help  accorded  by  the  engineers  in  charge  of  lighting  in  various 
cities  and  to  the  representatives  of  those  manufacturers  who  have 
furnished  information  and  data. 

Respectfully  submitted, 

F.  E.  Cady,  Chairman, 
P.  W.  Cobb, 
T.  J.  Litle,  Jr., 
L.  B.  Marks, 
T.  W.  Rolph. 

SUBJECTS. 

PAGE 

Gas  and  Oil  Lamps  and  Appurtenances 517 

Electric  Incandescent  Lamps 520 

Arc  Lamps 525 

Lamps  for  Projection  Purposes 527 

War 530 

The  Panama-Pacific  Exposition 534 

Street  Lighting 537 

Other  Exterior  Illumination 543 

Interior  Illumination 545 

Globes,  Reflectors  and  Fixtures 548 

Photometry 550 

Photography 556 

Legislation 557 

Illuminating  Engineering  in  General 559 

Literature 561 


REPORT   OF   THE    COMMITTEE   ON    PROGRESS  517 

GAS  AND  OIL  LAMPS  AND  APPURTENANCES. 


Burners. — A  very  important  development  in  incandescent  gas 
lighting  is  the  recent  introduction  of  an  upright  unit  fitted  with 
three  miniature  mantles  in  soft  form  and  made  from  artificial 
cellulose  fiber.  This  type  of  lamp  operates  well  over  a  reasonably 
fair  range  of  gas  pressure  and  qualities,  is  efficient  and  requires 
no  enclosing  draught-inducing  cylinders.  It  can  replace  open- 
flame  burners  without  glassware  change  on  present  fixtures  and 
furnishes  a  means  of  obtaining  semi-indirect  or  indirect  illumina- 
tion. 

Several  new  types  of  inverted  burners  provided  with  inclined 
chute-like  heat  baffles  to  divert  the  products  of  combustion 
entirely  away  from  the  fixtures  have  been  worked  out  in  sizes 
giving  approximately  100,  150  and  250  horizontal  candlepower. 
These  units  are  furnished  with  non-tarnishable,  heat-resisting 
lacquer  and  are  so  constructed  that  the  heat  discharge  vents  are 
completely  hidden.  Being  entirely  of  metal  they  can  be  finished 
to  match  the  fixture  on  which  they  are  to  be  used.  The  gas 
lamp  designed  to  take  advantage  of  the  fact  that  the  hottest  part 
of  the  flame  from  a  meeker  or  inverted  Bunsen  burner  is  in  the 
neighborhood  of  the  small  green  inner  cones  and  as  mentioned  in 
last  year's  report  has  been  in  use  in  Germany1  and  proved  the 
prediction  of  unusual  sturdiness  and  long  life. 

An  elaborate  study  of  the  room  ventilating  action  of  various 
types  of  gas  burners  has  been  made  in  England.2  The  results 
show  that  the  ventilating  efficiency  is  greatest  for  upright  burners ; 
that  of  the  inverted  burners,  those  giving  a  clear  passage  for 
the  gases  had  the  greatest  ventilating  efficiency ;  that  the  addition 
of  deflectors  intended  to  protect  the  fittings  from  the  action  of 
the  gases  reduced  the  ventilating  efficiency  by  as  much  as  9  per 
cent.  Experiments  made  in  this  country,  however,  show  that 
when  the  stack  is  properly  designed,  higher  efficiencies  are 
obtained  with  deflectors  due  to  a  superheating  of  the  mixture 
before  burning.  Globes  with  a  very  open  base  had  no  effect  on 
the  ventilating  efficiency,  but  those  with  a  constricted  opening 
produced  a  reduction  dependent  on  the  area  of  that  opening. 

ljuur.f.  Gas.,  July  25,  1914,  p.  741. 

2  Jour,  of  Gas  Light.,  June  8,    1915,  p.   573. 


518     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

To  produce  the  best  results  with  the  use  of  gas  for  lighting 
purposes,  the  character  of  the  Bunsen  flame  used  in  conjunction 
with  gas  mantles  must  not  change  materially.  In  order  to  enable 
a  manufacturer  to  ascertain  how  closely  his  service  is  maintain- 
ing constancy  of  burner  conditions,  a  gauge  has  been  developed.3 
It  consists  of  a  small,  slender  upright  Bunsen  tube  of  exact 
design  and  carefully  drilled  orifice,  mounted  on  the  same  base 
with  a  pressure  gauge.  A  scale  is  placed  at  the  side  of  the  Bunsen 
tube  in  order  to  check  the  length  of  the  inner  cone.  Any  varia- 
tion of  the  cone  length  above  or  below  a  specified  point  can  be 
easily  noted.  The  gauge  is  not  calibrated  to  indicate  any  specific 
quality  of  gas,  but  will  show  only  those  changes  which  will 
effect  Bunsen  burner  service. 

Despite  the  long  life  and  high  efficiency  of  the  present  day 
gas  mantle  efforts  are  still  being  made4  by  inventors  to  either 
strengthen  the  structure  or  intensify  the  illuminating  power  by 
the  application  of  some  solution  after  the  mantle  has  been  pur- 
chased.   Such  efforts  have  not  in  the  past  been  very  successful. 

Whether  illuminating  gas  causes  the  fading  of  colors  in  fabrics 
has  been  made  the  subject  of  careful  testing,5  experiments  having 
been  continued  for  a  period  of  ninety  days.  It  was  found  that 
the  deterioration  of  color  either  due  to  temperature,  illumination, 
or  the  products  of  combustion  arising  from  the  use  of  gas  light- 
ing is  of  no  practical  importance  compared  with  the  effect  of 
daylight. 

Automatic  Lighters. — The  protected  pilot  tip  so  successfully 
applied  to  outdoor  gas  arc  lamps  has  now  been  modified  for  use 
on  indoor  burners  reducing  the  pilot  flame  outages  to  a  minimum. 
A  very  simple  electric  gas  cock  for  the  distance  control  of  gas 
burners  has  been  produced.  In  Florence,  Italy,  a  system  of  dis- 
tance control  for  gas  lighting6  has  been  in  satisfactory  use  for 
the  past  three  years.  As  a  result  of  a  recent  successful  test  by 
military  authorities,  in  which  the  city  gas  was  shut  off  at  a  speci- 
fied time  and  relighted  after  a  predetermined  period,  it  is  expected 
that  this  system  will  shortly  be  employed  in  Italian  frontier  and 

3  Light.  Jour.   (U.S.),  Dec,  1914,  P-  82. 
*  Jour,   of  Gas  Light.,   Feb.  23,  1915,  p.  442. 
5  III.  Eng.   (Lond.),  June,  1915,  p.  292. 
8  Jour,  of  Gas  Light.,   Mar,  2,  1915,  p.  504. 


REPORT   OF   THE    COMMITTEE   ON    PROGRESS  51O, 

coast  towns.  In  general7  inventors  are  looking  toward  means  for 
making  distance  lighting  by  pressure  waves  selective. 

Artificial  daylight  units  using  gas  as  the  illuminant8  have  been 
developed  and  also  units  especially  designed  for  photographic 
work  which  will  be  mentioned  later. 

Heating  Value. — The  use  of  the  calorific  standard  for  gas  in 
place  of  the  candlepower  standard  is  increasing  in  this  country.9 
In  many  localities  both  standards  are  still  required,  but  it  seems 
to  be  a  quite  general  experience  that  if  the  gas  is  maintained  at 
the  right  calorific  value,  the  candlepower  value  will  be  satisfac- 
tory. At  the  1914  convention  of  the  American  Gas  Institute 
there  was  referred  to  the  Board  of  Directors  the  question  of 
adopting  the  Metropolitan  No.  2  (Carpenter  Argand)  burner  as 
the  standard  burner  in  the  determination  of  gas  candlepower.  It 
has  been  suggested10  by  the  Bureau  of  Standards  that  "for  those 
places  where  a  candlepower  specification  is  necessary  in  order  to 
afford  protection  to  users  of  open-flame  lights,  ...  an  open- 
flame  burner  should  be  used  in  testing  the  gas  candlepower."  As 
the  number  of  open-flame  burners  used  in  this  country  is  rela- 
tively small  the  advisability  of  adopting  this  suggestion  has  been 
seriously  questioned.  The  Bureau  also  suggests  that  the  adoption 
of  any  standard  burner  might  delay  the  present  tendency  toward 
the  adoption  of  heating  value  standards. 

Data  have  been  given11  of  experiments  which  indicate  that 
calorific  value,  specific  gravity,  and  gas  candlepower  do  not  defi- 
nitely specify  a  gas  for  commercial  purposes.  Gases  which  are 
identical  in  these  properties  may  yet  differ  so  in  composition  that 
the  resultant  flame  temperatures  will  differ  greatly  and  hence 
the  performance  of  incandescent  lighting  appliances  cannot  be 
predetermined  on  this  basis.  It  has  been  found,  however,  that 
heating  values  above  600  B.  t.  u.  are  not  desirable  for  incandes- 
cent gas  lighting. 

A  method  has  been  devised12  to  enable  a  gas  company  to  deter- 
mine the  candlepower  of  coal  gas  produced  at  night  as  well  as 

''Jour,  of  Gas  Light.,  May  18,    1915,  p.  409. 

8  Light.    Jour.    (U.S.),    Dec.,    1915,    p.    281.      Proc.    Amer.    Gas   Inst.,    vol.    IX, 
p.  886,  1914. 

•  Proc.  Amer.  Gas  Inst.,  vol.   IX,  1914,  p.  367. 

10  Gas  Inst.  News,   March,    1915,  p.   51. 

11  Amer.   Gas  Light  Jour.,  July  5,   1915,  p.    1. 

12  Amer.   Gas.   Lt.  Jour.,  Apr.   5,    1915,   p.  219. 


520    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

by  day.  A  holder,  3  ft.  (0.90  m.)  in  diameter  and  3  ft.  high  is 
used  and  the  flow  of  gas  into  it  is  regulated  so  that  it  will  just 
fill  up  during  the  night  or  during  the  day.  Tests  made  on  the 
candlepower  of  the  gas  collected  in  the  holder  agreed  exactly 
with  those  made  according  to  the  "periodic  method"  in  which 
readings  are  taken  periodically  when  the  candlepower  is  at  a 
maximum,  at  a  minimum,  and  at  the  average. 

Oil  Lamps. — Of  late  years13  the  use  of  high  pressure  oil  lamps 
with  incandescent  mantles  has  considerably  extended  the  employ- 
ment of  this  illuminant.  A  Swedish  type  using  Russian  paraffine 
oil,  consists  of  two  essential  parts,  the  lamp  itself  and  the  con- 
tainer for  the  oil.  The  latter  is  separated  into  two  compartments, 
one  containing  the  air  compressed  to  6  atmospheres  by  means  of 
a  small  hand  pump,  the  other  holding  about  2  gallons  of  oil.  The 
pressure  used  in  the  container  is  maintained  constant  at  2^2 
atmospheres  by  means  of  a  reducing  valve.  The  lamp  is  started 
by  means  of  a  little  methylated  spirit.  A  kerosene  oil  mantle 
lamp  is  now  being  used  in  this  country  which  on  recent  tests 
showed  a  candlepower  roughly  twice,  with  a  consumption  of  only 
half  as  much  oil  as  any  one  of  several  circular-wick  center  draft 
luminous  flame  lamps  of  the  ordinary  type. 

ELECTRIC  INCANDESCENT  LAMPS. 

Gas-filled  Tungsten  Lamps. — While  the  development  of  the 
tungsten  filament  electric  incandescent  lamp  has  been  fairly  rapid 
as  compared  with  that  of  the  carbon  filament  type,  it  would  seem 
as  if  the  progress  each  year  was  greater  than  that  of  the  previous 
year  and  that  salesmen  would  hardly  have  time  to  dispose  of  one 
product  before  an  improved  successor  was  available. 

In  last  year's  report14  reference  was  made  to  the  sizes  of  non- 
vacuum  gas-filled  tungsten  lamps  then  available,  400  being  the 
lowest  wattage  for  multiple  burning.  Now  100,  200  and  300- 
watt  sizes  are  made.15  In  May  all  sizes  from  200  to  1,000  watts 
for  circuits  of  220  to  250  volts  were  16  put  on  the  market.  In 
England17  60-watt  lamps  of  this  type  were  announced  July  1. 
In  the  60-watt  and  100-watt  lamps  argon  gas  is  used  instead  of 

13  III.  Eng.   (Lond),  Jan.,  1915,  p.  37. 

14  Trans.  I.  E.  S.,  9,  1914.  P-  522. 

15  Report  of  Lamp  Committee  Nat.  Elec.  Light  Assn.,  June,   1915. 

16  Elec.  Jour.,  June,   1915,  p.   252. 

17  Elec.   Times,  July   1,   1915,  p.    1. 


REPORT   OF  THE   COMMITTEE  ON    PROGRESS  521 

nitrogen.  In  Germany18  for  100  to  130-volt  circuits,  40  and  60- 
watt  sizes,  and  for  200  to  250-volt  circuits,  75  and  100-watt  sizes 
were  advertised  at  about  the  same  time. 

It  should  be  recalled,  however,  that,  while  in  lamps  with  fila- 
ments of  large  cross  section,  and,  for  multiple  burning  in  general 
of  high  wattage,  the  advantage  gained  in  being  able  to  run  the 
filaments  at  high  temperatures  and  hence  high  lumens  per  watt 
is  great  compared  with  the  loss  in  wattage  due  to  convection  and 
conduction  in  the  gas,  this  advantage  is  greatly  decreased,  in  the 
case  of  filaments  of  small  cross-section  such  as  those  used  for 
low  wattages  on  multiple  circuits,  and  hence  the  comparatively 
slow  introduction  of  the  latter. 

There  has  been  a  marked  improvement  in  the  various  mechan- 
ical features  of  the  gas-filled  tungsten  lamp.  Early  lamps  gave 
trouble  due  to  the  loosening  of  the  bases  because  of  the  effect 
of  the  heat  on  the  base  cement.  This  has  been  remedied.  A  new 
solder  has  been  devised  to  overcome  the  former  melting  of  the 
solder  at  the  junction  of  the  leading-in  wires  and  the  base.  Rust- 
ing or  scaling  of  the  leading-in  wires  has  been  eliminated  by  the 
use  of  a  special  coating.  The  distance  between  the  filament  and 
the  stem  seal  has  been  increased,  thus  decreasing  the  temperature 
of  the  seal. 

Another  important  step  in  advance  lies  in  the  standardizing  of 
the  bulb,19  which  now  incorporates  the  good  features  of  the  round 
and  straight-side  types,  previously  used,  together  with  the  long 
neck  containing  a  mica  disk  to  keep  the  seal  and  base  portion  of 
the  lamp  cool.  The  distance  from  the  light  center  to  the  base  has 
been  made  the  same  for  the  300  to  500-watt  sizes  so  that  one 
type  of  fixture  will  do  for  any  of  these  sizes.  The  use  of  the 
gas-filled  lamp  in  special  colored  bulbs  for  use  in  photography 
will  be  mentioned  under  another  caption. 

Before  the  advent  of  the  gas-filled  tungsten  lamp  the  use  in 
Germany  of  street  lamps  of  the  series  type  was  limited.  But20 
the  great  advantage  of  the  series  gas-filled  unit  was  evident,  and 

18  Elek.  Zeit.,  June  24,   1915,  p.  319. 
18  N.  E.  L.  A.  Bui.,  Apr.,  1915,  p  246. 
20  Zeit.  f.  Bel.,  Jan.,   1915,  p.  4. 


522     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

hence  an  effort  has  been  made  to  overcome  the  features  formerly- 
considered  objectionable.  A  carborundum  device  has  been  used 
to  some  extent  as  a  shunting  arrangement  for  burned-out  lamps. 

Physics. — There  has  been  a  continuation  of  the  study  of  the 
physical  properties  of  the  gas-filled  tungsten  lamp.  Thus  it  has 
been  found  that21  the  spectral  energy  curves  of  a  vacuum  lamp 
at  1.2  watts  per  candle  and  a  spiralled-filament  gas-filled  lamp 
operated  at  a  color  match  with  it,  superpose  very  closely  through- 
out the  infra-red  spectrum.  Tests  have  been  made  to  determine 
the  effect  of  winding  the  filament  in  the  gas-filled  lamp  in  the 
form  of  a  spiral  and  the  results  indicated  no  marked  difference 
in  the  quality  of  the  light  emanating  from  the  straight  and 
spiralled  filaments  of  tungsten  in  an  atmosphere  of  nitrogen. 
When  the  luminous  efficiency  (ratio  of  the  "visible"  to  the  total 
amount  of  radiation  emitted)  of  these  two  types  (straight  and 
spiral-wound  filaments  in  a  nitrogen  atmosphere)  was  practically 
the  same,  the  candles-per-watt  output  was  found  to  be  15  to  20 
per  cent,  higher  in  the  spiralled  filament,  owing  to  the  lessening 
of  convection  losses.  When  the  straight  filament  was  operating 
at  about  0.5  watt  per  candle  and  the  spiralled  filament  was 
operated  so  that  the  outside  surface  of  a  turn  was  set  to  the 
same  emissivity  as  that  of  the  straight  filament,  the  spectral 
energy  curves  of  the  two  showed  that  the  spiralled  filament 
emitted  about  7  per  cent,  more  infra-red  energy  than  the  straight 
filament.  Hence  the  luminous  efficiency  of  the  latter  under  the 
given  conditions  was  7  per  cent,  higher  than  the  former. 

Experiments  have  also  been  made22  showing  that  the  so-called 
"stationary"  film  of  gas  about  the  filament  of  a  gas-filled  lamp 
as  a  matter  of  fact  does  not  cling  to  the  filament,  but  moves 
upward  along  it. 

Vacuum  Tungsten  Lamps. — Since  last  year's  report  there  has 
been  an  increase  in  the  efficiency  of  the  vacuum  tungsten  lamp 
of  from  7  to  10  per  cent,  in  sizes  below  150  watts.  In  July  a 
sign  lamp  for  multiple  circuits,  105  to  125  volts,  was  announced 

21  Elec.   World,  Nov.  28,   1914,  p.   1048. 

22  Elec.    World,   Dec.   5,   1914,  p.   1111. 


REPORT   OF   THE   COMMITTEE   ON    PROGRESS  523 

using  7.5  watts  and  giving  5  candlepower.  This  is  the  smallest 
wattage,  standard  lighting-circuit  lamp  yet  manufactured.  The 
practise  of  introducing  chemicals  to  delay  the  discoloration  of 
the  bulb  has  been  extended  to  include  the  10,  15,  and  20-watt  sizes 
and  has  permitted  the  operation  of  all  vacuum  lamps  at  higher 
efficiencies.  The  spiral  winding  in  a  concentrated  form  is  now 
used  in  the  25,  40,  and  60-watt  sizes,23  in  addition  to  those  sizes 
in  which  it  was  previously  used.  These  lamps  use  the  same  size 
bulbs  and  have  the  same  average  mean  spherical  efficiencies  as 
the  regular  type  of  the  same  wattage,  but  have  a  somewhat  shorter 
life.  In  Germany  small  lamps  for  signal  purposes  have  been 
developed24  which  are  designed  to  be  burned  in  series  with 
apparatus  or  circuits  whose  active  or  inactive  operation  it  is 
desired  to  verify.  These  lamps  are  obtainable  for  a  range  of 
current  consumption  from  0.4  to  12  amperes. 

A  method  has  been  recently  patented,  in  which25  the  wires 
sealed  into  the  glass  stem  of  electric  lamps  are  coated  with  a 
chemical  salt,  thereby  making  a  better  seal.  The  patent  also 
covers  the  use  of  metal  plated  wire  for  use  in  such  seals. 

In  line  with  the  continued  efforts  towards  standardization  there 
has  been  considered  a  plan26  for  settling  upon  two  or  three  stand- 
ard lamp  voltages  to  be  adopted  as  a  basis  for  the  manufacturer's 
output.    This  will  simplify  specifications. 

The  completeness  with  which  the  gas-filled  street  series  lamps 
have  superseded  the  vacuum  type  has  resulted  in  the  withdrawal 
of  the  street  series  vacuum  lamps  from  the  listed  lamp  schedules. 

The  tantalum  lamp  has  now  disappeared  from  the  market  and 
is  being27  rapidly  followed  by  the  carbon  lamp.  The  demand  for 
gem  lamps  has  fallen  off  to  such  an  extent  that  it  is  difficult  to 
retain  the  present  limits  of  candlepower  and  wattage.  In  the 
case  of  miniature  lamps,  the  tungsten  filament  has  so  completely 

23  Light.  Jour.,  Mar.,   1915,  p.   65. 

24  Elek.  Zeit.,  Jan.  21,   1915,  p.   27. 

25  Elec.  World,  Apr.  24,  1915,  p.  1043. 
24  N.  E.  L.  A.  Bui.,  Mar.,  1915,  p.  169. 
27  Eamp  Com.   Report,  hoc.  Cit. 


524     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

replaced  carbon  that  sales  of  tungsten  comprise  over  85  per  cent. 
of  the  total  of  miniature  lamps  sold. 

Rating. — It  has  become  the  almost  universal  custom  to  rate 
metal  filament  lamps  in  this  country  according  to  their  watts  input 
and  apparently  this  method  of  rating  has  served  to  raise  the  pre- 
vailing standard  of  illumination.  In  England,  however,  a  dis- 
cussion before  the  British  Illuminating  Engineering  Society28  re- 
vealed the  fact  that  this  method  of  rating  is  by  no  means  generally 
accepted  as  satisfactory.  The  preponderance  of  opinion  seemed 
to  be  in  favor  of  a  return  to  some  form  of  candlepower  rating 
with  a  difference  of  opinion  as  to  whether  the  unit  should  be  the 
mean  spherical  candle  or  the  lumen.  In  Germany  also  the  sub- 
ject has  been  considered  at29  a  series  of  conferences  held  by  the 
German  Lamp  Manufacturers  who  proposed  the  continuance  of 
the  voltage-wattage  rating.  The  lighting  committee  of  the  Ger- 
man Association  of  Electrical  Engineers  discussed  this  proposal, 
but  could  come  to  no  full  agreement  on  the  subject.  A30  repre- 
sentative from  the  Associations  of  Central  Stations  urged  that 
it  should  be  required  by  law  to  state  the  voltage,  the  upper  and 
lower  hemispherical  candlepower,  the  total  watts  consumed  and 
the  watts-per-candle. 

At  the  request  of  the31  Society  of  Motor  Manufacturers  and 
Traders  the  British  Engineering  Standards  Committee  has  been 
investigating  standard  tungsten  filament  lamps  of  the  vacuum 
type  for  automobiles.  The  question  of  whether  such  lamps 
should  be  rated  at  all  in  candlepower  is  receiving  the  attention 
of  the  committee  and  in  the  meantime  they  are  rated  in  actual 
watts  or  nominal  candlepower.  Standard  bulbs  and  standard  volt- 
ages are  defined.  For  headlights  a  standard  distance  of  30  mm. 
from  the  contact  plates  to  the  center  of  the  filament  is  prescribed. 

In  Germany  the  gas-filled  lamps  were  formerly  widely  adver- 
tised as  "half -watt"  lamps.  Recently32  the  largest  manufacturers 
have  made  a  determined  effort  to  get  away  from  this  term,  real- 
izing that  it  is  as  misleading,  and  hence  a  cause  of  trouble,  as  the 
old  designation  of  "2,000  candlepower"  was  in  the  case  of  arc 
lamps. 

2S  III.  Eng.    (Lond.),  Apr.,   1915,  p.    167. 

29  Elek.  Zeit.,    May   13,   1915,  p.   236. 

30  Elek.  Zeit.,  May  20,   1915,  p.   248. 

81  Elec.  Eng.   (Lond.),  Feb.    18,1915,  p.  69. 
32  Zeit.  f.  Bel.,  Jan.,  1915,  p.  IX. 


REPORT   OF   THE   COMMITTEE   ON    PROGRESS  525 

Physics. — The  disappearance  of  almost  any  kind  of  a  gas 
introduced  at  low  pressure  into  a  bulb  containing  an  incandescent 
tungsten  filament  has  been  investigated  and  it33  has  been  found 
that  there  are  four  classes  of  reaction  involved.  The  filament  is 
directly  affected  by  the  gas;  or  the  gas  reacts  with  the  vapor 
given  off  by  the  filament;  or  the  filament  acts  catalytically  on 
the  gas,  producing  a  chemical  change  in  the  gas,  but  no  perma- 
nent change  in  the  filament ;  or  the  gas  is  chemically  changed  or 
made  to  react  with  the  filament  by  means  of  electric  discharges 
through  the  gas. 

Studies  have  been  made  also  on  the34  temperature  distribution 
in  the  neighborhood  of  a  cooling  junction  of  an  electric  incan- 
descent lamp  filament,  and  of  the  thermal  conductivities  of  tung- 
sten, tantalum,  and  carbon  at  incandescent  temperatures. 

ARC  LAMPS. 

A  flaming  arc  lamp  has  been  developed35  in  which  the  positive 
electrode  is  covered  by  an  outside  cylindrical  layer  of  illuminating 
salts,  which  protect  the  inner  electrode  core  against  the  oxygen 
of  the  air  so  that  consumption  is  reduced.  The  electrode  is  of 
homogeneous  carbon  and  the  layer  used  is  a  mixture  of  calcium 
fluoride,  sodium  tungstate  and  potassium  chromate.  The  nega- 
tive electrode  is  an  ordinary  homogeneous  carbon  with  a  central 
core.  The  electrodes  must  be  used  vertically  and  are  said  to 
have  a  life  of  from  40  to  50  hours.  The  specific  consumption 
including  the  series  resistance  for  direct  current  is  given  as  0.14 
watt  per  candle. 

In  the  report  of  the  Committee  on  Progress  for  1913,  reference 
was  made36  to  some  work  on  the  relation  of  pressure  and  tem- 
perature in  arc  lamps.  This  work  has  been  continued37  and  some 
striking  results  have  been  obtained.  From  these  results  the  true 
temperature  of  the  evaporating  solid  crater  of  the  positive  carbon 
at  atmospheric  pressure  was  deduced  as  4,200°  centigrade  abso- 
lute, a  value  higher  by  2000  or  3000  than  that  generally  ac- 
cepted heretofore.  The  temperature  of  the  negative  crater  was 
found  to  be  lower  by  several  hundred  degrees.     If  the  pressure 

33  Elec.    World,   May   15,    1915,   p.    1245. 

34  Phys.  Rev.,  vol.  4,   1914,  pp.   524  and  535- 
33  Elek.  Zeit.,  Nov.  26,   1914,  p.   1079. 

M  Trans.  I.  E.  S.,  Oct,   1913.  P-  328. 
31  Zeit.   f.  Beleu.,  Jan.,   1915- 


526     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

is  decreased  below  one  atmosphere  the  temperature  of  the  posi- 
tive crater  decreases.  When  the  atmospheric  pressure  is  in- 
creased the  temperature  of  the  positive  crater  increases  with  a 
corresponding  greatly  increased  efficiency.  At  a  pressure  of  22 
atmospheres  the  surface  brilliancy  had  increased  to  18  times  the 
value  at  one  atmosphere  pressure.  These  results  were  obtained 
with  impregnated  carbons,  it  having  been  found  impossible  to 
maintain  a  "true  arc"  with  pure  carbons  at  pressures  greater 
than  one  atmosphere.  Further  experiments  are  to  be  made  in 
connection  with  the  action  of  the  impregnating  salts,  the  dimen- 
sions of  the  carbons,  etc. 

In  a  study38  of  metallic  arc  lamps  comparative  tests  made  on 
ferro-ilmenite  and  magnetite  cathodes  using  solid  copper  anodes 
indicate  the  superiority  of  the  former.  A  definite  dependence  was 
found  between  the  temperature  of  the  arc  and  its  most  efficient 
length,  shorter  arcs  being  more  economical  at  low  amperages  and 
vice  versa.  Chromium  compounds  exercise  a  cooling  effect  simi- 
lar to  that  of  an  excessively  long  arc.  The  efficiency  of  the  arc 
was  increased  by  amounts  varying  from  190  to  133  per  cent,  by 
the  use  of  a  ferro-ilmenite  anode.  Indications  were  that  this  was 
due  to  the  heat  resistivity  of  the  material,  other  anodes  of 
materials  with  approximately  the  same  heat  resistivity  such  as 
cold  rolled  steel,  vanadium  steel  and  graphite  giving  similar 
favorable  results. 

On  alternating  current  circuits,  arcs  between  carbon  electrodes 
and  those  between  metal  electrodes  act  quite  differently  owing  to 
the  low  heat  conductivity  of  carbon.  The  relighting  potential  of 
carbon  electrodes  on  an  alternating  current  circuit  of  50  cycles 
and  3  amperes  does  not  exceed  100  volts,  but  the  relighting  po- 
tential of  metal  electrodes  under  identical  conditions  is  almost 
equal  to  a  static  discharge  potential.  Experiments  have  been 
made39  using  an  auxiliary  arc  to  counteract  the  tendency  of 
the  metal  arc  to  cool  down.  Combinations  were  tried  of  carbon 
and  ferro-ilmenite  electrodes.  The  results  indicated  the  possi- 
bility of  using  a  modification  of  Duddell's  musical-arc  circuit  for 
the  purpose  of  sustaining  the  alternating  ferro-ilmenite  arc  during 
the  zero  point  in  the  current  curve  by  supplying  the  necessary 

38  Elec.  Rev.  and   W.  E.,  Apr.   10,   1915,  p.  691. 
33  Elec.  Rev.  and  W.  E.,  May  8,  1915,  p.  871. 


REPORT   OF   THE    COMMITTEE   ON    PROGRESS  527 

relighting  potentials  from  the  circuit  itself.  It  is  hoped  that  a 
commercial  alternating  current  metal  arc  may  be  thus  developed. 

An  arc40  lamp  of  an  entirely  new  type  is  foreshadowed  in  a 
patent  issued  in  England  for  an  arc  between  tungsten  or  similar 
electrodes  enclosed  in  a  bulb  containing  nitrogen  or  other  inert 
gas.  The  electrodes  are  horizontal  and  of  small  diameter,  and 
the  arc  is  struck  by  a  simple  thermo-mechanical  device. 

Some  recent  experiments  on  the  temperature  of  the  mercury 
arc  as  used  in  work  on  fluorescence  have  given  results  indicating 
values  as  high  as  1,400°  centigrade.  Measurements  were  made 
on  the  discharge  in  a  tube  that  had  a  platinum-iridium  thermo- 
couple sealed  into  it  with  one  junction  situated  at  the  axis  of 
the  tube.  The  temperature  of  1,400°  C.  was  deduced  by  extra- 
polating about  200°  beyond  the  calibration  curve  of  the  thermo- 
couple. The  investigation  suggested  that  in  all  probability  the 
temperatures  indicated  by  a  thermo-couple  when  exposed  directly 
to  the  discharge  are  still  very  much  below  that  corresponding  to 
the  mean  molecular  kinetic  energy  of  the  luminous  vapor. 

LAMPS  FOR  PROJECTION  PURPOSES. 

Searchlights. — Recently  the41  United  States  Navy  has  secured 
a  searchlight  of  novel  form,  which  has  already  found  application 
in  Europe.  This  instrument  is  44  inches  in  diameter  and  has 
instead  of  the  usual  silver  mirror,  a  gold  mirror  which  can  be 
controlled  automatically  from  a  distant  station.  It  is  claimed 
that  the  use  of  gold  gives  a  beam  of  light  which  is  more  effective 
in  showing  detail  and  has  greater  penetrating  power  in  case  of 
fog  than  that  coming  from  a  silvered  mirror. 

In  the  Swedish  army  an  oxy-acetylene  searchlight  is  being 
adopted.42  This  apparatus  employs  a  pellet  of  ceria  on  which  the 
oxy-acetylene  flame  is  concentrated.  The  consumption  is  stated 
to  be  about  40  liters  of  acetylene  and  40  liters  of  oxygen  per  hour 
and  enough  of  both  is  carried  with  the  instrument  to  provide  for 
20  hours  burning. 

A  portable  searchlight43  has  been  developed  in  this  country  in 
which  a  20  in.  waterproof  projector  is  used  with  a  750-watt 

*"  Elec.   Bng.   (Lond.),   May  27,    1915,  p.   229. 

41  Sci.  Amer.,   Apr.   24,   1915,  p.   382. 

42  III.  Bng.   (Lond.),  Feb.,   1915,  p.  84. 

43  Elec.  Rlwy.  Jour.,  Mar.   27,    1915,  p.   639. 


528     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

focusing  type  non- vacuum  tungsten  lamp.  The  projector  and 
battery  weigh  600  pounds  and  are  mounted  on  a  two  wheeled 
carriage.  One  charge  of  the  battery  is  designed  to  give  7  hours 
continuous  service. 

Miner's  Lamps. — As  a  result  of  the  stringent  rules  of  the 
British  Home  Office  there  has  been  a  steady  development  in 
lamps  for  use  by  miners.     Six  new  types  have  been  approved.44 

The  Bureau  of  Mines  has  recently  revised  its  specifications  for 
miner's  lamps  under  the  caption  "Schedule  6-A."  The  principal 
changes  are  in  the  candlepower  rating  and  in  the  uniformity  test. 

Headlights. — A  big  reduction  in  power  consumption  without 
reduction  in  illuminating  effect45  in  street  and  surburban  railway 
headlights  has  been  made  possible  by  the  new  concentrated  fila- 
ment tungsten  lamps  which  are  replacing  arc  lamps  for  this  work. 

The  importance  of  the  problem  of  the  glaring  auto  headlights 
which  has  caused  so  much  adverse  legislation  and  ill-feeling  has 
been  recognized46  by  the  Society  of  Automobile  Engineers  as 
demanding  immediate  attention.  A  series  of  tests  have  been 
worked  out  which  may  be  used  as  a  standard  definition  of  what 
constitutes  a  dangerous  "glare"  and  the  results  of  such  tests  will 
be  submitted  to  manufacturers  of  headlights  with  a  view  to 
eliminating  the  trouble  at  the  source.  Future  headlights  are  to  be 
constructed  according  to  scientific  formulae  removing  the  glare 
but  thoroughly  retaining  the  far-reaching  effect  of  a  searchlight 
upon  the  road  itself. 

A  new  method47  of  reducing  the  glare  from  auto  headlights 
consists  in  the  use  of  small  curtains  mounted  on  shade  rollers 
contained  in  cylinders  which  may  be  attached  above  the  lamps. 
The  shades  are  raised  or  lowered  by  means  of  cords  connected 
to  a  device  operated  from  the  driver's  seat.  When  down  they 
still  transmit  sufficient  light  for  city  driving.  Another  arrange- 
ment48 consists  in  the  mounting  of  two  filaments  in  one  bulb,  one 
of  4  candlepower  for  city  use,  and  one  of  20  candlepower  for 
country  use.     Fittings  are  now  made49  which  enable  a  light  to  be 

"  Elec.  Eng.    (L,ond.),   May  6,    1915,  p.   197. 
45  Elec.   Rlu-y.  Jour.,    Mar.   27,    1915,  p.   639. 
**  Sci.  Amer.,  July  17,   1915.  P-   59- 
"Pop.  Mech.,  Mar.,  1915,  p.  397. 
48  Elec.  Rec,  Apr.,   1915,  p.  38. 
«  Elec.  Rec,  Feb.  5,  1915,  p.  26. 


REPORT  OF  THE   COMMITTEE  ON    PROGRESS  529 

mounted  almost  anywhere  on  an  automobile,  even  on  the  wind- 
shield or  fenders. 

Signal  Lights. — Fulfilling  the  forecast  made  in  last  year's 
report50  semaphores  are  eliminated  in  a  block  signal  system  now 
being  installed  on  one  of  the  large  railroad  systems.51  White 
electric  lights  are  arranged  on  a  black  background  so  that  the 
three  positions  of  a  semaphore  can  be  imitated.  Two  boards 
corresponding  to  two  semaphore  arms  are  used  for  each  track, 
the  upper  corresponding  to  the  stop  signal,  the  lower  to  the 
cautionary  signal.    These  signals  are  used  both  by  day  and  night. 

The  familiar  oil  lantern  carried  by  train  men  is  being  displaced 
by  an  electric  lantern52  built  along  exactly  the  same  lines,  a  dry 
battery  being  carried  in  the  space  formerly  occupied  by  the  oil, 
and  a  miniature  tungsten  lamp  furnishing  the  light.  Another 
portable  lantern  for  railroad  men  consists  of  a  nickel  plated 
casing,53  the  top  of  which  carries  the  battery,  the  bottom  being 
flared  so  as  to  act  as  a  projector  and  containing  an  incandescent 
lamp.  The  lamp  is  turned  on  or  off  by  the  bail  which  is  made 
to  snap  into  the  vertical  position  when  being  used. 

Owing  to  reckless  automobile  driving  the  old  "Stop,  look  and 
listen"  signs  at  grade  crossings  are  no  longer  as  efficient  as  for- 
merly in  preventing  accidents.  In  consequence  one  railroad  has 
inaugurated  the  use54  of  large  illuminated  billboards  to  educate 
the  public  in  "Safety  First"  and  warn  automobilists  and  others 
to  use  care  in  crossing  tracks.  A  new  type55  of  railroad  track 
warning  signal  consists  of  a  blackened  tube  containing  a  con- 
densing lens  behind  which  is  a  strong  incandescent  lamp  backed 
up  by  a  reflector.  The  tube  is  mounted  so  as  to  point  in  the 
direction  from  which  the  motorist  will  approach  and  the  placing 
of  the  light  well  back  in  the  tube  makes  it  almost  as  effective  by 
day  as  by  night. 

Street  traffic  controlled  by  means  of  signal  lights  described  in 
last  year's  report  is  being  tried  out56  in  Pittsburgh. 

There  is  evidence  of  the  increased  use  of  light  as  a  danger 

50  Trans.  I.  E.  S.,  IX,  No.  6,  1914.  P-  53°. 

61  Pop.  Mech.,  July,   1915,  p.   103. 

62  Elec.  Rec,  May,  1915,  p.   18. 

68  Pop.   Mech.,  June,    1915.   P-    893. 
M  Elec.   World,  July  17,   1915,  p.   146. 
M  Tech.    World,  Apr.,    1915,  p.   226. 
M  Municipal  Jour.,  Jan.  7,   1915,  p.   12. 
2 


530     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

signal.  A  power  station  has  installed57  a  system  of  red  lamps 
on  the  switchboard  gallery  which  indicate  when  and  where  an 
individual  is  entering  the  compartments  containing  the  dangerous 
high  tension  apparatus.  Another  central  station  uses  red  lights 
to  indicate  that  the  trolley  rail  of  the  ash  conveyor  is  energized 
and  therefore  dangerous. 

A  novelty58  in  the  way  of  a  signal  and  projection  light  is  a 
small  lamp  with  a  reflector,  to  be  attached  to  an  electric  iron. 
The  lamp  is  connected  to  the  wiring  inside  the  iron.  It  not  only 
illuminates  the  cloth  in  front  of  the  iron,  but  acts  as  a  tell-tale 
in  case  the  current  is  left  on  when  the  iron  is  not  being  used. 
Work  is  also  being  done  on  the  development  of  small59  pilot 
lamps  for  use  at  the  needles  of  industrial  sewing  machines. 

Flashlights. — Lately  there  has  been  an  unusual  development  in 
the  line  of  flashlights.  One  has  been  brought  out  exactly60  like 
a  fountain  pen  in  appearance  and  size.  It  is  provided  with  a 
pocket  slip,  is  S3A  m-  04-6o  cm.)  long  and  Y\  in.  in  diameter, 
and  weighs  only  iy2  ounces  (42.47  gr.).  A  modification  of  this 
idea61  includes  a  pencil  holder  and  the  lamp  can  be  operated  with 
or  without  the  pencil  by  means  of  a  thumb  slide  in  the  pencil 
barrel.  Still  another  type62  similar  to  these  employs  the  clip  as 
a  switch  and  is  provided  with  a  tongue  depressor  for  use  by 
physicians.  A  flashlight  has  also  been  developed  which  may63 
quickly  and  easily  be  attached  to  an  ordinary  dry  cell. 

WAR. 

The  great  war  furnishes  an  opportunity  for  the  study  and 
an  incentive  for  the  development  of  certain  classes  of  illuminants. 
In  its  activity  may  be  seen  the  application  of  the  latest  ideas 
regarding  such  factors  as  glare  and  the  power  of  light  of  certain 
colors  to  penetrate  fog.  Active  fighting  is  no  more  confined  to 
daylight  than  business  is,  and  the  old  type  of  romantic  sorties 
under  cover  of  darkness  are  made  almost  impossible  owing  to 
the  frequent  and  brilliant  flashes  of  illumination. 

57  Elec.    World,  June   12,    1915,   p.    1556. 

58  Elec.  Mds.,  June,    1915,  p.   165. 

59  Elec.   World,  June  12,   191S.  P-    1557- 

60  Elec.  News  (Can.),  Mar.   15,   1915,  p.   37. 

61  Elec.  Rec,  May,   191 5,  p.   18. 

62  Elec.    World,   May   15,   191S,  P-   1258. 

63  Elec.  Rec,  June,   1915.  p.  21. 


REPORT   OF   THE    COMMITTEE   ON    PROGRESS  53 1 

A  recently  designed  signal  device  consists  of  a  pair  of  binocu- 
lars over  which  is  mounted  a  small  parallel  beam  flashlight. 
The04  battery  for  lighting  the  lamp  is  carried  in  the  belt  of  the 
user.  The  average  range  of  the  instrument  is  about  3  miles 
(4.82  km.).  An  electric  flashlight  apparatus  used  by  the  British 
is  similar  in  size  and  appearance  to  an  ordinary  camera.  A 
large  lens  is  provided  at  the  front  of  the  box  and  flashes  are 
made  by  means  of  a  telegraph  key,  which  closes  the  lamp  circuit. 

Searchlights. — Traveling  searchlights  have  been  developed  by 
the  various  nations  at  war.65  Automobile  trucks  form  the  car- 
riers and  supply  the  power.  The  lights  may  be  operated  either 
on  the  truck  or  at  a  distance  from  it.  The  French  have  brought 
out  a  device  for  distance  control  employing  the  response  of  a 
tuning  fork  at  the  searchlight  to  a  vibrating  current  sent  from 
a  contact  breaker  tuned  in  unison  with  the  tuning  fork.  Gilded 
mirrors  are  being  used  instead  of  glass.  Searchlights  are  used 
not  only  to  detect  the  movement  of  the  enemy,66  but  to  blind 
troops  when  they  are  charging  across  the  zone  of  fire  and  to 
discomfort  the  pilots  of  aeroplanes.  Some  of  those  used  will 
throw  an  intense  light  for  miles.  Owing  to  the  blinding  and 
confusing  effect,  it  has  been  found  to  be  impossible  to  advance 
a  body  of  troops  in  the  face  of  strong  searchlights,  a  practical 
illustration  of  the  use  and  effect  of  glare. 

Illuminants. — Besides  searchlights  a  number  of  other  types  of 
illuminants  are  being  used.67  Among  these  may  be  mentioned 
the  luminous  cartridge  which  serves  for  the  illumination  of 
nearby  fields  and  especially  for  investigating  and  exploring  pur- 
poses. It  is  fired  from  its  own  pistol  and  has  a  range  of  action 
of  about  200  meters  and  a  luminous  area  of  about  100  meters. 
It  burns  from  8  to  10  seconds.  Similar  to  it,  but  with  much 
larger  luminous  activity  is  the  light-rocket  which  is  discharged 
from  a  musket.  It  is  fired  distances  from  45  to  900  meters  and 
its  intensity  is  so  great  that  it  lights  up  an  area  from  500  to  600 
meters  in  diameter  with  an  illumination  almost  as  great  as  day- 
light and  lasting  from  30  to  40  seconds.    Flares  have  been  devel- 

M  Set.  Amer.,  Oct.  24,   1914,  p.  334. 
M  Elec.  World,  May  15,  1915,  p.   1262. 

Sci.  Amer.  Sup.,  Oct.  3,  1914,  p.  209. 
M  Sci.  Amer.  Sup.,  July  10,  1915,  p.  23. 
"Jour.  f.  Gas.,  May  i,  1915,  p.  238. 


532     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

oped  from  fireworks  and  are  similar  to  what  are  known  as  red, 
white,  and  blue  fires  used  in  Fourth  of  July  celebrations.  These 
are  set  out  by  sappers  a  distance  in  front  of  the  battle  line  and 
are  controlled  from  the  headquarters  of  the  officers.  Ignited  at 
intervals  they  keep  the  battle  front  illuminated  throughout  the 
night.  Star  bombs  shot  from  mortars  maintain  an  intense  illumi- 
nation for  intervals  as  long  as  20  minutes.  For  distance  lighting 
a  projectile  similar  to  shrapnel  is  used,  so  constructed  that  it 
furnishes  light  after  a  definite  time  and  at  a  predetermined 
height.  Air  bombs  are  constructed  for  use  by  aeroplanes. 
Torches  have  been  developed  which  burn  from  2  to  3  hours. 

Profiting  by  conditions  in  the  European  war,  the  Secretary  of 
War  has  directed  the  Engineering  Corps  to  make  an  exhaustive 
study  of  and  experiments  with  the  use  of  searchlights,  flares, 
star  bombs,  and  other  lights  by  troops  in  the  field. 

Portable  Lamps. — The  war  has  caused  a  considerable  develop- 
ment in  the  way  of  pocket  lamps  in  Germany.68  In  one  type  of 
hand  lamp  an  ingenious  mounting  of  the  lamp  in  conjunction 
with  a  movable  screen  enables  the  light  to  be  directed  at  various 
angles  with  the  vertical  and  still  be  properly  screened  from 
observation.  Another  type69  has  an  arrangement  holding  a  pad 
and  pencil  with  the  light  so  concealed  that  only  the  pad  is  illumi- 
nated. Still  another  type70  is  in  the  form  of  a  hemisphere,  the 
inner  surface  of  which  is  polished,  and  with  the  lamp  may  be 
used  as  a  small  searchlight. 

Use  is  being  made  of  acetylene  for  the  illumination  of  portable 
hospitals.71  Limitations  in  the  supply  of  oil72  have  led  in  Ger- 
many to  an  effort  to  use  coal  gas  in  the  lighting* of  trains  in  place 
of  oil  gas  previously  used.  Among  the  other  sources  of  light 
for  ordinary  purposes  used  in  the  war  zones  should  be  mentioned 
kerosene  or  paraffin  oil  lamps  with  incandescent  mantles.73 

Safety  Lighting. — The  danger  from  night  raids  by  Zeppelins 
or  other  air  craft  has  made  it  advisable  to  reduce  the  lighting  in 

68  Elek.  Zeit.,  Oct.  22,  1914,  p.   1030. 
Elek.  Ans.,  Mar.  28,   1915,  p.   163. 
Elek.  Anz.,  May  9,   191S.  P-  240. 

69  Elek.  Anz.,  May  16,  1915.  P-  254. 

70  Elek.  Anz.,  May  23,   1915,  P-   269. 

71  Pop.   Mech.,   June,    1915,   p.    829. 

72  Acet.  Jour.,  April,  1915,  p.  387. 

73  Jour,  of  Gas  Light.,  June  15,   1915.  P-   659. 


REPORT   OF   THE    COMMITTEE   ON    PROGRESS  533 

cities  and  towns  in  England  and  France.  In  Paris74  in  the  neigh- 
borhood of  the  Eifel  tower,  lighting  has  been  cut  out  almost 
entirely.  As  a  sample  of  the  orders  for  reduced  lighting  used 
in  London  may75  be  mentioned  the  following:  In  all  brightly 
lighted  streets,  squares,  and  bridges  a  portion  of  the  lights  must 
be  extinguished  so  as  to  break  up  all  conspicuous  groups  or  rows 
of  lights  and  the  lights  not  extinguished  must  be  lowered  in 
intensity,  or  made  invisible  from  above  by  shading  them  or  paint- 
ing over  the  tops  of  the  globes,  providing  that  while  thick  fog 
prevails  normal  lighting  may  be  resumed.  Sky  signs,  illumined 
facias,  illuminated  lettering  and  powerful  lights  of  all  descrip- 
tion used  for  outside  advertising  or  for  the  illumination  of  shop 
fronts  must  be  extinguished.  Subsequently  the  above  orders76 
were  made  more  inclusive  by  prohibiting  all  lights  outside  of 
shops.  This  same  order  called  for  rear  lights  on  vehicles.  It 
is  interesting  to  note  that  while  we  have  had  rear  light  ordi- 
nances for  years  it  has  taken  war  conditions  to  make  the  desira- 
bility of  such  lights  apparent  in  London.  As  a  result  of  the 
above  requirements  special  reflectors  have  been  developed.77  In 
consequence  of  the  lighting  conditions  it  is  claimed  that  there 
has  been  a  large  increase  in  fatalities  caused  by  accidents.78 
Curious  complications  have  arisen  over  the  question  of  payment 
on  the  part  of  shopkeepers  for  exterior  illumination  which  they 
are  not  receiving.79 

Experiments  have  been  made  by  one  of  the  street  car  com- 
panies of  Londonso  to  meet  the  requirements  of  reduced  lighting 
and  still  furnish  light  enough  to  allow  the  passengers  to  read 
and  conductors  to  cancel  tickets.  As  a  result  of  these  experi- 
ments lamp  shades  used  in  the  lower  part  of  the  car  are  dipped 
in  a  violet  lacquer,  thereby  reducing  the  illumination  by  50  per 
cent.  In  the  upper  part  of  the  car  a  similar  treatment  is  given 
and  the  shades  arranged  so  as  to  throw  the  light  across  the  car. 

'*  III.  Eng.   (Lond.),  June,   1915,  p.  289. 
■  Jour,  of  Gas  Light.,  Dec.  22,   1914,  p.  652. 
u  Jour,  of  Gas  Light.,  Dec.   17,   1914,  p.   637. 
77  Elec.  Times,  Dec.  31,   1914,  p.  609. 
"  Elec.  Times,  May  6,    1915,  p.  399. 

///.  Eng..  (I,ond.),  July,  1915,  p.  300. 
'"Jour,  of  Gas  Light.,  Jan.  26,   1915,  p.   182. 
80  Elec.  Ry.  Jour.,  Dec.  26,   1914,  p.   1398. 


534    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  dash  lights  are  covered  over  with  yellow  paper.  Experi- 
ments on  dipping  the  lamps  themselves  were  found  to  give  unsat- 
isfactory results. 

The  restrictive  lighting  regulations  have  emphasized  the  waste 
occurring  in  many  show  windows81  and  the  desirability  of  con- 
sidering the  principles  of  illuminating  engineering,  in  order  to 
get  good  results.  Interesting  experiments82  are  to  be  carried  out 
in  London  to  diminish  the  inconvenience  to  the  public  due  to  the 
low  public  lighting.  Street  curb  stones  are  to  be  painted  white 
and  householders  are  requested  to  paint  similarly  all  door  steps 
leading  from  sidewalks.  Not  only  in  the  field  of  active  opera- 
tions but  also  at  home83  the  question  of  illumination  has  been  a 
matter  of  vital  importance  in  the  various  camps  formed  to  take 
care  of  troops  newly  recruited,  or  enroute  from  various  parts 
of  the  country.  Such  camps  cover  an  area  of  about  250  by  500 
yards  (228.6  by  457.2  m.)  and  contain  80  ordinary  huts,  27  offi- 
cers' huts,  dining  rooms,  guard  rooms,  etc.  About  1,200  lamps 
are  employed. 

The  restrictions  of  lighting  in  so  many  towns  in  England  has 
retarded  the  extensive  use  of  the  new  types  of  high  candlepower, 
high  efficiency  lamps.  One  of  the  effects  of  the  war  has  been  the 
recognition  in  Russia  of  the  need  of  manufacturing  her  own  in- 
candescent lamps.84 

THE  PANAMA-PACIFIC  EXPOSITION. 

In  its  use  of  light  the  Panama-Pacific  Exposition  furnishes  the 
most  striking  example  of  the  progress  of  illuminating  engineering 
that  has  ever  been  presented.  It  is  an  almost  complete  report  in 
itself.  For  the  first  time  in  the  history  of  such  institutions  a 
recognized  illuminating  engineer  has  been  called  in  to  take  care  of 
that  branch  of  the  work.  For  the  first  time  in  history  the  lighting 
of  an  international  exposition  was  completely  designed  and 
charted  before  the  buildings  were  erected,  and  the  results  bear 
eloquent  testimony  to  the  wisdom  of  that  action.  The  latest 
types  of  street  lighting  both  gas  and  electric  are  represented ;  the 
exteriors  of  the  buildings  are  brilliant  with  "flood  lighting" ;  the 
lighting  of  Festival  Hall  is  a  unique  example  of  totally  indirect 

81  Elec,  Dec.  n,  1915,  p.  331. 

82  Elec.   World,  July  17,   1915,  p.   158. 

83  Elec.  Eng.   (Lond.),  Dec.  24,   1914,  p.  649. 

84  Elec.  Rev.   (Lond.),   Mar.   12,   1915,  p.   346. 


REPORT   OF   THE   COMMITTEE   ON    PROGRESS  535 

lighting;  display  lighting  is  exemplified  in  the  wonderful  scintilla- 
tor system  and  in  the  Tower  of  Jewels ;  efforts  to  avoid  glare  are 
manifest  on  all  sides;  never  has  there  been  a  more  lavish  use  of 
colored  light.  And  so  this  exposition  stands  as  a  living  witness 
to  the  fact  that  illuminating  engineering  has  "come  into  its  own." 

No  attempt  will  be  made  to  discuss  all  the  novelties  to  be  found 
in  the  lighting  effects  but  reference  will  be  made  to  some  of  the 
more  prominent  features  of  the  illumination.  More  complete 
descriptions  will  be  found  by  reference  to  the  partial  bibliogra- 
phy.85 The  basic  idea  back  of  the  general  illumination  of  the 
buildings  was  the  desire  to  present  the  exposition  at  night  in  the 
same  relative  values  of  color  and  perspective  in  which  it  is 
observed  by  day.  On  this  account  the  old  outline-system  of 
illumination  in  which  incandescent  electric  lamps  were  used  to 
outline  the  architectural  features  of  the  buildings  was  abandoned 
in  favor  of  the  new  flood-lighting  idea  and  particular  attention 
has  been  paid  to  the  ocular  comfort  of  the  sightseer  while  at  the 
same  time  displaying  for  his  appreciation  wonderful  effects  pro- 
duced by  artificial  light. 

Four  principal  methods  of  illumination  are  employed.  Op- 
posite the  walls  of  the  exhibit  palaces  are  luminous  art  standards 
bearing  transparent  shields,  through  which  light  is  thrown  onto 
the  fascades.  A  second  method  of  illumination  is  found  in  the 
concealed  batteries  of  searchlight  projectors  which  are  used  to 
flood  the  monumental  sculptures,  towers  and  minarets  so  that  the 
minutest  architectural  details  are  visible.  A  third  source  of  light- 
ing is  that  of  the  concealed  light  which  proceeds  from  the  inner 
recesses  of  the  columns  which  encircle  the  courts  or  are  placed  on 
the  lofty  Tower  of  Jewels  and  the  Italian  Towers  commanding 
the  entrance  to  the  Court  of  Palms  and  the  Court  of  Flowers. 
This  method  of  lighting  is  also  used  in  the  vaults  of  archways  and 
in  other  situations  where  it  is  desired  to  cast  light  upon  the  mural 
paintings.  The  great  battery  of  48  searchlight  projectors  each 
with  a  36-in.  (91.44  cm.)  lens  forming  the  "scintillator"  makes  a 
fourth  source  of  illumination.86 

In  addition  to  these  four  principal  sources  of  lighting  there  are 

85  Light.  Jour.,  Mar.,   1915,  p.  49. 

Elec.  World,  Feb.   13,  1915,  p.  391. 

Elec.   World,  May  29,   1915,  p.   1383. 
"•  Sci.  Amer.,  Apr.  24,  1915,  p.  378. 


536    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

several  minor  sources.  In  various  parts  of  the  grounds  are 
globes  of  white  glass  the  light  from  which,  at  night,  dissipates 
the  shadows  under  the  foliage.  In  the  great  central  Court  of  the 
Universe  two  lofty  columns  of  dense  white  glass  are  parts  of  the 
two  fountains  and  are  the  principal  source  of  the  night  illumin- 
ation of  the  Court. 

The  striking  effect  of  the  Tower  of  Jewels  was  obtained 
through  the  use  of  specially  designed87  jewels  cut  from  glass 
obtained  in  Bohemia  and  having  an  index  of  refraction  of  from 
1.68  to  1.7 1.  Each  gem  is  suspended  so  as  to  be  free  to  swing 
with  air  currents  and  has  a  little  mirror  placed  within  one-six- 
teenth of  an  inch  of  the  apex,  thereby  increasing  the  number 
of  spectra  obtainable. 

A  noteworthy  feature  of  the  highway  lighting  is  the  use  of  18 
to  24-in.  (60.96  cm.)  globes  carrying  glassware  of  an  absorption 
of  approximately  50  per  cent,  and  of  a  warm  opal  tint  approach- 
ing amber.  The  illumination  of  the  interiors  of  the  buildings  is 
accomplished  by  the  use  of  250  and  500-watt  tungsten  lamps  in 
specially  designed  mirror  reflectors.  The  lamps  are  located  from 
40  to  100  ft.  (12.19  to  30.48  m.)  above  the  floor,  the  energy  is 
less  than  2  watts  per  square  foot  (9.29  sq.  dm.)  and  the  foot- 
candles  range  from  ^  to  ^  on  the  floor. 

The  first  commercial  installation  of  high  pressure  gas  lighting 
in  this  country88  and  one  which  is  said  to  show  many  improve- 
ments over  foreign  practise  is  to  be  found  in  the  State  and 
Foreign  Building  Section.  The  main  artery  for  traffic  is  the 
Avenue  of  Nations  and  this  and  other  streets  and  avenues  in  this 
section  are  lighted  by  high  pressure  two-mantle  lamps  enclosed 
in  opal  globes  mounted  single  on  the  top  of  ornamental  staff  work 
columns.  The  lamps  consume  21  cu.  ft.  (0.59  m.3)  of  gas  per 
hour,  operate  at  3  pounds  (1.36  kg.)  pressure,  reduced  at  the 
standard  from  30  pounds,  and  have  a  mean  spherical  candlepower 
of  408. 

Installations  of  the  same  lamps  have  been  made  at  all  the  en- 
trances and  exits  of  the  grounds.  At  the  entrances  and  exits  of 
the  main  group  of  exhibition  palaces  and  at  the  entrances  of  the 
courts,  lamps  of  the  low  pressure  type  are  used,  mounted  on 

87  N.  E.  L.  A.  Bui.,  Apr.,   1915,  p.  250. 

88  Amer.  Gas  Light.  Jour.,  Nov.   30,   1914,   p.  349. 
Jour,  of  Gas  Light.,  July  6,  1915,  p.  17. 


REPORT  OF   THE   COMMITTEE   ON    PROGRESS  537 

brackets.  In  the  "Zone"  gas  standards  35  ft.  (10.66  m.)  high  are 
placed  at  intervals  of  100  ft.  (30.48  m.)  on  both  sides.  There 
are  72  of  these  standards  each  carrying  5-mantle  lamps  with 
mercury  valve  distance  control.  Large  decorative  lanterns  are 
hung  about  these  lamps.  Decorative  effects89  are  obtained  by 
the  use  of  gas  to  produce  tongues  of  flame  from  serpent-headed 
urns. 

Some  very  spectacular  effects  are  obtained90  in  the  lighting  of 
the  glass  dome  of  the  Palace  of  Horticulture.  These  effects  are 
made  possible  by  the  use  of  sets  of  specially  designed  lens  plates, 
color  screens  and  high-powered  searchlights.  The  system  used 
in  lighting  the  interior  of  Festival  Hall  is  a  separate  and  distinct 
type  of  interior  lighting  which  is  unique.  In  a  pit  beneath  the 
center  of  the  floor  are  placed  a  number  of  searchlights  which  are 
set  to  throw  their  beams  upward  into  a  diffusing  disk  of  thick 
glass  sand-blasted  on  the  under  side,  which  distributes  the  light 
over  the  dome  covering  the  auditorium  and  the  dome  in  turn  acts 
as  a  diffusing  reflector. 

The  most  bizarre  and  spectacular  phenomena  are  produced  by 
the  "scintillator,"  over  300  effects  having  been  worked  out. 

At  the  San  Diego  Exposition91  neither  the  "flood-lighting"  nor 
the  "outline"  system  of  illumination  is  used,  but  ordinary  street 
lighting  supplemented  by  light  from  the  arches  of  the  arcades. 
This  has  been  found  very  satisfactory. 

STREET  LIGHTING. 

Display  Lighting. — A  general  survey  of  the  progress  in  the 
lighting  of  streets  shows  that  there  has  been  a  decided  increase  in 
ornamental  lighting92  for  advertising  purposes,  or  so-called  "White 
Way"  lighting.  Among  the  cities  where  such  installations  have 
been  made  during  the  past  year  may  be  mentioned  Portland, 
Ore.,93  where  a  system  has  been  placed  on  one  of  the  business 
streets  consisting  of  crossed  structural  steel  arches  bridging  the 
crossings  and  supported  on  concrete  columns.     Each  of  these 

89  Gas  Inst.  News,  Aug.,   1915,  p.  343. 

90  E lee.  Rev.  and  W.  E.,  June  5,  1915,  p.  1032. 
Sex.  Amer.,  Feb.  20,  1915,  p.   180. 

91  N.  E.  L.  A.  Bui.,  May,  191 5,  p.  340. 
Elec.   World,  Mar.  27,   1915,  p.  805. 

92  Municipal  Jour.,  June  24,   1915,  p.  886. 

93  Pop.  Mech.,  July,  1915,  p.   101. 


538     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

arches  is  outlined  by  192  incandescent  lamps  placed  on  the  under 
side.  "White  Way"  lighting  has  also  been  installed  in  Newark,94 
N.  J.,  using  lamps  of  500  candlepower ;  in  Louisville,95  Ky. ; 
in  Lowell,96  Mass.,  where  234  magnetite  6.6-ampere  arc  lamps 
have  been  used,  placed  14.5  ft.  (3.20  m.)  above  the  sidewalk  and 
with  a  maximum  distance  between  units  of  120  ft.  (36.57  m.) 
and  a  minimum  of  50  ft.  (15.24  m.),  lamps  being  located 
as  far  as  possible  on  alternate  sides  of  the  streets ;  in  Union,97 
N.  J.,  where  40  gas-filled,  500-watt  tungsten  lamps  were  used;  in 
Paterson,98  N.  J.;  in  Sioux  Falls,99  S.  D.,  where  156  luminous 
arc  6.6-ampere  lamps  have  been  placed  six  to  a  block  in  a 
staggered  arrangement;  in  Sandusky,100  O.,  where  14  city  blocks 
are  involved  and  380  gas-filled  tungsten  lamps  of  250  candlepower 
each  are  mounted  on  two-light  standards  approximately  50  ft. 
apart;  furthermore  a  complete  lighting  system  for  the  city  is 
being  installed  consisting  of  920  60-candlepower  and  100-candle- 
power  lamps  of  the  same  type ;  in  Cleveland,  where  600  gas-filled, 
20-ampere  tungsten  lamps  are  mounted  on  standards  with  a 
special  type  of  glassware  consisting  of  a  refractor  to  give  the 
desired  distribution  of  illumination,  and  an  enclosing  globe  with 
roughened  surface  which  is  designed  to  have  a  pleasing  appear- 
ance without  materially  changing  the  distribution  due  to  the  re- 
fractor ;  in  Charleston,  W.  Va.,101  where  62  ornamental,  luminous, 
4-ampere  arc  lamps  have  been  installed;  at  Malone,  N.  Y.,102 
where  400-candlepower,  gas-filled  tungsten  lamps  mounted  on 
ornamental  posts  were  installed;  at  St.  Cloud,  Minn.,103  where 
the  number  of  arc  lamps  was  increased  to  100  and  changed  to  the 
luminous  or  magnetite  type. 

There  is104  a  tendency  to  depart  from  the  use  of  five-lamp  stand- 
ards for  "White  Way"  lighting  inasmuch  as  they  are  too  prom- 
inent in  the  daytime.    Preference  to-day  inclines  toward  a  single 

94  Elec.  Rev.  and  W.  E.,  Nov.  14,  1914,  p.  954. 

95  Elec.  Rev.  and  W .  E.,  Nov.  14,  1914,  p.  954. 

96  Elec.  Rev.  and  W.  E.,  June  5,  1915,  p.   1039. 

97  Elec.    World,  June  26,    1915,  p.    1697. 

98  Municipal  Jour.,  May  27,  1915,  p.  740. 

99  Light.  Jour.   (U.S.),  May,   1915,  p.  98. 

100  Elec.  Rev.  and  W.  E.,  May  22,  1915,  p.  963. 

101  Municipal  Jour.,  July  22,   1915,  p.   114. 

102  Elec.  Rev.  and  IV.  E.,  July  31,  1915,  p.   180. 

103  Municipal  Jour.,  May  27,  1915,  p.  729. 

104  Elec.  World,  May  22,  1915.  P-  1328. 


REPORT  OF   THE   COMMITTEE   ON    PROGRESS  539 

or  at  most  a  double-light  unit  with  a  comparatively  high  candle- 
power  lamp.  The  introduction  of  the  gas-filled  tungsten  street 
series  unit  has,  in  general,  resulted  in  increasing105  the  candle- 
power  used  and  not  in  decreasing  the  wattage.  In  addition  to 
the  improvement  in  efficiency  the  new  construction  has  made 
possible  an  extension  in  the  range  of  candlepowers  available,  thus 
giving  greater  flexibility  to  this  type  of  lighting.  The  feasibility 
of  replacing  arc  lamps  with  incandescents  for  street  lighting  has 
been  agitated  ever  since  the  introduction  of  incandescent  units 
of  sufficient  intensity  to  produce  comparable  results.  The  question 
has  been  re-opened  since106  the  introduction  of  the  high  candle- 
power  tungsten  lamps.  Numerous  tests  have  been  made  and 
reports  given  on  the  relative  merits  of  the  two  types  of  illu- 
minants  and  on  the  relative  cost  of  operation.  But  there  are  so 
many  factors  entering  into  the  problem  that  it  seems  increasingly 
difficult  to  draw  even  general  conclusions. 

Street  lighting  progress  in  various  cities,107  aside  from  the 
special  ornamental  lighting  previously  mentioned,  may  be  seen 
in  the  following  record : 

Portland,  Ore. — Besides  the  ornamental  lighting  previously 
mentioned,  150  arc  lamps  have  been  added  for  general  street 
lighting. 

Tacoma,  Wash. — Installation  has  begun  on10S  126  new  orna- 
mental standards  each  using  a  250-watt  gas-filled  tungsten  lamp. 

San  Francisco,  Cal. — A  few  additional  lamps,  both  gas  and 
electric  arc,  have  been  installed,  making  a  total  of  3,423  arc 
lamps  and  7,838  gas  lamps.  The  most  notable  improvement  has 
been  the  installation  of  516  gas-filled,  250-candlepower  tungsten 
lamps  on  the  main  thoroughfare  leading  to  the  exposition  grounds. 
These  lamps  have  been  suspended  from  pipe  brackets  placed  on 
the  trolley  poles,  two  to  a  pole,  and  at  a  height  of  16  ft.  (4.87  m.) 
above  the  sidewalk.  The  distance  between  poles  is  approximately 
93  ft.  (28.34  m.).    It  is  expected  that  after  the  close  of  the  ex- 

1KN.  E.  L.  A.  Bui.,  Mar.,  1915,  p.   171. 
108  Jour.  f.  Gas.,  Aug.  1,  1915,  p.  777. 

Elec.    World,  June   19,   1915,  p.   1594. 

Ibid.,  July  10,  1915,  p.  109. 

Elek.  u.  Masch.,  Feb.  7,   1915,  p.  73. 

Elek.  Zeit.,  June  3,  1915,  p  269. 
1<n  Municipal  Jour.,  June  24,  191 5,  p.  890. 
108  Municipal  Jour.,  May  27,   1915,  p.   740. 


540     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

position  the  number  of  lamps  will  be  cut  down  as  the  illumina- 
tion is  much  more  brilliant  than  necessary  under  ordinary  con- 
ditions. 

Tuscan,  Ariz. — A  series  street-lighting  system  has  recently  been 
put109  in  the  business  section  consisting  of  75  five-light  stand- 
ards equipped  with  four  60-candlepower  and  one  100-candle- 
power,  6.6-ampere,  gas-filled  tungsten  lamps,  and  75  one-light 
standards  equipped  with  100-candlepower  similar  units. 

Dubuque,  la. — 585  600-candlepower  and  34  400-candlepower 
gas-filled  tungsten  lamps  have  replaced,110  with  a  decrease  of  20 
per  cent,  in  total  watt  consumption,  470  series  alternating  current 
6-6-ampere  arc  lamps. 

Milwaukee,  Wis. — The  report  on  the  street  lighting  survey 
authorized  in  1914,111  contains  among  others  the  following  recom- 
mendations: that  a  total  of  8,500  lamps  be  used;  on  residential 
streets  400-candlepower  units  hung  22.5  ft.  (6.24  m.)  high  on 
center  suspensions  at  the  street  corners,  with  100-candlepower 
lamps  at  the  curb  midway  between  corners  in  blocks  more  than 
420  ft.  (128.01  m.)  long;  for  business  streets  a  pair  of  30- ft. 
(9.14  m.)  posts  on  opposite  sides  of  the  street  every  180  ft., 
each  post  carrying  two  1,000  candlepower  lamps,  semi-residential 
streets  to  be  lighted  by  400-candlepower  units  360  ft.  (109.72  m.) 
apart  and  outlying  business  streets  by  600-candlepower  lamps  at 
the  curb  and  on  180  ft.  centers. 

Chicago,  III. — The  principal  changes  during  the112  year  have 
been  the  introduction  of  300-watt,  20-ampere,  gas-filled  tungsten 
lamps  in  place  of  450-watt  enclosed  alternating  and  direct  current 
arc  lamps  and  in  underground  work  the  replacing  of  80-watt, 
vacuum  type  tungsten  lamps  with  the  75-watt,  4-ampere  series 
gas-filled  type.  The  following  table  shows  the  number  of  lamps 
in  service  June  1,  1915,  as  compared  with  those  in  use  June 
1,  1914: 

109  Jour.  Elec.  Power  and  Gas,  May  22,  1915,  p.  407. 

110  Elec.  World,  June  19,  1915,  p.   1635. 

lu  Elec.  World,  June  27,  1914,  p.  1480. 

112  Elec.  World,  May  8,  1915,  p.  11 73. 
Trans.  I.  E.  S-,  Apr.   30,  1915,  p.  281. 


REPORT  OF   THE   COMMITTEE  ON    PROGRESS  541 

June  1,  1914  June,  1915 

Flame  arcs 10,283  10,021 

300-watt  gas-filled  tungsten —  9,020 

Alternating  current  enclosed  arcs 6,254  1 ,740 

Direct  current  open  arcs 1,272  — 

4-ampere  series  vacuum  tungsten 4,077  7«I93 

Gas,  standard  type 11,902  10,157 

Gas,  ornamental  type —  730 

Gasoline 5,286  4,690 

Rented  flame  arcs 1,161  i,3°2 

Indianapolis,  Ind. — Five  miles  of  boulevard  lighting  have  been 
installed113;  io-ampere,  gas  rilled  tungsten  lamps  have  been  used, 
four  250-candlepower  units  at  the  street  intersections  with  150- 
candlepower  lamps  at  irregular  intervals  between  corners  and 
staggered. 

Louisville,  Ky. — Two  hundred  and  fifteen  gasoline  lamps,  which 
have  been  in  service  in  the  parks  and  along  the  parkways  and 
operated  only  in  the  summer,  are  to  be  replaced114  by  250  gas-filled, 
1 00- watt  tungsten  lamps  which  will  run  throughout  the  year. 

Detroit,  Mich. — The  lighting  system  has  been  extended  by  the 
addition  of  1,186  additional  4-ampere,  luminous  arc  lamps  as 
well  as  483  luminous  arcs  of  the  6.6-ampere  inverted  type.  The 
latter  completes  the  illumination  of  eleven  miles  of  boulevard. 
Forty  series  incandescent  lamps  have  been  installed  in  the  alleys 
of  one  of  the  foreign  settlements. 

Philadelphia,  Pa. — Additions  during  the  year  include  400  arc 
lamps  650  gas-filled,  400- watt  tungsten  lamps,  179  gasoline  lamps 
and  300  gas  lamps. 

New  York,  N.  Y. — Prior  to  Jan.  1,  1915,  Greater  New  York 
was  lighted115  wholly  by  three  types  of  units,  the  enclosed  arc 
lamp,  the  100-candlepower  non-vacuum  tungsten  lamp  and  gas 
lamps.  Since  Jan.  1,  the  300  to  1,000- watt  multiple  and  400- 
candlepower  series  type  of  gas-filled  tungsten  lamps  have  replaced 
10,000  enclosed  carbon  and  flaming  arc  lamps.  In  Queens  and 
the  Bronx  about  5,000  non-vacuum  100-candlepower  tungsten 
units  have  replaced  gas.  Approximately110  600,  multiple,  arc 
lamps  in  use  on  the  bridges  connecting  the  several  boroughs  have 

113  Elec.   World,  May  8,   1915,  p.   1201. 

u*  Elec.  Rev.  and  W.  E.,  Feb.  20,  1915,  p.  332. 

115  Light.   Jour.,  May,   1915,   p.    108. 

118  Elec.   World,  June  19,   1915,  p.   1639. 


542     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

been  replaced  by  the  300-watt,  gas-filled  tungsten  units.  So  far 
these  lamps  have  withstood  traffic  vibrations  satisfactorily.  Nego- 
tiations are  under  way117  for  a  large  number  of  200-watt,  non- 
vacuum  tungsten  lamps  to  replace  gas  lamps  on  many  of  the 
side  streets. 

Brooklyn,  N.  Y. — All  direct  current  arcs  have  been  replaced 
by  300-watt,  non-vacuum  tungsten  lamps.  At  present,  June, 
191 5,  2,000  are  installed.  Gas  lamps  are  being  replaced  by  300- 
watt,  non-vacuum  tungsten  units. 

Montreal,  Can. — An  extension  of  the  lighting  system  is  being 
made  by118  the  addition  of  84  luminous,  6.6-ampere,  arc  lamps,  on 
ornamental  poles  of  special  design  placed  125  ft.  (48.1  m.)  apart. 

Canal  Zone,  Panama. — In  the  Canal  Zone  permanent  street 
lighting  systems  similar  to  those  in  use  in  Washington,  D.  C, 
are  to  be  installed  in119  the  principal  towns.  Gas-filled  tungsten 
lamps  probably  of  100-watt  size,  6.6-ampere  series  type  will  be 
used. 

Great  Britain. — The  report120  issued  by  the  British  Government 
on  the  use  of  gas  during  the  year  closing  June  1,  1914  has  been 
issued  and  shows  an  increase  in  the  number  of  gas  consumers  in 
Great  Britain  of  357,411.  The  report  also  states  that  while  the 
use  of  electricity  for  street  lighting  is  increasing  there  are  still 
779,442  incandescent  gas  units  in  use. 

Berlin. — The  number  of  gas  lamps  in  use  for  public  lighting 
in  Berlin,  Mar.  31,  1914,  was  43,78c,121  and  increase  of  2,324.  As 
in  previous  years  there  has  been  an  increase  in  high  pressure  light- 
ing in  the  prinicipal  streets.  In  the  inner  parts  of  the  city,  illum- 
ination has  been  strengthened  by  increasing  the  number  of  burn- 
ers in  a  lantern,  by  increasing  the  number  of  many-flame  low 
pressure  inverted  lamps,  as  well  as  by  increasing  the  number  of 
lamp  standards.  In  Victoria  Park  the  electric  lighting  has  been 
improved  by  the  addition  of  arc  and  metal  filament  lamps.  There 
are  still  in  use  a  small  number  of  petroleum  and  spirit  lamps. 

Investigations. — The  investigation  of  street  lighting  being  car- 
ried on  under  the  joint  auspices  of  committees  of  the  National 

117  Cent.  Sta.,  June,   1915,  p.  367. 

118  Elec.  News  (Can.),  May   1,   1915,  p.  39. 

119  Light.   Jour.,   Apr.,    1915,   p.   89. 

120  Amer.  Gas  Lt.  Jour.,  Apr.   5,  1915,  p.  217. 
m  Jour.  f.   Gas,   Mar.   20,    1915,   p.    143. 


REPORT  OF  THE   COMMITTEE   ON    PROGRESS  543 

Electric  Light  Association  and  the  Association  of  Edison  Illum- 
inating Companies  and  which  was  started  last  year  is122  still  un- 
completed. To  properly  interpret  results  already  obtained  re- 
quires a  complete  knowledge  of  the  conditions  and  no  attempt  will 
be  made  to  summarize  them  in  this  report.  Another  investigation 
of  the  factors  connected  with  effective  illumination  of  streets  has 
been  directed  toward  a  study  of  the  effect  of  glare  on  visual 
acuity.  The  method123  of  test  consisted  in  making  observations 
of  a  special  visual  acuity  test  chart  first  with  the  street  lamps  off 
and  then  under  ordinary  lighting  conditions.  Among  the  con- 
clusions reached  were  that  merely  surrounding  a  brilliant  source 
of  light  by  a  diffusing  globe  does  not  materially  diminish  blinding 
effects.  Mounting  heights  less  than  20  ft.  (6.09  m.)  should  be 
avoided  if  possible  and  heights  less  than  15  ft.  should  never  be 
employed.  When  the  height  is  relatively  low,  the  candlepower 
between  the  angles  of  65  °  and  900  from  the  vertical  should  also 
be  relatively  low.  So  far  as  avoidance  of  glare  is  concerned 
there  is  no  object  in  increasing  the  height  beyond  50  ft. 
(15.24  m.).  An  excellent  summary  of  technical  data  on  electric 
street  illuminants  was  presented  at  the  191 5  convention  of  the 
National  Electric  Light  Association. 

OTHER  EXTERIOR  ILLUMINATION. 

The  continued  improvement  in  illuminants  is  reflected  in  the 
spread  of  out-door-lighting  of  all  kinds  and  the  use  of  light  more 
than  ever  before  for  a  variety  of  purposes.  Thus  a  real  estate 
dealer  arranges  to  have  a  new  sub-division  highly  illuminated12* 
and  rapidly  sells  his  lots  to  customers  who  have  come  out  to 
view  them  at  night.  Improvements  in  distance  lighting  and  con- 
trol125 have  made  feasible  the  employment  of  gas  in  places  where 
its  use  had  previously  been  considered  impossible.  A  big  exten- 
sion is  to  be  noted  in  the  use  of  light  for  exterior  advertising 
purposes. 

Flood-lighting. — One  of  the  most  striking  illustrations  of  the 
modern  "flood-lighting"  method  of  illuminating  the  exterior  of 

122  Trans.  I.  E.  S.,  9,   1914,  P-  536. 

Report  of  Committee  on   St.   Light.  N.  B.  L.  A.,  June,   1915.     See  also  Trans. 
A.  I.  B.  B.,  July,  1915,  p.  1379. 

123  Elec.  Rev.  and   W.  B.,  Mar.   6,   1915,  p.  439. 

124  Elec.  Rev.  and  W.  B.,  May  8,  1915,  p.  856. 
123  Gas  Age,  July  1,  1915,  p.   5. 


544     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

buildings  is  to  be  found  in  the  lighting  of  the  Woolworth  build- 
ing120 in  New  York  City,  which  was  disclosed  to  public  view  at 
the  beginning  of  the  year.  It  has  been  said  that  more  light  is 
provided  for  the  illumination  of  the  tower  than  is  usually  em- 
ployed in  lighting  a  city  of  30,000  inhabitants.  600  automobile 
projector  units  fitted  with  250- watt,  gas-filled  tungsten  lamps  are 
used  to  throw  light  on  the  structure  from  the  thirtieth  to  the 
fifty-eighth  story.  These  projectors  are  arranged  so  that  some 
throw  their  light  upward  and  the  rest  throw  their  light  down- 
ward. Thus  there  is  one  continuous  diffusion  of  light  over  the 
whole  surface.  The  lamps  throwing  light  downward  are  care- 
fully screened  so  as  not  to  be  directly  visible  from  the  street. 
The  most  novel  point  of  the  installation,  however,  is  at  the  six- 
tieth story  called  the  "crow's-nest"  or  "lantern."  It  has  been  en- 
closed with  diffusing  glass  and  within  are  placed  twenty-four 
1,000-watt  lamps.  An  automobile  dimmer  connected  with  these 
lamps  continuously  alters  their  intensity  in  an  irregular  cycle. 
Thus  at  one  instant  the  glass  surface  of  the  lantern  shows  a  deep 
red  glow  no  brighter  than  the  adjacent  gilded  structure,  and 
again  it  flares  up  to  a  bright  white  light  many  times  this  bright- 
ness and  visible  for  miles. 

The  flood-lighting  idea  has  been  much  extended  in127  the  illum- 
ination of  advertising  signs  on  billboards,  water  tanks,  roofs  of 
buildings,  side  walls  and  elsewhere.  In  such  cases  the  effect  is 
accomplished  by  directing  a  beam  of  light  against  the  sign  from 
some  nearby  convenient  location;  a  new  lighting  unit  of  high 
intensity  utilizing  a  parabolic  reflector  has  been  recently  developed 
for  this  special  purpose. 

Lighting  of  Sports. — The  lighting  of  courts  for  tennis  and 
other  sports  has  proved  so  satisfactory  that  the  idea  is  being  tried 
out  in  a  number  of  different  ways.  A  playground  in  a  city  park 
has  been  illuminated  so  that128  its  various  amusements  are  avail- 
able at  night  as  well  as  by  day.  Five  750-watt,  gas-filled  tungsten 
lamps  are  used  to  light  the  football  field  while  1,000-watt  units 
are  used  to  illuminate  the  swings  and  gymnasium  apparatus. 
These  units  are  placed  20  ft.  (6.09  m.)  above  the  ground  on 
goose-neck  boulevard  posts.     A  test  was  made  at  the  Indiana 

126  Elec.  Rev.  and  W.  E.,  June  5,  1915,  p.  1048. 

121  Elec.  Merchandise,  Dec,   1915,  p.  306.     See  also  Cent.  Sta.,  May,   1915,  p.  346. 

128  Elec.   World,   May  22,   1915,  p.   1328. 


REPORT  OF   THE   COMMITTEE   ON    PROGRESS  545 

State  Fair  grounds  recently  of129  a  system  of  illumination,  in 
order  to  try  out  the  practicability  of  automobile  racing  at  night. 
The  result  was  a  complete  success.  Lights  of  the  type  used  in 
contracting  and  railroad  work  for  emergency  operations  at  night, 
were  placed  at  intervals  about  the  track.  Each  light  was  sup- 
plied from  its  own  cylinder  of  dissolved  acetylene.  In  another 
case130  an  outdoor  skating  rink  used  for  the  sport  of  curling  has 
been  lighted  by  tungsten  lamps  installed  on  two  lines  of  stray 
wires,  extending  the  length  of  the  rink,  and  about  35  ft.  (10.66  m.) 
apart.  Extra  illumination  is  furnished  at  the  ends  over  the  goals. 
The  lamps  hang  about  15  ft.  above  the  surface  of  the  ice. 

A  sign  of  progress131  is  to  be  noted  in  the  installation  of  a 
lighting  system  on  the  celebrated  wall  which  surrounds  the  block 
in  Salt  Lake  City  enclosing  the  famous  Tabernacle  and  Temple. 
The  wall  is  approximately  12  ft.  (3.65  m.)  high  and  will  be 
lighted  by  high  power  lamps  located  every  50  ft.  (15.24  m.). 

Because  of  the  scarcity  of  kerosene  there  has  been  an  exten- 
sion of  gas  and  electric  lighting  in  Germany,132  alcohol  and  acety- 
lene being  adopted  in  the  country  districts. 

INTERIOR  ILLUMINATION. 

The  trend  in  interior  lighting  continues  to  be  in  the  direction 
of  protecting  the  eyes  from  excessive  brightness. 

Hotel  Lighting. — A  recently  finished,  and133  what  is  claimed  to 
be  largest  hotel  in  Europe,  has  been  fitted  throughout  with  the 
semi-indirect  system  of  illumination.  The  lighting  has  been  so 
arranged  that  corridor  lights  are  independent  of  those  in  adjacent 
bed-rooms.  In  the  dome  of  the  rotunda  court  a  novel  plan  has 
been  adopted  of  introducing  opal  bulls-eyes,  with  a  lamp  behind 
each,  into  the  risers  which  support  the  glazing  of  the  dome. 
Around  the  dome  cornice  is  a  ring  of  lamps  which  are  concealed 
from  view  at  the  floor  level  but  throw  a  considerable  volume  of 
light  upward  into  the  dome.  Some  6,000  lamps  are  used  in 
this  hotel.  In  England134  the  use  of  high  pressure  gas  is  being 
extended  to  factory  lighting. 

129  So'.  Amer.,  June   12,   1915,   p.   587. 

130  Blec.  Rev.  and  W.  E.,  Feb.   13,   1915,  p.  311. 

131  Elec.  Merchandise,  Apr.,  1915,  p.  82. 

132  Pop.  Mech.,  May,   1915,  p.  651. 

133  Elec.  Times,  June  24,   1915,  p.  531. 

134  Jour,  of  Gas.  Lt.,  June  1,  1915,  p.  506. 
3 


546     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Municipal  Buildings. — While  a  private  enterprise  is  quick  to 
see  and  adopt  improvements  in  lighting  sources  and  methods,  the 
municipally  controlled  institution  has  in  the  past  exhibited  a 
decided  inertia  in  this  respect.  A  start  has  been  made  in  Boston135 
to  remedy  this  and  the  replacement  of  old  types  of  lamps  of  low 
efficiency  has  already  brought  about  a  marked  saving  to  the  city. 
The  change  has  been  so  satisfactory  that  one  of  the  city  engineers 
is  to  devote  his  entire  time  during  this  year  to  improving  the 
lighting  of  buildings  in  the  school,  police  and  fire  departments. 

Office  Buildings. — Heavy  glass  partitions  which  are  translucent, 
substantial,  sun-proof,  and  fire-proof,  are  being  introduced  as  a136 
means  of  distributing  sunlight  through  large  office  buildings, 
without  lessening  the  privacy  of  the  various  offices.  These  par- 
titions are  built  of  clear  glass  units,  2  in.  (50.8  mm.)  thick,  and 
either  6  or  8  in.  square,  which  are  reduced  to  translucency  by 
impressed  designs. 

Hospitals. — That  the  educational  work  of  the  Society  on  the 
subject  of  color  and  glare  is  bearing  fruit,  is  seen  in  the  use  of 
green  and  buff  for  the  color  of  the  walls  in  a  large  Western137 
hospital.  White  had  always  been  used,  but  it  was  found,  on 
trial,  that  the  discomfort  coming  from  the  necessity  of  eye- 
adaptation  on  the  part  of  surgeons  looking  up  from  their  work, 
and  seeing  only  white-clothed  assistants  and  white  walls  was 
largely  eliminated  with  the  use  of  other  colors.  The  effect  on 
patients  has  also  been  beneficial.  In  another  large  city  hospital 
a  rather  unique  use  of  the  mercury-vapor  lamp  is  found  in  its 
employment138  for  examination  of  X-ray  skyographs. 

Street  Railway  Cars. — A  growing  recognition  of  the  importance 
of  proper  lighting  in  every  sphere  of  activity  is  illustrated  in 
the139  recent  extensive  tests  conducted  by  a  large  municipal  rail- 
way. A  full  sized  template  car  was  built  and  tested  when 
equipped  with  direct,  semi-indirect,  and  totally  indirect  systems 
of  lighting.  The  general  effect  and  appearance  of  each  system 
under  test  were  judged  by  comparison  with  present  methods  of 
car  lighting  for  similar  service.     The  effect  of  the  light  on  the 

135  Elec.   World,  May  22,   1915,  p.   1327. 

136  Pop.  Mech.,  June,  1915,  p.  818. 

13T  Pop.  Elec.  and  Mod.  Mech.,  Dec,  1914,  p.  644. 

138  Elec.    World,  June   5,   1915,  p.   1475. 

139  Trans.  I.   E-   S.,   1915,  p.  227. 


REPORT  OF   THE   COMMITTEE   ON    PROGRESS  547 

eyes  was  particularly  noted  by  a  large  number  of  observers.  The 
system  finally  adopted  consists  of  a  single  row  of  56-watt,  bowl- 
frosted  tungsten  lamps  placed  symmetrically  down  the  center 
line  and  equipped  with  opal  glass  reflectors.  These  lamps  were 
supplemented  by  six  10-watt,  all-frosted  round  bulb  tungsten 
emergency  lamps.  One  big  unit  was  placed  on  each  end-bulkhead 
of  the  car  to  bring  up  the  illumination  at  these  points.  In  the  car 
as  finally  equipped  the  illumination  averaged  5.94  foot-candles,  at 
normal  and  3.85  at  85  per  cent,  voltage,  the  energy  consumption 
was  1.44  watts  per  square  foot,  effective  lumens  per  watt  4.14  and 
the  utilized  efficiency  50.6  per  cent. 

Another  street  railway  company  is  emphasizing140  the  "Safety 
First"  principle  by  providing  a  light  so  placed  as  to  directly 
illuminate  the  step  of  the  street  car.  A  practical  application  of 
signal  lights  has  been  adopted  by141  some  of  the  theaters  of 
Vienna.  On  the  back  of  each  seat  is  a  small  electric  lamp  which 
illuminates  the  seat  number.  As  long  as  the  seat  is  turned  up, 
as  it  usually  is  when  not  occupied,  the  light  is  burning,  but  is 
shut  off  when  the  seat  is  turned  down.  By  this  means  the  use  of 
ushers  has  been  materially  decreased. 

Clock  Tower. — A  novel  use  for  the  method  of  indirect  lighting 
is  to  be  found  in  the  illumination  of  clock  dials  in  the  new  Boston 
Custom  House.142  Behind  each  dial  is  a  chamber  with  white 
walls  illuminated  by  a  number  of  lamps.  Numerals  of  the  dial 
are  in  the  form  of  slots  set  in  concrete  and  the  lights  in  each 
chamber  are  so  arranged  that  no  unreflected  light  passes  through 
the  slot.  The  effect  is  to  make  each  numeral  appear  as  if  cut 
out  from  a  piece  of  uniformly  lighted  paper. 

An  application  of  the  "flood-lighting"  idea  was  made143  recently 
at  one  of  the  automobile  shows  where  a  machine  was  brilliantly 
illuminated  by  lights  in  two  ornamental  troughs  hung  by  chains 
about  8  ft.  from  the  floor,  and  9  ft.  (2.74  m.)  in  front  of  the  car. 

The  art-glass  dome  is  ordinarily  associated  only  with  the  light- 
ing of  dining-rooms,  but  it  has  been  added144  to  the  long  list  of 

140  Elec.  Ry.  Jour.,  Jan.   30,    1915,  p.  247. 

141  Pop.  Mech.,  Apr.,   1915,  p.   568. 

142  Pop.  Mech.,  July,   1915,  p.    75. 

143  Elec.   World,  May  15,  1915,  p.   1255. 

144  Elec.   World,  May  22,   1915,   p.    1315. 


548     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

illuminants  used  to  produce  an  attractive  show  window  illumin- 
ation. 

Reflection. — Now  that  semi-indirect  and  totally  indirect  light- 
ing systems  are  coming  more  and  more  into  use,  the  effect  of  the 
walls  and  ceilings  in  reflecting  light  is  of  great  importance.  The 
results  of  considerable  work  on  tests  of  the  reflecting  power  of 
paints  have  been  presented.  The145  colors  examined  ranged  from 
white  to  dark  buffs  and  greens.  The  highest  coefficient  obtained 
was  0.657  which  was  for  a  white  oil  paint  of  medium  gloss.  Less 
than  one  half  of  the  samples  tested  showed  coefficients  above  50 
per  cent,  and  all  of  those  that  did  so  were  of  very  light  creamy 
or  yellowish  tones.    A  rather  light  olive  color  gave  only  0.328. 

Code. — Reference  should  be  made  to  the  very  important  work 
of  the  Committee  on  Lighting  Legislation  and  the  Factory  Light- 
ing Committee  of  this  society,  as  a  result  of  which  a  code  on  the 
lighting  of  factories,  mills  and  work-places  has  been  prepared. 

GLOBES,  REFLECTORS  AND  FIXTURES. 

Having  plenty  of  light  available  either  from  gas  or  electricity, 
manufacturers  have  increased  the  variety  of  materials  used  in 
making  globes,  reflectors  and  shades.  At  one  extreme  might  be 
put  the  wicker  basket.  Provided  with  or  without  a  lining,  it 
is  used  suspended  from  the  ceiling  as  a  semi-indirect  fixture ;  or 
inverted  and  covered  with  suitable  material,  it  makes  a  shade  for 
a  table  lamp.  At  the  other  extreme  might  be  put  the  hammered 
brass  bowl  with  or  without  glass  inserts  and  used  for  either  totally 
indirect  or  semi-indirect  lighting.  There  is  a  growing  use  of 
floor  lamps  having  very  large  shades  and  mounted  on  standards 
5  or  6  ft.  (1.52  or  1.82  m.)  high.  Such  a  lamp  is  replacing  the 
old  center  table  lamp  for  family  reading  and  inasmuch  as  those 
using  it  can  all  have  the  light  properly  directed  for  reading  pur- 
poses, it  forms  a  step  in  the  direction  of  eye  protection.  There 
is  also  a  growing  trend  on  the146  part  of  architects  to  call  for 
lighting  fixtures  which  conform  to  the  period  of  their  surround- 
ings. 

In  school  rooms  an  increasing  tendency  toward  the  use  of 
denser  glassware  with  the  semi-indirect  lighting  method  is  notice- 
able and  in  general  for  both  direct  and  semi-indirect  system  the 

145  Blec.   World,  Jan.   23,   191s,  P-   211. 

146  Elec.   World,  Apr.  3,  1915,  p.  87:1. 


REPORT   OF   THE   COMMITTEE   ON    PROGRESS  549 

denser  glassware  is  used.  Furthermore  the  tendency  towards 
constantly  increasing  candlepower  in  small  units  has  led  to  a 
greater  use  of  diffusing  media  such  as  marble  and  alabaster,  and 
to  fixtures  carrying  several  lights  burning  upright  with  small 
semi-indirect  shades.  The  use  of  cloth  for  shades  is  growing 
and  an  umbrella  manufacturer  has  developed147  a  collapsible 
shade  of  cretonne,  which  can  be  foiled  up,  when  not  in  use,  for 
packing  or  storage  purposes. 

A  novel  arrangement  has  been  brought  out  in  England148  for 
converting  a  dining  room  fixture  into  a  combined  direct  and  semi- 
indirect  unit.  A  double  cone  of  white  silk  is  employed  in  con- 
junction with  the  common  "corona  band"  so  that  the  lamp  occu- 
pies a  position  in  the  lower  cone,  when  the  fitting  is  at  the  usual 
height,  giving  light  directly  downward,  while  at  another  height 
the  lamp  moves  up  into  the  upper  cone,  with  the  light  directed 
toward  the  ceiling. 

For  the  modern  very  large  office  building  an  equipment  of 
specially  designed  fixtures  is  not  uncommon.  In  one  case  of  this 
kind149  a  fixture  was  developed  which  can  be  utilized  either  for 
direct,  semi-indirect  or  totally  indirect  lighting.  There  is  evi- 
dence150 of  a  considerable  increase  in  the  employment  of  the  semi- 
indirect  type  of  fixtures  for  gas. 

A  great  advance  has  been  made  in  gas  fittings.151  The  old 
"goose  neck,"  fastened  with  a  wire,  is  being  replaced  by  straight 
pipe  tubing  with  gas-tight  adjustable  couplings,  which  make  a 
variety  of  brackets  available. 

Reflectors  have  been  developed  for  converting152  the  ordinary 
gas  "arc"  as  used  in  stores  and  warehouses  into  a  semi-indirect 
unit,  thus  meeting  the  demand  for  this  type  of  lighting  without 
the  necessity  of  scrapping  former  fixtures.  The  advent  of  the 
100-watt,  gas-filled  tungsten  unit  has  caused  the  development 
of  prismatic  and  mirrored  reflectors  for  use  in  show-window 
lighting. 

147  Light.  Jour,  and  Eng.    (Lond.),  Feb.,  1915,  p.  81. 
""///.  Eng.   (Lond.),  Mar.,   1915,  p.   103. 

149  Elec.   World,  Feb.  20,   1915,  p.  490. 

150  The  Gas  Age,  Jan.  1,  1915,  p.  8. 

151  Light.  Jour.    (U.S.),  Dec,    1914,   p.   281. 
Proc.  Amer.   Gas  Inst.,  vol.   IX,    1914,   p.   886. 

132  Amer.  Gas  Lt.  Jour.,  May  3,  1915,  p.  286. 


550    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

In  lighting  fixtures  of  ornate  design  and  equipped  with  electric 
candle  or  candelabra  lamps  the  use  of  ordinary  key  or  pull  sockets 
for  individual  lamp  control  is  often  undesirable  and  esthetically 
objectionable.  A  rotating  switch  has  been  devised  to  meet153  this 
condition,  which  is  operated  by  turning  an  outer  sleeve  forming 
part  of  the  candle.  The  replacing  of  arc  lamps  by  the  new  high 
efficiency  tungsten  lamps  has  resulted  in  an154  adaptation  of  the 
fixtures  of  the  former  to  act  as  housings  for  the  latter.  The  prin- 
cipal change  needed  is  the  introduction  of  baffle  plates  to  prevent 
the  entrance  of  rain  without  hindering  the  ventilation.  For  all 
classes  of  outdoor  lighting  by  electricity,  fixtures  have  been  de- 
signed which  include155  not  only  adaptability  to  series  or  multiple 
circuits,  to  pole  or  cross-span  suspension,  but  also  ventilating  and 
enclosing  glassware  if  desired,  so  that  a  complete  equipment  is 
available  in  one  fixture. 

A  reinforced-concrete  lighting  standard  of  attractive  design 
and  appearance  is  being  installed156  in  a  number  of  California 
cities  including  beach  resorts,  where  metal  standards  have  suf- 
ered  severely  in  the  past  owing  to  the  action  of  salt  air. 

PHOTOMETRY. 

The  measurement  of  light  sources  differing  in  color  value  con- 
tinues to  interest  the  photometrist.  Developments  have  followed 
two  general  lines,  one  the  elimination  of  the  color  difference, 
thereby  reducing  conditions  to  those  of  ordinary  photometry,  the 
other  the  use  of  the  flicker  photometer  which  has  not  yet  been 
generally  accepted  as  a  solution  of  the  problem. 

Secondary  Standards. — At  the  National  Physical  Laboratory 
in  England  there  has  been  completed  and  described157  a  careful 
and  exhaustive  research  having  for  its  object  the  establishment  of 
a  set  of  standards  matching  in  color  lamps  operating  at  the 
various  efficiencies  in  ordinary  use.  In  this  research  the  color 
problem  was  met  by  using  the  so-called  "Cascade"  method  in 
which  a  lamp  at  a  given  watts  per  candle  is  measured  against  one 
whose  watts  per  candle  differs  by  an  amount  which  will  make  the 

153  Blec.  Rev.  and  W.  B.,  May  29,  1915,  p.   1005. 

154  Elec.  World,  May  1,   1915,  p.   1131. 

155  B lee.  Rev.  and  W.  B.,  July  24,   1915,  p.   167. 
16a  Elec.  World,   Apr.  3,  1915,  p.  874. 

151  Phil.  Mag.,  July,    1915,  p.   63. 


REPORT   OF   THE    COMMITTEE   ON    PROGRESS  55 1 

color  difference  small  enough  not  to  be  objectionable.  Check 
measurements  were  also  made  in  which  the  maximum  color  diff- 
erence was  encountered.  The  experience  gained  from  these  and 
other  comparisons  was  that  whereas  an  observer  may  be  relied 
upon  for  constancy  of  judgment  in  measuring  with  an  ordinary 
contrast  photometer  sources  differing  by  a  small  amount  in  color 
value,  the  same  constancy  in  judgment  was  not  obtainable  where 
the  color  differences  were  large.  Efforts  were  made  to  use  the 
flicker  photometer  but  the  results  were  not  satisfactory  and  the 
accuracy  was  of  a  different  order  of  magnitude  from  that  found 
with  the  other  method. 

Color  Difference. — It  is  rather  interesting  to  note  that  else- 
where158 in  observations  on  color  differences  made  with  a  flicker 
photometer  and  extending  over  a  year,  individual  observers  re- 
produced their  results  with  very  few  exceptions. 

The  color  screen  method  of  eliminating  the  color  difference  in 
heterchromatic  photomery  has  been  extended  by  the  develop- 
ment159 of  a  blue  solution,  which  in  varying  degrees  of  satura- 
tion will  provide  a  color  match  between  a  standard  carbon  lamp 
and  another  lamp  operating  at  any  watts  per  candle  from  3.1 
to  0.5.  An  alternative  for160  the  color  absorbing  solution  in 
eliminating  color  differences  is  suggested  in  a  new  photometer 
using  polarized  light.  It  is  based  on  the  rotation  of  the  plane 
of  polarization  by  a  quartz  plate  and  the  fact  that  this  rotation  is 
different  for  light  of  different  wave-lengths. 

Flicker. — By  applying  to  a  modified  form  of  the  Conroy  pho- 
tometer161 an  oscillating  platinized  mirror  and  adding  an  optical 
wedge  having  its  density  gradient  vertical  and  different  by  two 
per  cent,  from  top  to  bottom  a  new  flicker-photometer  has  been 
developed.  Another  arrangement162  for  a  flicker-photometer 
consists  in  a  modification  applicable  to  the  ordinary  Lummer- 
Brodhun  photometer  head.  A  tube,  replacing  the  ordinary  eye- 
piece, carries  a  rotating  prism.  Means  are  provided  for  illumin- 
ating the  surrounding  field  and  for  accurate  speed  control. 

m  Trans.  I.  E.   S".,  Apr.  30,   1915,  p.  207. 

"•Trans.  I.  E.  S.,  Apr.  30,  1915,  p.  253. 

lv>  Phys.  Rev.,  July,  1915,  p.  64. 

181  Phys.  Rev.,   4,   1914,  p.   477. 

142  Light.   Jow.,   May,    1915,   p.    1 11. 


552     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

A  theory  of  the  flicker-photometer  has  been  presented  in163 
which  the  behavior  of  the  instrument  is  deduced  directly  from  the 
relationship  of  critical  freqency  and  illumination.  It  is  assumed 
that  a  fluctuating  stimulus  is  transmitted  as  a  considerably 
dampened  fluctuating  impression  whose  form  and  amplitude  can 
be  calculated  by  using  the  Fourier  linear  diffusion  equation.  The 
same  line  of  reasoning  is  used  to  explain  the  relationship  of  color 
flicker  to  brightness  flicker.  Further  work164  has  also  been  done 
on  the  question  whether  results  in  color  photometry  obtained  by 
the  flicker  method  and  the  acuteness  of  vision  method  are  the 
same.  The  data  obtained  in  these  experiments  indicated  they 
are.  A  Lummer-Pringsheim  spectro-flicker-photometer  was  em- 
ployed and  experiments  made  with  foveal  vision  and  portions  of 
the  retina  lying  20°  to  300  outside  the  direct  line  of  sight.  Means 
have  been  provided,105  using  colored  absorbing  media  for  correct- 
ing an  abnormal  eye.  It  is  claimed  that  by  the  practical  applica- 
tion of  this  method  to  the  flicker-photometer  it  is  possible  to  equip 
any  observer  so  that  he  will  read  correctly  color  differences  of  a 
given  type ;  and  to  equip  a  color  blind  observer  so  that  he  will  not 
only  read  such  differences  correctly,  but  also  measure  other  color 
differences  with  no  more  uncertainty  than  a  random  observer  of 
"normal"  vision  will  do. 

Integrating  Sphere. — At  the  last  convention  there  was  quite  a 
discussion  on  the  best  paint  to  use  for  the  inner  diffusing  surface 
of  an  integrating  sphere.  An  elaborate  research  was  undertaken  in 
Germany166  to  decide  not  only  this  point  but  also  the  best  material 
of  which  to  make  the  sphere  itself.  The  results  indicated  that 
iron  plate  is  to  be  preferred  to  zinc  for  the  construction  material 
and  that  zinc  white  as  the  diffusing  surface  gives  the  best  results. 

New  Instruments. — In  the  photometry  of  phosphorescent  gases 
and  certain  phosphorescent  solids,  the  light  to  be  measured  is  of 
rapidly  diminishing  intensity.  In  order  to  ascertain  the  errors 
occurring  in  the  measurement  of  such  a  light  a  modification  of 
the  ordinary  photometer  has  been  devised167  in  which  the  essential 
feature  is  a  sliding  carriage  supporting  one  of  the  lamps  and 

163  Phil.  Mag.,   May  28,    1915,  p.   708. 
184  Ann.   d.  Phys.,   Aug.    14,    1914,   p.    105. 

165  Trans.   I.  E-  S.,  Apr.  30,  1915,  p.  259. 

166  Elek.  Zeit.,  Mar.  25,   1915,  p.   37- 
107  Phys.  Rev.,  Oct.,   1914,  p.  289. 


REPORT   OF   THE   COMMITTEE   ON    PROGRESS  553 

capable  of  being  set  in  to  and  fro  motion  at  uniform  velocity  in 
the  photometric  axis.  Means  are  provided  for  recording  the 
position  of  the  carriage  while  in  motion.  Using  this  instrument 
an  investigation  showed  that  errors  as  high  as  15  per  cent,  or 
more,  and  apparently  due  to  retinal  fatigue,  may  occur  in  the 
photometric  measurement  or  phosphorescent  decays. 

A  new  portable  illumination  photometer  has  been  brought 
out168  which  is  a  modification  of  the  Weber  type  and  much  more 
compact.  Another  illuminometer169  has  been  described  for  use 
where  rapid  and  rough  measurements  of  light  intensity  are 
desired.  In  this  instrument  a  screen  of  black  silk  illuminated 
from  the  rear  is  viewed  in  comparison  with  tinted  sectors,  on 
which  falls  the  illumination  to  be  measured.  The  intensity  of 
the  light  from  the  comparison  lamp  is  controlled  by  an  iris 
diaphragm.  As  a  quick  means  of  determining  the  various  energy 
relations  in  tungsten  lamps,  a  direct  reading  instrument  has  been 
devised170  using  data  presented  at  the  last  convention.171  It  is 
made  up  of  volts,  watts  per  candle  and  per  cent,  candlepower 
scales.  The  volt  scale  has  a  range  from  94  to  166  volts,  while  the 
watts-per-candle  scale  limits  are  0.70  and  2.05.  Knowing  any 
two  relations  the  other  may  be  calculated  within  the  range  of  the 
instrument. 

A  study172  of  the  rotating  sectored  disk  when  used  in  pho- 
tographic photometry  has  shown  that  an  intermittent  exposure, 
such  as  that  given  by  the  disk,  has  the  same  integral  effect  as  a 
continuous  exposure  for  the  same  period.  The  conclusion  for 
ultra-violet  radiation  is  the  same  as  that  found  for  visible  radi- 
ation. Experiments  were  made  on  a  variety  of  plates  and  it  was 
found  that  the  results  were  independent,  within  wide  limits  of  the 
rate  of  rotation  of  the  sector  and  of  the  period  of  exposure. 

Gas-filled  Tungsten  Lamps. — The  measurement  of  the  candle- 
power  of  the  gas-filled  tungsten  lamps  has  developed  some  entirely 
new  problems  in  photometry.  Thus  it  was  early  discovered173 
that  both  the  watts  consumed  and  the  candlepower  of  the  lamp 
vary  when  the  lamp  is  rotated  at  different  speeds.     One  set  of 

168  Elec.  World,  Jan.  9,  1915,  p.   85. 

169  Elec.  World,  Jan.  16,  1915,  p.  170. 

110  Jour,   of  Frank.  Inst.,  July,    1915,   p.    102. 

171  Trans.  I.   E.   S.,  9,   1914,   p.   734. 

172  Ann.  d.  Phys.,   Nov.  3,    1914,  p.  801. 

173  Trans.   I.   E.    R,   9,    i9i4,   p.    i024. 


554     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

experiments174  showed  that  for  any  change  in  speed,  while  the 
change  in  candlepower  was  roughly  ten  times  the  change  in  cur- 
rent but  always  in  the  opposite  direction,  and  regardless  of  the 
position  of  the  lamp,  the  absolute  change  in  candlepower  with 
the  lamp  in  the  position  of  tip  up  is  about  twice  the  change  with 
the  tip  down  and  similarly  for  the  absolute  change  in  the  current. 
From  the  photometric  standpoint  a  favorable  condition  was  dis- 
covered in  that,  for  a  given  position  of  the  lamp,  the  current  and 
therefore  the  candlepower  return  to  the  stationary  value  at  the 
same  speed.  If  then,  a  gas-filled  lamp  is  photometered  in  the 
position  tip  down,  while  rotating  at  the  particular  speed  which 
gives  the  same  current  value  as  when  the  lamp  is  stationary,  the 
mean  horizontal  candlepower  as  measured  will  be  free  from 
errors  due  to  rotation. 

Various  explanations  have  been  offered  for  these  phenomena. 
It  has  been  suggested  that  they  may  be  due  to  variations  in  the 
contacts  between  the  filaments  and  the  anchor  wires ;  to  changes 
in  the  currents  of  gas  about  the  filament;  to  the  lengthening  of 
the  helically  coiled173  filament,  thus  changing  its  resistance;  to  a 
cooling  effect  due  to  the  action  of  the  external  air  in  the  bulb. 

Photo-electric  Cell. — In  astronomical  photometry176  work  is 
being  done,  with  some  success,  looking  toward  increasing  the  sen- 
sibility of  the  photo-electric  cell.  A  null  method  of  using  photo- 
electric cells  has  been  devised  which,177  it  is  claimed,  does  away 
with  the  so-called  "dark  current"  without  in  the  least  reducing 
the  sensitivity. 

Pentane  Standard. — A  redetermination  at  the  National  Phys- 
ical Laboratory178  of  the  constants  of  the  Pentane  lamp  gave  the 
following  as  the  equation  of  the  candlepower : 

C.P.  =  (  (I  -f  0.0063  (8  —  <?)  —  o.ooo85  (760  —  b)  ) 
e  being  the  humidity  in  liters  of  water  vapor  per  cubic  meter  of 
moist  air,  and  b  the  barometric  pressure  in  millimeters.  Evi- 
dence was  obtained  that  there  exists  a  temperature  coefficient  in 
the  case  of  the  pentane  lamp,  a  point  which  had  been  raised  pre- 
viously at  the  Bureau  of  Standards.    Apparently  the  temperature 

174  Elec.   World,  Dec.  26,   1914,  p.  1248. 

175  E lee.    World,  Jan.   9,   1915,  p.   78. 

176  Science,  June  4,   1915,  p.  810. 

177  Phys.  Rev.,  July,   1915,  p.   66. 

178  Phil.  Mag.,  July,   1915,  p.  80. 


REPORT   OF   THE   COMMITTEE   ON    PROGRESS  555 

and  humidity  effects  act  against  one  another  and  in  practise  it 
is  the  difference  between  the  two  which  is  operative.  It  is  sug- 
gested that  if  work  of  the  very  highest  accuracy  is  to  be  carried 
out  with  flame  standards  under  abnormal  humidity  conditions, 
the  combined  humidity  temperature  coefficient  should  be  deter- 
mined for  the  locality  in  which  the  work  is  to  be  conducted. 

Radiation. — Experiments179  on  the  emissivity  of  metals  at  high 
temperatures  have  given  results  indicating  a  change  in  the 
emissivity  of  platinum  for  wave-length  A  =  0.65/a.  This  fact  if 
verified  would  influence  the  constancy  of  the  Violle  standard  of 
light. 

Two  investigations  have  been  made  during  the  year  on  the 
determination  of  the  visibility  of  radiant  energy.  One  covered180 
the  whole  visible  spectrum  going  further  into  the  red  and  voilet 
than  heretofore.  The  other181  dealt  with  the  red  end  of  the 
spectrum  only,  results  being  obtained  out  as  far  as  A  =  0.770/i. 

Calculation. — Methods  of  calculating  the  illumination  produced 
by  a  direct-lighting  source  are  numerous  and  well  known.  But 
in  the  case  of  a  totally  indirect  or  semi-indirect  unit  the  calcula- 
tion is  decidedly  modified.  A  method  has  been  proposed182  in 
which  it  is  necessary  to  know  only  the  photometric  curve,  the 
coefficient  of  reflection  for  the  secondary  source  (usually  the 
ceiling),  the  distance  of  the  unit  below  the  ceiling  and  the  height 
of  the  ceiling  above  the  plane  of  illumination.  Roughly  the 
method  involves  the  consideration  of  the  ceiling  as  a  secondary 
light  source  considered  as  made  up  of  a  series  of  circular  annuli 
or  rings  of  uniform  intensity  of  illumination.  The  effect  of  each 
ring  is  calculated  independently. 

Nomenclature. — Considerable  attention  has  been  given  to  the 
subject  of  nomenclature  during  the  past  year.  It  has  been  pro- 
posed183 that  the  word  "lambert"  be  used  in  referring  to  bright- 
ness in  lumens  per  unit  projected  area.  The  "lambert"  is  inter- 
preted as  the  equivalent  in  appearance  to  the  eye  of  a  surface 
source  emitting  one  lumen  per  unit  area  in  accordance  with 
Lambert's  cosine  law.    The  following  resolution  which  was  sub- 

178  Phys .  Rev.,  Dec,   1914,  p.  547. 

180  Phil.  Mag.,  Feb.,  1915,  p.   301. 

181  Phys.  Rev.,  July,  1915,  p.  68. 

182  Elec.   World,  June  5,   1915,  p.    1463. 

183  Elec.   World,  Mar.  29,  1915,  p.  715. 


556     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

mitted  by  the  Committee  on  Nomenclature  and  Standards  has 
been  approved184  by  the  Council  of  the  Society : 
Resolved,  That  it  is  the  opinion  of  this  Committee 

(a)  That  the  output  of   all  illuminants   should  be  expressed  in 

lumens. 

(b)  That  illuminants  should  be  rated  upon  a  lumen  basis  instead 

of  a  candlepower  basis. 

(c)  That  the  specific  output  of  electric  lamps  should  be  stated  in 

lumens  per  watt  and  the  specific  output  of  illuminants 
dependent  upon  combustion  should  be  stated  in  lumens  per 
British  thermal  unit  per  hour. 

PHOTOGRAPHY. 

Sources. — The  use  of  gas  light185  for  taking  pictures  is  increas- 
ing and  special  mantles  have  been  designed  for  the  purpose.  In 
order  to  facilitate  the  use  of  the  high  intensity  gas-filled  tungsten 
lamp186  in  photographic  portrait  studios,  a  colored  glass  screen 
has  been  developed  which  reduces  the  luminous  intensity  of  the 
light  to  one-third  its  ordinary  value  without  appreciably  reducing 
the  actinic  value  for  ordinary  plates.  For  convenience  this  glass 
has  been  incorporated  in  the  lamp  bulb.  Thus  high  candlepower 
lamps  may  be  used  without  producing  an  uncomfortable  glare. 
It  has  been  found  possible187  to  use  such  lamps,  screened  as 
described,  in  moving  picture  production  studios.  In  a  big 
western  moving  picture  plantls8  there  is  used  a  combination  of 
mercury-vapor  lamps  and  2,000-candlepower  tungsten  gas-filled 
units  of  the  type  just  mentioned.  In  Germany189  tests  have  been 
made  on  the  use  of  the  gas-filled  tungsten  lamp  for  photographic 
work  at  voltages  higher  than  normal,  thus  giving  greater  actinic 
value.  This  same  idea  has  been  proposed  and  experimented 
on190  in  this  country. 

Tests  have  been  made  on191  the  density  of  the  photographic 
image  produced  under  fixed  conditions  of  distance  and  time  by 

184  Trans.  I.   E.   S.,  9,  p.  2,  1914. 

185  Gas  Age,  Mar.  15,  1915,  p.  304. 

Light.   Jour.    (U.  S.),  Dec,   1915.  P-  281. 
Proc.  Amer.   Gas  Inst.,  vol.  9,   1914,  p.  886. 

186  Elec.   World,  Nov.   14,   1914.  P-   95°. 

187  Trans.  I.  E.   S.,  No.  2,   1915,  p.   166. 

188  Elec.   World,  July  17,   1915.  P-   137- 

189  Zeit.  f.  Beleu.,  Mar.,  1915,  p.  33. 

190  Elec.   World,  Nov.  14,  1914,  p.  950. 

191  Elec.   World,   Nov.   14,   191 4,  p.   95  6. 


REPORT  OF   THE   COMMITTEE   ON    PROGRESS  557 

the  light  from  different  types  of  arc  lamps  under  various  condi- 
tions. The  lamps  tested  were  of  the  alternating  current  and 
direct  current  enclosed  carbon  and  flaming  arc  types  operated  at 
various  currents.  The  results  showed  that  the  highest  actinic 
efficiency  was  obtained  by  the  220- volt,  enclosed  carbon  arc ;  next 
in  value  were  respectively,  the  alternating  current  and  direct  cur- 
rent no-volt,  flaming  arcs  with  electrodes  designed  particularly 
for  photographic  work. 

A  photographic  paper  has  been  developed192  on  which  portraits 
may  be  reproduced  directly  without  the  preparation  of  the  usual 
negative.  For  operation  with  artificial  illuminants  the  paper  is 
treated  with  a  dye  which  makes  it  more  sensitive  to  yellow  light. 
The  pictures  are  mirror  images  of  the  original. 

LEGISLATION. 

Calorific  Standard. — The  Illinois  Commission  has  ruled193  that 
in  all  parts  of  the  state  excepting  Chicago  a  calorific  standard  of 
565  B.  t.  u.  for  gas  shall  be  used.  Chicago  is  to  remain  under 
the  candlepower  standard.  The  calorific  standard  has  been 
adopted  by  the  Maryland  Public  Service  Commission.194  A  heat- 
ing value  of  600  B.  t.  u.  is  specified.  It  was  estimated  by  the 
Commission  that  in  the  state  generally  only  6  to  10  per  cent,  of 
the  gas  used  is  burned  in  flat  flame  burners.  The  use  of  the 
calorific  standard  in  gas  undertakings  does  not  seem  to  be  grow- 
ing rapidly  in  England.195  Only  eight  companies  have  applied 
for  parliamentary  authority  during  the  session  of  1915.  Four 
of  these  companies  applied  for  a  500  B.  t.  u.  standard. 

Glare. — Extremely  bright  lamps  are  no  longer  allowed  on  resi- 
dential streets,  especially  in  front  of  isolated  stores,  in  Washing- 
ton, D.  C.196  Regulations  adopted  prohibit  the  use  of  lamps 
exceeding  100  candlepower  on  streets  other  than  business  streets. 
They  also  require  a  minimum  height  of  15  ft.  (4.57  m.)  for  all 
private  lamps  supported  from  sidewalks,  and  that  such  lamps 
are  to  be  enclosed  in  opalescent  globes  in  order  that  the  eyes  of 
passers-by  shall  be  protected  from  glare. 

192  Elec.   World,  Jan.    16,   1915,  p.   190. 

193  Proc.  Amer.  Gas  Inst.,  vol.  9,   1914,  p.  373. 

194  Jour,  of  Gas  Light.,  May  24,   1915,  p.  463. 
ias  Amer.   Gas  Light  Jour.,   Feb.   i,   1915,  p.   73. 
1M  Elec.   World,  Oct.   10,   1914,  p.  700. 


558    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

In  December  last197  the  War  Department  issued  regulations 
ordering  all  fishing  fields  to  be  protected  by  a  marine  lantern  of 
recent  invention  using  acetylene  as  the  illuminant.  These  lan- 
terns, capable  of  23  days'  service,  are  arranged  to  give  an  in-shore 
and  out-shore  light  to  warn  vessels  that  the  areas  thereabout 
comprise  fishing  pounds  and  are  not  open  to  navigation.  Already 
a  number  of  these  lights  have  been  placed. 

A  bill  has  been  introduced198  in  the  Utah  legislature  providing 
for  the  creation  of  special  lighting  improvement  districts,  under 
which  the  property  owners  on  any  street  or  sub-division  may 
petition  the  city  commission  to  create  such  districts  and  to  install 
therein  lighting  systems. 

Safety. — The  Ottawa  (Canada)  City  Council  have  recently199 
taken  up  the  matter  of  all-night  lighting  of  public  buildings  used 
for  residence  purposes.  A  by-law  has  been  passed  providing  that 
the  stairs,  halls  and  corridors  of  all  apartment  houses,  hotel  and 
lodging  houses  must  be  lighted  from  sunset  to  sunrise. 

In  places  where  public  safety  demands  it,  there  is  a  growing 
tendency  on  the  part  of  municipal  authorities  to  require  two 
independent  systems  of  illumination  so  that  in  case  of  failures 
on  the  part  of  either  the  other  will  be  available. 

Headlights. — The  Public  Service  Commission  of  Vermont  has 
issued  an  order200  concerning  the  use  of  headlights  on  locomotives. 
Railroad  corporations  doing  business  within  the  state  are  required 
to  equip  engines  with  headlights  of  not  less  than  2,500  apparent 
beam  candlepower  when  measured  with  the  aid  of  a  reflector, 
rated  in  accordance  with  the  average  of  the  center  readings 
between  500  and  1,000  ft.  (304.80  m.)  ahead  and  upon  a  refer- 
ence plane  3  ft.  (0.91  m.)  above  the  rails.  In  Nevada  an  amend- 
ment to  the  electric  headlight  law  has  been  passed,201  providing 
that  any  electric  headlight  "which  will  pick  up  and  distinguish  an 
object  the  size  of  a  man  dressed  in  dark  clothing  on  a  dark  and 
clear  night  at  1,000  ft."  will  be  deemed  equivalent  to  a  1,500- 
candlepower  headlight  measured  without  reflector.     Legislation 

187  Acet.  Jour.,  Feb.,  1915,  p.  305. 

198  Elec.  Rev.  and  W.  E.,  Feb.  27,   1915,  p.  376. 

199  Elec.  News  (Can.),  Apr.  1,  1915,  p.  38. 

200  Railway  Age  Gazette,  Jan.  22,   1915,  p.   127. 

201  Raihvay  Age  Gazette,  Jan.  22,   1915,  p.   123. 


REPORT   OE   THE   COMMITTEE   ON    PROGRESS  559 

regarding  headlights  for  motor  vehicles  has  also  been  passed  in 
New  Jersey. 

ILLUMINATING  ENGINEERING  IN  GENERAL. 

Daylight  Saving. — By  adopting  eastern  standard  time  Cleve- 
land, Ohio  has  added  one  hour  to  the  period  of  daylight.  The 
result202  has  caused  a  renewed  interest  in  the  so-called  "daylight 
saving  movement"  in  the  middle  west.  In  Holland  also  this  move- 
ment is  being  agitated.20'1 

The  use  of  light  sources  imitating  daylight  is  growing204  and 
has  been  found  advantageous  not  only  in  clothing,  painting  and 
wall  paper  stores  and  factories,  but  also  in  printing  and  litho- 
graphing establishments,  paper  mills,  oil  refining  plants,  cigar 
factories,  etc. 

It  has  been  proposed205  to  add  to  the  numerous  collections  in 
Berlin  a  museum  of  illuminating  appliances  in  which  the  devel- 
opment from  the  17th  century  of  lamps  and  other  devices  for 
street  lighting  will  be  shown. 

Luminous  Efficiency. — Values  of  the  radiant  luminous  ef- 
ficiencies (ratio  of  the  energy  radiated  evaluated  according  to  its 
effectiveness  in  producing  the  sensation  of  light  to  the  total  energy 
radiated)  of  various  light  sources  have  been  determined  using  the 
method  which  employs  an  absorbing  solution  whose  transmission 
curve  is  the  same  as  the  luminosity  curve  of  the  eye.206  Among 
the  results  obtained  were : 

4  w.p.c.  carbon  lamp 0.43 

0.8-ampere  Nernst  filament 1.08 

6.6-ampere  gas-filled  tungsten   at  0.65  w.p.c 2.93 

Ordinary  vacuum  tungsten  at  1  w.p.c i-99 

Open  burner,  gas 0.9 

Incandescent  mantle,  gas 0.5  to  1.2 

1.7  ampere  mercury  arc,  Pfund  type 30.0 

A  new  experimental  determination207  by  two  different  methods 
gives  for  the  mechanical  equivalent  of  light  a  mean  value  of 
0.00162  watt  per  lumen. 

202  Elec.   World,  Jan.  2,   1915,  p.    59. 

203  Jour.  Gas  Light.,  Jan.  5,  1915,  p.  16. 

204  Elec.  World,  July  10,  1915,  p.  71. 

205  Jour.   Gas  Light.,   May  4,    1915,   p.   292. 
20ePhys.  Rev.,  Mar.,   1915,  p.  208. 

207  Phys.  Rev.,  Apr.,   1915,  p.  269. 


560     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Physiology. — Further  work  has  been  done  on208  the  effect  on 
the  eye  of  ultra-violet  light.  It  has  been  shown  that  where  the 
protein  in  the  lens  of  the  eye  has  been  modified  by  the  action  of 
excess  sugar  in  the  body  fluids,  or  by  the  action  of  salts  of  cal- 
cium, magnesium,  silica  and  the  like,  ultra-violet  radiation  may 
cause  cataract,  but  that  unless  this  abnormal  condition  exists  cat- 
aract is  not  caused  by  this  form  of  radiation. 

Music  and  Color. — Several  attempts  to  correlate  music  and 
color  have  been  made  in  the  past.  A  Russian  composer  having 
written  a  score  in  which  was  included  a  part  to  be  rendered  by 
various  colors ;  a  "color  organ"  was  devised  for  use  in  a  recent 
presentation  of  the  composition.209  Incandescent  lamps  in  re- 
flectors and  equipped  with  color-filters  formed  the  light  source. 
The  screen  was  composed  of  strips  of  gauze  of  various  weights, 
mounted  vertically  and  8  by  10  ft.  (2.43  by  3.04  m.)  in  size.  The 
lightest  sheet  was  placed  at  the  front,  each  succeeding  one  back 
of  it  being  heavier.  The  rear  gauze  was  heavy  enough  to  reflect 
the  light  thrown  on  it.  The  deepest  colors  were  thrown  on  the 
back  and  the  lighter  colors  were  thrown  on  the  front  gauzes.  The 
color  equivalents  of  the  tone  scale  were  as  follows:  C,  red;  D, 
yellow;  E,  pearly  blue;  A,  green;  B-flat,  steel  gray;  together 
with  intermediate  values.  Color  organs  are  not  new,210  several 
having  been  constructed  in  recent  years.  The  largest  screen  used 
has  been  30  by  50  ft.  (9.14  by  15.24  m.). 

International  Commission. — At  the  meeting  of  the  National  Il- 
lumination Committee  of  Great  Britain  held  early  in  the  year211 
there  was  considered  the  question  of  "Rating  of  Light  Sources 
in  Candlepower  or  Consumption,"  and  the  following  resolution 
was  passed  and  transmitted  to  the  Secretary  of  the  International 
Commission  on  Illumination. 

It  is  desirable  that  a  uniform  international  method  be  adopted  for  rat- 
ing and  marking  all  sources  of  light.  It  is  recommended  by  the  National 
Illuminating  Committee  of  Great  Britain  that  the  matter  be  considered  at 
the  next  session  of  the  International  Commission  on  Illumination;  and 
the  administration  of  that  Commission  is  asked  to  take  the  necessary  steps 
to  bring  this  resolution  to  the  knowledge  of  the  different  national  com- 
mittees, with  the  view  to  their  co-operation. 
2°8  Elec.  World,  Apr.  19.  1915,  p.  912. 

209  Sci.  Amer.  Supp.,  June  26,  1915,  p.  408. 

210  Sci.  Amer.,  July  24,  1915,  p.  79. 
mjour.  Gas  Light.,  Feb.  9,  1915,  p.  326. 


REPORT  OF   THE   COMMITTEE  ON    PROGRESS  561 

LITERATURE. 
The  war  has  seriously  interferred  with  many  foreign  publica- 
tions having  articles  on  illumination.  The  French  Journal, 
Science  et  Art  de  I'Eclairage,  has  apparently  suspended  publica- 
tion and  other  French  and  German  journals  were  compelled  to 
omit  some  issues,  although  they  are  now  appearing  regularly. 
Among  the  books  published  during  the  year  should  be  mentioned : 

Modern  Illuminants  and  Illuminating  Engineering,  by  L.  Gaster 
and  J.  S.  Dow.    New  York,  The  MacMillan  Co.,  1915. 

La  Lumiere  Electrique  et  ses  Differentes  Applications  du  Theatre, 
by  V.  Trundelle.    Paris,  H.  Dunod  and  E.  Pinat. 

An  Introduction  to  Color  Vision,  by  Dr.  J.  H.  Parsons.  Cambridge 
University  Press,  1915. 


562     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

A    RESUME    OF    THE    PHYSICAL,    PHYSIOLOGICAL 
AND  PSYCHIC  PHASES  OF  VISION.* 


BY  NELSON   M.   BLACK,   M.D. 


Synopsis:  This  paper  is  a  compilation  in  brief  of  the  present  day 
theories  as  to  the  processes  involved  in  the  visual  act,  considered  under 
the  physical,  physiological  and  psychic  phases  of  vision. 


Generally  speaking  the  visual  act  may  be  considered  as  that 
process  whereby  light,  color  and  form  are  recognized  by  the 
visual  apparatus.  The  complex  act  of  seeing  is  best  studied  by 
dividing  it  into  three  distinct  phases  as  suggested  by  Lohmann : 
a  physical  phase  concerned  with  the  refraction  and  focusing 
rays  of  light,  emanating  or  reflected  from  a  visible  object,  to 
form  an  image  on  the  visual  surface;  a  physiological  phase  con- 
sisting in  the  transformation  of  the  light  stimulus  into  a  nerve 
impulse.  These  two  factors  alone  will  not  induce  sight,  they 
must  be  supplemented  by  the  third,  or  psychic,  phase  before  per- 
cipient vision  results. 

PHYSICAL  PHASES. 

The  visual  apparatus  consists  of  three  essential  parts:  (1)  the 
eyeball  with  its  contents;  (2)  the  optic  nerve,  and  (3)  the  visual 
centers  of  the  brain. 

The  eyeball  may  be  compared  with  a  camera  in  that  it  con- 
tains a  diaphragm  shutter  and  a  lens,  or,  focusing  system,  and 
has  to  do  with  the  physical  phase  of  vision.  The  optic  nerve 
terminals  act  as  the  sensitized  background  of  the  camera  and  the 
nerve  fibers  conduct  the  excitations  produced  during  the 
physiological  phase  to  the  various  centers  in  the  brain  which 
have  to  do  with  the  psychic  phase  in  the  recognition  of  light, 
color  and  form. 

The  structures  of  the  eyeball  concerned  in  the  physical  phase 
are  the  cornea  (Fig.  1)  which  is  situated  at  the  anterior  pole  of 
the  eyeball  and  differs  from  the  dense,  pearly  white,  semi-opaque 
protective  scleral  coat  of  which  it  is  a  part,  in  that  it  has  been 
specialized  to  admit  light  into  the  interior  of  the  eye.    It  is  very 

*  The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


black:    phases  of  vision  563 

transparent  and  has  a  refractive  index  (1.337)  slightly  higher 
than  that  of  water.  Its  two  surfaces  being  so  nearly  parallel, 
the  course  of  light  rays  is  not  appreciably  altered  in  passing 
through  it. 

Back  of  the  cornea,  in  an  especially  prepared  chamber  filled 
with  a  fluid  of  about  the  consistency  of  water,  in  which  it  can 
operate  with  greatest  ease,  is  the  diaphragm  shutter  or  iris. 
This  important  part  of  the  visual  apparatus  is  a  specialized  por- 
tion of  the  middle,  or,  choroid  coat,  which  furnishes  nourish- 
ment to  the  other  structures  of  the  eye  as  it  carries  the  blood 


Fig.  1. — Schematic  cross  section  of  eyeball. 

vessels.  This  coat  also  is  deeply  pigmented  and  shuts  out  ex- 
traneous light.  The  iris,  which  is  opaque  owing  to  the  deposits 
of  pigments  of  different  color  in  its  substance,  contains  circular 
muscular  fibers  for  making  the  pupil  smaller  and  radiating  fibers 
which  act  in  opposition.  The  inner  or  pupillary  edge  of  the  iris 
is  separated  from  the  lens  or  focusing  system  by  a  thin  layer  of 
fluid  known  as  the  aqueous  humor. 

The  lens  is  an  elastic  crystalline  body  held  in  suspension  be- 
tween two  layers  of  thin  transparent  membrane,  the  lens  capsule, 
which  meet  at  the  periphery  of  the  lens  and  is  attached  to  an- 
other specialized  portion  of  the  choroid  coat,  called  the  ciliary 
body  which  regulates  the  focusing  power  of  the  lens  by  con- 
trolling its  polar  diameter,  a  process  known  as  accommodation. 


564     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

When  the  ciliary  muscle  is  in  a  state  of  rest,  the  tension  of  the 
suspensory  ligament  acting  on  the  lens  flattens  it  to  such  an  extent,  that 
provided  the  refraction  of  the  eye  be  normal,  parallel  rays  of  light  fall- 
ing on  the  cornea  are  brought  to  a  focus  on  the  retina.  Rays  from  any 
nearer  point  are  divergent  when  they  strike  the  cornea,  and  the  refrac- 
tive power  of  the  lens  at  rest  is  only  sufficient  to  focus  them  at  a  point 
behind  the  retina.  When,  however,  the  circular  muscle  contracts,  the 
suspensory  ligament  relaxes,  and  the  lens,  by  virtue  of  the  elasticity  of 
its  capsule,  changes  its  shape  and  thereby  increases  its  refractive  power. 
The  result  of  this  is  that  the  divergent  rays  of  light  can  now  be  brought 
to  a  focus  upon  the  retina.     (Lohmann.) 

The  lens  fits  into  a  saucer-like  depression  of  the  vitreous  body. 
This  is  a  clear  jelly  like  substance  having  a  refractive  index 
(1.3365)  nearly  the  same  as  water,  surrounded  by  a  very  delicate 
perfectly  transparent  capsule,  the  hyaloid  membrane.  The 
function  of  the  vitreous  body,  which  occupies  about  two  thirds 


Fig.  2. — Changes  in  the  lens  during  accommodation. 


of  the  contents  of  the  eyeball,  is  of  considerable  importance  as  it 
helps  maintain  the  shape  of  the  globe  and  holds  the  lens  firmly 
in  position. 

Surrounding  about  four  fifths  of  the  vitreous  body  is  the 
retina  or  what  is  commonly  called  the  inner  or  third  coat  of  the 
eye.  In  reality  this  so  called  coat  is  an  outgrowth  of  the  brain 
and  consists  of  a  spreading  out  of  the  fibers  of  the  optic  nerve 
over  the  entire  back  four  fifths  of  the  eye.  By  process  of  evolu- 
tion this  tissue  has  become  a  highly  specialized  nervous  structure 
possessing  the  power  of  transforming  impinging  rediations  of 
known  wave-length  into  nerve  stimuli.  These  excitations  are 
transmitted  by  the  fibers  of  the  optic  nerves,  which  each  contain 
approximately  1,000,000  fibers,  to  the  visual  centers  of  the  brain. 

The  retina  or  eye  ground  is  the  receptive  layer  of  the  visual 


black:    phases  of  vision 


565 


apparatus  corresponding  to  the  sensitized  plate  of  the  camera 
upon  which  the  images  of  external  objects  are  constantly  being 
formed. 

The  fibers  of  the  optic  nerve  upon  reaching  the  interior  of  the 
eye  spread  out  in  all  directions  and  then  turn  back  in  the  direction 
they  entered,  Fig.  3.  Each  individual  fiber  is  connected  with  a  cell 
called  a  ganglion  cell,  c,  Fig.  3.  From  these  ganglion  cells  other 
fibers  pass  outward  to  so-called  bipolar  cells,  the  outer  poles  of 
which  end  in  many  branches  or  arborisations,  Fig.  3,  as  they  are 


Fig.  3. — Schematic  representation  of  distribution  of  nerve 
connections  in  retina. 


called,  which  connect  with  the  branches  of  other  bipolar  cells,  b, 
Fig.  3.  From  these  arborizations  fibers  extend  vertically  outward 
which  end  in  a  series  of  peculiar  bodies  called  the  rods  and  cones, 
a,  b,  Fig.  4.  These  are  the  terminals  of  the  optic  nerve  fibers,  and 
seen  from  above  form  a  mosaic  pattern,  composed  of  about  5,000,- 
000  minute  disks,  which  differs  in  various  portions  of  the  retina. 
It  is  particularly  noticeable  that  2  to  10  or  even  more  rods  are  em- 
braced by  a  single  arborization  which  represents  one  fiber  of  the 
optic  nerve,  Fig.  4.  On  the  other  hand  each  cone  has  a  nerve  fiber 
belonging  exclusively  to  it.  This  will  be  referred  to  later  on.  At 
or  near  the  periphery  of  the  retina  the  cones  are  few  in  number 
and  the  mosaic  pattern  is  made  up  of  a  larger  disk  surrounded 


566     TRANSACTIONS  OE  IEEUMINATING  ENGINEERING  SOCIETY 

by  many  rows  of  smaller  disks;  as  we  near  that  portion  of  the 
retina  corresponding  to  the  visual  axis  of  the  eye  the  cones  be- 
come more  numerous  and  the  rod  less  until  only  cones  are  found. 
The  ends  of  the  rods  are  in  contact  with  six  sided  cells  called 
pigment  cells  which  are  filled  with  fine  granules  and  have  a  net 
wrork  of  fine  spindle  shaped  bodies  which  push  forward  under 
the  action  of  light  between  the  ends  of  the  rods  as  far  as  the 
cones.    The  spaces  between  the  rods  and  cones  and  pigment  cells 


Fig.  4.— Schematic  representation  of  rods  and  cones. 


is  filled  with  a  fluid  which  contains  a  photochemical  substance 
very  sensitive  to  the  action  of  light  known  as  the  visual  purple. 
In  line  with  the  visual  axis  at  the  posterior  pole  of  the  eye  is 
situated  an  area  of  the  retina  in  which  vision  is  most  distinct 
called  the  macula.  This  area  is  about  2-2.5  mm-  in  diam- 
eter. Here  the  rods  are  found  in  much  less  number  until  in 
a  small  pit  at  the  center  of  the  macular  called  the  fovea  only 
cones  are  present.  The  cones  in  the  fovea  differ  from  those 
found  in  other  parts  of  the  retina  in  that  they  are  long,  very 


black:    phases  of  vision 


567 


narrow  cylinders  closely  massed  together  apparently  to  get  as 
many  as  possible  in  a  small  space.  Thus  an  image  projected 
upon  the  fovea  will  cover  many  more  cones  than  upon  other  areas 
of  the  fundus,  Fig.  5.  Microscopical  measurements  of  the  thick- 
ness of  the  cones  in  the  foveal  region  finds  they  vary  from  0.0015 
mm.  to  0.0054  mm.  in  diameter.  The  ability  to  distinguish  two 
points  depend  upon  the  diameter  of  the  cones  in  the  center  of 
exact  vision.  To  be  able  to  perceive  two  points  as  distinct  and 
separate  they  must  fall  upon  cones  which  are  separated  by  at 
least  one  resting  cone. 


Fig.  5. — The  fundus  or  background  of  the  eye. 


Distinct  vision  is  found  only  in  the  macular  area,  a  rounded 
patch  about  2  mm.  across  which  subtends  in  the  human  eye  an 
angle  of  about  5  minutes  in  the  field  of  vision  which  is  the  visual 
angle  of  the  macula.  Critical  vision  is  to  be  found  only  in  the 
fovea  which  occupies  an  angle  in  the  field  of  vision  of  less  than 
1  minute  which  is  the  visual  angle  of  the  fovea.  In  a  schematic 
eye  calculated  by  Listing  a  visual  angle  of  1  minute  corresponds 
on  the  retina  to  a  distance  of  0.00438  mm.  or  about  the  average 
diameter  of  a  cone. 

Outside  of  the  macular  region  we  obtain  a  general  impression 


568     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

of  the  form  and  color  of  objects  over  the  whole  of  the  retinal  field 
and  as  a  matter  of  fact  in  reading  ordinary  print  we  only  see 
words  of  about  four  letters  at  a  time  and  it  is  by  rapid  movements 
of  the  eye  in  various  directions  that  gives  the  idea  of  seeing  con- 
tinuously. 

This  brings  us  to  the  muscles  which  control  the  movements  of 
the  eyeballs  and  by  which  the  visual  axes  may  be  directed  to  any 
point  in  the  field  of  regard.  These  are  six  in  number  for  each 
eye  and  by  reason  of  their  attachment  on  the  eyeball  turn  it  up, 
down,  in,  out  and  if  working  in  conjunction  with  each  other 
orient  the  eye  in  any  of  the  intermediate  positions,  Fig.  6. 


Fig.  6. — Bxtrinsic  muscles  of  eye. 


The  discussion  so  far  has  shown  that  we  have  in  the  normal 
eye  an  apparatus  which  allows  the  entrance  of  impinging  rays  of 
light,  extraneous  rays  are  largely  cut  out  by  a  diaphragm,  which 
acts  reflexly  depending  upon  the  intensity  of  the  light;  a  lens 
brings  the  rays  of  light  to  a  focus  up  a  highly  organized  nervous 
structure  thus  completing  the  physical  phase  of  the  visual  act. 

PHYSIOLOGICAL  PHASE. 

The  highly  organized  nervous  structure  or  retina  transforms 
the  radiant  energy  waves  into  nerve  stimuli  constituting  the 
physiological  phase. 


black:    phases  of  vision 


569 


The  fibers  of  the  optic  nerve  are  as  insensible  to  light  as  the 
fibers  of  other  nerve  trunks,  as  is  demonstrated  by  the  experi- 
ment first  performed  by  Mariotte  who  discovered  the  blind  spot 
in  the  eye.  Purkinje  demonstrated  that  the  light  perceiving 
portion  of  the  eye  must  lie  behind  the  nerve  fiber  layer  of  the 
retina  from  the  fact  that  we  can  perceive  the  shadow  of  the  re- 
tinal vessels  in  our  own  eyes.    Exact  physiological  measurements 


Fig.  7.— Microphotograph  of  cross  section  of  retina,  showing  (a)  pigment 
cell  layer,  (b)  rod  and  cone  layer. 


has  shown  that  the  distance  between  the  vessels  and  the  light  per- 
ceiving layer  must  be  from  0.17  to  0.33  mm.  which  distance  takes 
us  to  the  rod  and  cone  layer.  Hence  it  follows  with  great  prob- 
ability that  the  latter  structures,  the  rods  and  cones,  are  the  light 
perceiving  parts  of  the  retina. 

This  in  fact  is  substantiated  by  the  anatomical  relations  of  the 
rods  and  cones  to  the  individual  nerve  fibers  of  the  optic  nerve. 

The  excitation  which  will  effect  the  receptive  portion  of  the 
specialized  organs  of  sense  differ  materially  from  those  capable  of 


570    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

stimulating  the  nerve  fibers  themselves  and  must  be  converted  by 
the  terminal  organ  into  the  adequate  kind  of  nerve  excitant. 
Nervous  stimuli  are  of  mechanical,  electrical,  thermal  or  chem- 
ical nature  and  into  such  character  must  external  energy  be 
transformed  when  it  varies  from  the  nervous  stimuli  in  quantity 
or  when  it  is  of  a  different  quality,  such  e.  g.,  as  waves  of  sound 
or  light. 

Retinal  Changes  Due  to  Light. — When  light  falls  upon  freshly 
exposed  retina  the  latter  undergoes  a  number  of  changes  which 
are  objectively  demonstrable.  The  spindle  shaped  pigment  gran- 
ules in  the  pigment  layer  migrate  toward  the  rod  and  cone  layer. 
The  pigment  will  not  move  if  the  central  nervous  system  is  de- 
stroyed, and  its  reaction  may  take  place  in  one  eye  as  a  conse- 


a 

— 

A  B 

Fig.  8.— Section  through  the  retina  of  a  frog's  eye,  after  Engelmannn.  A,  after  the  eye 
was  kept  for  from  one  to  two  days  in  complete  darkness  ;  B,  kept  for  24  hours  in  the 
dark,  then  exposed  for  one-half  hour  to  diffused  bright  daylight. 


quence  of  light  falling  on  the  opposite  retina.  The  cones  which 
in  darkness  or  dim  light  are  near  the  pigment  layer  move  inward 
toward  the  nerve  fiber  layer.  The  rods  on  the  other  hand  elon- 
gate under  the  influence  of  light,  their  movement  being  opposite 
to  the  cones.  The  galvanometer  shows  the  action  current  of  the 
retina  directed  from  the  nerve  fiber  layer  to  the  rod  and  cone 
layer  undergoes  a  positive  variation  which  changes  upon  the 
removal  of  the  light  stimulus. 

After  the  eye  has  been  kept  in  darkness  for  a  time  there  is  a 
marked   difference   in   the   sensitiveness   of   the   retina  to   light. 


13LACK:     PHASES   OF   VISION 


571 


This  is  known  as  dark  adaptation,  Fig.  9.  In  this  state  the  periph- 
eral regions  of  the  retina  are  relatively  more  sensitive  than  the 
fovea  to  light  of  moderate  intensity  and  to  short  wave-length. 
Adaptation  to  darkness  is  characterized  by  an  increase  in  respon- 
siveness to  short  waved  light,  and  this  change  is  mainly  if  not  en- 
tirely, extra  foveal.  The  perception  of  colored  light  varies  in 
different  portions  of  the  retina,  being  sharpest  at  the  fovea. 
Passing  toward  the  periphery  the  color  sense  gradually 
diminishes.  For  the  colors  yellow,  blue,  red  and  green,  yellow 
has  the  most  extensive  field,  blue  next  and  green  the  least.    Most 


ISO 
160 

170 
I6C 
150 
140 
130 
120 
110 
100 
90 
80 
70 
60 
50 
40 
30 
20 
10 
0, 


VISUAL  ACUITY  FOR 

LIGHT  ADAPTATION 

•  DARK  ADAPTATION 


60-  50  40  30  23  10    0°  10  20  30  40  50  60  70' 
Fig.  9.— Visual  acuity  curves  for  light  and  dark  adaptation. 


authors  state  the  extreme  periphery  of  the  retina  is  totally  color 
blind. 

The  visual  purple  which  is  present  in  all  parts  of  the  retina 
except  the  fovea  or  yellow  spot  (note  the  exception)  and  is 
found  mainly  in  the  outer  limbs  of  the  rods  fades  or  is  decom- 
posed when  exposed  to  light. 

The  bleaching  or  decomposition  of  the  visual  purple  depends 
on  the  intensity  of  the  light,  and  while  all  colored  light  has  the 
power  of  decomposing  this  substance,  with  weaker  light,  hours 
and  even  days,  are  needed  to  complete  the  action.  With  dif- 
ferent colors  of  monochromatic  light  the  process  takes  more  or 
less  time;  "in  yellow  green  the  purple  is  altered  instantaneously; 


572     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

in  the  spectral  colors,  from  greenish  yellow  to  indigo,  the  process 
requires  from  2  to  10  minutes;  in  yellow,  20  minutes;  in  violet 
and  orange,  30  minutes;  in  ultra-violet,  45  minutes,  and  in  red 
still  a  somewhat  longer  period  of  time."  While  blended  light, 
including  waves  of  greater  and  lesser  refrangibility  produces  the 


BLUE 


&REEN 


Fig.  10. — Chart  for  recording  boundaries  of  color  field.    Chart  on  right  shows 
boundaries  of  normal  color  field  by  Wm.  Mcl,ean. 


^0 


270° 
Fig.  11. — Binocular  field  of  vision. 


Fig.  12. — Binocular  field  of  view. 


maximum  effect,  each  individual  color  of  such  mixture  acts  for 
itself,  and  only  better  so  far  as  the  total  decomposition  of  the 
purple  is  concerned,  when  it  is  united  with  the  others.  The 
electrical  response  of  the  retina  appears  in  the  apparent  absence 
of  the  visual  purple,  although  the  reaction  is  more  intense  if  this 


black:    phases  of  vision  573 

pigment  be  present,  and  it  is  clear  that  the  whole  effect  varies  in 
intensity  with  the  part  of  the  spectrum  employed.  Regenera- 
tion of  the  visual  purple  in  the  outer  segments  of  the  rods  takes 
place  rapidly  in  darkness  or  dim  light,  apparently  being  derived 
from  a  substance  contained  in  the  pigment  cells  known  as 
rhodophyllia. 

Visual  Acuity. — The  sensitivity  curve  of  the  eye  for  lumin- 
osity at  ordinary  intensities  shows  a  maximum  effect  in  the  yel- 
low and  green  portion  of  the  spectrum.  Dr.  Louis  Bell  states  that 
it  is  only  by  virtue  of  the  high  maximum  point  in  the  luminosity 
curve  of  the  eye  that  we  are  able  to  see  distinctly  at  all,  and 
that  if  the  extremes  of  the  spectrum  were  highly  luminous  there 
would  be  no  definite  focal  surface  for  which  accommodation 
could  be  adjusted,  the  violet  rays  being  brought  to  a  focus  in 
front  of  the  retina  and  the  red  rays  behind  it  in  the  emmetropic 
eye.  It  is  a  well  known  fact  that  the  luminosity  curve  of  the 
eye  varies  with  the  intensity  of  the  light,  shifting  toward  the 
green  with  illumination  of  low  intensity  and  toward  the  orange 
and  red  with  illumination  of  high  intensity. 

Luckiesh  has  determined  that  visual  acuity,  for  a  reading  dis- 
tance of  2>Z  cm.  with  monochromatic  light,  is  greatest  in  the  yel- 
low green  of  the  spectrum.  Thus,  it  would  seem  that  the  radiant 
energy  which  has  the  greatest  decomposing  action  on  the  visual 
substance  is  productive  of  the  greatest  visual  efficiency,  that  is. 
the  yellow  green  waves. 

Duplicity  Theory  of  the  Function  of  the  Retinal  Structures. — 
The  reaction  of  the  different  areas  of  the  retina  to  light  stimuli 
in  the  conditions  known  as  light  and  dark  adaptation  studied  in 
conjunction  with  the  difference  in  the  histological  structures  be- 
tween the  fovea  and  the  surrounding  retinal  area  has  given  rise 
to  a  theory  of  the  function  of  the  rods  and  cones,  i.  e.,  two  dis- 
tinct mechanisms  exist.  The  cones  are  concerned  only  with  the 
recognition  of  colors  and  of  colorless  sensations,  can  only  act  in 
bright  light  and  their  responsiveness  is  little  if  at  all  increased  by 
resting  in  darkness.  The  rods  are  unaffected  by  colored  light 
but  are  brought  into  play  when  the  eye  has  been  shielded  from 
light,  and,  are  the  chief  factors  in  twilight  vision. 

Duplicity    Theory. — This    theory    does    not    account    for    the 


574     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

activity  of  the  cones  in  the  peripheral  portions  of  the  retina  which 
are  not  by  any  means  functionless  in  either  light  or  dark  adapta- 
tion. 

The  difference  between  acute  central  vision  and  indistinct 
peripheral  vision  is  marked  and  while  central  vision  is  far 
superior  to  peripheral  in  respect  to  the  optical  perfection  of  the 
image  of  an  object  and  the  fine  perception  of  detail,  peripheral 
vision  is  superior  in  the  perception  of  movement. 

Corresponding  to  these  functional  differences  the  eye  may  be 
considered  as  an  organ  which  unites  two  forms  of  apparatus  of 
different  functional  value. 

The  "central  eye"  is  an  elongated  eye  with  a  narrow-angle 
field ;  the  possibility  of  a  high  grade  of  visual  acuity  is  associated 
with  the  delicately  inlaid  sensory  elements,  and  the  provision  of 
an  isolated  sensory  path  for  each  end  element.  The  "peripheral 
eye,"  on  the  other  hand,  has  a  wide  angle  field  and  a  mosaic  of 
end  elements  with  concentrated  sensory  connections,  and  is  less 
adapted  for  keen  perception  of  detail.  The  periphery,  however, 
has  an  advantage  over  the  center  in  the  elements  necessary  for 
vision  in  dim  light.  This  great  difference  in  the  conditions  of 
acuity  in  the  center  and  in  the  periphery  of  the  retina  is  evidently 
connected  with  some  anatomical  peculiarity  of  the  area  in  the  cen- 
ter, and  this,  as  has  already  been  mentioned,  is  found  in  the  iso- 
lated individual  nerve  connections  of  this  part  in  contrast  to  the 
more  concentrated  ones  in  the  periphery.  The  areas  of  discrete 
sensation  in  the  retina,  therefore,  differ  according  to  their  posi- 
tion, and  in  the  elaboration  of  this  idea  the  gradual  diminution 
in  number  of  the  cones  from  the  center  to  the  periphery  is  sig- 
nificant. In  the  center  of  the  retina  cones  alone  occur,  but  as 
we  pass  outwards  rows  of  one,  two,  three  or  four  rods  are  in- 
terposed between  the  cones  which  themselves  become  thicker. 
The  correspondence  appears  a  simple  one,  but  a  more  careful 
comparison  will  show  that  the  diminution  in  acuity  is  propor- 
tionately greater  than  the  reduction  in  the  cones. 

In  support  of  the  duplicity  theory  various  facts  of  physiological 
optics  are  given: 

The  Colorless  Interval. — If  a  feeble  spectrum  be  observed  by 


BLACK  :     PHASES   OF   VISION  575 

an  eye  well  adapted  for  darkness,  colorless  light  will  first  be  seen, 
and  only  as  the  intensity  is  increased  will  color  be  perceived. 

Purkinje's  Phenomenon. — If  selected  matched  red  and  blue 
objects  are  placed  together  so  that  in  daylight  the  red  appears 
lighter  than  the  blue,  and  the  illumination  be  gradually  reduced, 
as  adaptation  increases  and  the  illumination  diminishes,  the  red 
object  will  grow  darker  and  even  appear  black,  while,  on  the 
contrary,  the  blue  will  grow  lighter  and  more  white. 

The  variation  of  the  maximum  point  of  the  luminosity  curve 
for  different  intensities  of  light  was  mentioned  above,  for  the  dark 
adapted  eye  the  maximum  point  is  found  to  be  in  the  green. 
(533  /*/*•)  Investigations  have  shown  a  correspondence  between 
the  curve  of  scotopic  or  dark  luminosity  and  that  obtained  by  the 
bleaching  effect  of  light  upon  the  visual  purple.  This  corres- 
pondence in  the  curves  can  not  be  accidental  and  the  upholders 
of  the  duplicity  theory  see  in  the  visual  purple  and  the  structures 
which  contain  it,  the  rods,  the  elements  and  the  visual  material 
for  vision  in  the  dusk.  The  view  of  the  duplicity  theory  that  the 
sensation  of  white  (and  grey)  in  the  light  adapted  eye  is  brought 
about  by  the  color-perceiving  cone  elements,  and  in  the  dark 
adapted  eye  by  the  rods  and  the  visual  purple,  is  freely  consid- 
ered to  be  very  doubtful.  It  must  not  be  forgotten  that  the  facts 
given  above  have  hardly  any  analogy  in  the  physiology  of  the 
other  senses.  The  supporters  of  the  duplicity  theory  consider 
total  color-blindness  as  a  condition  of  the  eye  in  which  sensation 
occurs  entirely  through  the  activity  of  the  retinal  rods,  which  con- 
tain the  visual  purple;  the  cones  being  absent  or  functionless. 
The  peculiar  distribution  of  luminosity  in  the  spectrum  of  the 
totally  color-blind  appears  to  favor  this  view,  the  complete  ab- 
sence of  color  vision  and  the  photophobia  also  agree  with  it. 
The  functional  activity  of  the  rods  alone  is  favored  by  the  con- 
dition of  visual  acuity,  which  differs  from  that  of  color  seeing 
people,  in  that  it  increases  in  a  different  manner  when  the  light 
is  increased,  and  does  not  show  that  sharp  bend  upwards,  which 
in  the  normal  can  be  referred  to  the  visual  power  of  the  cones. 

In  the  totally  color  blind  the  existence  of  a  central  scotoma  for 
color  such  as  is  found  in  the  dark  adapted  eye  with  feeble  light 
would  be  especially  significant,  for,  a  defect  must  be  present  at 


576     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

the  point  of  central  vision  to  correspond  with  the  dark  adapted 
eye.  In  many  cases,  though  not  in  all,  such  scotoma  can  be 
found. 

The  idea  that  the  cones  have  a  lower  sensibility  in  total  color- 
blindness is  a  very  attractive  one  as  their  complete  absence  does 
not  appear  proven  by  the  observations  which  we  have  been  con- 
sidering. The  defective  vision,  the  absence  of  color  sensation, 
and  the  other  symptoms  can  be  considered,  without  any  straining, 
as  due  to  a  severe  restriction  of  the  function  of  the  cones  along 
with  an  increase  in  that  of  the  rods. 

Mechanical  Theory  of  Vision. — It  has  been  assumed  by  some 
observers  that  the  light  waves  act  mechanically,  the  wave  move- 
ments setting  into  vibration  portions  of  the  external  segments  of 
the  rods  and  cones,  and  that  this  mechanical  movement  forms 
the  direct  excitant  of  the  nerve  impulses.  The  general  view  at 
the  present  time,  however,  is  that  the  process  is  photochemical  ; 
that  is,  the  impact  of  the  ether  waves  sets  up  chemical  changes 
in  the  rods  or  cones  which  in  turn  gives  rise  to  nerve  impulses 
that  are  transmitted  to  the  brain. 

Color  Vision. — This  brings  us  to  the  physiology  of  the  percep- 
tion of  colored  light  and  the  theories  advanced  to  account  for  the 
peculiar  condition  of  vision  found  in  about  one  out  of  every 
twenty-five  males  known  as  color-blindness.  There  are  many 
theories  advanced,  the  chief  among  which  are  those  of  Young- 
Helmholtz,  Hering,  and  Edridge-Green. 

The  Young-Helmholtz  Theory. — This  theory  (first  proposed  by- 
Thomas  Young  in  1807,  and  subsequently  modified  by  Helmholtz)  assumes 
that  the  terminal  fibrils  of  the  retina  are  arranged  in  three  distinct  sets 
for  the  reception  of  the  three  primary  colors — red,  green,  and  violet. 
These  groups  correspond  to  the  three  colors,  and  acting  simultaneously 
induce  the  sensation  of  white.  Red  light  entering  the  eye  affects  to  the 
greatest  extent  the  group  of  filaments  known  as  the  red  sensitive  elements, 
and  also  affects  the  others  to  a  slight  degree.  In  like  manner  green  and 
violet  are  perceived  by  their  corresponding  sensitive  elements.  The 
absence  or  imperfect  development  of  the  retinal  area  set  aside  for  one 
of  these  primary  colors  will  cause  this  color  to  be  seen  as  if  composed  of 
the  two  remaining  colors,  thus  giving  rise  to  color  blindness  corresponding 
to  the  deficient  color  elements. 


black:    phases  of  vision 


577 


Fig.  13  shows  the  manner  in  which  the  quantitative  stimula- 
tion of  the  individual  fibers  by  yellow  or  blue  is  to  be  appreciated 
on  this  hypothesis. 

The  conclusions  drawn  from  the  laws  of  light  mixture  have 
in  recent  times  found  a  technical  application  of  this  theory  in 
the  Lumiere  color  photography.  In  front  of  a  sensitive  plate 
is  a  screen  formed  of  minute  grains  of  starch  colored  red, 
green  and  violet.  The  variously  colored  light  passes  through 
the  starch  grains  in  a  selective  manner  with  respect  to  quantity 
and  quality,  according  to  the  valency  curves  and  makes  its 
impression  on  the  bromo  silver  plate.  The  plate  is  then  de- 
veloped as  a  diapositive,  and  will  filter  light  in  the  same  manner, 


RtO      0RAN6E  YELLOW 


Fig.  13. — Valency  curves  of  the  three  components  of  the  color  sense. 

only  allowing  the  original  colors  to  pass ;  thus  a  very  fine  photo- 
graph in  natural  colors  can  be  obtained. 

Hering  Theory  of  Color  Vision. — This  theory  assumes  the  existence 
of  three  separate  visual  substances  in  the  retina.  Each  of  these  substances 
is  decomposed  by  the  action  of  light  and  is  renewed  when  the  eye  is  per- 
mitted to  rest  in  the  dark.  Both  the  decomposition  and  the  renewal  of 
the  visual  substances  result  in  the  production  of  color  sensation. 

The  Hering  visual  substances  are  divided  into  three  sets  of  two  each, 
i.e.,  (1)  white-black  substance;  (2)  red-green  substance;  (3)  blue-yellow 
substance. 

When  the  black-white  substance  is  decomposed  the  sensation  of  white 
is  produced.  When  this  substance  is  renewed  the  sensation  of  darkness 
results. 

When  the  red-green  substance  is  decomposed  the  sensation  of  red  is 
produced,  and  when  it  is  renewed  the  sensation  of  green  results. 

When  the  yellow-blue  substance  is  decomposed  the  sensation  of  yellow 
is  produced;  when  it  is  renewed  the  sensation  of  blue  results. 

Red  light  produces  the  sensation  of  red  by  decomposing  the  red-green 
substance.  Orange  light  produces  the  sensation  of  orange  by  decom- 
posing both  the  red-green  and  the  yellow-blue  substances.  Yellow  light 
produces  a  sensation  of  yellow  by  decomposing  the  yellow-blue  substance, 
the  red-green  being  then  in  equilibrium.  Green  light  produces  the  sensa- 
5 


578     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

tion  of  green  by  the  renewal  of  the  red-green  substance,  the  yellow-blue 
being  now  in  equilibrium.  Blue  light  produces  the  sensation  of  blue 
by  the  renewal  of  the  yellow-blue  substance.  Violet  light  does  the  same, 
though  to  a  less  degree. 

This  objection  can  be  taken  to  Hering's  theory,  that  in  the 
black-white  form  of  sensation  there  is  no  different  point  which 
cannot  be  compared  to  white  or  to  black,  as  is  the  case  with  the 
red-green  or  the  blue-yellow;  there  is  also  a  doubtful  element  in 
the  hypothesis  in  that  it  is  not  only  the  process  of  dissimilation 
that  produces  a  stimulus,  but  perception  may  also  be  due  to 
assimilation.  The  well  known  phenomena  of  contrasts  are  well 
explained  by  this  hypothesis ;  i.  e.,  after  steadily  fixing  a  colored 
pigment,  and  then  looking  at  a  colorless  surface,  the  contrast 
color  appears.  Just  as  this  "successive  contrast"  is  well  explained, 
so  also  is  the  "simultaneous  contrast."  In  this  condition,  which 
is  shown  in  the  appearance  of  colored  fringes,  the  dissimilation 
of  a  definite  visual  substance  will  induce  the  assimilation  of  the 
same  substance  in  the  adjoining  parts,  and  thus  the  appearance 
of  the  complimentary  color.  Color  perception  in  peripheral  vision 
is  also  in  favor  of  Hering's  theory. 

The  Edridge-Green  Theory. — The  latest  and  probably  most 
comprehensive  theory  is  that  of  Edridge-Green  in  which  he 
accounts  not  only  for  vision  and  color  vision,  but  for  the  trans- 
formation of  radiant  energy  into  nerve  stimuli. 

Edridge-Green  conceives  that  the  cones  are  the  terminal  per- 
ceptive visual  organs.  The  rods  are  not  perceptive  elements,  but 
are  concerned  with  the  formation  and  distribution  of  the  visual 
purple.  Vision  takes  place  by  stimulation  of  the  cones  through 
the  photo-chemical  decomposition  by  light  of  the  liquid  surround- 
ing them  which  is  sensitized  by  the  visual  purple. 

The  character  of  the  stimulus  differs  according  to  the  wave- 
length of  the  light  causing  it.  In  the  excitation  itself  we  have  the 
physiological  basis  of  the  sensation  of  light,  and  in  the  quality 
or  wave-length  of  the  excitation  the  physiological  basis  for  the 
sensation  of  color. 

There  are  three  objections  made  to  the  Edridge-Green  theory 
that  the  visual  purple  is  the  visual  substance. 

(i)  The  chief  objection  is  that  it  is  not  present  in  the  cones. 
The  author  maintains  this  is  a  necessary  requisite  to  the  theory. 


black:    phases  of  vision  579 

(2)  That  animals  such  as  frogs  naturally  possessing  the  pig- 
ment continue  to  see  after  their  visual  purple  has  been  absolutely 
bleached  by  prolonged  exposure  to  strong  light.  The  author 
contends  that  the  retinas  which  were  bleached  by  sunlight  and 
with  which  the  frogs  were  still  able  to  see,  in  reality  contain 
sufficient  visual  purple  or  its  decomposition  products  for  vision, 
but  not  enough  for  external  recognition. 

(3)  That  the  visual  purple  is  entirely  wanting  in  some  animals 
which  see  very  well.  This  is  based  upon  erroneous  observations, 
and  in  case  of  certain  animals  supposed  to  have  no  visual  purple 
or  no  rods,  subsequent  observers  have  found  both ;  for  instance, 
the  butterfly,  bat  and  tortoise.  Even  if  there  were  no  visual 
purple  the  argument  fails  because  there  might  be  some  other 
means  of  stimulating  the  cones. 

The  following  are  a  number  of  arguments  given  in  support  of 
the  Edridge-Green  theory : 

( 1 )  Visual  Acuity :  This  corresponds  roughly  to  the  distribu- 
tion of  the  cones.  Though  the  rods  are  much  more  numerous  in 
the  periphery  of  the  retina  visual  acuity  is  very  much  less  with 
this  part. 

(2)  The  relation  between  the  foveal  and  the  para-foveal 
regions.  As  there  are  no  rods  in  the  fovea,  if  the  rods  and  cones 
were  percipient  elements  of  a  different  character  there  ought  to 
be  a  qualitative  difference  between  these  regions.  The  Purkinje 
phenomenon,  i.  e.,  the  alteration  of  optical  white  equations  by  the 
state  of  dark  adaptation,  the  colorless  interval  for  spectral  lights 
of  increasing  intensity,  the  different  phases  of  the  after-image, 
all  exist,  not  only  in  the  para-foveal,  but  also,  only  gradually 
diminished,  in  the  foveal  region. 

The  misstatement  has  been  made  that  the  Purkinje  phenomenon 
(the  fact  that  if  an  equally  bright  red  and  blue  be  viewed  by  a 
light  of  considerably  diminished  intensity  the  blue  appears  much 
brighter  than  the  red)  is  not  found  in  the  foveal  region.  One  can 
easily  ascertain  for  himself  that  the  Purkinje  phenomenon  is 
found  in  the  fovea  by  taking  a  red  and  a  blue  into  a  dimly-lighted 
room,  the  red  being  brighter  than  the  blue  in  ordinary  conditions, 
he  will  find  that  the  blue  will  appear  brighter  than  the  red  with 
direct  vision,  and  still  more  so  with  indirect  vision,  he  will  find 


580     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

that  in  no  position  of  the  eye  can  he  see  the  red  brighter  than  the 
blue. 

(3)  Chemical  Analogy:  The  visual  purple  gives  a  curve  which 
is  similar  to  that  of  many  other  photo-chemical  substances.  With 
such  substances  a  different  curve  is  obtained  with  weak  light  from 
that  observed  with  light  of  greater  intensity  and  it  is  reasonable 
to  suppose  that  the  visual  purple  which  is  formed  by  the  pigment 
cells  under  the  influence  of  a  bright  light  would  be  somewhat  dif- 
ferent in  character  from  that  which  is  formed  in  darkness. 

(4)  It  is  a  misstatement  that  the  periphery  of  the  retina  is 
color-blind.  It  is  entirely  a  matter  of  the  intensity  of  the  light 
employed.  Bright  spectral  colors  can  be  seen  at  the  extreme 
periphery  of  vision.  All  lights  when  sufficiently  small  and  feeble 
appear  white  even  at  the  fovea. 

(5)  The  varying  sensibility  of  the  fovea  is  explained  on  the 
theory  that  when  there  is  visual  purple  in  the  fovea  this  is  the 
most  sensitive  portion  of  the  retina;  when  there  is  none  there  it 
is  blind.  It  also  shows  conclusively  that  the  fovea  is  sensitized 
from  the  periphery. 

(6)  Disappearance  of  lights  falling  upon  the  fovea  shows  that 
when  the  visual  purple  in  this  area  is  used  up  and  not  renewed 
the  latter  is  blind. 

(7)  Currents  seen  in  the  field  of  vision  are  not  due  to  the  cir- 
culation but  are  formed  by  the  flow  of  sensitized  liquid. 

(8)  The  movement  of  positive  after  images  by  a  jerk  of  the 
head  shows  that  the  photo-chemical  stimulus  is  external  to  the 
cones  and  can  be  moved. 

(9)  Dark  adaptation  is  easily  explained  by  assuming  that  the 
liquid  round  the  cones  becomes  more  sensitive  through  a  greater 
percentage  of  visual  purple  being  poured  into  it.  In  light  adapta- 
tion the  anatomical  arrangement  is  such  as  to  prevent  as  far  as 
possible  the  decomposition  of  the  visual  purple. 

The  ability  of  the  normal  eye  to  distinguish  the  form  of  an 
object  depends  upon  (1)  the  size  of  the  image  received  upon  the 
retina;  (2)  the  amount  of  light  reflected  from  it;  (3)  the  con- 
trast with  the  background.  The  results  obtained  from  the  exam- 
ination of  a  great  many  individuals  with  good  sight  have  shown 
that  with  the  average  eye  the  form  of  an  object  can  be  recog- 


black:    phases  of  vision  581 

nized  if  the  angle  subtended  by  it  at  the  retina  equals  five  min- 
utes and  parts  of  the  object,  such  as  a  letter,  which  subtend  a 
5-minute  angle,  are  wide  enough  to  subtend  a  1 -minute  angle. 

The  amount  of  light  reflected  from  an  object  must  be  suf- 
ficient to  act  upon  the  photo-chemical  visual  substance  and  cause 
stimulation  of  the  nerve  endings.  The  coefficient  of  reflection 
between  an  object  viewed  and  the  background  must  differ  suf- 
ficiently to  make  a  contrast;  otherwise  the  object  will  be  in- 
visible. 

Summary  of  Physiological  Phases  of  Vision. — A  light  wave 
starts  on  its  journey  through  the  ether  from  some  luminous  ob- 
ject or  reflected  from  some  surface  which  is  its  source.  The 
various  rays  parallel,  divergent  or  convergent,  as  the  case  may 
be,  are  brought  to  a  focus  upon  the  background  of  the  eye.  The 
first  step  towards  its  becoming  a  visual  impulse  is  taken  when  it 
decomposes  the  photo-chemical  substance  of  the  retina,  thus 
setting  up  vibrations  in  the  cones  of  this  membrane. 

The  excitation  received  by  the  retinal  substance  and 
structures  is  conveyed  by  fibers  of  the  optic  nerve  back  to  centers 
at  the  base  of  the  brain,  and  either  directly  or  by  new  relays  of 
fibers  to  the  visual  centers  of  the  brain.  Definite  portions  of  the 
retina  are  related  to  equally  definite  portions  of  the  visual  center 
of  the  brain  which  first  receive  the  projected  retinal  excitations. 
The  result  in  the  brain  centers  first  receiving  the  impulses  is  a 
visual  sensation  or  percept.  Up  to  this  time,  however,  no  idea 
of  the  object  looked  at  is  obtained.  In  order  that  this  shall  come 
to  pass  the  brain  excitation  which  has  been  brought  about  must 
be  transmitted  to  another  region  of  the  brain  surface;  in  other 
words,  from  a  simple  perception  center  to  a  memory  center 
where  it  is  recognized. 

There  are  several  factors  which  interfere  with  the  adequate 
carrying  out  of  the  physical  phase  of  vision,  such  as  far-sighted- 
ness, near-sightedness  and  astigmatism.  However,  as  we  are 
considering  a  normal  or  emmetropic  eye,  this  will  not  be  gone 
into. 

The  sensitiveness  of  the  visual  apparatus  to  radiant  energy  is 
a  most  interesting  and  absorbing  study,  but  time  and  space  will 
not  allow  of  more  than  a  mere  mention. 


582     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Of  all  the  energy  emanating  from  a  light  source,  such  as  an 
incandescent  lamp,  only  5  per  cent,  is  perceived  by  the  eye  as 
light,  as  is  graphically  represented  by  slide  projected  on  the 
screen.  This  small  portion  of  the  radiant  energy  of  an  incan- 
descent body  appreciated  by  the  eye  is  known  as  the  visible  spec- 
trum, and  is  bounded  by  wave-lengths  760  fx/x,  recognized  as 
deepest  red,  and  wave-length  about  400  /*/*,  seen  as  deepest  violet. 
The  action  upon  the  eye  of  wave-lengths  longer  than  760  pn, 
known  as  infra-red  rays,  is  still,  to  a  certain  extent,  a  moot 
question,  but  they  are  considered  to  be  a  factor  in  producing 
opacities  of  the  lens.  The  wave-lengths  shorter  than  400  fifx  are 
designated  as  ultra-violet  rays,  and  are  known  to  produce  intense 
inflammatory  reactions  of  the  outer  coats  of  an  unprotected  eye, 
when  exposed  to  intense  light,  containing  a  high  percentage  of 
these  radiations. 

The  various  transparent  media  of  the  eye,  the  cornea,  aqueous 
humor,  lens  and  vitreous,  have  selective  absorption  characteris- 
tics for  these  rays,  which  protect  the  retina  under  ordinary  con- 
ditions. As  infra-red  and  ultra-violet  radiations  are  of  no  known 
aid  in  the  visual  act,  it  is  a  wise  precaution  to  shield  the  eyes 
from  them  by  means  of  protective  glasses,  which  have  selective 
absorption  action  for  these  particular  rays,  provided,  however, 
that  the  glass  does  not  cut  down  the  amount  of  light  gaining 
entrance  into  the  eye  to  an  extent  that  will  interfere  with  the 
proper  decomposition  of  the  visual  purple.  The  selective  absorp- 
tion of  some  of  these  glasses  is  shown. 

The  subject  of  after  images,  color  contrasts,  simultaneous  con- 
trasts, complementary  colors,  recurrent  vision,  binocular  vision 
and  spatial  vision,  cannot  be  gone  into  in  the  time  and  space 
allotted. 

PSYCHICAL  PHASE. 

The  psychical  phase  of  vision  will  be  briefly  mentioned,  and  is 
largely  quoted  from  Lohmann : 

While  color  perception  by  the  eye  is  induced  from  a  light  stim- 
ulus and  the  essential  conditions  are  generally  provided  by  physio- 
logical stimuli,  the  perception  of  color  itself  is  a  psychic  phe- 
nomenon. With  the  color  impression  called  forth  by  the  stimulus 
are  associated  those  representations  called  memory-colors,  and 


black:    phases  of  vision  583 

thus  the  same  percept  is  insured  even  though  surrounding  con- 
ditions vary.  Cloths,  whose  color  has  been  recognized  by  day, 
are  viewed  by  artificial  light,  when  to  a  really  unprejudiced  eye, 
they  present  quite  another  appearance,  but  seem  to  be  seen  in 
their  "correct"  colors  in  the  artificial  light ;  we  also  speak  of 
white  snow,  even  when  the  dusk  of  twilight  has  changed  it  to 
grey. 

The  psychic  element  in  vision  is  very  obvious  in  the  following 
example,  which  Helmholtz  gives  in  his  "Physiological  Optics." 
Imagine  oneself  to  be  in  a  brightly  lighted  room;  impressions  are 
then  accompanied  by  powerful  sensations.  We  find  ourselves 
at  dusk  in  the  same  room,  seeing  only  the  lighter  objects,  and 
these  indistinctly.  Everything  which  we  notice  so  fuses  with 
our  memory-pictures  that  we  can  readily  find  objects  looked  for. 
Even  in  absolute  darkness,  we  can  find  our  way  in  the  room  by 
virtue  of  the  memory  of  previous  visual  impressions.  This 
example  of  the  reduction  of  the  presentation  image  "by  an  ever 
increasing  elimination  of  its  sense  elements  to  a  pure  re-presenta- 
tion image,"  shows  us  the  intimate  connection  between  the  purely 
sensory  and  the  purely  psychic  in  our  concepts  and  ideas. 

In  fact,  our  concepts  are  not  induced  merely  by  the  visual  im- 
pressions of  the  moment,  but  necessitate  the  addition  to  these  of 
re-presentations  of  sensations;  these  we  adequately  term 
"factors  of  experience."  It  is  not  always  possible  to  separate  the 
pure  sensation  from  the  factor  of  experience. 

When  I  look  at  a  portrait  drawn  so  that  the  eyes  look  at  me, 
and  then  walk  about  the  room,  I  have  the  impression  that  the 
portrait  is  always  gazing  at  me.  This  fixed  gaze  of  the  portrait, 
an  easily  proved  empiricism,  is  not  induced  by  reflexion,  but  is 
the  result  of  an  overwhelming  sensory  impression. 

The  analysis  of  the  fact  that  the  factor  of  experience  is  so 
important  in  vision,  is  by  no  means  simple;  it  presents  a  difficult 
problem  to  the  psychologist.  A  relatively  simple  explanation  is 
provided  by  the  hypothesis  that  the  psycho-physical  substance 
as  a  result  of  its  activity  suffers  changes,  and  that  residual  sen- 
sations previously  left  behind  are  met  with  and  have  a  modifying 
action  on  a  new  sense  impression. 

To  produce  a  picture  from  the  individual  sensory  stimuli  of 


584     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

the  retina,  we  must  have  the  component  parts  built  up  into  a 
complex  percept.  Witasek  talks  of  a  "process  of  production," 
and  his  meaning  becomes  clear  when  we  consider  how  the  same 
form  of  stimulus  in  the  same  state  of  the  eye  can  produce  dif- 
ferent perceptions. 

Importance  of  Vision. — In  examining  the  importance  of  vision, 
we  must  take  into  account  the  relation  of  our  eye  to  objects  seen, 
and  also  the  relation  of  the  objects  to  us.  We  have  to  answer 
two  questions:  1.  What  does  sight  convey  to  us  regarding  ex- 
ternal objects?  2.  What  influence  has  sight  on  our  intellectual 
life  and  comfort? 

What  Does  Sight  Convey  to  Us? — The  first  question  intro- 
duces a  much  discussed  philosophical  problem,  and  ends  in  the 
well  known  question  of  objective  existence.  We  either  deny  a 
correspondence  between  our  perceptions  and  the  actual  objects, 
and  explain  all  sense  perceptions  as  subjctive  phenomena,  and 
sense  delusions  as  not  actual  realities ;  or  we  admit  a  conformity 
between  the  world  around  us  as  we  subjectively  find  it,  and  as  it 
objectively  exists. 

In  the  latter  case  we  speak  of  a  "pre-established  harmony" 
(Ehrhart),  and  consider  that  a  correlation  between  mind  and 
matter  is  shown  because  the  power  of  mind  is  derived  from  the 
same  source  as  are  the  forms  of  energy  in  the  world  around. 

In  contrast  to  such  speculative  answers  to  the  problem  of  the 
relation  between  vision  and  the  world  around,  Helmholtz  em- 
phasized the  practical  point,  which  appears  when  we  consider 
that  surrounding  objects  by  means  of  our  sense  impressions  be- 
come to  us  symbols  which,  when  we  have  learnt  to  interpret 
rightly,  make  it  possible  for  us  to  direct  our  actions  so  as  to 
bring  about  desired  results.  Although  the  eye  is  extremely  use- 
ful, practically,  it  cannot  see  at  all  distances,  nor  perceive  all  the 
vibrations  of  the  ether.  In  the  same  way  we  have  no  guarantee 
that  human  intelligence  might  master  everything  which  can  exist 
or  occur. 

The  common  view  of  simple  people  that  our  vision  says  some- 
thing about  an  object  has  led  to  an  unfortunate  method  of  ex- 
pression, which  appears  when  we  speak  of  "red"  sealing  wax. 


black:    phases  of  vision  585 

To  a  color-blind  eye,  this  is  not  red;  it  is  only  in  the  case  of  a 
normal  eye  under  ordinary  conditions  that  the  rays  of  light  re- 
flected from  the  sealing  wax  produce  that  definitely  character- 
ized sensation  (red). 

Influence  of  Sight  on  Intellect. — Regarding  the  second  ques- 
tion, the  importance  of  vision  to  our  intellectual  life,  the  view  was 
prevalent  amongst  the  ancients  that  the  many  distractions  which 
our  visual  impressions  bring  us,  prevented  an  undisturbed  devel- 
opment of  the  soul.  Cicero's  statement  that  Democritus  had 
blinded  himself  in  order  to  reason  more  clearly  would  thus  be 
easily  understood.  We  tend,  when  reasoning,  to  shut  our  eyes; 
but  their  closing  is  only  temporary  against  any  influence  which 
would  interfere  with  the  concentration  of  the  mind.  On  the  other 
hand,  we  must  recognize  that  the  "hasty  glance"  will,  through 
visual  impressions  advance  our  quickness  of  mind,  and  to  a  cer- 
tain extent  is  a  form  of  mental  gymnastics. 

The  eye  is  an  organ  which  enables  us  not  only  to  recognize 
objects  in  the  vicinity,  but  also  parts  of  the  country,  the  sea,  and 
the  starry  sky,  in  the  far  distance.  Our  visual  impressions  are 
closely  related  to  perceptions  of  space,  and  recognition  of  time. 
We  will  readily  be  convinced  that  a  spatial  sensation  of  depth  is 
transmitted  (extent  in  height  and  breadth  is  conveyed  by  each 
eye  separately)  if  we  attempt  to  estimate  the  position  of  an  ob- 
ject relative  to  ourselves  by  monocular  vision.  It  must  be  ad- 
mitted that  depth  is  only  recognized  indirectly  with  the  one  eye, 
in  contrast  to  the  immediate  and  obvious  estimation  of  the  posi- 
tion of  objects  one  behind  the  other  which  is  gained  binocularly. 
Impressions  as  to  succession  in  time  are  also  conveyed  by  our 
visual  sense;  and  it  might  be  added,  more  frequently  by  this 
means  than  by  the  other  sense  organs.  For  the  whole  field  of 
vision  forms  the  fundamental  chord,  the  continuous  impression, 
in  which  a  movement  or  an  alteration  occurs;  we  see  solid  ob- 
jects grouped  together  constantly,  changing  in  their  relative 
positions.  It  is  thus  quite  obvious  what  a  great  intellectual  use 
we  make  of  our  visual  impressions,  so  variable  in  space  and  time. 

The  whole  play  of  our  imagination  draws  freely  for  material 
on  memory  pictures  derived  from  vision,  so  that  visual  impres- 
sions are  the  source  of  a  large  portion  of  our  inner  life. 


586     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  true  importance  of  vision  to  us  will  be  clear  if  we  try  to 
imagine  what  would  remain  of  our  intellectual  existence  if  all 
visual  impressions  and  the  memory  of  them,  were  banished.  We 
must  confess  with  Goethe: 

"Place  yourself  in  what  state  you  will,  you  will  always  think 
of  yourself  as  seeing." 


ILLUMINATION    CALCULATIONS  587 

SIMPLIFICATION  OF  ILLUMINATION 
CALCULATIONS.* 


BY  A.   S.   MCALLISTER. 


As  marking  the  transition  of  the  science  and  art  of  illumination 
from  the  methods  of  the  physicist  to  those  of  the  engineer,  no 
one  milestone  stands  out  more  prominently  than  that  represented 
by  the  presidential  address  of  Dr.  Clayton  H.  Sharp  in  1907. 
Following  his  presentation  of  certain  concepts  and  terminology 
in  illuminating  engineering,  not  only  was  there  a  change  in  the 
output  rating  of  lamps  from  the  indefinite  and  much  abused 
candlepower  to  the  definite  and  now  well-understood  lumen,  but 
many  improved  methods  were  developed  for  solving  problems  in 
illumination.  In  many  respects  the  results  have  been  similar  to 
the  substitution  of  the  flux  method  for  the  isolated  unit  pole 
method  of  solving  problems  in  magnetism. 

While  from  the  point  of  view  of  physics  there  are  marked 
differences  between  the  concept  of  magnetic  lines  or  "tubes"  force 
and  that  of  lines  or  "cones"  of  radiant  energy,  yet  in  their  math- 
ematical treatment  the  problems  relating  to  the  one  are  quite 
similar  to  those  relating  to  the  other. 

So  far  as  numerical  results  are  concerned,  it  is  absolutely  safe 
to  ignore  the  direction  of  travel  and  mode  of  propagation  of  the 
radiant  energy  from  the  source  of  light  to  the  surfaces  upon  which 
this  energy  is  absorbed.  Of  one  relation  we  can  be  absolutely 
sure,  namely,  the  total  energy  absorbed  equals  the  total  energy- 
produced.  When  methods  of  calculation  give  results  not  in  con- 
formity with  this  relation  it  is  safe  to  state  that  the  methods  are 
wrong  either  in  principle  or  in  application.  Thus  for  checking 
results  obtained  by  more  laborious  methods  the  absorption-of-light 
method  is  highly  advantageous.  In  many  instances,  yes  in  most 
cases,  it  is  permissible  to  abandon  the  more  complicated  methods 
and  rely  upon  the  simplest  and  absolutely  correct  energy-ratio 
method,  with  merely  an  occasional  reference  to  some  more  in- 
direct method  for  determining  the  space  distribution  of  the 
illumination  where  this  is  of  importance. 

*  Presidential  address  at  ninth  annual  convention  of  the  Illuminating  Engineering 
Society,  Washington  D.  C,  Sept.  20-23,  I9I5- 


588    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Looking  back  over  the  Transactions  of  the  Illuminating  En- 
gineering Society  since  its  first  meeting  in  1906,  one  cannot  but 
be  impressed  by  the  fact  that  almost  all  of  the  solutions  offered 
for  problems  in  illumination  have  been  based  on  the  tacit  assump- 
tion of  point  sources  rather  than  surface  sources.  Even  when 
dealing  with  plane  surface  sources  the  authors  have  usually 
treated  them  as  made  up  of  an  infinite  number  of  point  sources 
arranged  in  one  plane,  and  have  based  their  solutions  on  the  "in- 
verse square"  law  and  other  relations  developed  from  the  funda- 
mental point-source  conception.  In  order  to  obtain  results  con- 
sistent with  the  known  facts  in  this  case,  it  has  been  necessary  to 
assign  to  each  infinitesimal  point  source  in  the  plane  certain 
physical  characteristics  not  possessed  by  ideal  point  sources,  such 
as  the  ability  to  produce  light  in  only  one  hemisphere  which  is  the 
fundamental  attribute  of  an  infinitesimal  plane  surface  source. 

It  needs  no  argument  to  show  that  all  calculations  are  im- 
mensely simplified  by  adopting  initially  the  surface  source  con- 
ception and  utilizing  at  once  the  well-known  relations  developed 
for  surface  sources. 

Instead  of  determining  the  illumination  produced  by  the  source 
on  a  chosen  plane  by  reference  to  the  "inverse  square"  law  and 
the  integrated  "candlepower,"  the  identical  value  can  be  derived 
more  conveniently  by  means  of  the  fundamental  ratio  existing 
between  the  "apparent  luminous  density"  of  the  source  and  the 
lumen  density  on  the  surface  illuminated,  which  ratio  depends 
solely  upon  the  solid  angle  subtended  by  the  source  when  viewed 
from  the  chosen  plane. 

Allow  me  to  call  attention  at  this  point  to  a  fact  learned  by 
us  all  in  our  school  days,  but  mostly  forgotten  since  then ;  namely, 
the  extreme  ease  with  which  solid  angular  relations  can  be  rep- 
resented by  straight  lines  and  circles  in  planes.  As  a  result  of 
this  fact  simple  circle  diagrams  can  be  utilized  for  solving  graph- 
ically problems  in  solid  angular  relations  the  solutions  of  which 
become  very  complicated  when  any  other  method  is  employed. 

Ignoring  for  the  moment  the  physical  interpretation  of  the 
change  in  conception  from  the  "point"  to  the  "surface"  source 
allow  me  to  mention  here  the  significant  fact  that  the  solution  of 
a  problem  when  based  on  the  one  conception  is  identical  with  that 


ILLUMINATION    CALCULATIONS  589 

found  when  the  other  conception  is  employed,  so  that  any  errors 
which  may  be  attributed  to  the  one  conception  must  likewise  be 
urged  against  the  other. 

When  dealing  with  surface  sources  it  is  necessary  to  take  into 
consideration  the  fact  that  not  all  surfaces  obey  the  so-called 
"cosine  law"  of  emission  in  accordance  with  which  a  surface 
would  appear  uniformly  bright  when  viewed  from  all  possible 
locations.  However,  it  is  equally  necessary  to  take  into  con- 
sideration the  fact  that  the  candlepower  from  a  so-called  point 
source  or  the  "apparent  candlepower  per  unit  area"  from  a  sur- 
face source  is  not  uniform  in  all  directions  in  space.  The  fact 
of  the  matter  is  that  all  practical  sources  omit  light  in  such  a 
way  as  to  appear  non-uniform  in  brightness  over  the  surface 
when  viewed  from  any  one  locality,  and  any  one  point  on  the 
surface  apparently  varies  in  brightness  when  viewed  from  differ- 
ent locations  in  space.  It  is  impossible  so  to  express  the  bright- 
ness that  its  value  will  not  be  subjected  to  the  changes  here  re- 
ferred to. 

If  the  surface  were  ideally  perfect  in  its  emission,  its  brightness 
would  be  everywhere  equal  and  uniform,  and  its  apparent  candle- 
power  would  vary  with  the  cosine  of  the  angle  of  deviation  of 
the  surface  from  normal  to  the  line  of  vision ;  that  is  the  surface 
would  obey  Lambert's  "cosine  law  of  emission."  A  surface 
which  is  not  ideally  perfect  in  emission  can  be  compared  directly 
with  one  which  follows  the  cosine  law  of  emission  irrespective 
of  the  units  in  which  the  outputs  or  appearances  are  expressed. 

For  convenience  in  calculation  and  purpose  of  comparison,  it 
is  advantageous  to  express  the  outputs  in  terms  of  the  lumens, 
and  the  output  density  in  terms  of  the  lumens  per  unit  area.  It 
is  equally  as  convenient  and  logical  to  express  the  appearance  in 
terms  of  the  luminous  output  density,  selecting  for  the  unit  the 
appearance  of  a  surface  emitting  in  accordance  with  Lambert's 
cosine  law.  For  this  unit  of  appearance  there  has  happily  been 
suggested  the  term  "lambert,"  which  is  applied  to  the  appearance 
of  a  surface  emitting  one  lumen  per  square  centimeter  in  ac- 
cordance with  Lambert's  cosine  law  of  distribution  and  is  equiva- 
lent in  appearance  to  that  of  a  perfect  matt  surface  of  100  per 
cent,  reflecting  power  illuminated  with  a  density  of  one  lumen 
per  square  centimeter. 


590     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Although  the  introduction  of  the  lambert  brightness  unit  is  of 
recent  date,  it  is  noteworthy  that  its  exact  physical  definition  was 
accurately  presented  before  this  society  eight  years  ago  in  the 
presidential  address  of  Dr.  Sharp,  who  stated  therein  that  "the 
brightness  of  a  diffusely  reflecting  or  transmitting  surface  is 
proportional  to  the  luminous  flux  which  it  emits  per  unit  of  area." 

In  view  of  the  fact  that  the  lambert  unit  is  based  on  the  surface 
source  conception,  this  method  of  expressing  the  brightness  (that 
is,  the  appearance  to  the  eye)  seems  to  me  to  be  fundamentally 
much  more  logical  than  the  more  common  method  involving  a 
reference  to  the  point  source  conception.  It  is  impossible  to 
derive  an  expression  of  brightness  which  does  not  in  some  way — 
either  directly  or  indirectly — involve  the  luminous  output  and 
the  surface  area.  That  is  to  say,  when  the  expression  of  bright- 
ness includes  a  reference  to  the  point  source  conception,  it  is 
evident  at  once  that  there  have  been  assigned  to  each  infinitesimal 
point  source  physical  characteristics  possessed  exclusively  by  a 
surface  source.  Simplicity  in  both  conception  and  mathematical 
analysis  dictate  the  reference  of  all  brightness  expressions  directly 
rather  than  indirectly  to  surface  sources  and  not  to  point  sources. 

Problems  relating  to  both  the  output  and  the  appearance  of 
practical  lighting  sources  are  greatly  simplified  when  use  is  made 
of  the  real  surface  source  conception  rather  than  the  fictitious 
point  source  conception. 

Independent  in  every  respect  of  the  units  employed  in  express- 
ing the  output  and  the  appearance  of  a  surface  source,  it  is  es- 
sential to  recognize  the  fact  that  only  in  the  case  of  emission  in 
accordance  with  Lambert's  cosine  law  is  either  the  output  density 
on  the  appearance  uniform  over  the  surface.  For  simplicity  in 
calculation  it  is  advantageous  to  assign  such  values  to  these 
variables  that  the  calculations  will  give  results  in  practical  accord 
with  the  actual  facts.  The  mean  value  of  the  output  density  can 
evidently  be  found  by  dividing  the  total  output  by  the  total  area 
of  the  emitting  surface ;  this  value  is  identical  with  the  mean 
effective  value  of  the  "appearance"  or  "brightness"  of  the  same 
source. 

For  all  practical  purposes  the  use  of  the  mean  effective  value 
(in  space)  of  the  brightness  introduces  errors  no  greater  than 


ILLUMINATION    CALCULATIONS  591 

those  caused  by  substituting  the  mean  effective  value  (in  time) 
of  an  alternating  current  for  its  cyclically  varying  value.  That  is 
to  say,  problems  in  illumination  from  surface  sources — and  prac- 
tically all  sources  are  surfaces — are  simplified  by  substituting  the 
mean  effective  value  of  the  output  density  and  appearance  for 
the  actual  values  with  their  variations  in  space,  in  exactly  the 
same  manner  and  to  the  same  extent  as  equivalent  problems  in 
alternating  current  phenomena  are  simplified  by  substituting  the 
mean  effective  value  of  the  alternating  current  for  the  actual 
values  with  their  variations  in  time. 

Let  us  carry  the  physical  analogies  somewhat  further.  The 
substitution  of  the  lumen  conception  for  the  candlepower  concep- 
tion has  simplified  illumination  calculations  just  as  the  substitution 
of  the  magnetic  flux  conception  for  the  isolated  magnetic  pole 
conception  has  simplified  magnetic  calculations.  Moreover,  the 
use  of  the  surface  source  conception  rather  than  the  point  source 
conception  permits  of  the  introduction  of  graphical  methods  of 
solving  problems  in  illumination  equally  as  accurate  and  conven- 
ient as  the  simplified  circle  diagrams  now  universally  employed  in 
solving  problems  relating  to  the  general  alternating-current  trans- 
former. 

To  persons  familiar  with  the  time-honored  laborious  calculating 
methods  of  the  electrophysicist  and  with  the  short-cut  but  equally 
accurate  methods  of  the  present-day  electrical  engineer,  no  ar- 
guments need  be  presented  in  favor  of  the  simplified  methods  of 
solving  problems  in  illumination  other  than  the  analogies  just 
outlined. 


592     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

REPORT  OF  COMMITTEE  ON  PRESIDENT'S 
ADDRESS.* 


The  committee  appointed  to  report  on  the  presidential  address 
of  Dr.  A.  S.  McAllister,  on  "Simplification  of  Illumination  Cal- 
culations," has  to  express  its  admiration  for  the  lucid  and  con- 
vincing expression  of  the  views  therein  contained. 

The  underlying  thought  in  the  address  is  that  illumination  cal- 
culations can  be  greatly  simplified  by  discarding  the  usual  method 
of  determining  the  illumination  produced  by  the  source  on  a 
chosen  plane  by  reference  to  the  "inverse  square"  law  and  the 
integrated  "candlepower,"  and  using  the  fundamental  ratio  ex- 
isting between  the  "apparent  luminous  density"  of  the  source 
and  the  lumen  density  on  the  surface  illuminated,  which  ratio 
depends  solely  upon  the  solid  angle  subtended  by  the  source  when 
viewed  from  the  chosen  plane.  The  use  of  the  surface-source 
conception  rather  than  the  point-source  conception  permits  of  the 
introduction  of  simple-graphical  methods  for  solving  problems  in 
illumination. 

The  committee  concurs  with  the  views  expressed  in  the  address 
and  believes  that  the  application  of  the  method  therein  outlined 
will  assist  materially  in  the  simplification  of  illumination  calcu- 
lations. 

Respectfully  submitted, 

C.  H.  Sharp, 

E.  P.  Hyde, 

P.  S.  Mieear, 

L.  B.  Marks,  Chairman. 

*  Presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineering  Society 
Washington,  D.  C,  Sept.  20-23,  1915. 


BENF0RD    AND    MAHAN  :     AVERAGE    ILLUMINATION  593 

A  FLUX  METHOD  OF  OBTAINING  AVERAGE 
ILLUMINATION.* 


BY  F.  A.  BENFORD,  JR.,  AND  H.  E.   MAHAN. 


Synopsis:  This  method  applies  particularly  to  the  calculation  of 
illumination  on  the  floor  or  working  plane  of  a  large  room  or  shop.  The 
basis  of  the  method  is  the  rating  of  lighting  units  by  the  percentages  of 
flux  in  the  three  zones  o°  to  300,  300  to  60°,  and  6o°  to  900.  An  index  in 
the  form  of  an  equilateral  triangle  is  provided.  Given  the  flux  distribution 
of  any  unit  the  index  indicates  a  standard  flux  distribution  of  similar  per- 
centages in  the  three  zones.  A  number  of  these  standard  distributions 
have  been  solved  and  made  up  in  the  form  of  charts.  By  an  inspection 
of  the  proper  chart  the  per  cent,  of  the  downward  flux  that  falls  within 
any  rectangle  is  readily  found.  By  adding  these  percentages  for  the  differ- 
ent units  of  an  installation,  multiplying  by  the  total  downward  flux  of 
one  unit  and  dividing  by  100  times  the  floor  area  the  average  direct 
illumination  is  obtained.  

The  location  of  outlets  and  specifications  for  lighting  equip- 
ment have,  in  the  past,  followed,  in  most  cases,  rather  empirical 
rules.  Those  responsible  for  the  lighting  of  buildings  had  very 
little  knowledge  of  the  fundamental  principles  governing  light- 
ing, and  hence  followed  the  precedents  and  custom  that  had 
grown  up  and  which  were  based  on  architectural  or  structural 
exigencies. 

While  the  authors  do  not  contend  that  structural  conditions 
should  be  ignored,  they  do  feel  that  more  consideration  should  be 
given  to  the  proper  quantity  and  distribution  of  light  than  is 
usually  accorded  them,  and  that  questions  relating  to  these  items 
should  enter  as  factors  in  determining  the  most  advantageous 
position  of  outlets  and  sizes  of  units. 

Feeling  the  need  for  a  more  rational  method  for  checking 
illumination  designs  and  arriving  at  a  reasonably  accurate  esti- 
mate of  the  average  illumination,  the  illuminating  engineering 
laboratory  of  the  General  Electric  Co.  has  adopted  the  plan 
described  in  this  paper. 

The  designer  of  a  lighting  installation  after  studying  the  re- 
quirements of  his  problem  decides  on  a  suitable  type  of  unit  and 
the  required  intensity.  He  is  guided  thus  far  by  consideration 
of  glare,  color,  power  required,  artistic  and  structural  details, 
etc.,   and  arrives  at  a  layout  which   satisfies  these   conditions. 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,    September  20-23,    191 5. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 

6 


594    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Before  passing  on  the  final  plans,  however,  he  wishes  to  check 
his  completed  design  and  determine  whether  or  not  the  required 
quantity  of  flux  is  being  delivered  on  the  working  plane  to  pro- 
vide the  desired  illumination  intensity. 

To  the  best  of  the  authors'  knowledge  there  are  four  methods 
in  use  at  the  present  time  by  which  the  average  illumination  of  a 
lighting  installation  may  be  calculated.  Each  has  some  peculiar 
advantage,  but  none  possess  all  the  qualifications  desired  for 
this  class  of  work.    These  various  methods  are: 

Average  Effective  Angle  Method. — The  light  within  some  fixed 
angle  from  the  axis  of  the  unit  is  assumed  to  be  totally  effective, 
the  remainder  being  wholly  lost.  A  variation  of  this  is  to  con- 
sider a  certain  per  cent,  of  the  light  from  a  given  type  of  unit  to 
be  useful,  and  changing  this  figure  according  as  the  walls  and 
ceiling  are  light,  medium  or  dark  in  color.  Usually  in  using  this 
method  no  account  is  taken  of  the  size  of  the  room,  the  spacing 
of  units  or  the  height  at  which  they  are  hung.  The  basis  of  the 
method  is  the  supposition  that  the  units  will  be  hung  low  in  a  small 
room  and  high  in  a  large  room,  there  being  a  fixed  relation 
between  height  and  area  to  be  illuminated.  But  as  the  services  of 
the  illuminating  engineer  are  often  asked  for  because  of  some 
peculiarity  or  difficulty  in  the  proposed  installation,  it  is  at  once 
evident  that  this  method  is  of  small  use. 

Hogner's  Method. — Starting  with  the  unit  as  a  center,  the 
angular  dimensions  of  the  rooms  are  laid  out.  A  table  of  con- 
stants is  provided  and  by  multiplying  the  constants  by  the  intensi- 
ties of  the  source  at  io°  intervals  until  the  boundaries  of  the 
room  are  reached,  a  figure  for  average  illumination  is  ascertained. 
This  method  contains  the  possibilities  of  a  great  deal  of  develop- 
ment, but  in  the  form  with  which  the  authors  are  familiar  the 
method  is  not  elastic  enough  to  meet  all  the  various  requirements. 
The  labor  involved  is  an  objection  as  is  the  probability  of  error 
in  handling  the  numerous  decimal  constants. 

Illumination  Curve  Method. — The  floor  area  is  covered  with  a 
network  of  illumination  lines.  The  average  illumination  is  found 
by  multiplying  the  illumination  at  a  series  of  points  by  proper 
area  factors,  adding,  and  then  dividing  the  sum  by  the  area  of 
the  room.    Considerable  experience  is  required  to  place  the  illumi- 


BENE0RD  AND   MAHAN  :     AVERAGE   ILLUMINATION  595 

nation  lines  in  the  best  position,  and  a  large  amount  of  labor  is 
required  for  the  various  calculations.  The  results  are  ordinarily 
very  accurate,  and  have  the  great  advantage  of  giving  detailed 
information  about  the  illumination.  If  the  lamps  are  irregular  in 
heights  or  spacing,  the  method  practically  fails  on  account  of  the 
time  taken  for  calculations. 

Lumen  Chart. — A  lumen  chart  devised  and  used  in  this  labora- 
tory gives  a  reasonably  quick  and  very  accurate  answer  to  prob- 
lems in  average  illumination.  The  great  objection  to  this  method 
is  that  the  chart  is  a  highly  specialized  device  and  it  requires  the 
use  of  a  draughting  board. 

In  the  above  review  the  better  methods  are  seen  to  be  either  too 
long  or  too  complicated  and  the  quickest  method  is  inaccurate. 
The  combination  of  quickness  and  accuracy  in  the  same  method 
naturally  presents  difficulties,  but  most  of  these  difficulties  have 
been  overcome  and  a  method  arrived  at  that  is  nearly  as  quick 
and  simple  as  the  first  method,  and  exceeds  all  of  the  above 
methods  except  the  fourth  in  accuracy. 

PRINCIPLES  OF  SOLID  ANGLE  FLUX  CHARTS. 

Several  new  departures  have  been  made  in  the  development 
of  these  charts.  First  among  these  is  the  complete  substitution 
of  lumens  for  candles,  and  second,  a  series  of  prototype  or 
standard  distributions  of  flux  have  been  made  and  substituted 
for  the  actual  flux  distributions  of  the  multitude  of  characteristic 
curves  in  the  laboratory  files.  The  number  of  conditions  that 
had  to  be  considered  and  taken  care  of  were  six  in  number: 
1,  character  of  distribution  of  flux  from  unit;  2,  quantity  of  flux; 
3,  height  of  suspension;  4,  length  of  area  to  be  illuminated; 
5,  width  of  area  to  be  illuminated;  6,  location  of  unit  with  respect 
to  boundaries  of  area. 

These  charts  apply  only  to  symmetrical  units  and  rectangular 
areas.  The  hemispherical  flux  of  the  unit  is  regarded  as  ioo  per 
cent,  divided  into  three  thirty-degree  zones,  o°-30°,  30°-6o°  and 
6o°-90°.  An  equilateral  triangle  is  used  to  index  and  classify 
both  the  photometric  distribution  curves  and  the  solid  angle  flux 
charts.  The  sum  of  the  distances  from  any  point  within  an 
equilateral  triangle  to  the  three  sides  is  a  constant  for  that  tri- 
angle.    Making  this  constant  ioo  per  cent.,  the  length  of  the 


596     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

three  lines  to  the  sides  may  then  represent  the  percentages  of 
flux  in  three  zones,  thus  giving  every  flux  distribution  a  definite 
point  in  the  index  triangle. 

The  triangle  is  divided  into  166  hexagons,  some  of  which  are 
not  complete,  see  Fig.  1,  and  the  central  point  of  each  is  taken 
as  a  "standard"  flux  distribution  and  an  arbitrary  number  as- 
signed it.  The  total  flux  up  to  300,  6o°,  and  900  for  each  stand- 
ard curve  was  plotted  and  a  smooth  curve  drawn  through  these 
points  furnished  the  data  necessary  to  find  the  candle  intensity 


So 
Fig.  1. — Index  triangle.    Solid  angle  flux  charts. 


9 


at  the  various  angles,  as  shown  in  the  upper  left  hand  corner  of 
Fig.  2.  These  distribution  curves  are  not  essential  parts  of  the 
method,  but  are  given  with  each  flux  chart  as  a  supplement  to  the 
index. 

These  standard  flux  curves  were  solved  to  find  the  flux  inci- 
dent upon  various  rectangles  and  the  results  plotted  on  the  charts. 
The  charts  were  then  provided  with  several  scales  of  lengths  and 
widths,  so  that  a  direct  reading  scale  may  be  found  for  almost 
any  lamp  height  and  for  any  size  area. 


BENFORD   AND   MAHAN  I     AVERAGE   ILLUMINATION 


597 


The  section  of  the  index  triangle  in  which  the  common  distri- 
butions fall  is  bounded  roughly  by  lines  drawn  from  hexagon  13 
to  21,   from  21   to   115  and  from   115  back  to   13.     Sixty-one 


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standard  flux  distributions  are  embraced  in  this  area,  and  they 
make  up  the  laboratory  set  of  charts.  Examples  of  three  extreme 
distributions  are  shown  in  Fig.  2,  Fig.  3,  and  Fig.  4. 


598     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

APPLICATION. 

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application  to  an  actual  installation,  such  as  is  described  below. 
The  units  were  arranged  as  shown  in  Fig.  5,  and  their  photo- 
metric characteristics  are  given  in  Fig.  6. 

The  first  step  is  to  determine  the  index  number  of  the  unit. 


BKNFORD   AND   MAHAN  '.     AVERAGE    ILLUMINATION 


599 


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600     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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BENFORD   AND   MAHAN  :     AVERAGE   ILLUMINATION 


601 


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seem  that  the  difference  between  the  two  would  lead  to  large 
errors,  but  such  is  not  the  case.  It  will  be  shown  later  that  the 
error  lies  within  practical  engineering  limits. 

The  room  is  considered  to  be  divided  into  four  quadrants  about 


602     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

each  unit.  Each  unit  is  solved  individually  for  the  entire  reading 
plane  area,  the  quadrants  being  taken  one  at  a  time.  In  Fig.  5 
the  quadrant  below  and  to  the  right  of  the  unit  No.  1  has  a 
width  of  4.25  ft.  (1.3  m.)  and  a  length  of  5.7  ft.  (1.74  m.).  The 
height  of  the  unit  above  the  reading  plane  is  6  ft.  (1.83  m.). 

In  the  lower  right  hand  corner  of  the  chart,  Fig.  7,  is  a  table 
giving  "height  of  lamp  and  scale  constant."  The  large  figures 
are  heights,  and  the  small  letter  and  figure  above  each  indicates 
the  scales  to  be  used  and  the  values  of  the  main  divisions  of  the 
same.  Thus  the  height,  6  ft.,  is  found  in  the  first  column,  second 
line  of  the  tabulation.  The  "a"  indicates  that  the  upper  "length 
of  quadrant"  scale  has  a  value  of  10  ft.  at  the  main  division 
marked  "a,"  and  also  the  left  hand  "width  of  quadrant"  scale 
has  the  same  value  at  the  point  "a."  With  this  information  other 
values  of  width  and  length  are  readily  found. 

TABLE  I. 

Lighting  plan,  Fig.  5. 

Photometric  distribution,  Fig.  6. 

Solid  angle  flux  chart  No.  64,  Fig.  7. 

Quadrant  Per  cent. 

Units  dimensions  Feet  effective  lumens 

No's.  1,  2,  5  and  6  4.25  x    5.70  10.5 

5.70  x  11.25  16.5 

11.25  x  25.10  22.2 

4.25x25.10  14.0 

63.2 

Four  units  4  x  63.2  =  252.8  per  cent. 

No's.  3  and  4  4.25  x  15.40  13.6 

11.25  x  15.40  21.5 

11.25  x  15.40  21.5 

4.25  x  15.40  13.6 

70.2 
Two  units  2  x  70.2  =  140.4  per  cent. 

Total  effective  flux  from  six  units 393-2  per  cent. 

Total  lumens  per  unit 638.0 

Total  effective  lumens 2509.0 

Reading  plane  area  15.5  feet  x  30.8  feet 477-Q  sq.  ft. 

Average  illumination 5.26  foot-candles 

The  flux  in  the  4.25  ft.  x  5.7  ft.  quadrant  may  now  be  found  by 
finding  where  4.25  comes  on  the  width  scale  and  noting  where 
this  point  is  in  relation  to  the  two  nearest  arrow  heads  on  the 
opposite  side  of  the  line.     In  this  particular  case  4.25  ft.  comes 


BENFORD   AND    MAHAN  :     AVERAGE    ILLUMINATION  603 

almost  exactly  midway  between  two  arrow  heads,  and  the  value 
of  effective  flux  will  accordingly  be  found  midway  between  the 
two  curves  immediately  to  the  left  and  directly  above  5.7  ft.  on 
the  scale  of  lengths.  This  value  is  10.5  per  cent.,  read  on  the 
scale  at  the  extreme  left,  and  shows  that  10.5  per  cent,  of  the 
flux  from  unit  No.  1  falls  within  the  quadrant  in  question. 

The  solution  for  the  entire  installation  is  shown  in  Table  I. 
The  same  "a"  scales  are  used  throughout,  and  the  successive  steps 
are  similar  to  the  one  illustrated  above. 

As  a  matter  of  interest  and  to  serve  as  a  check  on  the  calcu- 
lated results,  the  experimental  room  previously  mentioned  was 
equipped  with  six  outlets,  and  each  provided  with  one  100-watt 
clear  tungsten  lamp  and  porcelain,  enamelled  steel  reflector.  The 
general  arrangement  of  outlets  is  indicated  in  Fig.  5.  The  ceil- 
ing consisted  of  press  board;  three  of  the  walls  were  brick,  the 
fourth  wall  and  floor  of  wood.  The  coefficients  of  reflection  of 
the  various  surfaces,  obtained  by  means  of  a  Nutting's  reflec- 
tometer,  were  as  follows  : 

Per  cent. 

Floor 18.7 

Press  board 73-7 

Brick  walls 67.0 

Wood  wall 64.5 

The  room  was  divided  into  fifty  stations  as  shown  on  the  plan 
of  the  room.  Photometric  observations  were  made  at  the  center 
of  each  station  with  a  portable  photometer  and  the  entire  number 
averaged.  In  order  to  eliminate  the  direct  light  of  the  units  from 
the  photometric  screen  as  a  means  of  determining  the  illumina- 
tion due  to  wall  reflection,  diaphragms  were  constructed  consist- 
ing of  blotting  paper  of  approximately  the  same  coefficient  of 
reflection  as  the  room  and  mounted  on  portable  stands.  These 
stands  were  moved  about  for  each  photometric  station  so  as  to 
shield  the  photometer  screen  from  the  direct  light  coming  from 
the  unit.    The  test  results  were  as  follows : 

Foot-candles 

Total  direct  and  reflected  light 7.04 

Reflected  light 1.65 

Direct  light 5-39 

And,  as  a  comparison  with  the  calculated  data  we  have, 

..     .        Calculated  illumination        5.26 

Ratio      — — — r-rrj : — -. = =  0.98 

Actual  illumination  5.39 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 

Vol.  X  NOVEMBER  20,  1915  NO.  8 


CODE  OF  LIGHTING.* 


FACTORIES,  MILLS  AND  OTHER  WORK  PLACES. 


Article  I.  Daylight. — All  buildings  hereafter  constructed  must 
be  provided  with  adequate  window  area.  Awnings,  window 
shades,  diffusive  or  refractive  glasses  must  be  used  for  the  pur- 
pose of  improving  daylight  conditions  or  for  the  avoidance  of 
excessive  brilliancy  wherever  they  are  essential  to  these  ends. 

The  windows,  skylights,  saw-tooth  or  other  roof  lighting  con- 
structions, are  to  be  arranged  with  reasonably  uniform  bays,  and 
the  daylight  openings  shall  be  so  designed  and  proportioned  that 
at  the  darkest  part  of  any  work  space,  when  normal  exterior  day- 
light conditions  obtain,  there  shall  be  available  at  least  a  minimum 
intensity  equal  to  three  times  the  minimum  intensities  given  in 
Article  V  for  artificial  light. 

(Note:  The  intensity  requirements  for  daylight  are  higher 
than  those  for  artificial  light  because  the  physical  condition  of 
the  eye  during  the  daytime  is  usually  such  as  to  require  a  higher 
intensity  of  natural  light  for  satisfactory  vision  than  is  required 
at  night  under  ordinary  well  designed  artificial  lighting  systems.1) 

Article  II.  Old  buildings  at  present  constructed  and  not  having 
adequate  window  area,  must  be  provided  with  adequate  artificial 
light  according  to  the  following  articles,  so  as  to  supplement  the 
natural  light  during  normal  daylight  hours. 

*  For  an  amplification  of  the  following  articles  of  the  code  proper,  see  the  Explanatory 
Rules  on  page  608. 

1  For  detailed  information  on  this  daylight  requirement,  see  Section  I  of  the  Ex- 
planatory Notes  on  page  609. 


606     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Article  III.  All  buildings,  whether  old  or  hereafter  constructed, 
must  be  provided  during  those  hours  of  work  when  natural  light 
is  insufficient  or  not  available,  with  adequate  artificial  light  ac- 
cording to  the  following  articles. 

Article  IV. — Adequate  intensity  of  the  light  must  be  provided 
for  each  class  of  work,  both  on  a  horizontal  plane  as  well  as  on  a 
vertical  plane  passing  through  the  work,  according  to  Article  V. 
In  all  cases,  however,  glare  on  working  surfaces  is  to  be  avoided 
as  it  tends  to  reduce  the  visual  efficiency  of  the  workmen  and  to 
increase  the  likelihood  of  accidents. 

Article  V.  Artificial  Light;  Intensity  Required. — The  average 
illumination  intensity  throughout  any  month  actually  measurable 
in  foot-candles  on  a  horizontal  plane  through  the  work  is  to  con- 
form to  the  following  table.  Uncertain  cases  which  arise  as  to 
how  to  classify  given  manufacturing  operations  are  to  be  left  tc 
the  judgment  of  a  lighting  expert. 

Class  of  work 

Storage,  passageways,  stairways,  and  the  like 
Rough  manufacturing  and  other  operations . . 
Fine  manufacturing  and  other  operations .... 
Special  cases  of  fine  work 

Where  operations  are  performed  on  the  sides  of  the  work  in 
hand,  they  shall  be  classified  according  to  this  table,  and  if  the 
illumination  is  furnished  from  an  overhead  system,  it  shall  pre- 
ferably be  not  less  than  50  per  cent,  of  the  foregoing  values,  when 
measured  on  a  vertical  surface.  If  the  illumination  is  furnished 
by  an  individual  lamp  or  by  lamps  close  to  the  work,  the  intensity 
shall  conform  to  the  minimum  or  desirable  intensities  required 
in  the  foregoing  table. 

(Note:  As  a  guide  to  inspectors  and  others,  it  may  be  stated 
that  with  modern  lamps  roughly  1  candlepower  per  square  foot 
produces  an  effective  illumination  of  3  foot-candles  when  the 
lamps  are  arranged  according  to  the  uniformly  distributed  over- 
head system,  with  mounting  heights  ranging  from  12  to  16  ft. 
above  the  floor,  and  when  the  light  is  directed  from  said  lamps 
to  the  work  in  an  efficient  manner.  A  rough  idea  may  thus  be 
secured  of  the  candlepower  per  square  foot  necessary  to  conform 


Minimum 

foot-candles 

intensity 

Desirable 

foot-candle 

intensity 

0.25 

0.25-  0.5 

1-25 

1.25-  2.5 

3-50 

3-5  -  6.0 

— 

10.0  -15.0 

CODE   OF   LIGHTING  607 

to  the  foregoing  table  of  intensities  by  taking  one  third  of  the 
intensity  values  given  in  the  foregoing  table.) 

Thus  for  fine  manufacturing  and  other  operations,  the  min- 
imum foot-candle  intensity  is  3.5,  which  is  approximately  equal  to 
1.2  candlepower  per  square  foot.  The  use  of  a  portable  photo- 
meter or  illuminometer,  however,  is  recommended  for  the  de- 
termination of  existing  systems  and  all  uncertain  cases  are  finally 
to  be  established  by  these  instruments. 

Article  VI.  Lamps  and  machinery  jointly,  are  to  be  so  arranged 
as  to  avoid  the  casting  of  shadows  over  belts  and  other  obstruc- 
tions on  important  parts  of  the  work,  and  the  distribution  of  light 
from  the  lamps  should  be  such  as  to  avoid  sharp  contrasts  of  light 
and  shade  on  the  work. 

Article  VLT.  Inspection  and  regular  maintenance  of  all  lighting 
systems  is  required  in  spaces  where  work  is  being  conducted,  and 
in  no  case  must  the  lighting  devices,  whether  windows,  lamps 
or  auxiliaries  such  as  globes  and  reflectors,  be  allowed  to  deter- 
iorate, due  either  to  dirt  accumulations  or  to  burned-out  lamps, 
more  than  20  per  cent,  below  the  minimum  intensity  values 
required  by  Article  V. 

Article  VLII.  Roadways,  yards  and  places  not  usually  fre- 
quented must  either  be  provided  by  illumination  during  working 
hours  when  natural  light  is  absent  or  partly  absent,  to  make  them 
safe  against  accident  to  employees  traversing  or  engaged  in  such 
places,  or  a  convenient  control  or  controls  must  be  placed  at  the 
entrance  to  basements,  stock  rooms,  and  the  like,  so  that  a  person 
on  entering  can  readily  turn  on  the  lamps  beforehand. 

Article  IX.  Stairways  and  passageways  must  be  provided  with 
lamps  and  reflectors  or  shades  carefully  located  so  as  to  shed  their 
light  generally  over  the  entire  space  or  spaces  involved,  and  in 
sufficient  quantity  to  make  the  stairways  and  passages  safe  against 
accident  to  employees  traversing  or  engaged  in  such  places.  For 
intensities  see  Article  V. 

Article  X.  Each  working  space  is  preferably  to  be  illuminated 
by  lamps  mounted  overhead  according  to  the  system  of  general 
lighting,  in  preference  to  individual  lighting.  The  overhead 
method  of  lighting,  besides  possessing  many  other  advantages, 
also  tends  to  reduce  dark  spots  throughout  the  floor  area,  a 


608     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

feature  usually  objectionable  with  the  use  of  individual  lamps. 
This  particular  Article  is  not  an  absolute  requirement,  but  a  sug- 
gestion enforceable  at  the  discretion  of  a  lighting  expert. 

Article  XI.  Auxiliary  lighting  should  be  provided  in  all  large 
work  spaces,  such  lamps  to  be  in  operation  simultaneously  with 
the  regular  lighting  system,  so  as  to  be  available  in  case  the  latter 
should  become  temporarily  deranged.2 


EXPLANATORY  RULES. 

The  foregoing  articles  are  supplemented  by  the  following 
rules,  which  will  aid  in  the  observance  of  the  requirements  con- 
tained in  the  articles;  tend  to  reduce  eye  trouble  and  accidents; 
and  help  in  the  securing  of  favorable  results  in  planning  lighting 
systems. 

1.  Lamps  should  be  equipped  with  reflectors  or  shades  for 
minimizing  glare  and  economizing  light.  Bare  lamps  should  not 
be  used  except  in  rare  cases  and  then  only  when  out  of  the  line  of 
vision. 

2.  As  a  general  plan,  mount  the  lamps  high  and  out  of  the 
ordinary  line  of  vision. 

3.  Although  the  types  of  reflectors  and  shades,  and  reflector 
and  shade  holders  or  fitters  on  the  market  are  numerous,  it  is 
recommended  that  the  holder  or  fitter,  as  well  as  the  reflector  or 
shade  be  selected  with  reference  to  placing  the  light  source  at  the 
proper  point  in  the  reflector  or  shade  so  as  to  eliminate  glare,  due 
to  exposure  of  the  light  source,  and  also  for  the  purpose  of  di- 
recting the  light  from  the  lamp  effectively  to  the  work,  that  is, 
for  obtaining  a  distribtuion  of  light  which  meets  the  desired  re- 
quirements. 

4.  Light  thrown  vertically  downward  is  not  the  only  important 
component  of  the  resulting  illumination.  The  sides  of  machinery, 
machine  tools  and  work,  as  well  as  horizontal  surfaces  often  re- 
quire good  light. 

5.  Control  few  lamps  in  each  group  so  that  lamps  not  needed 
may  be  turned  off  conveniently. 

6.  Keep  windows,  lamps  and  reflectors  clean  since  large  losses 
of  light  result  from  the  accumulations  of  dust  and  dirt. 

2  See  Auxiliary  Systems  for  Safety,  Section  XVI  of  the  Explanatory  Notes  on  page  640. 


CODE   OF  UGHTIXG  609 

7.  Provide  a  maintenance  department  if  the  shop  is  large 
enough  to  warrant  it,  so  that  all  the  items  associated  with  the 
upkeep  of  the  lighting  system  may  be  cared  for  systematically. 

8.  Keep  ceilings  and  upper  portions  of  walls  a  light  color  for 
the  purpose  of  rendering  both  natural  and  artificial  lighting  more 
efficient  and  better  diffused.  The  lower  portions  of  walls  should 
be  a  color  which  is  restful  to  the  eyes,  preferably  a  medium  tint, 
typified  by  the  tint  known  as  factory  green,  or  a  rather  dark 
shade  of  yellow.    Other  medium  tones  are  also  available. 

EXPLANATORY  NOTES. 

Section  I.  Daylight. — Adequate  daylight  facilities  through 
large  window  areas  together  with  light  cheerful  surroundings, 
are  highly  desirable  and  necessary  features  in  every  work  place, 
and  they  should  be  supplied  through  the  necessary  channels  not 
only  from  the  humane  standpoint,  but  also  from  the  point  of  view 
of  maximum  plant  efficiency. 

Importance  of  Daylight. — The  unusual  attention  to  gas  and 
electric  lighting  in  factories,  mills  and  other  work  places  during 
the  past  few  years ;  the  perfection  of  various  lamps  and  auxiliaries 
by  means  of  which  an  improved  quality  and  quantity  of  lighting 
effects  are  obtained ;  and  the  care  which  has  been  devoted  to  in- 
creasing the  efficiency  in  various  industrial  operations ; — all  go  to 
emphasize  the  many  advantages  and  economies  that  result  from 
suitable  and  adequate  window  space  as  a  means  for  daylight  in 
the  proper  quantities  and  in  the  right  directions  during  those  por- 
tions of  the  day  when  it  is  available. 

Three  Considerations. — Three  important  considerations  of  any 
lighting  method  are  sufficiency,  continuity  and  diffusion.  With 
respect  to  the  daylight  illumination  of  interiors,  sufficiency 
demands  adequate  window  area;  continuity  requires  (a)  large 
enough  window  area  for  use  on  reasonably  dark  days,  (b)  means 
for  reducing  the  illumination  when  excessive  due  to  direct  sun- 
shine, and  (c)  supplementary  lighting  equipment  for  use  on  par- 
ticularly dark  days  and  especially  towards  the  close  of  winter 
days;  diffusion  demands  interior  decorations  that  are  as  light  in 
color  as  practicable  for  ceilings  and  upper  portions  of  walls,  and 
of  a  dull  or  mat  finish  in  order  that  the  light  which  enters  the 
windows  or  that  which  is  produced  by  lamps  may  not  be  absorbed 


6lO    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

and  lost  on  the  first  object  that  it  strikes,  but  that  it  may  be 
returned  by  reflection  and  thus  be  used  over  and  over  again. 
Diffusion  also  requires  that  the  various  sources  of  light,  whether 
windows,  skylights  or  lamps,  be  well  distributed  about  the  space 
to  be  lighted.  Light  colored  surroundings  as  here  suggested  result 
in  marked  economy,  but  their  main  object  is  perhaps  not  so  much 
economy  as  to  obtain  a  result  that  will  be  satisfactory  to  the 
human  eye. 

Requirements. — The  following  requirements  may  now  be  listed 
for  natural  lighting: 

i.  The  light  should  be  adequate  for  each  employee. 

2.  The  windows  should  be  so  spaced  and  located  that  daylight 
conditions  are  fairly  uniform  over  the  working  area. 

3.  The  intensities  of  daylight  should  be  such  that  artificial  light 
will  be  required  only  during  those  portions  of  the  day  when  it 
would  naturally  be  considered  necessary. 

4.  The  windows  should  provide  a  quality  of  daylight  which  will 
avoid  a  glare  due  to  the  sun's  rays  and  light  from  the  sky  shining 
directly  into  the  eye,  or  where  this  does  not  prove  to  be  the  case 
at  all  parts  of  the  day,  window  shades  or  other  means  should 
be  available  to  make  this  end  possible. 

5.  Ceilings  and  upper  portions  of  walls  should  be  maintained 
a  light  color  to  increase  the  effectiveness  of  the  lighting  facilities 
from  window  areas.  The  lower  portions  of  walls  should  be 
somewhat  darker  in  tone  to  render  the  lighting  restful  for  the 
eye.  Factory  green  or  other  medium  colors  may  be  used  to  good 
effect. 

Classification. — Means  for  natural  lighting  may  be  classed 
under  three  broad  divisions  as  follows : 

(a)  That  case  in  which  the  windows  are  located  on  the  sides 
of  the  building  or  in  the  framework  of  saw-tooth  construction, 
where  diffused  light  from  the  sky  reaches  the  work  during  a  large 
portion  of  the  day. 

(b)  That  case  in  which  windows  are  located  overhead  on  a 
horizontal  or  nearly  horizontal  plane  in  the  form  of  skylights, 
thus  furnishing  direct  light  from  the  sky  during  a  large  portion 
of  the  day. 


CODE   OF   LIGHTING 


6ll 


(c)  That  case  in  which  prismatic  glass  takes  up  the  direct  light 
from  the  sky  and  redirects  it  into  the  working  space. 

Method  (a)  is,  of  course,  the  most  common  of  the  three,  and 
it  may  be  noted  that  the  saw-tooth  or  other  roof  lighting  con- 
structions have  become  very  popular  and  result  in  an  excellent 
quality  and  quantity  of  light  for  given  window  areas  provided 
the  size  and  location  of  windows  are  in  accord  with  modern 
practise. 

Increasing  the  Value  of  Floor  Space. — Adequate  and  well  dis- 


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PARITIVE  ABSENCE  AnFOIIATF  DAYLISKT'        ' 

OF  DAYLIGHT.  ARTI"  ^UtUUAI  L  UATUyw,         f 

FICIAL0AYLI6HT  -'  ,.'    •         / 

REQUIRED  NEARLY  _,,"       .-'  I 

ALL  DA.Y  ,"    j  1 t~'VA< 


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ELEVATION 


OiO  0  0 
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PLAN 

Fig.  i. — Diagram,  of  a  large  office  with  windows  on  one  side  only. 

tributed  natural  light  means  that  certain  portions  of  the  floor 
space  which  ordinarily  would  not  be  available  for  work,  are  con- 
verted into  valuable  manufacturing  space.  In  a  general  way, 
therefore,  the  average  factory,  mill  or  other  work  place,  if  prop- 
erly designed,  should  possess  natural  lighting  facilities  which 
produce  the  best  practicable  distribution  of  daylight  illumination. 
Wide  Aisles. — With  low  ceilings  and  very  wide  aisles,  work- 
men located  at  the  central  portion  of  the  building  must  sometimes 
depend  for  their  natural  light  on  windows  located  at  a  consider- 
able distance  away  from  their  working  position.     In  these  cases 


6l2     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

it  may  be  impossible,  in  general,  to  depend  altogether  on  daylight 
over  an  entire  floor  space,  even  at  those  times  of  the  day  when 
daylight  conditions  would  be  entirely  adequate  under  other  cir- 
cumstances. This  statement  applies  to  side  windows  rather  than 
to  skylights  or  to  saw-tooth  construction.  Fig.  I  illustrates  this 
feature. 

Varying  Conditions. — In  a  case  of  this  kind,  employees  located 
next  to  the  windows  are  furnished  with  suitable  daylight  in  the 
early  morning  and  towards  the  latter  part  of  the  afternoon,  the 
upper  portions  of  the  windows  being  particularly  serviceable  in 
lighting  areas  at  some  distance  away  from  the  windows.  A 
southern  exposure,  however,  results  in  such  excessive  light  from 
the  sky  during  the  middle  of  the  day,  that  heavy  shades  are 
nearly  always  pulled  down  so  as  to  cover  the  entire  window  area. 
This  plan  makes  it  necessary  to  use  artificial  light  throughout  the 
larger  part  of  the  office  during  the  brightest  portion  of  the  day, 
and  reduces  the  daylight  at  those  points  where  it  would  supposedly 
be  the  best,  namely,  near  the  windows.  Here  the  location  of 
the  windows  is  a  large  factor  in  the  excellence  of  the  daylight 
conditions,  but  the  manipulation  of  the  shades  is  perhaps  even 
more  important.  To  avoid  such  a  difficulty,  adjustable  translu- 
cent upper  window  shades  with  adjustable  opaque  lower  shades 
might  be  employed. 

Upper  Portions  of  Windows. — It  should  be  further  noted  in 
this  illustration  that  the  upper  portions  of  the  windows  give  a 
reduced  illumination  in  proportion  to  their  areas,  to  the  floor 
space  near  them.  In  rooms  of  moderate  size,  therefore,  the 
windows  should  be  placed  as  near  the  ceiling  as  practicable. 
When  the  sun  shines  through  windows  so  located,  the  direct  light 
must  be  reduced  or  diffused.  This  may  be  accomplished  by  the 
use  of  ribbed  glass  in  ordinary  factory  and  mill  buildings,  and 
in  offices  by  the  use  of  translucent  sun  shades  or  awnings. 

Tempering  the  Light. — The  light  due  to  the  sunshine  on  such 
shades  and  awnings  will  be  as  bright  as  ordinary  skylight  if  the 
shade  is  well  chosen,  and  the  ribbed  glass  will  be  still  brighter. 
If  the  windows  are  large,  the  illumination  is  likely  to  be  too  great 
near  the  windows  as  previously  pointed  out  and  it  must  be  re- 
duced-    This  should  not  be  done,  however,  by  pulling  down  an 


CODE   OF   LIGHTING 


613 


opaque  shade  over  the  top  of  the  windows  because  the  top  por- 
tion of  the  window  is  the  part  that  is  particularly  needed  to  give 
light  to  the  interior  of  the  room.  The  better  scheme  is  to  employ 
an  opaque  shade  which  should  be  raised  from  the  bottom  of  the 
window.  This  will  reduce  the  illumination  near  the  window 
without  affecting  it  over  the  interior  of  the  room  to  any  marked 
degree. 

Bench  Locations. — Fig.  2  shows  how  benches  are  commonly 
located  with  respect  to  windows,  so  that  the  light  received  on  the 
work  may  be  most  satisfactory.  This  sets  a  certain  limitation 
upon  the  possible  arrangement  of  the  work  over  the  floor  space, 
depending  on  the  way  the  daylight  is  furnished  to  the  floor  area. 


/////////^/////^////////////////////////////////I 


///////////. 


/////); •/$/  ////;//;///)///; '/// V/////////A 


PLAN 

Fig.  2. — Diagram  showing  benches  located  with  respect  to  the  windows  so  as  to  receive 

the  natural  light  advantageously. 

This  limitation  can  be  eliminated  almost  completely  in  the  case 
of  artificial  light  through  a  uniform  distribution  of  lamps  over- 
head. This  statement  applies  to  those  cases  where  natural  light 
is  transmitted  through  side  windows,  and  includes  a  feature 
specially  noticeable  in  buildings  of  more  than  one  story.  In  con- 
trast, the  work  may  be  arranged  almost  independently  of  the 
natural  light  in  buildings  where  the  natural  light  is  furnished 
by  overhead  windows  or  through  the  means  of  saw-tooth 
construction. 

Windoiv  Glasses. — Both  translucent  and  clear  glass  are  em- 
ployed for  factory  and  mill  windows.  There  is  a  slight  reduction 
in  the  transmitted  light  through  ordinary  translucent  wire  glass, 


614     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

but  it  is  often  required  by  insurance  regulations  for  a  reduction 
in  the  fire  risk  where  a  given  building  is  located  in  close  proximity 
to  other  buildings.  Wire  glass  is  also  used  quite  generally  with 
steel  window  frames,  here  being  an  added  protection  from  the 
standpoint  of  fire  risk.  Wire  glass  may  be  obtained  in  clear 
form,  but  its  expense  in  contrast  to  the  translucent  form  is  such 
as  ordinarily  to  prohibit  its  use  for  industrial  purposes. 

Wire  Glass. — Wire  glass,  also  known  as  ribbed  glass,  should 
be  used  and  is  advocated  for  practically  all  factory  and  mill  win- 
dows where  prisms  are  not  required.  Wires  of  rather  open 
mesh  cause  so  little  reduction  in  light  as  to  warrant  no  mention 
of  this  feature.  Special  care  should  be  taken  to  get  such  glass 
as  is  smooth  both  on  the  flat  side  and  on  the  ribbed  side  to  facili- 
tate cleaning.  Wire  or  ribbed  glass  gives  better  diffusion  than 
plain  glass. 

Prism  Glass. — Where  the  sky  outside  of  the  windows  is  ob- 
structed by  buildings,  prism  glass  is  recommended  if  the  room  is 
deep.  Different  kinds  of  prisms  cannot  be  used  to  advantage 
interchangeably.  The  amount  of  prism  glass  required  in  any 
case  depends  much  upon  the  surroundings  and  to  obtain  excel- 
lent results,  of  which  such  glass  is  capable,  it  must  be  used 
intelligently. 

Skylights. — Skylights  are  sometimes  installed  in  long  narrow 
continuous  strips  in  a  sloping  roof.  The  ribs  of  the  ribbed  glass 
are  generally  so  arranged  that  it  is  convenient  to  make  them  at 
right  angles  to  the  length  of  the  strips.  The  result  is  that  the 
sunshine  is  diffused  by  the  ribs  over  a  narrow  area  parallel  to 
the  strip  of  skylight,  thus  lighting  one  part  of  the  room  much 
more  brilliantly  than  the  remainder.  If  the  ribs  are  installed  to 
run  parallel  to  the  strips,  they  will  give  a  much  more  general  dis- 
tribution of  the  sunlight.  In  the  foregoing,  the  word  strip  refers 
to  the  long  belt  of  skylight  and  not  to  the  individual  sheet  of 
glass.  Ribbed  glass  in  vertical  windows  should  generally  be 
placed  with  the  ribs  horizontal.  They  thus  roughly  fulfill  some 
of  the  functions  of  prisms. 

Dirt  Accumulations. — While  translucent  wire  or  ribbed  glass 
reduces  the  amount  of  light  transmitted  through  the  windows, 
the  roughness  of  the  outside  surface  of  such  glass  often  causes 


CODE   OF   LIGHTING  615 

accumulations  of  dust  and  dirt,  which  are  more  to  blame  for  the 
reduction  of  transmitted  light  in  some  cases  than  the  translucent 
nature  of  the  glass  itself.  Remedies  of  this  difficulty  are  to 
secure  smooth  glass  and  to  restort  to  frequent  cleaning. 

Wire  Glass  as  a  Safeguard. — Wire  glass  for  skylights  is,  of 
course  a  practical  necessity  as  a  safeguard  against  accidents  due 
to  accidental  breakage  of  the  glass  or  due  to  objects  falling  on 
top  of  the  glass. 

Calculations  for  Natural  Light. — In  certain  typical  localities, 
the  average  brightness  of  the  sky  during  business  hours  is  about 
250  candles  per  square  foot.  This  is  probably  a  fair  average 
value  for  the  entire  United  States.  The  lower  or  minimum  value 
of  sky  brightness,  excluding  particularly  stormy  days,  may  be 
taken  as  about  100  candles  per  square  foot.  Allowing  for  a 
reduction  of  25  per  cent,  for  losses  in  the  windows  themselves, 
the  brightness  of  the  sky  as  seen  through  a  window  becomes 
equal  to  a  minimum  of  say  75  candles  per  square  foot  in  any 
directions  from  which  the  sky  can  be  seen  through  the  windows. 
This  brightness  value  if  multiplied  by  the  part  of  the  window 
area  through  which  sky  is  visible  from  a  given  point  in  the  work 
space  gives  the  available  candlepower  through  the  window  in 
question,  and  this  candlepower  is  then  divided  by  the  square  of 
the  distance  between  the  given  point  and  the  window  to  obtain 
the  foot-candle  intensity  of  the  illumination  at  the  given  point. 

Method  illustrated. — To  illustrate  this  method,  consider  a  hall- 
way 40  ft.  long,  lighted  by  a  window  5  ft.  by  5  ft.  at  one  end, 
with  the  sky  visible  from  the  darker  end  of  the  hall  through  the 
upper  half  of  the  window  only.  The  illumination  at  the  dark 
end  of  the  hall  will  then  be  equal  to : 

5  X  5  X  0.5  X  -~-  =  0.58  foot-candles, 
1,600 

under  the  assumed  window  brightness  of  75  candles  per  square 
foot.  The  1,600  in  this  calculation  results  from  the  square  of 
40  ft.,  the  length  of  the  hall,  or  in  other  words  the  distance  from 
the  point  considered  to  the  window ;  and  the  factor  0.5  takes  into 
account  the  fact  that  the  sky  is  visible  through  only  one  half  of 
the  window  area  from  the  point  considered. 

Checking  the  Intetisity. — The  intensity  is  not  sufficient  at  this 


6l6     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

darkest  part  of  the  hall  since  the  requirements  of  Article  I  of 

the  Code  proper  call  for  three  times  the  minimum  values  given 

in  Article  V,  and  the  minimum  value  given  in  Article  V  for 

passageways  is  0.25.     Three  times  this  value  is  0.75  which  is 

somewhat  greater  than  the  value  found  in  this  calculation.     The 

window  area  must  therefore  be  increased  in  size  by  about  50 

per  cent.,  or  if  this  is  impossible  or  impracticable,  the  hallway 

must  be  provided  with  artificial  light  at  those  points  where  the 

natural  light  falls  below  the  requirement. 

Calculation  for  a  Skylight. — As  another  illustration,  assume 

that  fine  manufacturing  work  is  to  be  performed  under  a  skylight 

20  ft.  above  the  work.     If  the  brightness  is  assumed  to  be  75 

candles  per  square  foot  as  before,  the  minimum  intensity  must 

be  3  X  3-5  foot-candles,  that  is,  10.5  foot-candles,  based  on  the 

requirements  of  Article  I  of  the  Code.     The  window  area  must 

then  equal : 

400 
10.5  X  — -  =  56  sq.  ft. 

Part  of  Window  Area  to  Consider. — It  is  important  in  esti- 
mating the  illumination  of  any  work  room  to  consider  only  that 
portion  of  the  window  area  through  which  clear  sky  is  visible, 
provided  the  window  is  equipped  with  ordinary  clear  glass. 

Sunshine  Not  Desirable. — In  all  the  work  of  providing  natural 
light,  it  should  be  kept  in  mind  that  direct  sunshine  in  itself,  from 
the  illumination  standpoint  but  irrespective  of  sanitary  condi- 
tions, is  not  wanted.  The  idea  that  sunshine  is  the  important 
item  is  a  common  but  an  erroneous  impression.  For  example, 
in  saw-tooth  construction,  the  windows  do  not  face  the  south  to 
get  all  the  sunshine  possible,  but  they  face  the  north  to  exclude 
the  sunshine.  Ordinary  windows,  on  the  other  hand,  face  all 
directions  because  not  enough  light  can  be  distributed  to  interiors 
from  north  windows  alone.  Windows  on  the  other  than  north 
fronts  admit  sunshine  to  be  sure,  and  this  makes  sun  shades  and 
awnings  necessary  to  exclude  the  excessive  brightness. 

Section  II.  Value  of  Adequate  Illumination. — Factory  and  mill 
owners  are  concerned  in  the  matter  of  securing  the  largest  output 
for  a  given  manufacturing  expense.  An  improved  machine  tool 
capable  of  increasing  the  product  for  given  labor  costs  is  most 


CODE   OF   LIGHTING  617 

attractive,  provided  its  first  cost  is  within  returnable  limits  out  of 
the  larger  profits.  Improved  small  tools,  better  methods  of  hand- 
ling material,  adequate  crane  service,  fire  protection,  good  shop 
floors,  accurate  and  efficient  time-keeping  methods,  and  similar 
items,  vitally  concern  the  shop  manager;  money  is  expended  to 
realize  excellence  in  these  features  because  they  afford  increased 
economies  and  protection,  thus  resulting  in  a  higher  efficiency  of 
the  plant. 

Energy  Consumption  a  Minor  Item. — Many  arguments  leading 
to  the  sale  of  gas  and  electric  lamps  for  use  in  factory  and  mill 
buildings  are  based  on  reducing  the  lamp  operation  cost  by  sub- 
stituting a  new  for  an  older  system.  Arguments  of  this  kind  are 
of  value,  however,  only  when  such  a  reduction  in  operation  cost 
can  be  effected  without  sacrifice  in  the  adequacy  of  the  illumin- 
ation. It  would  be  a  poor  policy,  in  the  extreme,  to  argue  a  sav- 
ing in  energy  consumption  by  the  substitution  of  one  type  of 
lamp  for  another  on  a  basis  of  equal  candlepower  in  both  old  and 
new  systems. 

Effect  of  Good  Light  on  Production. — Arguments  of  a  con- 
vincing nature,  which  insure  to  the  factory  or  mill  manager  an 
increased  output  through  improved  illumination  service,  are  of 
importance  and  even  greater  at  times  than  reductions  in  the 
cost  of  illumination  for  the  same  quantities  of  light.  In  view  of 
the  fact  that  resulting  advantages  of  superior  illumination  on 
increased  output  are  apt  greatly  to  exceed  economies  in  operation 
cost  as  regards  the  lighting  system,  it  is  a  distinct  advantage  to 
direct  and  hold  the  attention  on  the  former  rather  than  on  the 
latter.  This  statement  will  be  more  apparent  when  interpreted 
into  definite  items  as  follows : 

Advantages  of  Good  Light. — While  the  necessity  of  good  nat- 
ural and  artificial  light  is  so  evident  that  a  list  of  its  effects  may 
seem  commonplace,  these  same  effects  are  of  such  great  im- 
portance in  their  relation  to  factory  and  mill  management,  that 
they  are  well  worth  careful  attention.  The  effects  of  good  light, 
both  natural  and  artificial,  and  of  bright  and  cheerful  interior 
surroundings,  include  the  following  items: 

1.  Reduction  of  accidents. 

2.  Greater  accuracy  in  workmanship. 


6l8     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

3.  Increased  production  for  the  same  labor  cost. 

4.  Less  eye  strain. 

5.  Promote  better  working  and  living  conditions. 

6.  Greater  contentment  of  the  workmen. 

7.  More  order  and  neatness  in  the  plant. 

8.  Supervision  of  the  men  made  easier. 

In  this  list  it  will  be  noted  that  items  4,  5,  6,  7  and  8  all  have  a 
bearing  on  accident  prevention. 

Interpreting  the  Advantages  of  Good  Light. — While  the  major 
consideration  in  the  eyes  of  the  factory  or  mill  owner  is  un- 
doubtedly and  quite  naturally  the  money  value  of  good  light  in 
the  larger  return  of  both  quantity  and  quality  of  work  which  may 
result  from  the  installation  of  a  superior  as  compared  with  an  in- 
ferior lighting  system,  it  should  be  noted  that  it  is  very  difficult 
to  interpret  into  dollars  and  cents  the  value  of  good  light  made 
possible  by  such  returns.  This  difficulty  is  due  to  the  necessity 
of  keeping  all  conditions  in  a  factory  or  mill  section  absolutely 
constant  while  varying  the  amount  of  illumination  from  poor  to 
good  conditions,  in  an  effort  to  determine  the  output  and  its  de- 
pendency on  the  lighting  facilities.  As  accurate  data  becomes 
available,  giving  the  increases  in  production  for  certain  specific 
improvements  in  artificial  lighting,  it  will  doubtless  prove  helpful 
to  a  proper  interpretation  of  adequate  light  and  its  worth  to  any 
plant. 

The  eight  foregoing  points  are  emphasized  as  forming  the 
most  important  features  in  the  problem  of  good  lighting.  Al- 
though difficult  to  interpret  into  money  values,  and  somewhat  in- 
tangible, they  are  indisputable  arguments  in  favor  of  the  best 
available  illumination  from  the  standpoint  of  the  factory  or  mill 
owner. 

Practical  Example. — Continuing  from  the  manufacturer's  point 
of  view,  it  may  be  said  that  certain  assumptions  as  to  energy  cost, 
cleaning,  interest  and  depreciation,  show  that  the  annual  opera- 
tion and  maintenance  cost  for  the  illumination  of  a  typical  shop 
bay  of  640  sq.  ft.  area,  may  be  taken  at  $50.00.  If  five  workmen 
are  employed  in  such  a  bay  at  an  average  wage  of  say  25  cents 
per  hour,  the  gross  wages  of  the  men  in  such  a  bay,  plus  the  cost 
of  superintendence  and  indirect  shop  expense,  may  equal  from 


CODE   OF   LIGHTING  619 

$5,000,  to  $7,000  per  annum.  In  a  case  of  this  kind,  therefore, 
the  lighting  will  cost  from  7/10  to  1  per  cent,  of  the  wages,  or  the 
equivalent  of  less  than  4  to  6  minutes  per  day.  We  may  roughly 
say  that  a  poor  lighting  system  will  cost  at  least  one  half  this 
amount  (sometimes  even  more  through  the  use  of  inefficient 
lamps  and  a  poor  arrangement  of  lamps),  or  the  equivalent  of 
say  2  to  3  minutes  per  day.  Nearly  all  factories  and  mills  have  at 
least  some  artificial  light,  hence,  in  general,  if  good  light  enables 
a  man  to  do  better  or  more  work  to  the  extent  of  from  2  to  3  min- 
utes per  day,  the  installation  of  good  lighting  will  easily  pay  for 
the  difference  between  good  and  bad  light,  through  the  time  saved 
for  the  workmen. 

Actual  Losses. — Superintendents  have  stated  in  actual  instances, 
that  due  to  poor  light  their  workmen  have  lost  much  time,  some- 
times as  much  as  from  one  to  two  hours  per  day  or  certain  days. 
If  good  light  will  add  an  average  of  say  one-half  an  hour  per  day 
to  the  output,  these  30  additional  effective  minutes  represent  an 
increase  in  output  of  5  per  cent.,  brought  about  through  an  ex- 
penditure equal  to  l/>  oi  1  per  cent,  of  the  wages  for  improved 
lighting,  or  a  saving  equal  to  ten  times  the  expense. 

Safety. — While  these  features  are  of  special  interest  in  the 
eyes  of  the  manufacturer,  the  principle  item  to  consider,  perhaps, 
from  the  legislative  side  of  the  question,  is  the  necessity  of  an 
act  or  acts  to  provide  employees  of  workshops  with  proper  and 
sufficient  illumination  from  the  standpoint  of  safety.  The  legal 
aspect  of  the  safety  question  in  its  relation  to  illumination  in  fac- 
tory and  mill  buildings  is  a  topic  of  unusual  importance. 

Section  III.  Old  and  New  Lamps. — The  inadequate  means  avail- 
able for  illumination  by  artificial  methods  in  the  past  have  con- 
tributed to  the  slowness  of  an  appreciation  of  the  features  of 
artificial  light  which  influence  the  working  efficiency  of  the  eye. 
Open  flame  gas  burners,  carbon  incandescent  and  arc  lamps, 
practically  the  only  illuminants  available  ten  years  or  so  ago,  play 
but  a  small  part  in  the  present  approved  methods  of  factory  and 
mill  lighting. 

New  Lamps. — The  large  variety  of  comparatively  new  lamps 
available  for  factory  and  mill  lighting  includes  the  mercury  vapor, 
metallized  filament,  tungsten,  gas  filled  tungsten,  metallic  flame 


620     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

or  magnetic  arc,  the  flame  carbon  arc,  the  quartz  mercury  vapor, 
and  various  types  of  gas  arc  lamps.  Remarkable  improvements 
have  thus  been  made  in  both  the  electric  and  gas  lighting  fields, 
the  same  general  rules  of  applying  the  lamps  covering  both  of 
these  fields.  Possibilities  in  factory  and  mill  lighting  are  now 
attainable  which,  before  the  introduction  of  these  new  lamps, 
were  either  unthought  of  or  impossible.  Consideration  of  the 
eye  as  a  delicate  organ,  together  with  the  new  ideas  of  the  items 
which  affect  its  comfort  and  efficiency,  have  resulted  in  establish- 
ing certain  principles  in  illumination  work,  and  have  directed  at- 
tention naturally  and  in  a  growing  manner  to  the  proper  use  and 
application  of  these  new  lamps. 

Section  IV.  Effects  on  Factory  and  Mill  Lighting  Produced 
by  Modern  Lamps. — With  the  introduction  of  these  new  gas  and 
electric  lamps,  broader  possibilities  have  been  presented  in  fac- 
tory and  mill  lighting.  The  use  of  units  of  sizes  adapted  to  the 
purposes,  allows  results  which  it  has  been  hitherto  impossible  to 
obtain  satisfactorily,  either  by  the  arc  lamp,  carbon  filament  or 
open  flame  gas  burner,  formerly  available. 

New  Possibilities. — It  is  evident  that  the  introduction  of  the 
many  new  lamps  has  made  possible  what  may  be  termed  a  new 
era  in  industrial  illumination,  a  distinctive  feature  of  which  is 
the  scientific  installation  of  the  lighting  units,  suiting  each  to  the 
location  and  class  of  work  for  which  it  is  best  adapted.  Before 
the  availibility  in  recent  years  of  medium  sized  gas  and  electric 
units  the  choice  of  the  size  of  unit  for  a  given  location  was  often 
no  choice  at  all.  In  many  cases,  due  to  small  clearance  between 
cranes  and  ceilings,  or  other  conditions  making  it  necessary  to 
mount  the  lamps  very  high  above  the  floor,  but  one  size  or  type 
of  unit  was  available,  the  carbon  filament  or  open  flame  gas 
burner  in  the  former,  and  the  arc  lamp  in  the  latter  case. 

Low  Ceilings. — For  low  ceilings,  up  to  18  ft.,  the  use  either  of 
carbon  filament,  open  flame  gas  burner,  or  arc  lamps  resulted 
usually  in  anything  but  uniform  light  over  the  working  plane,  and 
often  produced  merely  a  low  general  light  which  was  practically 
useless  for  the  individual  machine.  In  such  instances,  individual 
lamps  had  to  be  placed  over  and  close  to  the  machines.  With  this 
arrangement,  relatively  small  areas  are  lighted  by  each  lamp,  and 


code;  of  lighting  621 

the  metal  shades  usually  employed,  serve  only  to  accentuate  the 
"spot  lighting"  effect.  Such  a  form  of  illumination  for  factory 
and  mill  work  is  unsatisfactory  and  inefficient,  but  as  stated,  was 
in  the  past,  in  many  cases,  the  only  available  scheme.  The  ab- 
sence of  lamps  of  the  proper  size  is  no  longer  an  excuse  for  the 
existence  of  such  conditions  in  industrial  plants. 

Section  V.  General  Requirements  of  Artificial  Lighting. — The 
following  requirements  for  factory  and  mill  lighting  are  made 
all  the  more  important  by  the  peculiar  limitations  and  the  wide 
variety  of  conditions  to  be  found  in  factory  and  mill  buildings 
and  in  factory  and  mill  work : 

1.  Sufficient  illumination  should  usually  be  provided  for  each 
workman  irrespective  of  his  position  on  the  floor  space. 

2.  The  lamps  should  be  installed  and  selected  so  as  to  avoid  eye 
strain  to  the  workmen. 

3.  The  lamps  should  be  operated  from  sources  of  supply  which 
will  insure  reliable  illumination  results,  particularly  on  account  of 
the  demoralizing  effect  produced  by  intermittent  service,  just 
when  the  light  may  be  most  needed. 

4.  Adequate  illumination  should  be  provided  from  overhead 
lamps  so  that  sharp  shadows  may  be  prevented  as  much  as  possi- 
ble, and  in  such  measure  that  individual  lamps  close  to  the  work 
may  be  unnecessary  except  in  special  cases. 

5.  The  type  and  size  of  lamp  should  be  adapted  to  the  partic- 
ular ceiling  height  and  class  of  work  in  question. 

6.  In  addition  to  the  illumination  provided  by  overhead  lamps, 
individual  lamps  should  be  placed  close  to  the  work  if  they  are 
absolutely  necessary  in  the  eyes  of  a  lighting  expert,  and  in  such 
cases  the  lamps  should  be  provided  with  suitable  opaque  re- 
flectors. 

These  requirements  may  now  be  met  by  means  of  the  new 
types  of  gas  and  electric  lamps,  one  type  of  which  can  usually  be 
found  for  practically  each  factory  and  mill  location,  specially 
adapted  to  the  general  physical  conditions  of  the  location  as  typi- 
fied by  the  clearance  between  cranes  and  ceiling  and  other  similar 
items. 

Section  VI.  Overhead  and  Specific  Methods  of  Artificial  Light- 
ing.— Factory   and   mill   lighting  may  be    classified   under   two 


622     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

general  divisions :  first,  distributed  illumination  furnished  from 
lamps  mounted  overhead;  and  second,  specific  illumination  fur- 
nished by  individual  lamps  located  close  to  the  work.  For  practi- 
cal purposes  this  classification  is  sufficient.  In  numerous  cases  a 
combination  of  these  two  methods  becomes  necessary. 

Mounting  the  Lamps  High. — Where  the  lamps  are  high  enough 
to  be  out  of  the  line  of  ordinary  vision,  and  are  of  a  size  and  so 
spaced  as  to  furnish  illumination  at  any  position  of  the  floor 
where  work  may  be  carried  on,  the  system  is  referred  to  as  the 
overhead  method  of  lighting.  This  method  has  many  advantages. 
Its  general  adoption,  which  has  been  somewhat  slow,  has  in- 
creased with  the  appearance  of  the  many  new  types  of  lamps  and 
with  the  growing  appreciation  of  the  value  of  good  lighting. 

Where  a  small  amount  of  general  or  overhead  lighting  is 
coupled  with  specific  lighting  from  individual  lamps,  a  large  part 
of  the  floor  space  in  many  shops  is  in  relative  darkness,  and  much 
dependence  must  be  placed  on  the  hand  lamps  close  to  the  work. 
The  small  number  of  overhead  lamps  generally  used  in  such 
cases,  furnishes  merely  a  small  amount  of  additional  illumination 
over  the  floor  space  which  is  not  sufficient  to  be  of  much  value. 
However,  where  sufficient  intensity  is  provided  by  general  illum- 
ination, this  is  pften  a  very  effective  means  of  lighting  a  large 
work-room. 

Low  Ceilings. — Locations  with  low  ceilings,  until  recently, 
have  been  lighted  by  the  individual  hand  lamp  method,  because 
the  old  carbon  filament  lamps,  being  of  low  candlepower,  could 
not  well  be  used  close  to  the  ceiling,  while  the  old  type  of  arc 
lamp  was  often  impracticable,  due  to  its  large  physical  size,  as 
well  as  its  relatively  high  candlepower.  This  statement  is  sub- 
ject to  some  modification,  because  low  candlepower  units  have 
sometimes  been  used  in  clusters  for  low  ceilings  as  a  compromise 
between  a  single  small  or  a  single  large  unit,  this  scheme  being, 
however,  usually  insufficient  and  unsatisfactory  in  comparison 
with  modern  methods  of  lighting.  In  a  particular  manner,  there- 
fore, suitable  illumination  has  been  difficult  with  low  ceilings. 

New  types  of  gas  and  electric  lamps  have  a  range  of  candle- 
power  from  very  low  to  very  high  values,  and  the  overhead 
system  with  the  elimination  of  individual  lamps  is  thus  possible; 


CODE  OF   LIGHTING  623 

in  other  words,  a  size  of  gas  or  electric  lamp  may  now  be  selected 
from  a  large  available  list  of  sizes  for  nearly  every  factory  or 
mill  condition. 

Section  VII.  Various  Locations  Illustrated.3 — Figs.  3  to  12  in- 
clusive are  given  to  indicate  how  the  problem  of  adequate  illu- 
mination has  been  solved  in  a  number  of  actual  instances,  and  the 
following  notes  apply  to  some  of  the  considerations  involved. 

There  are  two  main  items  to  consider  in  deciding  for  or  against 
high  candlepower  lamps  for  the  factory  or  mill.  First,  how  high 
are  the  lamps  to  be  mounted;  and  second,  will  the  light  at  any 
given  point  on  the  machines  or  other  operations  be  satisfactory 
if  it  comes  from  a  few  lamps  or  should  it  come  from  many 
sources  ?  If  the  ceiling  or  overhead  construction  is  under  16  ft, 
lamps  of  high  candlepower  can  hardly  be  used  in  sufficient  num- 
bers to  produce  uniform  illumination  over  the  floor  space.  If 
they  are  to  be  mounted  at  a  height  between  16  and  25  ft.,  it  is 
largely  a  question  of  whether  light  from  a  relatively  few  lamps 
will  produce  satisfactory  results.  For  mounting  heights  over 
25  ft.,  lamps  of  high  candlepower  possess  some  advantages,  chief 
of  which  is  their  large  volume  of  light  for  given  energy  consumed, 
always  provided  the  light  is  effectively  directed  towards  the  floor. 

Three  Groupings. — These  three  groupings  by  mounting  heights 
are  conveniently  shown  in  Figs.  15,  16,  17  and  18.  In  Fig.  15, 
a  single  shop  bay  with  a  ceiling  height  of  12  ft.  is  shown  as  typical 
of  the  first  grouping.  The  single  high  candlepower  lamp  fur- 
nishes approximately  the  same  amount  of  light  to  the  machines 
as  do  the  eight  small  lamps.  Note,  however,  that  the  illumination 
from  the  large  lamp  is  not  nearly  as  uniform  as  that  from  the 
small  lamps,  although  the  spacing  of  both  the  small  and  the  large 
lamps  as  represented  in  this  illustration  is  typical  of  many  actual 
installations.  Note  also,  that  the  shadows  cast  by  the  large  lamp 
at  certain  portions  of  the  floor  space  must  be  so  marked  as  to 
make  the  illumination  it  furnishes  very  inferior  in  this  respect  to 
the  illumination  from  the  smaller  lamps,  because  of  their  larger 
number. 

Here,  if  the  number  of  large  lamps  for  the  given  floor  area  be 

3  Figs.  3  to  12  inclusive  are,  in  general,  arranged  in  the  order  of  their  mounting 
heights.  The  low  mounting  heights  are  shown  in  the  earlier  illustrations  and  the  higher 
mountings  in  the  later  views. 


624    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

increased  in  an  endeavor  to  make  the  illumination  more  uniform 
and  to  reduce  the  shadows,  the  expense,  as  compared  with  that  for 
smaller  lamps,  makes  the  large  lamps  a  very  unfavorable  proposi- 
tion. These  two  features  are  the  basis  for  stating  that  in  general 
large  lamps  are  not  desirable  for  mounting  under  16  ft.,  and  an 
analysis  of  conditions,  together  with  a  careful  and  unbiased  com- 
parison with  the  illumination  produced  by  smaller  lamps,  will 
nearly  always  bear  out  this  conclusion. 

Second  Grouping. — In  Fig.  16,  a  20  ft.  ceiling  has  been  selected 
as  typical  of  the  second  grouping,  a  single  shop  bay  being  shown. 
Here  the  work  is  assumed  to  be  rough  assembly,  mostly  on  hori- 
zontal surfaces,  and  the  single  high  candlepower  lamp,  besides 
giving  more  nearly  uniform  illumination,  because  the  light  is  dis- 
tributed more  broadly  due  to  the  increased  height,  is  correspond- 
ingly more  satisfactory  as  to  shadows  produced  by  the  large  lamp 
in  the  preceding  illustration  (Fig.  15),  on  account  of  the  improved 
direction  in  which  much  of  the  light  reaches  the  work.  In  this 
case,  the  arrangement  of  both  large  and  small  lamps  is  typical  of 
many  existing  installations. 

In  Fig.  17,  however,  although  the  height  is  the  same  as  in 
Fig.  16,  the  work  is  quite  different,  being  conducted  on  the  inside 
of  large  vertical  tanks.  It  would  obviously  be  impossible  to 
perform  this  work  by  the  light  from  the  single  large  lamp  as  well 
as  with  that  from  the  larger  number  of  medium  sized  lamps,  even 
if  the  actual  amount  of  light  from  each  was  the  same,  on  account 
of  the  poor  direction  of  the  light  at  certain  positions  of  the  work 
from  a  single  unit  in  such  a  case.  The  medium  sized  lamps 
furnish  approximately  the  same  quantity  of  light  and  yet  no 
matter  where  the  tanks  may  be  placed,  they  will  receive  consid- 
erable light  from  the  medium  sized  lamps  directly  over  or  nearly 
over  them,  at  least  far  more  than  is  apt  to  reach  them  from  a 
single  unit  in  every  other  bay  (the  assumed  arrangement  of  the 
large  lamps). 

For  this  second  grouping  of  mounting  heights,  then,  the.  large 
lamp  may  or  may  not  be  adapted,  depending  on  whether  the 
reduction  of  shadows  is  of  much  importance,  as  is  the  case  in 
Fig.  17.  The  large  lamp  is,  however,  more  likely  to  be  satisfac- 
tory here  than  in  the  first  case  (Fig.  15),  because  of  the  better 


Fig-  3- — Night  view  of  a  rather  low  factory  section  showing  tungsten  lamps  of  the  250-watt 
size  mounted  12  ft.  above  the  floor.    Note  the  original  individual  lamps  over  the  machines. 


Fig.  4.— Night  view  showing  mercury-vapor  lighting  in  low  factory  section.      The  lamps 
are  about  12  ft.  above  the  work.    Note  the  comparative  absence  of  shadows. 


Fig.  5.— Day  view  of  a  gas  lighting  installation  in  a  low  factory  section.    This  photograph  shows 
merely  the  general  arrangement  of  lamps  and  gives  no  idea  of  the  illumination  effect. 


Fig.  6.— Night  view  of  a  planing  mill  showing  an  installation  of  250-watt  tungsten  lamps  with  a 
16  ft.  mounting.  Note  the  excellent  distribution  of  the  light  and  the  comparative  absence 
of  shadows.     This  is  an  example  of  the  overhead  method  of  lighting. 


Wn-W" 


Fig.  7. — Night  view  of  a  boiler  shop. 


Fig-  s- — Day  view  showing  arrangement  of  gas  lamps  in  a  medium  high  factory  space. 
Note  the  pierced  reflectors  over  the  machine  tools  near  the  center  of  the  picture. 


Fig.  9.— Night  view  of  factory  section  with  relatively  high  mounting  of  250-watt  tungsten  lamps. 
The  lamps  are  20  ft.  above  the  floor.  Note  the  excellent  distribution  of  the  light  and  the 
shielding  effect  of  the  girders  which  serve  to  reduce  the  glare  as  one  looks  down  the  aisle. 


Fig.  10.— Night  view  of  arc  lamp  installation  with  40  ft.  mounting  at  center  of  picture, 
and  20  ft.  at  sides.    Excellent  distribution. 


UH 


Fig.  ii. — Day  view  of  relatively  high  section,  showing  a  system  of  gas  lighting. 


Fig.  12. — High  section  showing  a  system  of  mercury-vapor  lamps.     Note  the  excellent 
distribution  of  light  over  the  floor  area. 


Fig.  13.— Excessively  bad  lighting.    Bare  lamps  produce  a  glare  which  is  harmful 
and  renders  the  illumination  very  ineffective.    Compare  with  Fig  14. 


Fig.  14.— Example  of  good  tungsten  lighting  with  metal  reflectors.  Note  the  row  of  lamps 
near  the  ceiling  for  producing  general  illumination.  This  is  known  as  combined  general 
and  localized  illumination.    Compare  with  Fig.  13. 


CODE   OF   LIGHTING 


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626     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


distribution  of  the  light  due  to  the  higher  mounting,  a  fact  made 
evident  in  Figs.  15  and  17  on  account  of  the  decreased  number 
of  small  lamps  and  the  increase  in  their  size  made  possible  in 
Fig.  17  as  compared  with  Fig.  15,  where  the  mounting  is  lower. 
By  the  same  line  of  argument,  it  can  be  shown  that  for  higher 
mountings,  large  lamps  are  still  more  likely  to  prove  satisfactory. 


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Fig.  18. — Diagram  showing  the  use  of  large  lamps  for  a  mounting  height  of  50  ft. 

In  Fig.  17,  the  number  of  large  lamps  might  have  been  increased 
for  the  given  floor  area,  but  to  have  done  so  would  mean  that 
the  cost  for  the  lamps  themselves  and  for  the  energy  and  upkeep 
to  maintain  them  would  be  excessive  in  comparison  with  the 
smaller  types  of  lamps. 

Third  Grouping. — In  Fig.  18,  the  third  grouping  of  mounting 
heights  is  shown  with  the  lamps  about  50  ft.  above  the  floor.     In 


CODE   OF   LIGHTING 


62J 


this  illustration  the  distribution  of  the  light  from  the  large  lamps 
will  be  far  more  satisfactory  both  for  flat  and  tall  work  than  in 
the  two  preceding  cases.  It  will  be  noted  further  that  the  in- 
creased height  of  the  lamp  causes  the  light  to  fall  in  such  direc- 
tions as  to  evenly  distribute  it  over  the  entire  floor  space  taken 
care  of  by  this  one  lamp  in  much  better  shape  than  for  the  lower 
mounting  heights.     (See  also  Figs.  19  to  21  inclusive.) 

Section  VIII.  Lighting  Circuits  for  Electric  Lamps  and  Supply 
Mains  for  Gas  Lamps. — The  question  of  lighting  circuits  is  men- 
tioned here  with  particular  reference  to  factory  and  mill  condi- 


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ment  of  artificial  lighting  by  means  of       with  Fig.  19.     It  indicates  an  improved 
large  lamps  mounted  too  close  to  the  floor.        scheme  over  that  shown  in  Fig.  19,  made 
Compare  this  poor  lighting  scheme  with        possible  by  the  use  of  smaller  lamps 
the  improved  plan  in  Fig.  20. 


tions,  where  motor  loads  are  apt  to  be  large  in  comparison  to  the 
energy  consumption  of  electric  lamps  which  are  in  service.  In 
some  cases,  the  proportion  of  motor  load  to  lighting  load  is  in 
the  ratio  of  10  to  i,  in  others  7  to  1,  and  so  on,  and  the  varying 
demands  on  the  circuits  by  motors  may  greatly  affect  the  lamps. 
Hence  it  is  important  to  maintain  strictly  separate  supply  circuits 
for  the  lamps  in  order  to  avoid  varying  voltage  which  is  apt  to 
result  if  the  motors  are  connected  to  the  same  circuits  with  the 
lamps. 


628    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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CODE   OF   LIGHTING  629 

Constant  Voltage. — In  addition  to  the  superior  illumination  re- 
sulting from  lamps  supplied  from  constant  voltage  mains,  some 
types  operate  with  longer  life  or  very  much  better  mechanically 
when  supplied  with  constant  voltage  than  otherwise.  These 
features  will  therefore  generally  more  than  offset  the  somewhat 
greater  cost  of  maintaining  separate  circuits  for  each  class  of 
service.  In  like  manner  and  for  similar  reasons,  it  is  advisable 
to  place  gas  lamps  on  supply  lines  separate  from  those  delivering 
gas  for  power  purposes. 

Section  IX.  Control  of  Lamps  and  Arrangement  of  Switches. — 
The  control  of  lamps  in  factory  and  mill  lighting  is  important  in 
all  cases,  but  specially  so  where  a  large  number  of  lamps  is  used 
in  preference  to  a  small  number  for  a  given  floor  area.  For  ex- 
ample, where  an  overhead  system  of  tungsten  lamps  of  small  size 
is  used,  a  large  number  will,  of  couse,  be  necessary  for  a  given 
floor  area,  and  in  such  cases  the  number  of  control  circuits  may 
at  times  seem  excessive  when  planned  out  for  sufficient  flexibility 
of  operation.  Such  circuits,  however,  in  rendering  the  system 
more  flexible,  will  be  more  than  paid  for  by  the  saving  in  energy 
and  maintenance  due  to  the  turning  out  of  lamps  not  needed  in 
certain  sections  of  the  factory  or  mill,  provided  the  number  of 
hours  per  day  during  which  the  lamps  are  used  on  the  average  is 
relatively  large,  and  the  differences  in  daylight  intensities  over  the 
floor  area  is  also  relatively  large. 

Control  Parallel  to  Windows. — The  lamps  most  distant  from 
the  windows  will  usually  be  required  at  times  when  the  natural 
light  near  the  windows  is  entirely  adequate,  thus  making  it  an 
advantage  to  arrange  the  groups  of  lamps  in  circuits  parallel  to 
the  windows.  The  advantage  of  this  method  is  further  apparent 
when  it  is  considered  that  if  the  lamps  are  controlled  in  rows  per- 
pendicular to  the  windows,  all  lamps  in  a  row  will  necessarily  be 
on  at  one  time,  while  a  portion  only  may  be  required. 

Practical  Case. — The  foregoing  statement  may  be  developed 
into  a  definite  proposition.  Thus,  to  install  a  single  switch  may 
involve  say  $5.00  as  its  first  cost.  If  ten  lamps  are  to  be  con- 
trolled from  a  single  switch,  these  ten  lamps  must  obviously  either 
all  be  turned  off  at  a  time  or  all  turned  on  at  a  time.  An  addi- 
tional switch  at  a  cost  of  $5.00  will  permit  either  half  of  these 


63O     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ten  lamps  being  turned  off,  if  not  required  at  certain  times  when 
the  remaining  five  are  needed.  This  extra  switch  may  or  may 
not  be  an  economy.  Consider,  for  example,  the  case  where  these 
five  lamps  are  of  the  60-watt  tungsten  type,  and  that  they  are 
turned  off  by  the  extra  switch  on  an  average  of  one-half  an  hour 
per  day  while  the  others  are  needed,  or  vice  versa.  In  a  year's 
time,  the  energy  saved  at  1  cent  per  kilowatt-hour,  will  amount  to 
perhaps  50  cents.  At  this  rate  it  will  require  ten  years  for  the 
energy  saved  to  pay  for  the  first  cost  of  the  extra  switch.  This 
would  not  be  considered  a  distinct  economy.  If,  however,  the 
energy  cost  be  greater,  and  more  nearly  the  average  under  actual 
conditions,  or  if  the  number  of  hours  per  day  during  which  a 
portion  only  of  the  lamps  will  not  be  used,  be  greater,  then  these 
values  will  be  correspondingly  modified. 

Locating  Switches  and  Controls. — In  locating  switches  or  con- 
trols in  factory  and  mill  aisles,  care  should  be  exercised  to  ar- 
range them  systematically,  that  is,  on  columns  situated  on  the 
same  side  of  the  aisle  and  on  the  same  relative  side  of  each 
column.  This  plan  materially  simplifies  the  finding  of  switches 
or  controls,  by  those  responsible  for  turning  on  and  off  the  lamps, 
and  is  particularly  important  where  a  given  floor  space  is  illumin- 
ated by  a  large  number  of  small  or  medium  sized  lamps  distri- 
buted uniformly  over  the  ceiling  area,  a  feature  which  is  usually 
accompanied  by  the  use  of  a  relatively  large  number  of  switches 
or  controls. 

Section  X.  Systematic  Procedure  Should  be  followed  in  Chang- 
ing a  Poor  Lighting  System  Over  to  an  Improved  Arrangement. — 

When  undertaking  the  change  from  an  old  to  a  new  lighting 
system,  the  various  forms  of  illumination  which  are  adapted  to 
factory  and  mill  spaces  should  be  studied,  and  an  investigation 
made  of  the  various  types  of  gas  and  electric  lamps  on  the  market 
which  are  available  for  the  purpose. 

Time  should  be  allowed  for  a  study  of  the  given  locations  to 
be  lighted ;  for  preparing  the  plans  of  procedure  in  the  installation 
of  the  gas  or  electric  lamps  and  auxiliaries ;  and  for  customary 
delays  in  the  receipt  of  the  necessary  supplies  and  accessories  to 
the  work  in  hand.  Altogether,  therefore,  work  of  this  kind  re- 
quires considerable  time  for  its  completion. 


CODE   OF   LIGHTING  63 1 

Using  the  Shop  Force. — In  large  factories  or  mills,  a  wiring 
or  gas  fitting  force  is  sometimes  a  part  of  the  maintenance  divi- 
sion. The  work  of  the  wiremen  or  fitters  is  likely  to  be  heaviest 
in  the  winter  due  to  the  dark  days.  Where  this  condition  exists, 
there  is  all  the  more  reason  to  apportion  out  new  work  so  as  to 
accomplish  it  during  the  months  of  least  wiring  and  piping  repair 
activity,  and  further,  at  that  time  of  the  year  when  employees  will 
be  comparatively  unaffected  by  the  disturbances  usually  asso- 
ciated with  a  change  from  an  old  to  a  new  lighting  system  through 
possible  irregularities  in  the  illumination  service  while  the  wire- 
men  or  fitters  are  at  work. 

Distribution  of  Expense. — Another  feature  different  from  the 
foregoing  viewpoint,  is  in  the  distribution  of  the  installation  cost 
over  a  relatively  long  interval.  If,  for  example,  the  system  is 
desired  for  the  approaching  winter,  the  complete  wiring  or  piping 
plans  may  be  drawn  up  and  blocked  out  into  three,  four  or  even 
more  sections,  thus  spreading  the  expense  over  as  many  months. 

Yearly  Appropriation. — In  some  shops  a  given  appropriation 
may  be  allotted  each  year  for  building  equipment.  From  the 
standpoint  of  finance  plans,  it  may  thus  be  desirable  to  distribute 
outlays  of  this  nature  over  the  year,  lather  than  to  concentrate 
them  at  any  one  time.  An  important  consideration  in  this  method 
of  installing  lamps,  however,  is  to  prepare  in  as  far  as  possible  the 
complete  plans  in  advance,  at  least  as  regards  given  factory  or 
null  sections,  so  as  to  insure  a  uniform  and  symmetrical  installa- 
tion as  a  whole  when  the  component  parts  are  finished. 

Section  XI.  Reflectors  and  Their  Effect  on  Efficiency. A  re- 
flector or  shade  is  used  in  conjunction  with  a  lamp  for  the  pur- 
pose of  reducing  the  glare  otherwise  caused  by  looking  directly 
into  the  bare  lamp,  as  well  as  for  the  purpose  of  redirecting  the 
light  most  effectively  to  the  work. 

Reflectors  and  shades  are  now  obtainable  so  designed  as  to  be 
specially  adapted  to  give  sizes  and  types  of  the  smaller  and  med- 
ium sized  line  of  lamps,  and  hence  care  should  be  used  to  be  sure 
that  both  reflectors  and  lamps  are  of  the  correct  size  in  their 
relation  to  each  other.  This  is  of  the  utmost  importance  in  se- 
curing uniform  illumination  for  a  given  spacing  distance  and 
mounting  height  of  the  lamps.     For  a  certain  ratio  between  the 


632     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

spacing  and  the  height  of  the  lamps,  a  reflector  can  nearly  always 
be  selected  which  will  furnish  uniform  illumination  over  the 
working  surface.  (These  remarks  concerning  reflectors  apply 
particularly  to  lamps  of  the  tungsten  type  and  to  small  gas  units.) 
Function  of  Reflector. — Owing  to  the  direction  of  the  light 
from  the  lamp,  nearly  all  types  of  lamps,  in  addition  to  the  down- 
ward light,  furnish  some  rays  which  go  upwards  and  away  in 
other  directions  from  the  objects  to  be  illuminated,  and  are  there- 
fore relatively  not  useful.  Furthermore,  a  bright  source  in  the 
field  of  vision  causes  an  involuntary  contraction  of  the  pupil  of 
the  eye,  which  is  equivalent  to  a  decrease  in  illumination  in  so 
far  as  the  eye  is  concerned.  Hence,  while  reflectors  or  shades 
may  at  first  seem  to  reduce  the  amount  of  light  in  the  upper  part 
of  the  room,  their  use  actually  increases  the  amount  of  light  in  a 
downward  useful  direction,  and  improves  the  "seeing"  due  to  the 
better  conditions  which  surround  the  eyes.  The  economic  func- 
tion of  the  reflector,  as  contrasted  with  the  easier  conditions  it 
affords  the  eyes,  is  to  intercept  the  otherwise  useless  or  compara- 
tively useless  rays  which  do  not  ordinarily  reach  the  wrork,  and 
to  reflect  them  in  a  useful  direction.  In  performing  this  function, 
there  is  a  choice  through  the  design  of  the  reflector,  in  the  manner 
of  distributing  the  light  so  as  to  make  the  illumination  on  the 
floor  space  uniform  with  certain  spacing  distances  and  mounting 
heights  as  previously  mentioned. 

Avoiding  Dark  Spots. — With  the  use  of  lamps  for  which  a 
large  variety  or  reflectors  is  available,  the  proper  reflector  should 
therefore  be  chosen  so  as  to  give  the  desired  distribution  of  light. 
In  other  cases,  as  in  the  use  of  the  gas  or  electric  arc  lamps, 
where  the  globe  or  reflector  is  usually  a  fixed  part  of  the  lamp, 
care  must  be  exercised  to  space  the  lamps  at  sufficiently  close 
intervals  to  insure  uniformity  of  the  illumination,  that  is,  a  free- 
dom from  the  relatively  dark  spaces  which  exist  between  lamps 
when  spaced  too  far  apart. 

Light  Interiors. — With  a  light  ceiling,  the  reflection  of  that 
part  of  the  light  which  passes  through  a  glass  reflector  to  the 
ceiling,  and  which  is  added  to  the  light  thrown  downward  from 
the  under  surface  of  the  reflector,  is  a  factor  in  building  up  the 
intensity     of  the  illumination  on  the  working  surface.     Great 


CODE  OF  LIGHTING  633 

importance  is  therefore  attached  to  light  interior  colors,  especially 
on  ceilings  and  the  upper  portions  of  walls,  both  in  reinforcing 
the  direct  illumination,  and  in  giving  diffusion,  zvhich  in  turn 
adds  to  the  amount  of  light  received  on  the  side  of  a  piece  of 
work.  It  shoidd  also  be  stated  that  the  intensity  of  the  light  from 
bare  overhead  lamps  when  measured  on  the  working  surface  may 
be  increased  by  as  much  as  60  per  cent,  through  the  use  of  effi- 
cient reflectors.  This  is  due  to  the  utilization  of  the  horizontal 
rays  of  light  as  previously  stated,  which  predominate  in  the  bare 
lamp,  whereas  the  most  effective  light  in  factory  and  mill  work 
is  apt  to  be  that  which  is  directed  downward. 

Glass  and  Metal  Reflectors  Compared. — The  question  is  some- 
times raised  as  to  the  use  of  glass  reflectors  in  connection  with 
lamps  for  factory  and  mill  lighting.  This  question  is  largely 
one  of  economy  and  maintenance,  and  it  may  be  answered  either 
in  an  off  hand  way  or  on  a  basis  of  practical  experience  with  both 
types. 

In  large  installations  of  small  units  there  has  been  an  effort 
to  establish  the  merits  of  glass  and  of  metal  reflectors,  by  equipp- 
ing lamps  in  adjacent  bays  with  glass  reflectors  in  one  case  and 
with  metal  reflectors  in  the  other.  It  has  been  found  almost 
invariably  that  if  the  choice  is  left  to  the  workmen  and  superin- 
tendents, glass  reflectors  will  be  given  preference  over  metal, 
mainly  on  account  of  the  added  cheerfulness  they  produce.  If, 
therefore,  the  first  cost  and  maintenance  expense  of  the  glass 
reflectors  in  practically  the  same  as  with  metal,  then  glass  may  be 
employed  to  advantage. 

Reflector  Efficiency.— Class  reflectors  on  the  market  are  cap- 
able of  producing  an  amount  of  illumination  equal  and  even 
greater  in  some  cases  than  that  produced  by  the  best  metal  re- 
flectors, and  even  if  the  first  cost  is  somewhat  higher,  the  added 
advantage  of  glass  as  opposed  to  metal  is  usually  sufficient  to 
make  the  small  difference  in  cost  a  negligible  item.  This  factor 
is  all  the  more  noticeable  when  one  considers  that  the  reflector 
itself  is  a  small  part  of  the  total  cost  connected  with  the  wiring 
or  piping  of  the  lamp  and  its  reflector. 

Pierced  metal  reflectors  are  also  available.  These  are  designed 
with  small  openings  at  the  upper  portion  of  the  metal  so  that 


634     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  reflector  may  give  the  same  distribution  characteristics  as  a 
given  glass  reflector,  thus  affording  a  suitable  metal  reflector  for 
use  where  glass  may  be  objectionable.  Some  of  the  advantages 
of  the  pierced  metal  reflector  are  that  it  is  unbreakable  and  that 
accumulations  of  dust  on  the  outer  surface  do  not  decrease  the 
efficiency.  It  is  also  true  that  the  light  which  passes  through  the 
openings  in  this  reflector  to  the  ceiling  cannot  be  diminished  by 
dust  on  the  outer  surface  as  in  the  case  of  glass  reflectors.  (This 
type  of  reflector  is  shown  in  Fig.  8  under  the  main  line  shafting.) 

Reflector  Maintenance. — Regarding  the  maintenance  of  glass 
reflectors  under  rough  factory  and  mill  conditions,  it  may  be 
stated  that  glass  reflectors  are  used  quite  widely  with  almost  a 
negligible  increase  due  to  breakage.  Thus,  out  of  the  total  main- 
tenance cost  in  one  representative  installation,  it  was  found  that 
the  charges  were  proportioned  as  follows : 

Renewals,  cost  of  lamps   (tungsten) 75  per  cent. 

Renewals,  broken  glass  reflectors 3  per  cent. 

Labor,  making  renewals  and  changing  reflectors 

for  washing   16  per  cent. 

Labor,  reflector  washing 2  per  cent. 

Additional  indirect  charges   4  per  cent. 

Total    100  per  cent. 

Points  to  Consider. — Reflectors  will  not  be  classified  here  from 
the  commercial  standpoint,  but  the  following  items  should  be 
given  consideration  in  the  selection  of  the  type  of  reflector  for 
factory  or  mill  use  : 

1.  Utilization  efficiency:  how  much  does  the  reflector  contri- 
bute to  the  effective  illumination  on  the  work  ? 

2.  The  effect  in  reducing  glare. 

3.  Natural  deterioration  with  age  through  accumulations  of 
dust  and  dirt. 

4.  Ease  in  handling  and  uniformity  of  manufacture. 

5.  Physical  strength  and  the  absence  of  projections  which  may 
increase  the  breakage  in  case  of  glass  reflectors. 

A  study  of  the  various  reflectors  on  the  market  with  the  aid 
of  these  items  as  a  basis,  will  determine  what  reflectors  are  best 
adapted  to  given  conditions.  Regarding  the  third  item  in  the 
foregoing  list,  it  may  be  stated  that  under  comparative  tests  in 


CODE  OF  LIGHTING  635 

service,  the  accumulations  of  dust  and  dirt  on  glass  reflectors 
do  not  seem  to  be  any  greater  than  the  coating  of  dirt  which  ac- 
cumulates on  the  inside  of  a  metal  reflector  in  the  same  length 
of  time. 

Section  XII.  Side  Light  Important  in  Some  Factory  and  Mill 
Operations. — It  has  been  customary  in  many  cases  to  measure  the 
effectiveness  of  illumination  in  terms  of  the  vertically  downward 
component  of  the  light.  This  method  has  ignored  the  value  of 
side  components  in  relation  to  vertical  surfaces  and  openings  in 
the  side  of  the  work.  It  is  sometimes  more  necessary  to  light 
the  side  of  the  machine  or  the  side  of  a  piece  of  work  than  the 
horizontal  surface.  If,  then,  in  designing  a  factory  or  mill  light- 
ing system,  the  prime  object  is  the  production  of  the  greatest 
amount  of  downward  illumination,  it  may  happen  that  the  side 
component  is  so  small  that  the  sides  of  machinery  or  of  work  are 
inadequately  lighted. 

Tzvo  Ways  to  Secure  Side  Light. — Experience  indicates  that 
there  are  two  general  ways  in  which  to  secure  adequate  side 
lighting.  One  of  these  methods  is  to  lower  the  lamps,  and  the 
other  is  to  use  broader  distributing  reflectors  than  are  called  for 
by  the  rules  which  consider  uniformity  of  the  downward  illumin- 
ation only.  Side  walls  or  other  reflecting  surfaces  will  modify 
the  results.  Thus,  after  the  determination  of  a  certain  type  of 
reflector  for  producing  uniform  vertically  downward  illumina- 
tion, it  may  be  found  that  more  side  light  is  necessary,  and  this 
extra  side  component  may,  as  stated,  usually  be  secured  by  se- 
lecting a  somewhat  more  distributing  reflector.  Broader  distri- 
buting reflectors  are  apt  to  result  in  less  downward  illumination 
and  will  sometimes  call  for  larger  lamps  than  found  necessary  by 
preliminary  calculations. 

Practical  Case. — As  an  illustration,  in  a  certain  lighting  system 
a  vertically  downward  intensity  of  about  3  foot-candles  was 
deemed  sufficient  for  the  work  involved.  Measurements  and 
observations  showed  that  the  side  light  was  insufficient.  In  this 
particular  installation  it  was  found  necessary  to  produce  a  verti- 
cally downward  intensity  of  about  5  foot-candles  on  the  average 
in  order  to  secure  an  intensity  of  about  2  foot-candles  on  the  side 
of  the  work,  and  also  to  use  a  somewhat  broader  distributing  re- 
3 


636    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

flector  than  at  first  chosen.  Two  foot-candles  on  the  sides  of  the 
work  were  sufficient  in  this  case  where  bench  work  and  work  in 
the  vise  on  small  machine  parts  were  conducted. 

Keeping  the  Lamps  High. — It  is  recommended  that  the  lamps 
be  mounted  near  the  ceiling  in  all  reasonable  cases  where  side 
light  is  necessary,  and  that  the  side  light  be  increased,  not  by  low- 
ering the  lamps,  but  through  the  medium  of  broader  distributing 
reflectors  and  larger  lamps,  if  required.  This  attitude  is  taken 
on  account  of  the  glare  which  results  when  lamps  are  mounted 
too  close  to  the  work,  a  feature  most  noticeable  in  the  absence  of 
a  reflector  or  where  glass  reflectors  are  used. 

Section  XIII.  Maintenance. — The  importance  of  system  in  the 
upkeep  of  natural  and  artificial  lighting  equipment  may  not  ap- 
peal to  every  reader  at  the  outset,  but  a  consideration  of  the 
points  involved  will  indicate  that  neglect  of  such  work  is  apt  to 
result  in  excessive  losses  of  otherwise  useful  light. 

Windows. — Factory  and  mill  windows  become  covered  in  time 
with  dirt,  and  produce  greatly  decreased  values  of  natural  light 
in  consequence.  These  losses  may  easily  be  great  enough  to 
affect  the  workmen  seriously,  and  to  necessitate  the  use  of  arti- 
ficial light  at  times  when  otherwise  it  would  not  be  required. 
Dark  surroudings  also  increase  the  likelihood  of  accidents.  Regu- 
lar window  cleaning  should  therefore  be  a  part  of  the  routine  of 
every  factory  and  mill  building  or  group  of  buildings. 

Lamps. — Carbon  filament,  mercury-vapor,  gas  mantle  and 
tungsten  lamps  burn  out  or  break,  globes  and  reflectors  become 
soiled,  and  the  various  other  items  of  deterioration  take  place  so 
gradually  that  in  many  cases  they  are  given  no  special  concern 
in  the  practical  economy  of  the  shop.  Moreover,  it  is  hardly 
necessary  to  mention  the  fact  that  often  lighting  systems  are  al- 
lowed to  deteriorate  to  an  extreme  point  and  nothing  is  done  un- 
less complaints  come  in  from  employees  after  the  lighting  facili- 
ties here  and  there  throughout  the  shop  have  become  so  poor  that 
work  has  to  be  discontinued  temporarily.  The  losses  of  time 
from  such  circumstances,  when  added  up  throughout  a  year,  are 
more  than  likely  to  exceed  the  expense  of  systematic  attention  to 
such  maintenance  items  in  advance. 

Overhead  System. — Furthermore,  with  modern  methods  where 


CODE   OF   LIGHTING 


637 


the  lamps  are  usually  mounted  overhead  rather  than  close  to  each 
machine,  the  importance  of  relieving  the  workmen  from  any 
care  of  the  lamps  and  placing  it  in  the  hands  of  a  maintenance 
department  is  even  greater  than  has  been  the  case  in  the  past  par- 
ticularly in  large  plants.  To  indicate  the  wisdom  of  a  daily  re- 
newal of  electric  lamps,  Fig.  24  has  been  worked  up  from  the 
experiences  in  one  large  factory.  In  this  factory  all  burned-out 
lamps  are  renewed  each  day  except  Saturday  and  Sunday,  these 
renewals  being  based  on  a  daily  inspection  of  every  lamp  to  as- 
certain whether  or  not  it  is  in  working  condition. 

Lamp  Renewals. — A  reference  to  the  diagram  shows  that  the 
renewals  are  considerably  greater  on  Monday  than  on  any  other 
day  of  the  week,  this  increase  being  due  to  renewals  not  given  at- 


0 

o- 

-a; 

_i 
u 

hj 

3 
2 

SUN        MON.      TUES.    WED     THURS.    FRI        SAT.      SUN. 
Fig.  24. — Fluctuations  in  daily  lamp  renewals. 

tention  on  the  two  preceding  days.  Obviously,  therefore,  a  con- 
tinued neglect  of  the  inspection  and  renewal  of  these  lamps  would 
soon  result  not  only  in  inferior  lighting  conditions,  but  to  large 
losses  of  time  for  the  employees,  not  to  speak  of  the  annoyance 
involved. 

Reflector  Cleaning. — The  serious  loss  of  light  when  globes  and 
reflectors  are  allowed  to  go  for  long  periods  without  cleaning,  is 
shown  in  Fig.  25.  This  set  of  curves  resulted  from  a  test  on  a 
glass  reflector  used  with  a  tungsten  lamp.  The  one  curve  shows 
the  value  of  the  light  given  by  the  lamp  at  different  angles  when 
the  lamp  and  reflector  are  clean,  while  the  smaller  curve  shows 
the  enormous  reduction  of  light  after  the  lamp  and  reflector  has 
been  in  service  for  about  four  months  without  being  cleaned. 


638    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

In  this  paricular  case,  which  is  a  typical  one,  the  loss  of  light 
at  the  end  of  the  four  month  interval,  amounted  to  about  50  per 
cent.  The  cost  of  electrical  energy  in  this  shop  was  such  that  the 
loss  of  light  during  the  four  months  amounted  to  about  12  cents, 
while  the  total  cost  of  taking  down,  washing  and  replacing  this 
reflector  amounted  to  about  3  cents.  The  economy  of  a  fairly 
frequent  attention  to  cleaning  of  such  reflectors  is  at  once  ap- 
parent, even  if  the  improved  condition  of  the  light  in  itself  be 
ignored. 

The  examples  just  given,  in  the  one  case  associated  with  the 
renewals  of  the  lamps,  in  the  other  with  the  washing  of  the  re- 
flectors, will  serve  to  illustrate  the  class  of  upkeep  problems  which 


Fig.  25. — Curves  showing  serious  losses  of  light  from  a  tungsten  lamp  and  its  reflector  due 
to  accumulations  of  dirt.  This  is  a  condition  applicable  to  all  types  of  lamps,  as  other 
illuminants  suffer  corresponding  losses  from  dirt  accumulations. 

are  involved  in  shop  lighting.  The  most  forcible  emphasis  is  ap- 
plicable to  the  idea  that  system  may  properly  be  called  a  first  step 
towards  success  in  this  line  of  maintenance  work. 

A  Method  of  Inspection  and  Maintenance. — In  one  large  fac- 
tory a  regularly  developed  method  of  inspection  and  renewals  is 
employed.  As  an  example,  the  method  as  applied  to  several 
thousand  tungsten  lamps,  which  are  in  service  in  the  various 
buildings,  will  be  described.  All  the  lamps  are  inspected  once 
per  day,  except  Saturday  and  Sunday.  A  regular  route  is 
followed  by  the  inspector,  and  all  burned  out  lamps,  broken 
switches,  loose  fuses,  and  similar  items  are  noted.  Careful  ob- 
servation is  also  made  of  reflectors  which  appear  to  need  washing 
and  any  other  points  which  might  affect  the  efficiency  of  the 


(.3S 


Fig.  2b. — Very  poor  lighting  in  a  worsted  goods  factory.  The  wiring  is  badly  arranged,  the 
contrasts  between  light  and  dark  portions  of  the  room  are  excessive,  and  in  some  cases  the 
wrong  size  of  lamp  is  used  in  a  given  reflector.  The  system  is  unsightly  and  represents 
bad  practise.    Compare  with  Fig.  27. 


Hig.  27.-  Worsted  mill  with  localized  general  illumination.  This  is  an  example  of  excellent 
illumination  with  tungsten  lamps  and  metal  reflectors.  Note  the  reflection  from  the  goods 
to  the  ceiling.    Compare  with  Fig.  26. 


Fig.  28. — Very  poor  arrangement  of  arc  lamps.  The  lamps  are  mounted  to  one  side  of 
aisle  over  line  shafting.  Very  little  light  reaches  the  machinery  to  the  right.  Com- 
pare with  Fig.  29. 


Fig.  29. — Well  planed  system  of  arc  lighting.    The  lamps  are  high  and  above  the 
ordinary  line  of  vision.     Compare  with  Fig.  28. 


CODE   OF   LIGHTING  639 

system,  after  which  a  report  is  made  up  about  noon  and  promptly 
sent  to  the  maintenance  department  to  permit  all  renewals  and 
repairs  to  be  made  before  night.  In  this  manner  the  lamps  are 
well  maintained  from  day  to  day. 

Marking  Columns. — To  facilitate  this  renewal  work,  it  has  been 
found  advantageous  to  mark  all  columns  through  this  shop.  The 
inspector  is  thus  enabled  to  indicate  clearly  the  location  of  each 
burned  out  lamp  and  the  renewal  man  to  locate  it  without  delay. 
It  is  helpful  now  and  then  in  like  manner  to  have  the  inspector 
note  the  unnecessary  lamps  found  burning  when  artificial  light 
is  not  required.  If  lamps  are  found  burning  at  such  times,  a  note 
sent  to  the  head  of  the  department  calling  attention  to  the  matter 
is  usually  sufficient  to  remedy  the  difficulty. 

Noting  Soiled  Reflectors. — As  a  check  on  a  regular  cleaning 
schedule,  the  inspector  should  note  all  reflectors  in  need  of  clean- 
ing. The  frequency  of  each  cleaning  will  depend  on  the  rate  of 
deterioration  due  to  the  settlement  of  dirt  on  the  surface  of  the 
glass  or  metal  and  also  on  the  surface  of  lamps,  and  the  fact 
should  be  kept  in  mind  that  the  amount  of  dirt  on  a  reflector  is 
nearly  always  deceptive,  that  is,  reflectors  which  have  suffered 
a  large  deterioration  in  efficiency  due  to  dirt  often  appear  fairly 
clean,  and  for  this  reason  it  is  best  to  increase  the  frequency 
of  cleaning  somewhat  over  that  which  seems  sufficient  from  ob- 
servation, particularly  in  view  of  the  fact  that  tests  indicate  large 
reductions  of  light  from  apparently  small  accumulations  of  dust 
and  dirt. 

A  Method  of  Washing. — In  the  factory  just  referred  to,  all 
reflectors  are  removed  to  a  central  washing  point.  Where  the 
number  of  reflectors  to  be  hauled  is  large,  a  truck  is  used.  Often, 
however,  where  only  a  small  number  of  reflectors  is  to  be  trans- 
ported, small  hand  racks,  devised  for  the  purpose,  are  employed. 
When  an  installation  is  in  need  of  washing,  the  scheme  is  to  haul 
sufficient  clean  reflectors  to  the  location  in  question.  The  soiled 
reflectors  are  then  taken  down  and  clean  ones  immediately  put 
into  place,  after  which  the  soiled  reflectors  are  removed  to  the 
central  washing  point,  washed  and  put  into  stock  for  the  next 
location. 


64O     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Section  XIV.  Expert  Assistance  Suggested. — The  advantages  of 
securing  expert  assistance  in  dealing  with  illumination  is  strongly 
emphasized.  The  points  which  come  up  for  solution  are  complex 
and  require,  in  many  cases,  the  judgment  of  one  who  has  had 
wide  experience  in  the  lighting  field.  In  particular,  anyone  who 
undertakes  to  adopt  any  part  or  all  of  these  suggestions  will  do 
well  to  secure  the  co-operation  of  a  lighting  expert  capable  of 
interpreting  the  legislative  articles  and  of  advising  in  a  con- 
structive manner. 

Section  XV.  Other  Features  of  Eye  Protection. — Care  is  urged 
on  the  part  of  those  responsible  for  the  health  and  welfare  of 
employees  to  see  that  adequate  eye  protection  is  afforded  in  all 
operations  which  are  apt  to  cause  injury  to  eyesight,  if  such 
protection  is  neglected.  As  typical  of  such  other  causes  of  danger 
to  eyesight,  arc  welding  may  be  mentioned,  where  the  operator, 
according  to  accepted  practise,  must  wear  a  helmet  serving  as  an 
eye  shield  as  well  as  a  shield  for  the  face  and  head  in  general. 
Protective  glasses  for  this  purpose  should  not  be  judged  as  to 
their  protective  properties  by  mere  visual  inspection.  They 
should,  hoivever,  be  analysed  for  their  spectral  transmission  of 
invisible  radiation.  Protective  measures  should  also  be  taken  to 
prevent  on-lookers  from  being  unduly  exposed  to  such  eye 
dangers,  by  enclosing  the  welding  operations  with  suitable  parti- 
tions. These  general  remarks  apply  with  equal  force  from  the 
standpoint  of  those  handling  the  operations  to  such  other  cases 
as  the  testing  of  arc  lamps,  inspection  of  hot  metal  and  similar 
cases. 

Section  XVI.  Auxiliary  Systems  for  Safety. — The  auxiliary 
system  of  lighting  called  for  in  Article  XI  of  the  Code,  is  a  safety 
first  precaution  which  is  insisted  upon  in  a  large  proportion  of 
the  1,200  buildings  coming  under  the  control  of  the  Bureau  of 
Water  Supply,  Gas  and  Electricity  in  New  York  City,  particu- 
larly such  buildings  as  are  occupied  by  large  numbers  of  people. 
The  same  precaution  is  now  observed  by  the  Bell  Telephone  Com- 
pany's offices  fairly  generally  throughout  the  country,  also  by  a 
large  number  of  private  manufacturers  and  by  local  ordinances 
compelling  all  types  of  amusement  places  to  take  this  precaution. 


CODE   OF   LIGHTING  64I 

Section  XVII.  Good  and  Bad  Lighting  Compared. — In  order  to 
give  an  idea  of  good  and  bad  lighting,  Figs.  13,  14,  26,  27,  28  and 
29  are  shown.  These  illustrations  indicate  the  use  of  various 
types  of  lamps  and  a  reference  to  the  captions  under  the  illustra- 
tions will  bring  out  the  weak  points  of  the  poorly  lighted  spaces, 
as  well  as  the  points  of  excellence  in  those  cases  which  are  de- 
signed in  conformity  with  good  illumination  practise. 


642     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

1915  REPORT  OF  THE  COMMITTEE  ON  NOMENCLA- 
TURE AND  STANDARDS  OF  THE  ILLUMIN- 
ATING ENGINEERING   SOCIETY.* 


DEFINITIONS. 

Luminous  flux  is  radiant  power  evaluated  according  to  its 
capacity  to  produce  the  sensation  of  light. 

The  stimulus  coefficient  KA  for  radiation  of  a  particular  wav 
length  is  the  ratio  of  the  luminous  flux  to  the  radiant  power  pro- 
ducing it. 

The  mean  value  of  the  stimulus  coefficient,  Km,  over  any  range 
of  wave-lengths,  or  for  the  whole  visible  spectrum  of  any  source, 
is  the  ratio  of  the  total  luminous  flux  (in  lumens)  to  the  total 
radiant  power  (in  ergs  per  second,  but  more  commonly  in  watts). 

The  luminous  intensity  of  a  point  source  of  light  is  the  solid 
angular  density  of  the  luminous  flux  emitted  by  the  source  in 
the  direction  considered;  or  it  is  the  flux  per  unit  solid  angle 
from  that  source. 

Defining  equation : 

Let  I  be  the  intensity  for  the  flux  and  w  the  solid  angle. 

Then  I  =  * 

aw 

or,  if  the  intensity  is  uniform, 

CO 

Illumination,  on  a  surface,  is  the  luminous  flux-density  over 
that  surface,  or  the  flux  per  unit  of  intercepting  area. 

Defining  equation : 

Let  E  be  the  illumination  and  S  the  area  of  the  intercepting 
surface. 

Then  E  =  d 


or,  when  uniform, 


dS' 


K-^"' 


*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,  D.   C,   September  20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


191 5    REPORT    ON    NOMENCLATURE    AND    STANDARDS  643 

Candle — the  unit  of  luminous  intensity  maintained  by  the 
national  laboratories  of  France,  Great  Britain,  and  the  United 
States.1 

Candlepower — luminous  intensity  expressed  in  candles. 

Lumen — the  unit  of  luminous  flux,  equal  to  the  flux  emitted  in 
a  unit  solid  angle  (steradian)  by  a  point  source  of  one  candle- 
power.2 

Lux— a  unit  of  illumination  equal  to  one  lumen  per  square 
meter.  The  C.  G.  S.  unit  of  illumination  is  one  lumen  per  square 
centimeter.  For  this  unit  Blondel  has  proposed  the  name  "Phot." 
One  millilumen  per  square  centimeter  (milliphot)  is  a  practical 
derivative  of  the  C.  G.  S.  system.  One  foot-candle  is  one  lumen 
per  square  foot  and  is  equal  to  1.0764  milliphots. 

Exposure — the  product  of  an  illumination  by  the  time.  Blondel 
has  proposed  the  name  "phot-second"  for  the  unit  of  exposure 
in  the  C.  G.  S.  system. 

Specific  luminous  radiation — the  luminous  flux-density  emitted 
by  a  surface,  or  the  flux  emitted  per  unit  of  emissive  area.  It  is 
expressed  in  lumens  per  square  centimeter. 

Defining  equation : 

Let  E'  be  the  specific  luminous  radiation. 

Then,  for  surfaces  obeying  Lambert's  cosine  law  of  emission. 

E'  =  ^0. 

Brightness,  b,  of  an  element  of  a  luminous  surface  from  a  given 
position,  may  be  expressed  in  terms  of  the  luminous  intensity  per 
unit  area  of  the  surface  projected  on  a  plane  perpendicular  to 
the  line  of  sight,  and  including  only  a  surface  of  dimensions 
negligibly  small  in  comparison  with  the  distance  to  the  observer. 
It  is  measured  in  candles  per  square  centimeter  of  the  projected 
area. 

Defining  equation: 

Let  6  be  the  angle  between  the  normal  to  the  surface  and  the 

line  of  sight. 

Then 

dl_ 

~~     dS  cos  & 

1  This  unit,  which  is  used  also  by  many  other  countries,  is  frequently  referred  to  as 
the  international  candle. 

2  A  uniform  source  of  one  candle  emits  4  n  lumens. 


644     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Normal  brightness,  b0,  of  an  element  of  a  surface  (sometimes 
called  specific  luminous  intensity)  is  the  brightness  taken  in  a 
direction  normal  to  the  surface.3 

Denning  equation: 

or,  when  uniform,  60  —  — . 

Brightness  may  also  be  expressed  in  terms  of  the  specific 
luminous  radiation  of  an  ideal  surface  of  perfect  diffusing  qual- 
ities, i.  e.,  one  obeying  Lambert's  cosine  law. 

Lambert — the  C.  G.  S.  unit  of  brightness,  the  brightness  of  a 
perfectly  diffusing  surface  radiating  or  reflecting  one  lumen  per 
square  centimeter.  This  is  equivalent  to  the  brightness  of  a  per- 
fectly diffusing  surface  having  a  coefficient  of  reflection  equal 
to  unity  and  illuminated  by  one  phot.  For  most  purposes,  the 
millilambert  (0.001  lambert)  is  the  preferable  practical  unit. 

A  perfectly  diffusing  surface  emitting  one  lumen  per  square 
foot  will  have  a  brightness  of  1.076  millilamberts. 

Brightness  expressed  in  candles  per  square  centimeter  may  be 
reduced  to  lamberts  by  multiplying  by  it  =  3.14. 

Brightness  expressed  in  candles  per  square  inch  may  be  re- 
duced to  foot-candle  brightness  by  multiplying  by  the  factor 
144  7T  =  452. 

Brightness  expressed  in  candles  per  square  inch  may  be  re- 
duced to  lamberts  by  multiplying  by  71-/6.45  —  0.4868. 

In  practise,  no  surface  obeys  exactly  Lambert's  cosine  law  of 
emission;  hence  the  brightness  of  a  surface  in  Lamberts  is,  in 
general,  not  numerically  equal  to  its  specific  luminous  radiation 
in  lumens  per  square  centimeter. 

Defining  equations : 


L  = 


d$ 


or,  when  uniform, 


*-f 


3  In  practise,  the  brightness  b  of  a  luminous  surface  or  element  thereof  is  observed, 
and  not  the  normal  brightness  ba.  For  surfaces  for  which  the  cosine  law  of  emission 
holds,  the  quantities  b  and  ba  are  equal. 


191 5    REPORT   ON    NOMENCLATURE   AND    STANDARDS  645 

Coefficient  of  reflection — the  ratio  of  the  total  luminous  flux 
reflected  by  a  surface  to  the  total  luminous  flux  incident  upon  it. 
It  is  a  simple  numeric.  The  reflection  from  a  surface  may  be 
regular,  diffuse  or  mixed.  In  perfect  regular  reflection,  all  of 
the  flux  is  reflected  from  the  surface  at  an  angle  of  reflection 
equal  to  the  angle  of  incidence.  In  perfect  diffuse  reflection  the 
flux  is  reflected  from  the  surface  in  all  directions  in  accordance 
with  Lambert's  cosine  law.  In  most  practical  cases  there  is  a 
superposition  of  regular  and  diffuse  reflection. 

Coefficient  of  regular  reflection  is  the  ratio  of  the  luminous 
flux  reflected  regularly  to  the  total  incident  flux. 

Coefficient  of  diffuse  reflection  is  the  ratio  of  the  luminous 
flux  reflected  diffusely  to  the  total  incident  flux. 

Defining  equation: 

Let  m  be  the  coefficient  of  reflection  (regular  or  diffuse). 

Then,  for  any  given  portion  of  the  surface, 

E' 
m  =  —  . 
E 

Lamp — a  generic  term  for  an  artificial  source  of  light. 

Primary  luminous  standard — a  recognized  standard  luminous 
source  reproducible  from  specifications. 

Representative  luminous  standard — a  standard  of  luminous 
intensity  adopted  as  the  authoritative  custodian  of  the  accepted 
value  of  the  unit. 

Reference  standard — a  standard  calibrated  in  terms  of  the  unit 
from  either  a  primary  or  representative  standard  and  used  for 
the  calibration  of  working  standards. 

Working  standard — any  standardized  luminous  source  for  daily 
use  in  photometry. 

Comparison  lamp — a  lamp  of  constant  but  not  necessarily 
known  candlepower  against  which  a  working  standard  and  test 
lamps  are  successively  compared  in  a  photometer. 

Test  lamp,  in  a  photometer — a  lamp  to  be  tested. 

Performance  curve — a  curve  representing  the  behavior  of  a 
lamp  in  any  particular  (candlepower,  consumption,  etc.)  at  differ- 
ent periods  during  its  life. 

Characteristic  curve — a  curve  expressing  a  relation  between 


646     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

two  variable  properties  of  a  luminous  source,  as  candlepower 
and  volts,  candlepower  and  rate  of  fuel  consumption,  etc. 

Horizontal  distribution  curve — a  polar  curve  representing  the 
luminous  intensity  of  a  lamp,  or  lighting  unit,  in  a  plane  perpen- 
dicular to  the  axis  of  the  unit,  and  with  the  unit  at  the  origin. 

Vertical  distribution  curve — a  polar  curve  representing  the 
luminous  intensity  of  a  lamp,  or  lighting  unit,  in  a  plane  passing 
through  the  axis  of  the  unit  and  with  the  unit  at  the  origin. 
Unless  otherwise  specified,  a  vertical  distribution  curve  is  as- 
sumed to  be  an  average  vertical  distribution  curve,  such  as  may 
in  many  cases  be  obtained  by  rotating  the  unit  about  its  axis, 
and  measuring  the  average  intensities  at  the  different  elevations. 
It  is  recommended  that  in  vertical  distribution  curves,  angles  of 
elevation  shall  be  counted  positively  from  the  nadir  as  zero,  to 
the  zenith  as  1800.  In  the  case  of  incandescent  lamps,  it  is 
assumed  that  the  vertical  distribution  curve  is  taken  with  the 
tip  downward. 

Mean  horizontal  candlepower  of  a  lamp — the  average  candle- 
power  in  the  horizontal  plane  passing  through  the  luminous  center 
of  the  lamp. 

It  is  here  assumed  that  the  lamp  (or  other  light  source)  is 
mounted  in  the  usual  manner,  or,  as  in  the  case  of  an  incan- 
descent lamp,  with  its  axis  of  symmetry  vertical. 

Mean  spherical  candlepower  of  a  lamp — the  average  candle- 
power  of  a  lamp  in  all  directions  in  space.  It  is  equal  to  the 
total  luminous  flux  of  the  lamp  in  lumens  divided  by  477-. 

Mean  hemispherical  candlepower  of  a  lamp  (upper  or  lower) — 
the  average  candlepower  of  a  lamp  in  the  hemisphere  considered. 
It  is  equal  to  the  total  luminous  flux  emitted  by  the  lamp  in  that 
hemisphere  divided  by  2-n. 

Mean  zonal  candlepower  of  a  lamp — the  average  candlepower 
of  a  lamp  over  the  given  zone.  It  is  equal  to  the  total  luminous 
flux  emitted  by  the  lamp  in  that  zone  divided  by  the  solid  angle 
of  the  zone. 

Spherical  reduction  factor  of  a  lamp — the  ratio  of  the  mean 
spherical  to  the  mean  horizontal  candlepower  of  the  lamp.4 

4  In  the  case  of  a  uniform  point-source,  this  factor  would  be  unity,  and  for  a  straight 
cylindrical  filament  obeying  the  cosine  law  it  would  be  jt/4. 


191 5    REPORT    ON    NOMENCLATURE   AND    STANDARDS  647 

Photometric  tests  in  which  the  results  are  stated  in  candlepower 
should  be  made  at  such  a  distance  from  the  source  of  light  that 
the  latter  may  be  regarded  as  practically  a  point.  Where  tests 
are  made  in  the  measurement  of  lamps  with  reflectors,  the  results 
should  always  be  given  as  "apparent  candlepower"  at  the  distance 
employed,  which  distance  should  always  be  specifically  stated. 

The  output  of  all  illuminants  should  be  expressed  in  lumens. 

Illuminants  should  be  rated  upon  a  lumen  basis  instead  of  a 
candlepower  basis. 

The  specific  output  of  electric  lamps  should  be  stated  in  terms 
of  lumens  per  watt  and  the  specific  output  of  illuminants  depend- 
ing upon  combustion  should  be  stated  in  lumens  per  British  ther- 
mal unit  per  hour.  The  use  of  the  term  "efficiency"  in  this  con- 
nection should  be  discouraged. 

When  auxiliary  devices  are  necessarily  employed  in  circuit 
with  a  lamp,  the  input  should  be  taken  to  include  both  that  in 
the  lamp  and  that  in  the  auxiliary  devices.  For  example,  the 
watts  lost  in  the  ballast  resistance  of  an  arc  lamp  are  properly 
chargeable  to  the  lamp. 

The  specific  consumption  of  an  electric  lamp  is  its  watt  con- 
sumption per  lumen.  "Watts  per  candle"  is  a  term  used  com- 
mercially in  connection  with  electric  incandescent  lamps,  and 
denotes  watts  per  mean  horizontal  candlepower. 

Life  tests — Electric  incandescent  lamps  of  a  given  type  may  be 
assumed  to  operate  under  comparable  conditions  only  when  their 
lumens  per  watt  consumed  are  the  same.  Life  test  results,  in 
order  to  be  compared  must  be  either  conducted  under,  or  reduced 
to,  comparable  conditions  of  operation. 

In  comparing  different  luminous  sources,  not  only  should  their 
candlepower  be  compared,  but  also  their  relative  form,  bright- 
ness, distribution  of  illumination  and  character  of  light. 

Lamp  Accessories. — A  reflector  is  an  appliance  the  chief  use  of 
which  is  to  redirect  the  luminous  flux  of  a  lamp  in  a  desired 
direction  or  directions. 

A  shade  is  an  appliance  the  chief  use  of  which  is  to  diminish 
or  to  interrupt  the  flux  of  a  lamp  in  certain  directions  where  such 
flux  is  not  desirable.  The  function  of  a  shade  is  commonly  com- 
bined with  that  of  a  reflector. 


648     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


A  globe  is  an  enclosing-  appliance  of  clear  or  diffusing  material 
the  chief  use  of  which  is  either  to  protect  the  lamp  or  to  diffuse 
its  light. 

Photojmetric  Units  and  Abbreviations. 


Photometric 
quantity 

Luminous  flux 
Luminous  intensity 


Name  of 
unit 

Lumen 
Candle 


Abbreviations,  symbols 
and  defining  eqations 


* 


dF 


d* 


du '  du> 


3- 

Illumination 

Phot,  foot-candles,  lux 

E  = 

dF         I 
dS  —   r2 

4- 

Exposure 

Phot-second 
Apparent  candles 

El 

per  sq.  cm. 

b  — 

dl 

5- 

Brightness 

Apparent  candles 
per  sq. in. 

dS  cos  6 

Lambert 

L  = 

dF 

~ds 

6. 

Normal  bright: 

aess 

Candles  per  sq.  cm. 
Candles  per  sq.  in. 

h  = 

dl 

~~  dS 

7- 

Specific  luminous 
radiation 

Lumens  per  sq.  cm. 
Lumens  per  sq.  in. 

E'= 

:  ir£0,  0' 

8. 

Coefficient  of 
flection 

re- 

— 

m  = 

E/ 
E 

9.  Mean  spherical 
candlepower 

10.  Mean  lower  hemi- 

spherical candle- 
power 

11.  Mean  upper  hemi- 

spherical candle- 
power 

12.  Mean  zonal  candle- 

power 

13.  1  lumen  is  emitted  by  0.07958  spherical  cp. 

14.  1  spherical  candlepower  emits  12.57  lumens. 

15.  1  lux  =  1  lumen  incident  per  square  meter  ; 

phot. 

16.  1  phot  =  1  lumen  incident  per  sq.  cm.  =  10,000  lux  =  1000  milliphot. 

17.  1  milliphot  =  0.001  phot  =  0.929  foot-candle. 

18.  1  foot-candle  =  1  lumen  incident  per  square  foot  =  1.076  milliphot 

10.76  lux. 

19.  1  lambert  =  1  lumen  emitted  per  square  centimeter.* 

20.  1  millilambert  =  0.001  lambert. 


scp 

lcp 

ucp 
zcp 

0.0001  phot  =  0.1  milli- 


191 5   REPORT   ON    NOMENCLATURE   AND   STANDARDS  649 

21.  i  lumen,  emitted,  per  square  foot*  =  1.076  millilambert. 

22.  1  millilambert  =  0.929  lumen,  emitted,  per  square  foot.* 

23.  1  lambert  =  0.3183  candle  per  sq.  cm.  =  2.054  candles  per  sq.  in. 

24.  1  candle  per  sq.  cm.  =  3.1416  lamberts. 

25.  1  candle  per  sq.  in.  —  0.4868  lamberts  =  486.8  millilamberts. 

SYMBOLS. 
In  view  of  the  fact  that  the  symbols  heretofore  proposed  by 
this  committee  conflict  in  some  cases  with  symbols  adopted  for 
electric  units  by  the  International  Electrotechnical  Commission, 
it  is  proposed  that  where  the  possibility  of  any  confusion  exists 
in  the  use  of  electrical  and  photometrical  symbols,  an  alternative 
system  of  symbols  for  photometrical  quantities  should  be  em- 
ployed. These  should  be  derived  exclusively  from  the  Greek 
alphabet,  for  instance  : 

Luminous  intensity T 

Luminous  flux & 

Illumination /3. 

DISCUSSION. 

Mr.  F.  A.  Benford  :  I  note  in  the  text  that  the  words  "candle" 
and  "candlepower"  are  used  interchangeably.  I  wonder  if  Dr. 
Sharp  will  tell  us  if  this  Society  has  ever  taken  a  stand  as  to 
preference  in  the  use  of  the  word  "candle"  or  "candlepower?" 

Mr.  R.  ff.  Pierce  :  I  should  like  to  call  attention  to  the  possi- 
bility that  the  rating  of  lamps  in  the  terms  set  forth  on  the  sixth 
page  might  introduce  some  confusion  commercially.  It  is  recom- 
mended that  the  specific  output  of  illuminants  depending  on  com- 
bustion shall  be  stated  in  British  thermal  units  per  hour.  In 
actual  practise  in  the  case  of  illuminants  operated  by  gas,  it  has 
been  demonstrated  that  the  light  output  is  practically  independent 
of  the  calorific  value  of  the  gas.  As  the  adoption  of  such  a 
system  of  rating  might  conflict  with  or  confuse  commercial  rat- 
ings, I  should  urge  that  it  be  offered  in  such  a  way  as  to  make 
impossible  any  such  confusion ;  it  is  not  a  practical  way  of  rating 
commercially  lamps  of  that  type. 

Mr.  P.  S.  Millar:  On  the  second  page  the  committee  defines 
the  word  "lux."  I  should  like  to  ask  if  the  committee  wishes  us 
to  use  that  unit  of  illumination?  It  is  used  in  Germany,  based 
upon  the  Hefner.  It  is  proposed  here  in  connection  with  candle.  If 

*  Perfect  diffusion  assumed. 


650     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  committee  does  not  wish  us  to  use  the  word  "lux"  in  our  work, 
I  think  it  should  not  be  featured  so  prominently  in  the  report. 

Most  of  the  paragraph  under  lux  is  devoted  to  a  discussion  of  the 
phot.  If  the  committee  wishes  us  to  use  the  phot,  I  think  it  should 
be  featured;  it  is  given  rather  incidentally  at  the  present  time. 

Mr.  J.  R.  Cravath  :  I  believe  I  am  correct  that  the  new 
unit  of  brightness  called  the  lambert  is  the  first  one  to  be  dis- 
tinctly originated  within  our  Society  through  its  Committee.  I 
hope  those  who  are  working  in  brightness  values  will  promptly 
adopt  this  new  unit  in  publications  relating  to  brightness. 

Dr.  C.  H.  Sharp  :  Mr.  President,  the  first  question  was,  "Has 
the  Society  said  anything  on  the  subject  of  candle  versus  candle- 
power?"  At  the  top  of  the  second  page  of  the  report  you  will 
find  this : 

Candle,  the  unit  of  luminous  intensity  maintained   by  the  national 
laboratories  of  France,  Great  Britain  and  the  United  States. 
Candlepower,  luminous  intensity  expressed  in  candles. 

Mr.  Pierce  made  some  statement  regarding  the  luminous  output 
of  gas  lamps.  He  raised  an  objection  to  the  rating  of  them  in 
terms  of  British  thermal  units.  That  is  a  question  the  merits  of 
which  I  am  unable  to  go  into.  I  would  say,  however,  that  the 
proposition  which  came  to  the  committee  first  was  that  gas  lamps 
should  be  rated  in  lumens  per  cubic  foot  per  hour,  but  the  prom- 
inent gas  engineers  on  the  committee  preferred  a  rating  in  terms 
of  lumens  per  British  thermal  units  per  hour,  because  the  lumens 
were  proportional  to  the  British  thermal  units  of  the  gas. 

Mr.  Millar  has  raised  the  question  of  the  prominent  featuring 
of  the  term  "lux."  I  think  his  criticism  is  pretty  well  taken.  My 
understanding  of  it  has  been  that  we  have  put  in  this  tentative 
proposal  of  the  word  "phot,"  as  made  by  Blondel,  largely  with 
the  idea  that  it  would  form  a  basis  eventually  for  a  real,  inter- 
national unit  of  illumination.  Now,  the  lux  is  unfortunately  a 
kind  of  a  bipartisan  unit;  so  that  perhaps  the  best  thing  under 
present  conditions  would  be  for  us  to  drop  lux  entirely  and  to 
come  out  squarely  and  say  we  propose  to  use  the  phot  and  milli- 
phot.  The  milliphot  has  a  considerable  advantage  in  being  only 
7  per  cent,  removed  from  the  foot-candle,  and  we  would  under- 
stand illumination  values  in  milliphots  very  readily  on  this  ac- 
count. 


chapman:    office  lighting  651 

ARTIFICIAL  LIGHTING  OF  TYPICAL  OFFICES  IN 
STATE,  WAR,  AND  NAVY  DEPART- 
MENT BUILDING.* 


BY  W.  F.  CHAPMAN. 


Synopsis:  This  paper  describes  the  old  and  new  lighting  conditions 
in  the  State,  War,  and  Navy  Department  Building  which  was  constructed 
in  1871-1886.  Especial  attention  is  given  to  the  present-day  lighting 
requirements  in  the  building  and  the  new  system  of  general  illumination 
by  which  they  have  been  satisfactorily  met.  The  colors  used  on  the  walls 
and  ceilings  of  the  rooms  with  the  view  to  obtaining  the  maximum  effi- 
ciency of  tungsten  filament  incandescent  lamps  of  about  1  watt  per  candle- 
power  are  also  discussed ;  and  it  is  shown  that  in  the  new  system  the 
energy  consumption  is  1  watt  per  square  foot  of  floor  space. 


The  State,  War,  and  Navy  Department  Building  at  Washing- 
ton, D.  C,  which  was  constructed  during  the  period  of  1871  to 
1886,  at  a  cost  of  upwards  of  $10,000,000,  and  whose  combined 
floor  space  is  upwards  of  ten  acres,  has  since  its  completion  been 
referred  to  as  the  largest  and  finest  office  building  in  the  world. 
The  architectural  arrangement  of  its  rooms  for  natural  light  and 
ventilation,  as  well  as  for  convenience  of  access,  is  unexcelled  to- 
day; but  naturally  enough  the  artificial  lighting  system  originally 
installed,  consisting  at  first  of  gas  burners  attached  to  large 
ornamental,  solid  brass  chandeliers,  and  later  a  crude  combina- 
tion of  both  gas  and  electricity,  was  soon  outstripped  by  the  rapid 
developments  in  illuminating  engineering. 

There  was  one  four-burner  gas  chandelier  installed  in  the 
center  of  each  room  containing  400  square  feet  of  floor  space, 
which  in  general  is  the  uniform  size  of  all  the  office  rooms.  From 
the  standpoint  of  beauty  and  uniformity  this  arrangement  of  the 
gas  fixtures  was  splendid,  but  its  impracticability  was  developed 
as  soon  as  the  rooms  were  occupied,  and  it  was  found  on  cloudy 
days,  when  artificial  light  was  indispensable,  that  these  fixtures 
furnished  sufficient  light  only  for  those  desks  and  files  which 
were  located  directly  under  them  and  for  a  short  radius  from 
the  center  of  the  room.  The  great  number  of  desks  and  files 
required  by  each  of  the  three  departments  especially  in  rooms 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,   September   20-23,    I9I 5- 

The   Illuminating   Engineering   Society   is   not    responsible    for    the   statements    or 
opinions  advanced  by  contributors. 
4 


652     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

occupied  by  the  large  clerical  forces  made  necessary  the  placing 
of  many  desks  and  files  at  convenient  intervals  in  all  parts  of  the 
room.  In  the  natural  order  of  things  the  larger  files,  which  were 
put  in  in  rapidly  increasing  numbers,  many  of  them  extending 
from  the  floor  to  an  18  foot  (548  m.)  ceiling,  were  placed  against 
the  partition  and  the  interior  walls,  where  the  light  faded  into 
insufficiency  for  practical  purposes.  Many  desks  and  files  were 
of  necessity  placed  beyond  the  zone  of  sufficient  illumination,  so 
that  on  dark  days  the  efficiency  of  the  employees  was  consider- 
ably lowered,  while  some  of  the  employees  suffered  from  im- 
paired eyesight. 

To  overcome  these  difficulties  an  electric  lighting  system  was 
added  throughout  the  building  in  1887  and  1888;  the  arrangement 
of  the  lamps  was  governed  by  the  location  of  the  gas  lights  and 
desks  and  files,  and  therefore  without  any  rule  of  uniformity. 
This  installation,  though  void  of  beauty,  proved  to  be  practical, 
at  least,  for  the  time  being;  but  as  the  business  of  the  departments 
grew,  increasing  the  personnel,  desks,  files,  and  such  office  appli- 
ances as  the  typewriter,  adding  machine,  etc.,  the  furniture  and 
fixtures  had  to  be  rearranged  in  the  rooms  accordingly.  Such 
rearrangement  meant  constant  rearrangement  of  the  electric  lamps 
and  later  the  installation  of  many  desk  lamps  of  different  makes 
and  of  a  variety  of  styles.  Two  to  four  electricians  were  kept  busy 
most  of  the  time  making  these  changes  and  the  rooms  were  soon 
filled  with  unsightly  wires  and  old  style  rosettes  and  fixtures; 
the  ceilings  and  walls  were  marred  with  plugs  and  broken  plaster. 
Some  of  the  units  were  in  use,  and  as  often  as  not  many  of  them 
were  out  of  service. 

The  desk  lamp  feature  was  particularly  annoying  and  came  to 
be  known  in  the  superintendent's  office  as  the  "desk  lamp 
nuisance"  not  only  in  the  matter  of  changes  required  by  rear- 
rangements of  desks,  etc.,  but  because  these  lamps  would  often 
appear  within  the  working  vision  of  persons  occupying  desks  in 
other  parts  of  the  rooms.  Wires  leading  to  them  were  also  in 
the  way  and  these  and  the  other  lamps,  including  gas  chandeliers, 
became  the  lodging  places  for  large  quantities  of  dirt  which,  ex- 
cept in  a  few  instances,  was  never  removed. 

Moreover,  when  the  original  electrical  installation  was  made, 
a  conically  shaped  metal  reflector  was  used.    These  reflectors,  of 


CHAPMAN  :     OFFICE    LIGHTING 


653 


course,  prevented  the  rays  of  artificial  lights  from  reaching  the 
upper  sections  of  file  cases  which,  in  almost  all  instances,  are  in- 
dexed on  the  outside  of  the  box  or  drawer  units  that  fill  up  their 
framework.  Some  means  had  to  be  provided  to  afford  artificial 
light  for  these  files  and  even  the  cumbersome  wire-guarded  port- 
able lamp  was  furnished  in  many  of  the  offices  and  file  rooms,  so 
that  users  of  the  files  could  see  well  enough  to  do  their  work. 


rO— 


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I  CROSS-SECTION 
OF  CEILING  ARCH 


O^ 


9 


n 
1    1 

LJ 


n 


p 


■« 


n  CEILING  OUTLETS 

t]  BASEBOARD  OR  WALL 

OUTLETS 
Ei  JUNCTION  BOX 

S    SWITCH 

MANNER  IN  WHICH 

CIRCUITS  ARE  TO  BE  RUN 


Fig.  1. — Plan  of  rewiring  a  typical  room. 

It  became  apparent  that  this  chaotic  condition  had  to  be  over- 
come by  the  installation  of  some  general  and  uniform  system  of 
illumination,  and  with  this  end  in  view  the  superintendent  of  the 
building  set  about  a  careful  and  exhaustive  study  of  the  problem. 
In  this  study  he  sought  and  obtained  the  advice  of  some  of  the 
most  celebrated  illuminating  engineers  and  experts  of  the  coun- 
try. He  also  consulted  with  a  number  of  the  larger  manufac- 
turers of  modern  fixtures,  who  furnished  him  with  various  sam- 
ples representing  their  different  styles  and  sizes  of  lighting  units 
which  he  installed  and  tested  under  different  conditions.  In  con- 
nection with  the  efficiency  and  adaptability  of  these  units,  he 


654     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

studied  the  effects  of  the  color  of  walls  and  ceilings  on  the  artifi- 
cial light  and  on  the  eye  to  determine  what  color  scheme  would 
serve  best  for  use  with  both  natural  and  artificial  light  from  the 
standpoint  of  its  being  one  that  would  harmonize  with  and  be  a 
proper  reflector  of  light,  and  upon  the  principle  that  such  a 
scheme  must  also  afford  the  eye  a  restful  relief  when  raised  from 
the  routine  of  office  duty. 

Particularly  on  account  of  the  frequent  criticism  of  the  ven- 
tilation, especially  during  the  winter  months  when  doors  and 
windows  are  closed  and  artificial  lighting  is  most  in  use,  the 
superintendent  decided  to  use  electric  incandescent  lamps 
throughout. 

Photometric  tests  were  made  to  ascertain  the  quantity  of  light 
required  per  square  foot  of  floor,  wall  and  ceiling  space  within 
the  rooms  with  different  color  combinations  and  different  sizes 
of  lamps.  These  tests  covered  a  period  of  about  one  year  and 
certain  rooms  were  wired  and  refinished  in  this  scheme  to  ascer- 
tain its  adaptability. 

With  the  adopted  scheme  the  walls  were  given  a  flat  finish  of 
buff,  near  cream,  and  the  ceilings  a  finish  of  ivory  white.  The 
lighting  was  by  means  of  tungsten  filament  incandescent  lamps  of 
about  I  watt  per  candlepower,  selected  and  placed  uniformly  so 
as  to  give  an  energy  consumption  of  I  watt  per  square  foot.  The 
floor  area  of  each  room  was  divided  into  squares  of  about  100 
square  feet  (9.29  sq.  m.)  each  and  a  bowl-frosted  lamp  with  a 
modern  translucent,  light  opal  reflector  suspended  over  the  center 
of  each  square  at  a  height  of  9  feet  (2.7  m.)  above  the  floor. 
(See  Fig.  2.) 

The  frosted  bowl  prevented  any  direct  rays  of  light  from  strik- 
ing the  eye  through  that  portion  of  the  lamp  which  was  exposed 
at  the  bottom  of  the  reflector.  The  reflector  of  course  served  to 
avoid  glare  from  rays  appearing  through  the  clear  portion  of  the 
lamp  and,  being  of  a  high  quality  of  illuminating  glass,  diffused 
the  rays  of  light  against  the  ceilings  and  the  upper  half  of  the 
walls.  The  ivory  white  ceilings  and  buff  walls  reflected  a  great 
portion  of  the  upward  light  rays,  establishing  a  special  diffusion 
at  the  lighting  units  and  a  general  diffusion  at  the  walls  and 
ceilings,  particularly  from  the  ceiling. 


LS"4- 


Fig.  2. — A  typical  small  office  occupied  by  clerks. 


Fig.  3.— Standard  fixtures  used  in  building. 


Fig.  4.— Seven  four-unit  rooms  brought  together  by  removal  of  partitions. 


Fig.  5. — A  drafting  room  with  special  spacing  of  fixtures. 


CHAPMAN  :     OFFICE   LIGHTING 


655 


The  fixtures  proper  are  of  two  kinds :  solid  brass  chains  in  the 
principal  office  rooms  and  gold  colored  silk,  duplex  No.  16 
Brown  and  Sharpe  gauge  lamp  cord  suspended  from  a  brass  egg 
and  dart  canopy  which  rests  against  the  ceiling.  Chain  pull 
sockets  were  installed  for  individual  control  of  the  lamps  with  only 
chain  enough  to  reach  to  within  about  one  inch  of  the  lower  edge 
of  the  reflector.  One  switch  to  control  all  four  lamps  in  each 
room  was  installed  at  a  location  convenient  of  access,  usually 
near  the  door,  one  attachment  plug  being  placed  adjacent  to  the 
switch  and  all  mounted  with  one  brass  cover  flush  with  the  wall, 


30*  IS*  0°         15°  30° 

REFLECTOR  WITH  FROSTED  BOWL  LAMPS 


Fig.  6. — Photometric  distribution  curve  of  reflector  with  a  frosted  bowl  lamp. 


5 

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DISTANCE  IN  FEET  FROM  CENTER  OF  ROOM 
Fig.  7. — Illumination  on  a  horizontal  plane  6  ft.  6  in.  below  two  ioo-watt,  bowl-frosted 
tungsten  lamps  with  reflectors  spaced  10  ft.  apart. 

where  possible.  The  pull  switches  permit  the  two  lamps  nearest 
the  windows  to  be  turned  off  without  disturbing  the  other  two 
when  the  latter  are  needed  in  the  darker  part  of  the  room. 

The  accompanying  drawing,  Fig.  I,  shows  how  the  lamps 
and  the  circuits  to  them  as  well  as  fan  circuits  are  arranged  in 
the  rooms.  Such  a  system  of  course  reduces  but  does  not  elim- 
inate distinct  shadows,  as  it  is  readily  apparent  that  the  light  re- 
flected by  the  walls  and  ceiling  and  appearing  from  the  respective 
units  cannot  be  strong  enough  to  prevent  an  object  from  casting 


656     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


as  many  shadows  as  there  are  lamps  in  a  room,  the  intensity  of 
each  shadow  depending  largely  upon  the  relative  position  of  the 
object  from  the  various  lamps. 

These  reduced  shadows  have  been  found  to  be  of  practically  no 
no  prejudicial  consequences  to  any  of  our  people  except  the  drafts- 
men, and  they  have  not  had  occasion  to  offer  any  serious  complaint. 

It  would  appear  to  be  worthy  of  mention  here  also  that  in  his 
efforts  to  arrive  at  a  satisfactory  system  of  general  illumination, 
the  superintendent  sought  to  approach  as  nearly  as  possible  a 
flat  curve  of  illumination  throughout  all  parts  of  the  room,  walls 
and  ceilings  included ;  and  the  wall  and  ceiling  reflections  in  addi- 
tion to  the  diffusion  at  the  lamps  go  as  far  towards  accomplish- 
ing such  a  result,  perhaps,  as  could  be  by  the  use  of  exposed 
illuminating  units. 

To  replace  all  the  old  objectionable  special  illumination  with 
an  efficient  system  of  general  illumination  throughout  the  build- 


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Fig.  8. — Illumination  on  a  horizontal  plane,  6  ft.  6  in.  below  4,100-watt,  bowl-frosted  tung- 
sten lamps,  with  translucent  reflectors,  spaced  10  ft.  apart.  Curve  taken  on  a  line 
through  center  of  four-unit  room,  2  ft.  6  in.  above  the  floor,  or  at  about  the  top  of  the 
ordinary  desk. 

ing  was  the  one  paramount,  thing  to  be  accomplished,  and  it  was 
the  determination  of  the  superintendent  that  this  should  be  done. 
Many  persons  accustomed  to  the  use  of  desk  or  individual  drop 
lamps  registered  vigorous  protests  against  their  being  compelled 
to  use  the  general  system,  but  once  it  was  installed  and  the  walls 
and  ceilings  changed  from  the  old  dark,  light-absorbing  blue  to 
the  more  cheerful,  light-reflecting  buff  and  white,  the  value  and 
practicability  of  the  change  was  immediately  appreciated. 

The  work  of  re-illuminating  the  entire  building,  except  for  a 
few  special  rooms,  was  commenced  in  November,  1914,  and  com- 
pleted in  February,  1915. 

In  practise  so  far  the  new  scheme  has  produced  eminently 
satisfactory  results,  and  it  is  believed  that  it  will  meet  all  ordinary 
office  requirements  for  a  long  time  to  come. 


OFFICE   LIGHTING  657 

DISCUSSION. 

Mr.  W.  A.  Durgin  :  Figs.  7  and  8  show  a  maximum  foot- 
candles  intensity  below  3.  Does  this  represent  the  "new  lamp 
and  clean  reflector"  condition?  With  the  marked  increase  in 
lamp  efficiencies  it  would  seem  that  our  government  should  em- 
ploy much  higher  intensities  not  only  to  secure  higher  output 
from  the  workers,  but  also  to  take  position  in  the  forward  line 
of  progress. 

Mr.  W.  E.  Chapman  (In  reply)  :  Lighting  conditions  are 
such  that  during  the  daytime  there  is  enough  natural  light  in  most 
of  the  rooms,  except  on  cloudy  days.  It  is  not  required  that  the 
artificial  lighting  units  shall  supply  all  of  the  light.  They  are 
merely  auxiliary  to  the  natural  light.  Persons  working  at  night, 
however,  find  the  artificial  light  adequate  for  all  general  pur- 
poses. 

Mr.  G.  S.  Barrows:  This  is  a  very  interesting  paper,  but  I 
cannot  add  much  to  the  discussion  except  simply  to  agree  with 
Mr.  Durgin.  I  think  we  ought  to  be  rather  careful  to  note  the 
difference  between  new  and  clean  lamps  and  the  average  con- 
dition. Mr.  Chapman's  curves  show  a  fair  average  condition; 
that  was  a  point  that  was  not  quite  clear  to  me,  but  that  has  just 
been  explained. 

Mr.  W.  E.  Chapman  :    That  was  the  condition. 

Mr.  G.  S.  Barrows:  I  don't  understand  from  the  paper 
that  there  has  been  any  attempt  to  install  indirect  or  semi-indirect 
lighting.  I  should  like  to  know  whether  the  architectural  con- 
struction is  such  that  it  is  inadvisable,  or  why  some  attempt  was 
not  made  to  install  either  of  these  systems. 

Mr.  W.  E.  Chapman  :  The  reason  is  quite  clear.  We  have 
a  condition  that  would  permit  of  semi-indirect  or  indirect  light- 
ing, but  it  was  a  question  of  funds.  We  were  dependent  upon 
the  appropriation  of  Congress  for  making  the  improvements  that 
were  necessary;  it  was  impossible  to  get  sufficient  money  from 
Congress  to  make  a  better  installation.  We  had,  therefore,  to  do 
the  next  best  thing  and  use  the  system  outlined  in  my  paper. 

When  the  wiring  in  the  State,  War  and  Navy  Department 
Building  was  installed  in  1887  and  1888,  the  circuits  were  simply 


658     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

run  in  wooden  mouldings,  which  were  exposed  and  altogether  it 
was  a  very  poor  and  hazardous  installation ;  but  in  the  new  wiring 
process  the  circuits  have  been  run  in  metallic  conduits  in  all  in- 
stances so  that  they  are  now  thoroughly  up  to  date  throughout 
the  building. 


DICKER  AND   KIRK:     LIGHTING   IN    OFFICE   BUILDINGS      659 

LIGHTING  IN  DOWNTOWN  OFFICE  BUILDINGS.* 


BY  ALFRED  O.  DICKER  AND  JAMES  J.  KIRK. 


Synopsis:  This  paper  contains  data  in  tabular  form  concerning  elec- 
tric lighting  service  in  certain  office  buildings  in  the  downtown  district 
of  Chicago.  The  buildings  were  selected  as  typical  examples  of  lighting 
installations  made  thirty,  twenty-five,  twenty,  fourteen  and  six  years  ago; 
and  one  which  was  completed  recently.  Curves  are  given  to  show  the 
relation  between  watts  per  square  foot  and  foot-candles  for  the  thirty 
years,  and  also  the  relation  of  cost  per  square  foot  per  month  for  the 
various  buildings.  No  attempt  has  been  made  in  the  paper  to  give  a 
technical  description  of  the  present  installations  or  to  give  recommenda- 
tions for  changes.  The  installations  have  been  taken  as  they  are  and  the 
description  given. 


The  illuminating  engineer  is  by  nature  attracted  to  the  proposed 
building  rather  than  to  the  older  one  which  he  passes  in  his  every- 
day walks  of  life.  He  is  desirous  of  having  the  lighting  in  the 
new  building  when  completed  typical  of  the  best  lighting  practise, 
and  in  the  age  of  "tear-down-the-old  and  build-a-new"  he  has 
found  a  large  field.  Nevertheless  in  the  older  buildings  lies  a 
much  larger  field  of  almost  untouched  harvest.  In  these,  the 
older  buildings,  are  thousands  of  workers  toiling  under  lighting 
conditions  typical  of  the  first  installations  that  were  made.  These 
lighting  systems  will  soon  be  changed.  They  are  so  old  now  that 
either  the  wiring  will  be  condemned  by  the  various  inspection 
departments,  or  else  the  tenants  or  owners  will  realize  that  for 
their  own  mercenary  benefit  more  and  better  light  must  be  pro- 
vided for  their  employees. 

The  lighting  of  thirty  years  ago  is  as  absurd  to-day  as  the 
business  policies  of  that  period  when  applied  to  present-day 
business.  It  is  also  true  that  antiquated  lighting  installations 
are  just  as  much  a  source  of  real  loss  as  are  antiquated 
business  systems.  Proper  lighting  is  now  generally  considered 
an  essential  part  of  factory  equipment  and  an  essential  item 
in  the  reduction  of  manufacturing  cost;  but  at  present  it  is  not 
generally  accepted  among  business  men  as  an  item  in  reducing 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing Society,  Washington,  D.   C,   September  20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


660     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

office  costs.  Data  showing-  the  reduction  of  office  cost  are  diffi- 
cult to  obtain,  but  few  engineers  would  dispute  the  statement 
that  the  working  efficiency  of  a  clerk  or  stenographer  is  reduced 
25  per  cent,  after  sundown  in  a  poorly  lighted  office.  This  is 
the  period  of  the  day  when  the  workers  are  tired  and  is  therefore 
the  period  during  which  their  comfort  and  efficiency  should  be 
considered. 

One  of  the  objects  of  this  paper  is  to  show  the  progress  of 
lighting  practise  in  downtown  office  buildings  during  the  last 
thirty  years,  by  taking  as  examples  buildings  typical  of  the  periods 
during  which  they  were  built.  For  this  purpose  six  buildings 
were  chosen  as  follows : 

Building  No.  1  built  30  years  ago 


2     ' 

'     25 

3      ' 

1     20 

4     ' 

'     14 

5     ' 

'       6 

In  all  these  buildings,  even  the  most  modern,  are  installations 
which  the  illuminating  engineer  would  refuse  to-day  to  accept  as 
proper  lighting;  but  nevertheless  they  are  considered  typical  for 
the  purpose  of  this  paper. 

It  so  happens  that  the  oldest  building  chosen  is  one  in  which 
the  owners  had  foresight  enough  at  the  time  of  its  construction 
to  wire  for  electricity.  In  the  next  two,  in  age,  wiring  was 
omitted  at  the  time  of  construction  but  soon  thereafter  it  was 
wired  in  exposed  conduit  or  wooden  moulding.  In  all  three  of 
these  buildings  the  lighting  is  crude  both  from  point  of  construc- 
tion and  resulting  illumination.  The  installation  has  been  made 
without  thought  or  design — a  drop  cord  installed  over  the  desk 
or  table  where  light  was  required.  At  this  period  electric  light 
was  expensive  and  the  minimum  amount  was  therefore  utilized. 
A  summary  of  the  lighting  of  these  three  buildings  is  of  little  or 
no  interest  except  as  a  comparative  basis.  The  lighting  is  local- 
ized without  reflectors  in  many  cases  and  where  reflectors  are 
found  a  very  cheap  and  inefficient  one  has  been  installed.  The 
lighting  is  very  inadequate.  The  original  installation  was  of 
carbon  lamps  which  have  now  been  replaced  by  tungsten  lamps, 
usually  of  40  and  60-watt  size.  Cluster  fixtures  as  a  rule  pre- 
vail— the  most  predominant  type  being  a  three  or  four-arm  fixture 


DICKER  AND    KIRK:     LIGHTING   IN   OFFICE   BUILDINGS      66l 

suspended  on  a  rigid  stem  installed  approximately  6  ft.  6  in. 
(1.98  m.)  above  floor.  Wall  switches  were  used  occasionally, 
but  as  a  rule  key-sockets  have  been  utilized.  The  esthetic  con- 
siderations were  not  developed,  but  rather  the  lighting  fixture 
was  considered  a  necessary  evil  and  not  an  ornament. 

The  next  three  buildings  in  chronological  order  show  somewhat 
the  effect  of  the  illuminating  engineer,  at  least  it  may  be  said 
that  the  lighting  equipment  has  been  given  some  attention.  The 
fixtures  are  more  efficient,  more  ornate,  and  general  illumination 
has  been  introduced.  The  spacing  shows  a  decided  tendency 
away  from  localized  lighting  although  in  many  of  the  offices, 
desk  lamps  have  had  to  be  relied  upon.  Particularly  in  these 
newer  buildings  the  individual  taste  of  the  tenant  as  regards  his 
lighting  is  evident,  and  so  there  are  seen  suites  with  semi-direct 
and  indirect  systems  in  all  their  variations. 

The  general  building  conditions  are  tabulated  in  Table  I,  which 
will  answer  at  a  glance  many  of  the  questions  which  might  arise 
as  to  the  details  of  the  physical  characteristics  of  the  building  and 
its  lighting  equipment.  Its  only  value  will  be  for  purposes  of 
comparison  with  Table  II  and  a  description  of  the  lighting  fixtures 
used.  A  continued  advancement  in  fixture  design,  the  tendency 
toward  larger  lamps  and  the  deviation  from  localized  lighting 
toward  general  illumination  is  seen  in  columns  6  to  16,  with  the 
addition  in  the  newer  buildings  of  semi-direct  and  indirect.  It 
would  be  well  to  add  here  that  even  in  the  oldest  building  there 
exist  installations  of  semi-direct  and  direct  but  these  do  not  occur 
in  sufficient  numbers  to  change  the  typical  lighting  system  of  the 
building.  It  must  be  remembered  that  these  buildings  were  not 
selected  as  examples  of  good  lighting,  but  rather  as  buildings 
containing  lighting  installations  typical  of  the  age  in  which  they 
were  built. 

Table  II  shows  the  total  building  light  and  power  load  to- 
gether with  such  factors  as  influence  the  cost  of  such  service. 
The  connected  load  may  be  referred  to  Table  I  for  reference  to 
the  size  of  the  building. 

The  load-factor1  varies  from  6.34  per  cent.,  or  1.52  hours,  to 

1  Load-factor,  as  used  in  this  paper,  may  be  described  as  follows  :    The  ratio  of 
actual  monthly  meter  consumption  (Kw-h.)  to  continuous  use  of  maximum  demand,  or 
Kw-h.  (consumption) 
720  X   Kw-h.  (maximum) 


662     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


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DICKER   AND    KIRK  :     LIGHTING   IN    OFFICE   BUILDINGS      663 


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664    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


17.48  per  cent.,  or  4.2  hours  use  of  maximum  demand.  The 
minimum  may  be  explained  by  the  fact  that  this  building  is  one 
in  which  the  lighting  was  installed  after  the  building  was  com- 
pleted and  the  installation  was  very  inadequate.  The  maximum 
load-factor  occurs  in  a  newspaper  building  of  such  design  that 
many  of  the  lights  burn  of  necessity  most  of  the  day. 

The  rates  for  electric  service  upon  which  is  based  the  "average 
net  bill  per  month"  is  as  follows :  the  building  owner  buys  the 
electric  service  for  light  and  power  either  on  a  wholesale  con- 
tract, if  the  building  is  of  sufficient  size,  or  on  separate  contracts 
for  light  and  power.  In  either  case  in  the  buildings  chosen  for 
discussion  in  this  paper  the  tenants  are  individual  customers  of 
the  Commonwealth  Edison  Company.  In  the  determination  of 
the  item  of  cost,  the  ratio  of  maximum  demand  to  connected  load 
is  a  prominent  factor  and  for  this  reason  it  is  here  included. 
TABLE  II-A.— Comparative  Lighting  Data. 


Age 

Total  building  light  and  power 

Bldg. 

Connected 

Per  cent, 
load- 
factor 

Av.  Kw-h. 

Av.  max. 

Av.  net 

bill 

per  month 

Ratio  max. 
connected 

load  Kw. 

per  month 

per  month 

load 
per  cent. 

1 

2 

3 

4 

5 

6 

7 

8 

I 

30 

IOO.I08 

IO.45 

7,535-8 

70.O 

1  388.37 

70 

2 

25 

I59.2IO 

6-34 

7,212.9 

63-3 

357.52 

39 

3 

20 

380.124 

7-33 

20,062.7 

232.4 

1,008.75 

61 

4 

14 

877.823 

17.48 

110,486.4 

424.2 

2,347.20 

48 

5 

6 

I99.089 

13-03 

18,241.1 

134-4 

745-47 

67 

6 

1 

342.790 

6.38 

15,978.7 

96.0 

610.82 

28 

TABLE  II-B.— Comparative  Lighting 

Data. 

Elevators  and  Public  lights 

Bldg. 

Elevators 

Connected 
load  Kw. 

Per  cent, 
load- 
factor 

Av.  Kw-h. 
per  month 

Av.  max. 

Kw. 
per  month 

Av.  net 

bill 

per  month 

Ratio  of 

max.  to 

connected 

load 

I 
2 

3 
4 
5 
6 

9 

5  hyd. 
2  elec. 

12  elec. 

8  hyd. 

6  elec. 
8  elec. 

10 

4-500 
78.250 
41.472 

688.602 
70.870 

220.090 

11 

30.91 
8.25 
17.42 
19.88 
23.II 
6.71 

12 

1,001.5 

4,626.0 

5,201.5 

98,553-6 

12,007.5 

10,789.3 

13 

3-96I 
50. 700 
16.165 
3H.666 
68.625 
45.OOO 

14 

$     40.74 
183.74 
185.23 

L 753-31 
403.37 
338.12 

15 

SS 
64 
38 
45 
96 
20 

DICKER  AND    KIRK:     LIGHTING   IN    OFFICE   BUILDINGS      665 


Similarly  the  second  portion  contains  data  on  elevators  and 
public  lamps. 

This  table  contains  a  separation  of  Table  II-A  showing  the 
same  data  on  that  part  of  the  total  service  which  is  used  for 
elevators  and  public  lamps.2 

The  percentage  of  this  portion  of  the  electric  consumption  to 
the  total  building  consumption  is  shown  below : 

Building  Per  cent. 

No.  1 13-3 

No.  2 64.1 

No.  3  ?5-9 

No.  4s 89.1 

No.  5 65.8 

No.  6 67.5 

or  an  average  of  39.3  per  cent,  for  all  of  the  buildings  (excluding 
No.  4). 

TABLE  II-C— Comparative  Lighting  Data. 


Offices 

Bldg. 

Connected 
load  Kw. 

Load- 
factor 

Number 

offices 

occupied 

Av.  Kw-h. 
per  office 
per  month 

Av.  max. 
per  office 
per  month 

Av.  net  bill 
per  office 
per  month 

Ratio  of 

max.  to 

connected 

load 

I 

2 

3 
4 
5 
6 

16 

73-748 

80.960 

307.242 

I5I-6S3 

II2.900 

53-90I 

17 

6.76 
4.64 
5.22 
6.16 
4.70 
2.43 

18 

88 
80 
305 
73 
60 

3i 

19 
40.6 

32.3 
37-8 
92.1 
64.8 
95-6 

20 

0.632 
0.684 
0.667 
1. 2l8 
O.936 
I.32 

21 

$2.62 
2.17 
2.24 

4-97 

4.09 

5.82 

22 

75 
64 
66 
58 

49 
76 

Here  are  displayed  the  same  conditions  applied  to  the 
office  or  rentable  area  of  the  building.  This  portion  represents 
17.0  per  cent,  of  the  total  building  consumption.  The  tenant's 
load-factor  is  extremely  low,  showing  a  use  of  the  demand  of 
from  one  half  to  one  and  one  half  hours  per  day.  The  minimum 
load-factor  occurs  in  the  newest  building.  This  is  due  to  the 
fact  that  the  building  occupies  a  small  land  area  with  good  ex- 
posure facing  Lake  Michigan,  and  it  is  higher  than  the  surround- 

2  Public  lamps  include  all  lighting  contained  in  or  around  building  which  is  not 
chargeable  to  tenants'  meters,  t.  e.,  corridors,  exterior  lighting,  toilets,  etc.  Elevators 
include  all  electricity  used  for  power  purposes. 

8  This  includes  power  for  printing  presses  and  is  therefore  not  typical  for  this  class  of 
ouilding. 


666     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


ing  buildings.     The  conditions  make  daytime  burning  of  lamps 
unnecessary  in  many  of  the  offices. 

TABLE  II-D. — Comparative  Lighting  Data. 


Store 

space 

Bldg. 

Connected 
load  Kw. 

I<oad- 
factor 

Av.  Kw-h. 
per  month 

Av.  max. 

Kw. 
per  month 

Av.  net 

bill 

per  month 

Ratio  of 
max.  to 

connected 
load 

per  cent. 

23 

24 

25 

26 

27 

28 

I 

2I.86o 

18.78 

2,955-7 

IO.4 

$116.63 

47 

2 

80.960 

4.64 

32-3 

O.68 

2.17 

67 

3 

31.410 

14.62 

3,307-0 

12.6 

I37-40 

40 

4 

37-538 

I9-25 

6,203.3 

23.6 

230.45 

63 

5 

I.5.3II 

20.97 

2,343-2 

9.6 

96.41 

63 

6 

68.899 

4-32 

2,223.2 

10. 1 

92.15 

14 

Inasmuch  as  the  store  and  shop  areas  on  the  first  and  second 
floors  represent  a  load-factor  of  considerably  higher  value  than 
the  office  space,  a  further  separation  has  been  made.  In  this 
table  the  load  used  by  the  store  or  shop  is  analyzed.  This  portion 
represents  9.5  per  cent,  of  the  total  building  consumption.  It 
will  be  noted  that  the  average  load-factor  of  this  portion  of  the 
building  is  13.76  per  cent.  (3.3  hours)  as  against  4.99  per  cent. 
(1.2  hours)  for  the  office  portion,  and  the  ratio  of  maximum 
demand  to  connected  load  is  49.3  per  cent,  for  this  portion  as 
against  73.3  per  cent,  for  the  office  portion,  which  shows  the  store 
to  be  the  longer-hour  user,  while  the  office  uses  a  higher  propor- 
tion of  the  connected  load  for  a  very  short  time.  The  former  load 
is  by  far  the  most  desirable  one  from  the  central-station  point  of 
view.  The  fact  that  the  office  uses  the  lamps  for  such  a  short 
period  is  probably  the  reason  that  the  office  is  the  most  dilatory 
in  considering  lighting  improvement;  but,  as  already  stated,  the 
time  that  the  office  requires  light — short  though  it  may  be — is 
the  very  time  that  light  is  most  essential. 

Table  II-E  sums  up  all  the  lighting  data  which  have  preceded. 
It  will  be  noted  that  during  the  thirty  years  there  has  been  little 
change  in  the  watts  per  square  foot  provided,  while  the  intensity 
has  increased  with  each  period  and  the  cost  per  square  foot  has 
decreased.  It  must  be  borne  in  mind  that  the  reason  for  the 
fact  that  the  provided  load  has  not  increased  during  this  thirty- 


Fig.  i.— An  installation  in  the  oldest  office  building. 


Fig.  2. — An  installation  in  the  newest  building. 


..,-' 

FOOT-CANDLES  - 



- 

»*--*" 

,.-- 

-"" 

-" 

YEARS 

Curve  i. 


Curve  2. 


DICKER  AND   KIRK:     LIGHTING   IN    OFFICE   BUILDINGS      667 

year  period  is  because  the  older  buildings  were  not  provided  with 
what  is  to-day  called  sufficient  illumination,  together  with  the 
increased  efficiency  of  illuminants.  The  standards  of  to-day  are 
greatly  in  excess  of  those  of  previous  years.  These  relations  are 
shown  graphically  in  curves  1  and  2. 

TABLE  II-E.— Comparative  Lighting  Data. 


Bldg. 

Watts  per  sq.  ft. 

Intensity 
foot-candles 

Cost  of  light  per 
sq.  ft.  per  month 

1 

I 
2 

3 

4 
5 
6 

29 

I.02 

0.75 
I.09 
I.24 
O.94 
I.02 

3° 

1-5 
2.0 

3-o 
3-5 
4.0 

4-5 

31 

$0,042 
0.018 
O.03I 
0.029 
O.025 
O.OI6 

Curve  1  shows  the  increased  intensity  of  illumination  with 
practically  the  same  provided  load. 

Curve  2  shows  the  reduction  in  cost  of  electric  light  due  to 
increased  efficiency  of  illuminants  and  fixtures.  Curve  3  shows 
the  reduction  in  cost  due  to  increased  efficiency  of  illuminant, 
fixtures  and  reduction  in  rates  for  lighting. 

Table  III  shows  data  on  the  office  portion  of  the  first  four 
buildings  using  carbon  lamps  as  was  the  case  when  the  lighting 
systems  were  installed.  In  this  table  the  rating  of  the  lamp  is 
five  watts  per  candle.  The  cost  data  are  shown  graphically  on 
curve  3. 

TABLE  III.— Carbon  Lamp. 
Offices. 


Bldg. 

Connected 
load  Kw. 

Per  cent, 
ratio  of 
max.  to 

connected 
load 

Per  cent, 
load-factor 

Average 

Kw-h. 
per  office 
per  month 

Average 

net  bill 

per  month 

per  office 

Cost  in  cents 
per  sq.  ft. 
per  month 

I 
2 
3 
4 

368.740 

404.800 

1,536.210 

758.415 

75-48 
67.18 
66.282 
58.607 

6.764 
4.64 
5-223 
6.162 

203.325 
161.650 
189.400 
460.915 

|I3.I2 
IO.86 
II.24 
24.89 

3-975 
1. 810 
2.810 
6.220 

Progress  during  these  thirty  years  may  be  very  forcefully  shown 

5 


668     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

by  a  comparison  of  the  two  photographs.  The  first  one  is  of  an 
original  installation  in  the  oldest  building  and  the  second  of  the 
newest  installation  in  the  newest  building.  These  two  pictures 
indicate  two  extremes :  one  is  merely  a  method  of  supporting  the 
light  source,  the  other  an  efficient  ornate  lighting  fixture. 


DISCUSSION. 

Mr.  G.  H.  Stickney:  There  are  a  few  classes  of  workers 
who  are  subjected  to  more  severe  eye-strain  than  office  employees. 
Casual  observation  will  show  many  examples  of  inadequate  and 
glaring  illumination.  It  is  to  be  hoped,  therefore,  that  the  ex- 
cellent papers  dealing  with  this  subject  will  be  influential  in  bet- 
tering conditions. 

Owing  to  the  crowding  of  buildings  in  our  large  cities,  artificial 
lighting  is  used  to  supplement  daylight  fully  as  much  as  for  night 
work.  When  used  in  the  daytime  a  higher  intensity  is  demanded 
than  for  night  work.  On  the  other  hand  glare  effect  is  less  ser- 
ious. I  have  in  mind  an  office  illuminated  by  direct  lighting 
which  in  the  evening  appears  glary  and  somewhat  overlighted, 
but  in  the  dusk,  which  represents  the  period  of  maximum  use, 
the  lighting  is  unusually  good.  I  mention  this  to  bring  out  the 
point  that  an  installation  often  has  two  distinct  requirements  to 
meet  which  may  necessitate  a  compromise  in  the  design.  In  gen- 
eral it  is  apparent  that  the  practise  in  office  lighting  is  tending 
strongly  toward  the  use  of  the  semi-indirect  and  indirect  types 
of  equipment  and  with  this  is  coming  a  considerable  improvement 
in  the  standard  of  office  lighting. 

Mr.  G.  S.  Barrows:  This  paper  states:  "It  so  happens  that 
the  oldest  building  chosen  is  one  in  which  the  owners  had  fore- 
sight enough  at  the  time  of  its  construction  to  wire  for  elec- 
tricity." That  building  has  been  built  about  30  years  and  I  won- 
der if  the  wiring  put  in  at  that  time  will  meet  with  the  approval 
of  the  underwriters.  I  should  like  to  ask  the  authors  if  they 
found  it  necessary  to  change  the  wiring  in  this  building.  I  think 
that  is  a  point  that  possibly  is  being  lost  sight  of  in  an  attempt  to 
simply  provide  for  proper  illumination.  It  seems  to  me  that  it  is 
most  desirable  for  us  to  impress  on  architects  and  builders  the 


LIGHTING   IN   OFFICE    BUILDINGS  669 

necessity  of  providing  for  proper  wiring  and  also  gas  piping  in 
all  buildings  that  are  being  erected.  There  is  no  telling  what  the 
developments  may  be  in  the  future  and  provision  should  be  made 
for  the  use  of  either  form  of  energy.  The  cost  of  providing  for 
either  electric  wiring  of  any  kind,  that  is,  providing  for  wiring 
that  may  be  done  at  some  future  time,  in  accordance  with  some 
future  ruling  of  the  underwriters,  or  the  installation  of  gas 
piping  is  but  a  very  small  fraction  of  a  per  cent,  of  the  total  cost 
of  the  building;  whereas  after  the  building  is  erected,  the 
proper  wiring  or  piping  may  amount  to  a  very  large  per  cent,  of 
the  total  cost  of  the  building.  Beyond  the  simple  use  of  energy 
for  light  there  is  no  telling  what  the  developments  may  be  for 
the  use  of  energy  for  some  other  purpose,  for  heating  or  we  don't 
know  what,  and  so  I  think  that  as  illuminating  engineers,  or  as 
engineers,  I  should  say,  we  ought  to  go  a  little  further  than  sim- 
ply taking  care  of  the  illumination  at  the  present  time.  We  ought 
to  impress  on  the  architects  and  builders  to  provide,  as  far 
as  they  can,  for  all  future  demands.  That  question  has  been,  and 
is  being,  pretty  carefully  studied  by  a  good  many  people  at  the 
present  time  and  I  think  we  should  provide  for  supplying  in  the 
future  energy  for  almost  any  purpose. 

Mr.  James  J.  Kirk  :  I  might  say  a  few  words  in  regard  to 
the  wiring  conditions  of  the  building  that  was  built  30  years  ago. 
At  the  time  this  building  was  completed  it  was  inspected  and  was 
passed  by  the  City  Inspection  Department.  Since  that  time  it 
has  been  reinspected  for  defective  wiring.  Wiring  for  new  in- 
stallations have  also  been  made  in  accordance  with  the  latest  rules 
of  the  Department  of  Gas  and  Electricity. 


6/0    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

PILOT  FLAME  IGNITION  OF  INCANDESCENT 
GAS  LAMPS  * 


BY  C.  W.  JORDAN. 


Synopsis:  Despite  the  fact  that  many  ingenious  mechanisms  have 
been  devised  for  securing  automatic  distance  ignition  of  gas  lamps,  the 
simple  by-pass  pilot  flame  remains  as  the  most  positive,  serviceable  and 
economical.  A  description  of  various  types  of  pilot  tips  and  by-passes  is 
given,  together  with  illustrations  of  the  most  successful  types.  The 
troubles  which  are  often  encountered  in  service  are  enumerated,  as  well 
as  means  which  have  been  devised  for  their  elimination.  The  application 
of  a  new  type  of  pilot  in  giving  ample  general  illumination  to  distinguish 
objects  in  rooms  at  night  is  described  in  detail. 


INTRODUCTION. 

The  subject  of  pilot  flame  ignition  of  incandescent  gas  lamps 
may  appear  to  many  to  be  rather  a  minor  or  unimportant  detail 
of  the  broad  general  subject  of  gas  lighting,  and  yet  on  analysis 
it  will  be  found  to  be  extremely  vital  for  the  successful  operation 
of  lamps  in  practise. 

Convenience  in  gas  lighting  has  become  a  necessity  and  many 
devices  have  been  perfected  for  securing  automatic  ignition,  in 
some  cases  controlled  from  distant  points.1- 2- 

Despite  the  ingenuity  shown  in  the  design  and  mechanical  con- 
struction of  these  devices,  for  one  reason  or  another  they  have 
not  recommended  themselves  as  competent  to  meet  the  practical 
requirements  of  service. 

Those  which  are  apparently  satisfactory  automatically  actuate 
a  mechanism,  turning  on  the  main  gas  supply  which  in  turn  is 
ignited  by  means  of  a  pilot  flame.  Therefore  the  convenience  of 
such  mechanical  devices  is  dependent  not  only  upon  their  own 
merits,  but  also  upon  that  of  the  pilot. 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,   Washington,   D.   C,    September  20-23,    191 5- 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 

1  Gilpin,  F.  H.,  Automatic  and  Distant  lighters  ;  Proceedings  A.  G.  I.,  vol  VIII,  1913, 
Part  II. 

2  Jordan,  C.W.,  Recent  Advances  in  Indoor  Gas  lighting;  Trans.  I.  E-  S.,  vol.  IX,  1914. 


JORDAN:     INCANDESCENT   GAS   LAMPS  671 

Other  devices,  which  do  not  use  pilots,  while  ingenious,  well 
constructed  and  positive  in  action,  owing  to  their  high  initial  cost 
do  not  find  wide  application. 

Pyrophoric  igniters,  self-lighting  mantles,  etc.,  are  not  exten- 
sively used  because  of  the  ease  with  which  the  mechanical  parts 
get  out  of  order  or  on  account  of  the  short  life  of  the  active 
material. 

The  simple  pilot  by-pass  and  gas  cock  actuated  by  pulling  a 
chain  meet  the  demand  for  convenience,  economy  and  service  in 
the  most  satisfactory  manner. 

This  paper,  therefore,  will  be  devoted  to  telling  the  history  of 
the  use  and  improvement  of  this  simple  means  of  ignition,  which 
depends  upon  the  same  energy  or  fuel  that  supplies  the  lamp 
itself,  and  which  is  operated  by  the  same  mechanical  movement 
that  controls  the  lamp.  Every  consideration  points  to  this  as  the 
ideal  as  well  as  common  sense  method  of  ignition,  if  it  can  be 
perfected. 

PILOT  BY-PASSES. 

The  term  pilot  by-pass  may  be  defined  as  a  device  by  means  of 
which  a  supply  of  gas  is  regulated  and  led  from  a  point  just 
ahead  of  the  gas  cock  of  a  lamp  to  a  pilot  tip  or  point  of  dis- 
charge conveniently  placed  near  the  mantle. 

The  gas  cock  and  pilot  take-off  are  in  some  cases  of  separate 
construction  from  the  lamp  and  easily  detachable,  while  in  others 
they  constitute  a  true  part  of  the  lamp  construction. 

The  length  of  the  pilot  flame  is  regulated  by  turning  a  small 
screw  which  moves  in  or  out  of  a  constriction  in  the  passageway 
leading  to  the  pilot  tip. 

In  some  instances  lamps  are  equipped  with  so-called  "flash 
pilots."  A  flash  pilot  may  be  defined  as  one  in  which  the  pilot 
momentarily  elongates  during  ignition  and  shoots  across  the  top 
of  or  into  one  or  more  mantles  of  the  lamp.  The  means  for 
successfully  accomplishing  this  are  several. 

In  one  lamp  a  secondary  cock  is  connected  to  the  primary  gas 
cock  so  that  upon  pulling  the  chain  to  light  the  lamp  it  is  turned 
1800  and  the  gas  passes  through  to  the  pilot  tip  at  unrestricted 
pressure,  by-passing  the  ordinary  regulating  screw. 

Another  device  consists  of  an  additional  passageway  bored  in 


6/2     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

the  gas  cock,  which  on  being  turned  on  supplies  gas  at  unrestricted 
pressure  through  a  small  tube  by-passing  the  regulating  screw. 
When  the  cock  is  turned  on  full  the  passageway  in  the  gas  cock 
is  no  longer  opposite  the  passageway  leading  around  the  regu- 
lating screw  and  the  gas  to  the  pilot  is  supplied  only  through 
the  usual  regulating  screw. 

Flash  pilots  are  effective,  especially  in  arc  lamps,  in  that  they 
secure  more  positive  and  softer  ignition  of  all  the  mantles. 

PILOT  TIPS. 

Little  trouble  has  been  experienced  in  constructing  efficient 
means  for  regulating  and  conveying  the  pilot  gas  supply  to  the 
point  of  discharge,  but  the  construction  of  a  satisfactory  pilot  tip, 
especially  for  inverted  lamps,  has  been  very  difficult. 

The  main  troubles  encountered  are  (1)  carbon  formation,  (2) 
clogging  of  the  tip,  due  to  disintegration  of  the  gas,  etc.,  and 
(3)  the  ease  of  extinguishing  the  flame  by  draughts. 

With  upright  lamps  a  plain  metal  tube  of  small  diameter,  placed 
properly  in  a  vertical  position,  burns  satisfactorily,  but  the  flame 
is  easily  extinguished  if  the  lamp  is  subjected  to  excessive 
draughts. 

A  center  pilot  was  then  designed  which  consists,  briefly,  of 
placing  the  pilot  flame  directly  above  and  in  the  center  of  the 
burner  cap  gauze,  thus  utilizing  the  mantle  as  a  means  of  effec- 
tively protecting  the  flame  from  draught.  The  construction  of 
a  center  pilot  by-pass  is  shown  in  Fig.  1. 

With  inverted  lamps  it  was  necessary  to  use  pilot  tips  made  of 
lava  or  other  refractory  material  in  order  to  overcome  the  com- 
mon troubles  before  mentioned. 

Lava  pilot  tips  have  undergone  decided  changes,  both  in  the 
principle  upon  which  they  operate  and  in  design.  The  first  type 
consisted  of  a  simple  passage,  drilled  through  the  tube  and  having 
a  side  outlet  for  discharging  a  luminous  flame  horizontally.  A 
pilot  tip  was  then  developed  which  gives  a  blue  Bunsen  flame 
while  burning.  The  gas  discharges  horizontally  through  a  small 
orifice  into  a  mixing  tube  provided  with  two  air  inlets.  When 
operating  at  normal  consumptions,  between  0.1  and  0.15  cu.  ft. 
per  hour,  a  perfect  Bunsen  flame  is  obtained  which  is  extinguished 
by  draught  with  far  greater  difficulty  than  the  luminous  flame 


JORDAN:     INCANDESCENT   GAS   LAMPS 


673 


pilot  and  has  the  additional  advantage  of  eliminating  troublesome 
carbon  formation  or  smoky  flame.  Changing  the  position  of  the 
primary  air  inlets  from  a  vertical  to  a  horizontal  position  was 
found  to  render  the  pilot  appreciably  more  resistant  to  draughts. 
Six  types  of  lava  tips  are  shown  in  Fig.  2. 

In  the  early  development  of  the  Bunsen  flame  pilot  a  series  of 
unlooked-for  defects  were  found,  a  description  of  which  may  be 
of  interest.  In  order  to  obtain  a  true  Bunsen  flame  it  is  necessary 
to  make  the  orifice  of  very  small  diameter,  0.016  in.  (0.40  mm.). 
After  several  hundred  hours  burning  of  the  lamp  the  orifices 
invariably  become  clogged.    The  tips  were  made  of  natural  lava, 


A- LUMINOUS  F1AMT.    LAVA  TIP 

3-  EUNSEH  FLAME    LAVA  TIP-  tEKncAl   NA  H0l£S 
C"  EUHStW  CLAMB     LAVA   TrP-    HORIZONTAL   AIR  MOLES 
P-FAHSHATCD   LUMIMCL5    FLAME     LAVA  TIP 
C    SL'fCtK  FLAME   LAVATtP. 
T-  SEMI- BUNSEN  FLAME  METAL  TIP 


Fig.  1.— Center  pilot  burner. 


Fig.  2. 


baked,  and  on  the  interior  a  hard  glossy  coating  of  carbon, 
resembling  flaked  graphite,  was  found.  This  extended  through 
the  entire  passageway  to  the  orifice  which,  on  account  of  its  small 
diameter,  became  stopped  first.  An  investigation  was  made  and 
it  was  found  that  the  decomposition  of  the  hydrocarbons  in  the 
gas  to  carbon  was  influenced  not  only  by  the  high  local  tempera- 
ture (6200  C.  at  the  orifice),  but  also  by  the  physical  properties 
of  the  substance  used  in  construction.  By  using  a  tip  made  of 
finely  crushed  natural  lava,  repressed  and  baked,  the  trouble  was 
practically  eliminated.  A  small  amount  of  carbon  formed  in  the 
passageways,  which  was  grayish  instead  of  black,  and  after  the 


674     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

lamps  were  burned  several  thousand  hours  was  found  not  to  give 
trouble. 

An  interesting  series  of  experiments  was  made,  the  results  of 
which  clearly  illustrate  the  influence  of  the  physical  and  chemical 
properties  of  the  pilot  tip  material  upon  the  decomposition  of  the 
gas.  Various  substances  were  placed  in  a  transparent  quartz 
tube,  through  which  illuminating  gas  was  passed,   and  heated 


Fig-  3- 


slowly  and  uniformly  by  means  of  an  electric  furnace.  Certain 
substances,  like  metallic  oxides  (particularly  mantle  ash)  became 
covered  with  carbon  at  a  temperature  as  low  as  2600  C,  while 
others,  like  glass,  quartz,  etc.,  only  darkened  at  a  temperature  of 
above  650  °  C. 

A  still  more  recent  change  has  occurred  both  in  the  design  of 
pilot  tips  and  in  the  position  in  which  they  burn.  The  pilot  tip 
of  the  lamp  shown  in  Fig.  3  is  mounted  vertically  and  in  this 


JORDAN:     INCANDESCENT   GAS   EAMPS  675 

position  the  flame  is  very  well  protected  from  draughts  and  at 
the  same  time  is  positive  in  its  ignition  of  the  mantle. 

The  advantages  of  this  type  of  tip  are  (1)  that  there  is  no 
orifice  which  may  become  clogged  with  carbon  from  the  decom- 
position of  gas,  (2)  in  case  the  pilot  flame  becomes  overadjusted 
there  is  no  danger  of  cracking  the  enclosing  glass  cylinder, 
and  (3)  that  when  subjected  to  excessive  draught  the  pilot  flame 
retreats  within  the  pilot  tip  and  is  effectively  protected. 

SERVICE  TROUBLES. 

Pilot  devices  are  subject  to  numerous  troubles  in  service.  In 
certain  localities  the  methods  of  manufacturing  and  purifying 
gas  are  liable  to  change  suddenly  from  normal  and  often  tar 
particles  are  carried  in  suspension  by  the  gas  for  considerable 
distances  from  the  works.  In  this  event  the  tar  rapidly  accumu- 
lates on  the  pilot  adjusting  needles  of  the  lamps  and  completely 
closes  the  minute  annular  opening  through  which  the  gas  dis- 
charges. In  order  to  overcome  this  trouble  a  purifying  device, 
shown  in  Fig.  4,  was  designed.  Essentially  it  consists  of  passing 
the  gas  through  a  small  cylindrical  brass  tube  which  has  been 
packed  with  asbestos  wool,  glass  wool,  mineral  wool  or  other 
suitable  material.  The  gas  to  the  pilot  flame  is  completely 
detarred  by  this  method  for  a  long  period.  When  the  filtering 
material  becomes  clogged  or  saturated,  the  brass  tube  is  removed, 
cleaned  and  repacked.  This  simple  device  has  proven  to  be  very 
effective  and  in  a  few  instances  absolutely  essential  for  the  proper 
working  of  pilots. 

Pilot  outage  due  to  draughts  is  a  condition  which  lamp  manu- 
facturers have  been  attempting  to  minimize  and  eliminate.  The 
seriousness  of  this  trouble  is  primarily  dependent  upon  the  con- 
ditions under  which  the  lamp  burns  and  whether  it  is  an  indoor 
or  outdoor  lamp. 

The  luminous  flame  pilot  is  far  from  desirable  in  this  respect, 
unless  it  is  properly  surrounded  by  a  protecting  casing  in  which 
case  it  is  very  liable  to  carbonize.  With  upright  lamps  the  pilots 
can  be  readily  enclosed  by  the  mantle  (see  Fig.  1)  and  are  thus 
very  efficiently  protected. 

In  the  case  of  inverted  lamps  the  problem  was  more  difficult. 
Investigation  led  to  the  adoption  of  the  Bunsen  flame  pilot  tip 


676     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

and  finally  in  a  later  modification  to  a  type  which  is  very  difficult 
to  extinguish  (see  Fig.  3). 

With  outdoor  lamps  the  use  of  semi-Bunsen  pilots,  surrounded 
by  a  protecting  casing  (see  Fig.  5),  has  proven  very  satisfactory. 

Radical  changes  in  the  construction  of  pilot  tips,  being  experi- 
mented with  at  present,  give  promise  of  producing  a  practically 
inextinguishable  pilot  in  the  near  future. 

PILOT  CONSUMPTION. 

A  consideration  of  the  consumption  of  gas  by  pilots  is  of 
importance  in  that  consumers  are  often  badly  misinformed  or 
entirely  ignorant  of  its  magnitude.  The  consumption  is  not  only 
influenced  by  the  length  of  flame  which  is  judged  adequate  by 
the  adjuster,  but  also  upon  the  particular  type  of  pilot  by-pass 
used. 

The  so-called  "sub-flame"  pilot  by-pass  is  in  reality  a  simple 
device  for  turning  low  a  gas  lamp.  As  the  flame  must  burn  over 
the  entire  surface  of  the  burner  gauze  without  danger  of  flash- 
back, the  consumption  is  naturally  greater  than  that  of  an  ordi- 
nary pilot. 

The  use  of  the  "sub-flame"  pilot  by-pass  is  rather  limited  and 
the  pilot  consumption  should  not  be  taken  as  representative  of 
the  more  efficient  types. 

The  following  table  shows  the  normal  consumptions  of  various 
types  of  indoor  and  outdoor  lamps  and  the  ratios  of  the  total 
gas  consumption  to  that  of  the  pilot  consumption. 

Approx. 
Normal       length 
pilot  cons.        of 
per  hour      flame 
I,amp  (Cu.  ft.)  (Inches) 

i  burner  inverted  indoor, 

Bunsen  pilot 0.120        % 

1  burner  upright  indoor, 

luminous  pilot 0.095         % 

3  burner  inverted  indoor 

arc,  semi-Bunsen  pilot  0.147  V% 
5  burner  inverted  outdoor 

arc,  semi-Bunsen  pilot  0.213  % 
1  burner  inverted  outdoor, 

luminous  pilot 0.152         ys         i33!-5        3-45        5.°37        20.9 

These  calculations  are  made  on  the  assumption  that  the  lamps 


Pilot 
ons.  per 

year 
(Cu.  ft.) 

Normal 

lamp 

cons. 

per  hour 

(Cu.  ft.) 

I,amp 

cons, 
per  year 

4  hrs. 

daily 
(Cu.  ft.) 

Pilot 
cons. 

per  cent. 

of  total 
cons. 

1051.2 

3-50 

5»110 

I7.I 

832.2 

4.65 

6,789 

IO.9 

1287.7 

IO.OO 

14,600 

8.1 

1865.9 

I7-50 

25.55o 

6.S 

JORDAN  :     INCANDESCENT    GAS    LAMPS 


677 


operate  on  mixed  gas  at  2.5  in.  (63.5  mm.)  pressure, 
value  650  B.  t.  u.  per  cu.  ft. ;  specific  gravity  0.660. 


Total  heat 


NOVEL  USE  OF  BLUE  FLAME  PILOTS. 

As  mentioned  before,  the  essential  reasons  for  changing  from 
the  luminous  flame  to  the  non-luminous  Bunsen  flame  pilot  were 
because  of  the  greater  difficulty  of  extinguishing  the  flame  of 
the  latter  by  draughts  and  the  elimination  of  troublesome  carbon 
formation  or  smoky  flames. 

In  addition  to  these  features  the  non-luminous  flame  lends  itself 
to  a  novel  and  efficient  use.  It  has  long  been  contended  that  the 
luminous  flame  pilot  instead  of  being  considered  a  necessary 
expensive  accessory  of  a  gas  lamp  is  in  reality  an  efficient  adjunct, 
in  that  it  serves  the  purpose  of  guidance  to  the  consumer  desiring 
in  turning  on  a  lamp  in  a  dark  room.3  By  placing  the  Bunsen 
flame  pilot  so  as  to  impinge  to  the  extent  desired  upon  the  mantle 
an  increase  in  the  intensity  of  light  of  over  five  times  that  of  the 
luminous  flame  pilot  is  obtained. 


J*\ 


Fig.  4.— Tar  scrubber. 


Fig.  5.— Semi-Bunsen  protected  pilot. 


The  following  table  shows  the  maximum  horizontal  candle- 
power  obtained  from  the  two  types  of  pilot  flames: 


Max.  horizontal    Corr.  cons,    candlepower 
Type  flame  candlepower      cu.  ft.  hour      per  cu.  ft. 

Bunsen  flame    0.1612  0.126  1.28 

Luminous  flame 0.0319  0.130  0.245 

Open  flame  candlepower  of  gas  burned  in  8  ft.  tip  22.0  at  a  5  ft. 
rate. 

Litle,  T.  J.,  Convenience  of  Gas  Lighting,  Trans.  I.  E.  S.,  vol.  IV,  1909. 


678     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  increase  in  intensity  not  only  serves  as  a  better  guidance 
in  turning  on  the  lamps  at  night,  but  to  the  dark  adapted  eyes  it 
affords  sufficient  illumination  to  comfortably  distinguish  many 
objects  in  an  ordinary  living  room.  This  is  obtained  at  a  cost 
no  greater  than  that  of  maintaining  the  luminous  pilot  flame.  In 
addition  it  is  more  difficult  to  extinguish  the  flame  of  a  pilot 
impinging  on  the  mantle. 

In  cases  where  pilot  illumination  would  be  objectionable,  it  is 
merely  necessary  to  turn  the  pilot  flame  aside  from  the  mantles 
and  practically  no  light  is  obtained. 
Physical  Laboratory, 

The  United  Gas  Improvement  Co., 
Philadelphia,  Pa. 
Sept.  3,  1915. 

DISCUSSION. 

Mr.  F.  A.  Vaughn:  I  am  particularly  interested  in  the 
pilot  light  and  the  automatic  lighter  and  extinguisher  for  street 
lighting  gas  lamps  and  if  there  is  any  one  in  the  room  who  could 
give  me  any  information  on  this  particular  application  of  the 
pilot,  I  would  be  very  glad. 

Mr.  T.  J.  LitlE:  There  is  an  erroneous  impression  among  a 
great  many  people  that  the  average  pilot  flame  burner  in  the 
house  consumes  a  great  deal  of  gas.  The  pilot,  as  Mr.  Jordan 
has  very  clearly  shown  in  his  paper,  not  only  serves  as  a  form 
of  ignition  for  the  gas  burner  itself,  but  also  serves  to  give 
enough  illumination  in  the  room  to  be  used  as  a  night  lamp,  etc. 
Now  that  in  itself  is  extremely  valuable.  The  pilot  on  a  gas 
lamp  in  a  room  can  be  said  to  perform  the  same  function  as  the 
electric  lamp  that  can  be  turned  low  by  the  pull  of  the  chain. 
The  pilot  will  enable  one  to  see  about  the  room  and  it  must  be 
considered  as  part  of  the  illumination.  Considering  the  con- 
venience and  very  slight  expense  of  such  an  arrangement  for 
the  various  rooms  in  a  house,  I  think  it  is  possibly  the  cheapest 
form  of  night  illumination. 

Mr.  Vaughn  asked  a  question  regarding  street  lamps.  It  is 
the  practise  in  using  pilots  on  street  lamps,  or  for  lamps  used 
commercially  in  front  of  buildings,  to  protect  the  flame  by  some 
draft-proof   arrangement.     In   Europe   and  America   the  usual 


INCANDESCENT   GAS    LAMPS  679 

practise  is  to  use  a  perforated  cup.  This  scheme  is  working  out 
very  well.  Remote  control  of  street  lamps  and  the  clock  and 
pressure  wave  lighting  systems  have  been  tried. 

Mr.  C.  W.  Jordan  :  In  reply  to  Mr.  Vaughn's  inquiry  regard- 
ing automatic  igniters,  I  wish  to  refer  him  to  an  article  published 
in  the  American  Gas  Institute  Proceedings,  Vol.  VIII,  1913, 
Part  II,  by  Mr.  F.  H.  Gilpin,  entitled  "Automatic  and  Distant 
Lighters."  This  article  thoroughly  covers  the  application  of 
many  types  of  automatic  igniters  to  American  practise  under  the 
existing  climatic  conditions. 


680    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

THE  LIGHTING  OF  A  PASSENGER  STEAMER.* 


BY  H.  T.  SPAULDING. 


Synopsis:  This  paper  introduces  the  subject  by  a  brief  historical 
sketch  of  past  and  present  practise  in  marine  lighting.  The  lighting 
requirements  of  a  passenger  boat  are  discussed  and  compared  with 
similar  installations  ashore.  To  illustrate  how  these  requirements  can 
be  satisfied  the  author  describes  the  lighting  system  designed  by  him,  in 
co-operation  with  the  architects,  for  the  S.  S.  Noronic,  a  lake  passenger 
boat,  and  gives  the  results  of  illumination  tests  in  some  of  the  more 
important  portions  of  the  vessel.  In  conclusion  it  is  recommended  that 
a  departure  be  made  from  the  ordinary  boat  lighting  systems  so  common 
at  present,  and  it  is  urged  that  a  closer  relationship  between  marine  archi- 
tects and  illuminating  engineers  be  established. 


Boat  lighting  is  similar  with  regard  to  the  question  of  utiliza- 
tion efficiency  and  choice  of  system  of  illumination  to  installations 
on  land  having  similar  requirements,  and  it  is  therefore  not  the 
intention  in  this  paper  to  cover  these  subjects.  There  are,  how- 
ever, certain  factors  governing  marine  lighting  which  are  dif- 
ferent from  those  usually  encountered,  and  it  is  these  factors,  to- 
gether with  the  requirements,  and  the  manner  in  which  they  can 
be  satisfied,  that  are  to  be  discussed  and  illustrated  by  means  of 
a  description  of  the  lighting  of  the  S.  S.  Noronic,  which  was  de- 
signed by  the  writer  in  co-operation  with  the  architects  of  the 
interior  finish  and  decoration. 

There  is  a  tendency  among  marine  engineers  to  regard  the  cost 
of  generating  power  as  a  small  item,  and  this  has  resulted  in 
the  continued  use  of  carbon  lamps  to  a  considerable  extent  for 
boat  lighting.  Insufficient  attention  has  also  been  given  to  the  in- 
stallation of  the  lamps  and  their  equipment  to  conform  with  the 
principles  of  good  lighting,  and  reduction  of  glare.  It  is  not  un- 
common to  find  a  boat  with  elaborate  equipment  in  all  other  re- 
spects fitted  with  bare  lamps  studded  in  the  ceiling,  or  perhaps, 
equipped  with  so-called  decorative  glassware  mounted  upon 
fixtures  at  such  a  height  that  they  are  directly  in  the  line  of 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,   September   20-23,    J9i 5- 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


spaueding:    lighting  of  a  passenger  steamer        68i 

vision.  This  is  well  illustrated  in  a  paper1  read  before  the  New 
York  section  about  three  and  a  half  years  ago  which  was  de- 
scriptive of  the  lighting  systems  on  a  number  of  boats  of  various 
classes  in  service  at  that  time.  Figs,  i  and  2,  which  are  photo- 
graphs of  the  social  hall  and  dining  room  respectively  on  one  of 
our  lake  boats,  show  installations  typical  of  the  methods  com- 
monly employed.  In  Fig.  1  the  lighting  units  shown  are  all- 
frosted  carbon  lamps.  The  lighting  of  the  dining  room  is  more 
satisfactory  as  tungsten  filament  lamps  are  used  and  glare  is 
somewhat  reduced  by  means  of  diffusing  glassware.  The  lighting 
is,  however,  hardly  in  keeping  with  the  remainder  of  the  ap- 
pointments of  the  boat.  No  radical  changes  in  the  methods  illus- 
trated have  been  made  in  the  last  few  years,  except  in  the  case  of 
a  few  of  the  more  recent,  larger  boats. 

A  passenger  boat  has  requirements  similar  to  a  hotel,  with  its 
divisions  corresponding  on  a  smaller  scale  to  the  rooms  used  for 
similar  purposes  on  land.  The  entrance  hall,  like  a  hotel  lobby, 
should  be  brilliantly  lighted.  Social  halls,  as  a  rule,  require  less 
illumination;  but  as  these  rooms  are  often  used  for  reading,  it 
is  necessary  that  the  light  be  well  diffused,  and  glare  eliminated. 
Enclosing  glassware,  semi-indirect,  or  indirect  fixtures  will  ful- 
fill the  requirements  but  usually  the  low  ceiling  height  interferes 
with  the  use  of  the  last  two  systems.  For  parlors,  observation 
rooms,  drawing  rooms,  and  smoking  rooms  similar  requirements, 
and  also  the  same  limitations,  exist.  Dining  rooms  should  have  a 
higher  intensity,  and  here  it  is  often  possible  to  make  use  of  semi- 
indirect  lighting  regardless  of  the  low  ceiling.  As  the  tables  are 
usually  fixed,  lighting  units  located  directly  above  them  will  not 
interfere  with  the  necessary  head  room. 

The  more  pretentious  suits  are  very  similar  to  hotel  guest 
rooms  in  every  respect,  and  their  lighting  requirements  are  iden- 
tical, but  the  ordinary  staterooms  require  a  different  treatment. 
They  are  usually  of  such  a  size  that  a  single  low  wattage  lamp 
is  ample  for  all  needs,  and  the  small  space  between  decks,  to- 
gether with  the  berth  arrangement,  practically  limits  the  location 
to  the  side  walls.  This  is  one  of  the  few  places  on  a  boat  where 
the  use  of  bare,  all-frosted  lamps  cannot  be  criticized,  although 

1  Porter  I,.  C,  The  Lighting  of  Passenger  Vessels;  Trans.  I.  E.  S.  Vol.  VII,  p.  116, 
1912. 


682     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

equally  satisfactory  illumination  and  improved  appearance  will 
obtain  if  clear  lamps  equipped  with  diffusing  glassware  are 
used.  Berth  lights  similar  to  those  used  in  train  lighting  are  a 
convenience  greatly  appreciated,  and  should  be  installed  when- 
ever the  expense  is  not  considered  prohibitive.  Writing  rooms, 
barber  shops,  lavatories,  passages  etc.,  can  generally  be  treated 
in  the  usual  manner.  An  appendix  is  attached  giving  the  inten- 
sities of  illumination  to  be  recommended  and  the  equipment  de- 
sirable for  lighting  the  various  portions  of  a  passenger  boat. 

Mention  has  been  made  above  to  the  limitations  imposed  due  to 
the  low  ceilings  almost  universally  found  on  boats.  The  space 
between  decks  is  not  often  over  8  ft.  (2.44  m.),  usually  less,  so 
that  by  the  time  the  thickness  of  the  deck,  the  depth  of  the  deck 
beams  and  the  ceiling  finish  are  subtracted,  there  is  little  space 
available  for  the  lighting  unit.  Steel  deck  beams  are  common, 
and  increase  the  difficulties  of  electrical  construction.  Usually  the 
floor  of  the  deck  above  forms  the  ceiling  of  the  one  below,  and 
hence  there  is  no  space  in  which  the  wiring  can  be  concealed  or 
the  lighting  units  recessed.  Shallow  bowls,  very  close  ceiling 
fixtures,  or  a  suspended  ceiling  with  recessed  lighting  units,  are 
some  of  the  methods  in  which  the  difficulty  can  be  overcome. 
Wall  brackets,  or  lamps  set  into  the  partitions  behind  diffusing 
plaques  can  also  be  employed  in  certain  cases.  Generally,  how- 
ever, the  necessity  for  utilizing  all  possible  space  has  resulted  in 
the  partitions  being  constructed  of  but  a  single  thickness  of  wood, 
so  that  there  is  little  chance  of  recessing  the  units ;  in  fact  there 
is  little  space  in  which  to  run  conduit  for  wall  brackets. 

The  Northern  Navigation  Company's  S.  S.  Noronic  was  de- 
signed to  be  one  of  the  best  and  most  completely  equipped  boats 
upon  the  lakes,  and  the  finish,  furnishings  and  lighting  equipment 
were  given  more  than  usual  consideration.  Five  decks  are  de- 
voted wholly  or  in  part  to  the  use  of  the  public.  At  the  entrance 
on  the  main  deck,  a  small  hall,  panelled  in  oak,  leads  to  the  stair- 
way to  the  spar  deck.  Here  are  the  office  and  lobby.  On  this 
deck  are  also  located  150  staterooms,  each  equipped  with  hot  and 
cold  running  water.  The  promenade  deck  above  contains  the 
smoking  room,  ladies'  drawing  room  or  lounge,  10  parlor  rooms, 
social  hall,  and  additional  state  rooms.    The  finish  throughout  is 


Fig.  i.— Social  hall  of  lake  passenger  boat. 


Fig.  2.— Dining  room  of  lake  passenger  boat. 


spaulding:   lighting  of  a  passenger  steamer       683 

in  panelled  mahogany.  The  public  portion  of  the  fourth  or  ob- 
servation deck  consists  of  only  two  rooms,  the  observation  room 
and  the  dining  room,  with  an  orchestra  platform  between.  The 
dining  room  is  finished  in  mahogany  and  light  green,  while  the 
observation  room,  enclosed  on  three  sides  by  large  windows,  has 
rugs,  upholstery,  hangings,  and  woodwork  in  a  greenish  gray 
tone.  The  boat  deck  contains,  in  addition  to  the  pilot  house  and 
officers'  quarters,  a  social  hall  panelled  in  light  oak  which  is  util- 
ized as  a  writing  room.  Fig.  3  which  is  a  plan  view  of  the  various 
decks,  shows  the  arrangement  of  these  rooms,  and  the  location  of 
all  lighting  outlets  in  the  public  areas  of  the  boat. 

In  designing  the  lighting  system,  the  unusual  good  fortune 
was  experienced  of  being  called  upon  before  the  plans  of  the 
interior  were  complete,  and  within  limits,  other  considerations 
were  secondary  to  the  satisfaction  of  the  principles  of  good 
lighting  and  the  architectural  requirements.  The  following  para- 
graphs describe  the  lighting  units  installed  and  some  of  the 
features  influencing  their  choice. 

The  lighting  of  the  dining  room  is  somewhat  of  a  departure 
from  the  usual  methods,  in  that  semi-indirect  lighting  was  em- 
ployed with  the  outlets  so  arranged  that  a  bowl  was  suspended 
directly  over  each  table.  A  ceiling  at  the  level  of  the  under  side 
of  the  deck  beams  was  provided  with  a  small  circular  panel  above 
the  lighting  unit,  recessed,  and  finished  with  a  smooth  surface,  so 
that  the  brightly  lighted  area  directly  above  the  lamp  was  cir- 
cumscribed. Even  with  the  low  ceiling  height,  about  7  ft. 
(2.13  m.),  and  the  short  fixture  length,  this  arrangement  re- 
sulted in  the  ceiling  appearing  fairly  uniformly  lighted,  and  pro- 
vided a  contrast  to  the  relief  decorations  upon  the  remainder  of 
the  ceiling.  To  insure  that  the  entire  effect  would  be  pleasing,  a 
full  sized  model  of  a  portion  of  the  ceiling  was  constructed  and 
a  large  number  of  bowl  and  lamp  combinations  were  investigated 
before  the  one  finally  approved  was  adopted.  A  heavy  density 
bowl2  16  in.  (40.64  cm.),  in  diameter,  etched  with  a  special  de- 
sign harmonizing  with  the  decorations  as  shown  in  Fig.  4a,  was 
used  with  a  100-watt  round  bulb  lamp.  Fig.  5  is  a  view  of  the 
room  with  the  lamps  on.  Illumination  readings  in  a  horizontal 
plane  at  the  table  level  were  taken  in  the  representative  area 

2  No.  1265  Calla  72  bowl. 


684     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


C-BOAT  DECK 


e-5MOKING-f?00M  S'SOCIAL  HALLS-WALLS 


f-5QCIAL  HALLS  -CEILING  BEAMS 


h-ENTRANCE  HALL 


Fig.  4.— Fixture  designs  for  S.  S.  Noronic. 


spaulding:   lighting  of  a  passenger  steamer       685 

shown  by  the  shading  in  Fig.  3.  At  the  time  of  the  test  the  boat 
was  not  in  commission,  and  the  voltage  was  about  3  volts  below 
normal.  The  lamps  had  been  burned  over  half  their  rated  life, 
and  lamps  and  glassware  were,  not  cleaned  previous  to  the  test, 
so  that  the  intensity  of  3.7  foot-candles  obtained  after  correcting 
for  voltage  is  indicative  of  average  conditions. 

The  low  clearance  in  the  observation  room  prevented  the  use 
of  any  type  of  fixture  which  would  project  far  down  from  the 
ceiling,  and  the  area  of  the  room  was  such  that  lighting  from  the 
side  would  not  have  produced  satisfactory  effects.  It  was  possi- 
ble, however,  to  employ  a  suspended  ceiling,  with  a  few  inches 
between  the  ceiling  and  the  deck  above  in  which  the  lamps  could 
be  recessed,  and  this  course  was  decided  upon.  An  eliptical  dish3 
was  used  as  a  relief  from  the  uniformity  of  the  square  ceiling 
panels.  In  the  opinion  of  the  architect  it  was  also  desirable  be- 
cause of  the  note  of  individuality  conveyed.  A  single  100-watt 
round  bulb  lamp,  backed  by  a  white  enamelled  reflector  was 
made  use  of  for  these  fixtures  as  shown  in  Fig.  4b.  It  would  have 
been  possible  to  have  a  more  shallow  dish  with  two  lamps  burn- 
ing horizontally  except  for  the  fact  that  the  architect,  for  esthetic 
reasons,  desired  that  the  dish  should  not  be  lighted  with  absolute 
uniformity,  but  should  show  a  brighter  area  near  the  center.  A 
test  in  the  area  shown,  with  conditions  as  outlined  above,  gave 
1.8  foot-candles  in  a  horizontal  plane  2.5  ft.  (0.762  m.)  above 
the  floor.  Fig.  6  is  a  daylight  view  of  this  room  with  the  lights 
on. 

For  lighting  the  writing  room  or  social  hall  on  the  boat  deck, 
and  for  the  portion  of  the  promenade  deck  below  the  light  well 
extending  down  through  two  decks,  a  single  row  of  250  watt 
lamps,  with  totally-enclosing  diffusing  globes4  of  the  design 
shown  in  Fig.  4c,  were  located  on  the  ceiling  of  the  boat  deck. 

The  smoking  room  and  lobby  were  handled  in  about  the  same 
manner.  The  "squat"  ceiling  bowls  shown  in  detail  in  Fig.  4d 
and  4e  were  used.  Shallow  bowls  were  necessary  in  these  loca- 
tions to  allow  of  sufficient  headroom,  and  a  heavy  density  glass 
was    chosen   to   conceal   the    lamp    filament.      Twenty-five-watt 

3  Alba  glass  No.  3772. 

*  Druid  glass  No.  01218  12  in. 


686     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

lamps  were  used  in  the  6-inch  (15.25  cm.)  bowls5  in  the  smok- 
ing room;  and  the  10-inch  (25.4  cm.)  bowls0  in  the  lobby  were 
equipped  with  100-watt  lamps.  Here,  as  in  a  number  of  other 
locations,  it  was  necessary  to  use  the  round  bulb  lamp  because 
of  its  shorter  over-all  length. 

The  ceilings  of  the  lounge,  and  the  social  halls  on  the  spar  and 
promenade  decks  were  beamed,  with  insufficient  room  below  to 
permit  the  use  of  even  a  shallow  dish,  and  with  so  small  a  space 
between  the  ceiling  in  the  panelled  portions  and  the  floor  above, 
as  to  prevent  the  location  of  units  in  these  areas.  It  was  found 
that  the  narrow  hallways  and  the  portions  of  the  larger  rooms 
adjacent  to  the  walls  could  be  cared  for  by  means  of  side  light- 
ing. For  this  purpose  the  oblong  plaques7  shown  in  Fig.  4f  were 
developed.  The  illumination  of  the  central  portions  of  the  larger 
areas  was  brought  up  by  recessing  larger  plaques8  of  a  similar 
shape  in  the  sides  of  the  ceiling  beams.  A  single  60-watt  lamp 
was  used  in  the  wall  outlets,  and  those  on  the  beams  contained 
either  two  25-watt  or  two  60-watt  lamps,  depending  upon  the 
location.  Details  of  the  larger  units  are  shown  in  Fig.  2g.  Illum- 
ination measurements  taken  at  representative  points  showed  an 
illumination  upon  a  horizontal  plane  2.5  ft.  (0.762  m.)  above  the 
floor  averaging  about  0.7  foot-candles.  The  vertical  illumination 
was  higher,  and  as  the  function  of  the  lighting  in  most  of  these 
portions  is  only  to  enable  the  passengers  to  see  their  way  around, 
the  results  were  satisfactory.  In  those  rooms  which  were  likely 
to  be  used  for  reading,  a  higher  wattage  was  installed,  so  that  the 
illumination  was  ample.  Fig.  7  shows  the  lighting  of  the  social 
hall  on  the  promenade  deck,  and  also  the  units  installed  on  the 
ceiling  of  the  boat  deck  above  the  well. 

The  entrance  hall  on  the  main  deck  was  also  lighted  by  means 
of  wall  plaques,9  but  of  a  somewhat  different  design.  The  means 
which  it  was  necessary  to  employ  to  obtain  sufficient  wattage  in 
the  allowable  space  is  shown  in  Fig.  4I1. 

The  lighting  of  the  staterooms  was  accomplished,  as  is  the 
usual  custom,  by  means  of  all  frosted  lamps  on  wall  brackets  at 

6  Sudan  glass  No.  431  6  in. 

6  Calla  glass  No.  328  10  in. 

7  Alba  glass  No.  3370. 

8  Alba  glass  No.  3771. 

9  Sudan  glass  4%  in.  X  2%  in. 


Fig.  5. — Dining  room  of  S.  S.  Xoronic. 


Fig.  6. — Observation  room  of  S.  S.  Xoronic. 


Fig.  7. — Social  hall  of  S.  S.  Noronic. 


Fig.  8.— Parlor  room  of  S.  S.  Noronic. 


spaulding:    lighting  of  a  passenger  steamer 


687 


the  side  of  the  mirror.  Each  berth  was  also  equipped  with  a 
small  lamp.  The  parlor  rooms  contained  a  number  of  wall 
brackets  fitted  with  dense  opal  shades  as  shown  in  Fig.  8. 

While  the  illumination  in  no  part  of  the  boat  might  be  con- 
sidered as  brilliant,  yet  it  was  found  to  be  entirely  satisfactory. 
This  is  due  in  part  to  the  isolation  from  other  contrasting  brilliant 
illumination,  but  primarily  to  the  fact  that  no  bright  light  sources 
are  within  the  field  of  vision. 

In  conclusion,  I  wish  to  extend  my  thanks  to  the  Northern 
Navigation  Co.,  the  architects,  the  Holophane  Works,  and  to  Mr. 
Ward  Harrison,  for  co-operating  in  securing  and  preparing  the 
material  for  this  paper. 

APPENDIX 
Recommendations  for  Passenger  Boat  Lighting. 

Intensity 
Location  foot-candles  Equipment  and  location 

Baggage  room 1. 0-1.5     Direct  lighting — Glass  reflectors  at  ceiling. 

Ball  room 2.0-3.0     Enclosing    glassware    at    ceiling,    or    wall 

fixtures. 

Barber  shop 4.0-5.0    Semi-indirect  units  over  or  near  chairs. 

Bath-room 1.5-2.0     Diffusing  glassware,  or  all  frosted  lamps  on 

wall  brackets  at  side  of  mirrors. 
Cafe 1.5-2.5     Enclosing  glassware,  or  direct   reflectors  of 

warm  tone  on  ceiling  or  wall  fixtures. 

Dining-room 3.0-4.0    Enclosing  glasswase,  or  semi-indirect  units. 

Drawing-room 1.5-2.5     Enclosing  glassware  or  wall  fixtures. 

Freight  deck 0.5-1.0    Steel  distributing  reflectors. 

Grand  saloon 1.5-2.5     Enclosing  glassware,  semi-indirect,    or  wall 

fixtures 

Halls 1. 0-1.5     Wall  fixtures. 

Kitchen 2.0-3.0    Direct  lighting — Glass  reflectors  at  ceiling. 

Lobby 1.5-2.5     Enclosing  glassware,  or  wall  fixtures. 

Lounge r-5-2-5     Enclosing  glassware,  or  wall  fixtures. 

Observation  room  ..    1.5-2.5     Enclosing  glassware,  or  wall  fixtures. 

Office 3.0-4.0    Direct  lighting  glass  reflectors  at  ceiling,  or 

on  brackets  over  desks. 

Parlor 1.5-2.5     Enclosing  glassware,  or  wall  fixtures. 

Parlor  rooms 1. 0-1.5     Wall  brackets  with  diffusing  glassware. 

Passages 0.5-1.0     Wall  fixtures. 

Social  hall 1.0-2.0     Wall  fixtures,  or  enclosing  glassware  at  ceiling. 

State  rooms-general       —       Diffusing  glassware,    or  all   frosted   lamp   on 

bracket  at  side  of  mirror. 
State   rooms-berths.       —       Low  candlepower  all  frosted  lamp  in  each  berth. 
Toilets 1. 0-1.5    Direct  lighting  glass  reflectors  at  ceiling,    or 

wall  bracket  with  diffused  glassware. 
Writing  rooms 2.5-4.0     Enclosing  glassware   at    ceiling,    or    special 

direct  lighting  on  tables. 


688     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

DISCUSSION. 

Mr.  L.  C.  Porter:  It  seems  to  me  there  is  considerable  dif- 
ference in  the  illumination  problems  of  ships  and  those  on  land, 
because  on  most  ships  the  finish  is  almost  entirely  white  and  this 
makes  considerable  difference  in  figuring  the  amount  of  light 
necessary.  In  regard  to  the  tendency  among  marine  engineers 
to  regard  the  cost  as  a  small  item — the  cost  of  generating  power 
is  not  the  only  figure  that  enters  into  the  calculation.  The  cost  of 
installation  makes  considerable  difference.  In  ferryboat  lighting 
it  is  customary  to  use  a  large  number  of  small  lamps  located  on 
each  side  of  the  passenger  compartment.  In  a  recent  boat  the 
wattage  was  reduced  to  one  half  and  the  installation  cost  to 
one  third  the  figures  considered  common  practise.  This  was 
done  by  using  a  small  number  of  large  lighting  units  located  down 
the  center  of  the  cabin  instead  of  a  large  number  of  small  units 
located  in  wall  brackets. 

The  ceiling  over  the  social  hall  (Fig.  7)  is  rather  high.  This 
is  the  typical  condition  in  river  and  lake  steamers.  For  such 
places  having  high  ceiling  room  the  open  mouth  reflectors  can  be 
used  to  advantage  and  a  little  more  efficiency  gained  than  is 
obtained  through  the  totally  enclosing  globe. 

The  foot-candle  illumination  given  for  the  observation  room, 
seems  to  be  a  little  high.  On  the  Washington  Irving,  the  largest 
river  steamer  in  the  world,  a  low  illumination  in  the  observation 
room  was  desired  because  passengers  usually  like  to  see  what  is 
outside,  particularly  along  towards  evening  and  at  night.  With 
a  high  illumination  inside  the  observation  room  one  cannot  see 
the  scenery  outside  as  well  as  when  there  is  a  low  illumination  in 
the  observation  room.  I  believe  that  half  a  foot-candle  would 
be  much  better  than  a  value  near  two. 

Mr.  W.  R.  Moulton  :  The  lighting  problems  in  boat  con- 
struction are  rather  unusual,  therefore  very  interesting.  The 
decoration  of  boat  interiors  is  usually  favorable  to  good  lighting. 
On  the  other  hand  special  conditions  confront  one,  such  as  the 
low  head  room  and  the  rafter  ceiling  construction. 

I  have  recently  had  some  interesting  experience  in  lighting 
two  private  yachts,  where  each  room  seemed  to  present  a  problem 
of  its  own.     In  one  the  cabin  was  very  low,  and  there  was  a 


LIGHTING   OF  A    PASSENGER   STEAMER  689 

birth  seat  along  either  side.  Inverted  brackets  equipped  with 
heavy  density  opal  reflectors  were  placed  about  12  in.  from  the 
ceiling.  The  upper  side  wall,  the  bulkhead  and  deck  were 
finished  in  light  ivory  which  assisted  in  producing  a  very  pleas- 
ing lighting  result.  Light  was  reflected  from  the  side  wall  and 
also  from  the  ceiling,  and  some  penetrated  the  shades. 

The  pilot  house  ceiling  was  but  6  ft.  2  in.  high.  The  owner 
desired  it  lighted  from  a  center  ceiling  outlet.  It  was  necessary 
to  use  a  shallow  bowl-shaped  dome  of  medium  density  opal, 
directly  at  the  ceiling.  This  was  about  8  in.  in  diameter  and 
about  3  in.  deep.  On  account  of  the  size  of  this  unit  it  was  im- 
possible to  use  standard  lamps;  so  two  15-watt  candelabra  base 
tubular  lamps  were  used.  The  use  of  special  lamps  for  such 
circumstances  is  surely  justified. 

On  the  same  yacht  electric  running  lights  were  installed.  It 
is  a  serious  offense,  subject  to  a  heavy  fine  and  also  very  danger- 
ous, for  a  boat  to  operate  without  running  lights  burning.  To 
give  proper  warning  as  to  the  operation  of  the  running  lights, 
tell-tale  lamps  were  installed  in  the  pilot  house,  connected  in  series 
with  the  main  lamps.  If  these  tell-tale  lamps  were  burning,  they 
indicated  that  the  running  lights  also  were  burning.  The  tell- 
tale light  not  burning,  immediately  warned  the  pilot  of  the  outage 
of  his  running  light;  he  could  then  either  replace  the  electric 
bulb  at  once,  or  place  a  temporary  oil  lamp  in  its  stead. 

Mr.  H.  T.  Spaulding  (In  reply)  :  There  is  only  one  point 
which  I  wish  to  mention  and  that  is  in  reference  to  the  obser- 
vation room.  This  area  was  also  to  be  used  at  various  times 
as  a  ball  room  and  consequently  sufficient  lighting  for  this  use 
had  to  be  provided. 


69O    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

SEMI-DIRECT  OFFICE  LIGHTING  IN  THE  EDISON 
BUILDING  OF  CHICAGO.* 


BY  WM.  A.  DURGIN  AND   J.   B.  JACKSON. 


Synopsis:  The  equipment  of  a  typical  office  test  room  and  compara- 
tive tests  on  five  lighting  systems  to  show  relative  eye  fatigue,  glare, 
shadows,  uniformity  of  intensity  on  desk  plane,  utilization  efficiency  and 
effective  flux  color,  are  described.  The  test  results,  leading  to  the  develop- 
ment of  a  particular  semi-direct  unit  for  lighting  the  offices  of  the  Com- 
monwealth Edison  Company,  are  discussed  and  the  details  of  the  adopted 
fixture  structure  and  glass  bowl  characteristics  presented.  Data  are  given 
on  the  illuminating  effectiveness,  arrangement,  appearance,  and  dust  factor 
of  the  completed  installation,  especial  emphasis  being  placed  upon  the 
importance  of  the  use  of  higher  intensities  and  filtered  flux. 


The  great  stride  in  the  economical  generation  of  light  flux 
achieved  in  the  one-watt  and  higher  efficiency  incandescent  lamps, 
has  enlarged  the  resources  of  the  lighting  engineer  many  fold. 
In  the  age  of  the  three-watt-per-candle  lamp  it  was  necessary  to 
consider  all  radiation  which  was  capable  of  exciting  the  optic 
nerve  as  valuable  illuminating  material  if  lighting  was  to  be  ac- 
complished at  reasonable  cost,  and  the  lowest  intensity  under 
which  seeing  became  moderately  comfortable  was  perforce  re- 
garded as  satisfactory.  Flux  generation  at  three  to  five  times 
this  efficiency,  however,  permits  economical  use  of  much  higher 
intensities,  and  the  filtering  of  the  light  to  secure  only  those  color 
components  which  are  best  adapted  to  producing  the  desired  ef- 
fect. 

Such  higher  intensities  and  controlled  light  quality  may  or  may 
not  prove  to  be  the  ultimate  solution  of  the  good-lighting 
problem.  The  possibilities  at  least  are  most  attractive,  but  only 
extended  experience  with  installations  involving  considerable  de- 
partures from  the  current  usage  in  intensity  and  flux  color  can 
evaluate  these  characteristics. 

The  lighting  of  offices  aggregating  82,000  sq.  ft.  (7,600  sq.  m.) 
for  the  use  of  one  of  the  largest  central  station  companies  has 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,   Washington,   D.   C,   September   20-23,    191 5- 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


DURGIN  AND  JACKSON  I    SEMI-DIRECT  OFFICE  LIGHTING      69I 

given  opportunity  for  applying  these  ideas,  and  this  paper  pre- 
sents some  account  of  the  preliminary  tests  of  various  possible 
systems  and  of  the  development  and  final  installation  of  a  special 
unit  embodying  the  features  of  color  modification  and  high  in- 
tensity while  meeting  the  more  generally  recognized  require- 
ments of  acceptable  illumination. 

For  the  preliminary  tests  a  typical  office  in  the  new  building 
of  the  Commonwealth  Edison  Company  was  equipped  with  metal 
moulding  and  outlets  to  permit  a  symmetrical  two,  four  or  six 
unit  installation.  The  room  was  approximately  24  ft.  6  in. 
(7.5  m.)  long,  19  ft.  (5.8  m.)  wide,  and  10  ft.  6  in.  (3.2  m.) 
high.  Three  sides  were  clear  wall  space  and  although  the  fourth 
or  corridor  side  contained  the  door  and  a  line  of  windows,  all 
glass  was  covered  with  heavy  coatings  of  calcimine  to  match  the 
walls.  With  the  exception  then  of  the  baseboard,  chair  rail, 
picture  moulding,  lower  panels  of  door,  and  frames  of  corridor 
windows,  all  of  which  were  finished  in  dark  mahogany,  the  entire 
wall  surface  of  the  room  was  calcimine. 

The  tints  chosen  were  light  cream  for  the  ceiling  (reflection 
coefficient  for  vacuum  tungsten  lamp  flux  0.8),  dark  cream  for 
the  walls  above  chair  rail  (reflection  coefficient  0.7),  and  light 
brown  below.  The  floor  was  bare  maple.  It  was  originally  in- 
tended to  test  several  color  schemes,  but  this  first  selection  proved 
so  satisfactory  to  the  committee  charged  with  the  final  approval 
of  the  installation  that  it  was  adopted  and  no  other  tints  con- 
sidered. An  outline  of  the  room  showing  position  of  the  outlets, 
as  well  as  the  desk  employed  in  eye  fatigue  tests,  is  given  in 
Fig.  1. 

Five  distinct  methods  of  office  illumination  were  investigated: 
direct  lighting  with  prismatic  reflectors  in  velvet  finish;  direct 
lighting,  with  opal  reflectors  giving  very  light  amber  tone;  semi- 
direct  lighting  with  art  glass  reflectors  of  amber  tone;  semi-direct 
lighting  with  dense  opal  reflectors  of  slightly  greenish  tone;  and 
indirect  lighting,  with  silvered  glass  reflectors.  Each  of  these 
systems  was  tested  for  eye  fatigue,  glare,  shadows,  color  of  the 
light,  uniformity  of  intensity  on  30-inch  desk  plane,  and  utiliza- 
tion efficiency  for  this  plane.  The  detail  of  test  equipment  and 
procedure  will  be  found  in  Appendix  I,  the  principal  results  being 
summarized  in  Table  I,  and  the  following  paragraphs : 


692     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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DURGIN  AND  JACKSON  I    SEMI-DIRECT  OFFICE  LIGHTING      693 

TESTS. 

Eye  Fatigue. — The  results  of  the  Ferree  tests  made  a  part  of 
this  investigation  by  Mr.  J.  R.  Cravath  have  been  presented  pre- 
viously to  the  society.1  The  judgment  of  the  subject  in  these 
tests  and  of  the  present  authors,  a  judgment  substantiated  as  to 
the  order  of  excellence,  if  not  entirely  as  to  the  degree  of  super- 
iority, by  the  Ferree  tests  was  as  follows : 

Both  direct  lighting  systems  showed  marked  inferiority  to  the 
semi-direct  and  indirect  systems  when  rated  by  eye  fatigue.    The 


Fig.  1.— Plan  of  test  room.    Underlined  figures  indicate  outlets  used  with 
corresponding  number  of  units  in  symmetrical  arrangement. 


preference  of  the  testers  was  for  the  art  glass  semi-direct  system 
due  probably  to  the  amber  tone  of  the  light  and  the  attractive  ap- 
pearance of  the  units,  but  both  semi-direct  installations  were  very 
satisfactory. 

Glare. — All   observers   were   impressed   with   strain   resulting 
from  the  excessively  bright  walls  under  the  direct  system.     As 

1  Cravath,  J.  R.,  Some  Experiments  with  the  Ferree  Test  for  Eye  Fatigue ;  Trans. 
I.  E.  S.,  vol.  IX,  p.  1033 ;  1914. 


694     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

computed  from  column  8,  Table  I,  which  gives  the  measured 
value  of  the  brightest  area  on  the  walls  below  the  picture  mould- 
ing, the  100-watt  direct  units  produced  a  wall  brightness  of  the 
order  of  one  half  that  of  a  mat  white  paper  on  the  desk  plane, 
deduced  from  the  mean  intensity  shown  in  column  4,  Table  I. 
The  semi-direct  system  when  reduced  to  the  same  horizontal  il- 
lumination gave  only  one  third  as  high  wall  brightness,  and  with 
the  walls  thus  about  one  sixth  as  bright  as  the  paper  upon  which 
the  observer  was  working  no  strain  was  noticed.  The  high  wall 
brightness  shown  under  the  indirect  system  is  somewhat  mis- 
leading as  it  applied  only  to  a  narrow  strip  near  the  picture  mould- 
ing which  would  rarely  come  within  the  field  of  view.  The  test- 
ers' judgment  indicated  that  both  semi-direct  and  indirect  sys- 
tems were  satisfactory  as  regards  wall  glare,  and  that  all  three 
were  reasonably  good  in  reducing  desk  glare,  although  the  art 
glass,  semi-direct  reflectors  were  of  such  light  density  as  to  be 
inferior  to  the  heavy  density  semi-direct  and  the  indirect  systems. 
In  the  desk  work  with  the  direct  system  the  surface  reflection 
glare  from  the  desk  top  and  glazed  paper  was  very  trying. 

Ceiling  brightness  perhaps  is  rather  outside  the  glare  question 
since  in  medium-sized  offices  ordinary  lines  of  sight  bring  no 
part  of  the  ceiling  into  the  field  of  view.  It  is  interesting  to  note, 
however,  that,  as  shown  in  column  9,  Table  I,  a  small  part  of 
the  ceiling  immediately  above  the  direct  units  was  quite  as  bright 
as  any  part  with  the  semi-direct  units  and  two  thirds  as  bright  as 
the  ceiling  illuminated  with  the  indirect  silvered  reflectors  when 
the  figures  are  reduced  to  the  same  horizontal  illumination.  This 
unusual  result  was  produced  by  the  high  mounting  of  the  direct 
units,  which  brought  the  glowing  reflectors  within  a  few  inches 
of  the  ceiling. 

Shadows. — The  bookkeeper  working  under  the  various  sys- 
tems was  much  annoyed  by  the  multiple  shadow  from  the  two 
six-unit  direct  lighting  installations.  While  some  shadow  re- 
sulted with  the  light  density  semi-direct  system  it  produced  no 
comment  and  appeared  acceptable  to  all  observers  for  office  work, 
as  did  the  almost  total  lack  of  shadow  from  the  other  two  sys- 
tems. Shadowgrams,  made  as  outlined  in  Appendix  I,  served  to 
record  the  conditions  of  light  direction  for  the  inspection  of  the 


DURGIN  AND  JACKSON  '.    SEMI-DIRECT  OFFICE  LIGHTING      695 

lighting  committee  and  to  display  the  difference  between  the 
clear-cut  and  comparatively  dense  shadows  from  the  direct  sys- 
tem, and  the  hazy  outline  and  lesser  density  of  those  from  the 
art-glass  semi-direct  installation.  The  practical  equality  of  a 
moderately  dense  bowl  semi-direct  system  and  the  indirect  sys- 
tem in  lack  of  shadow  production  was  especially  well  shown  and 
it  was  agreed  that  each  of  these  installations  diffused  the  light  too 
much  for  the  best  esthetic  effect. 

Color  of  Light. — The  warmer  tone  of  light  from  the  art-glass 
semi-direct  units  was  very  agreeable,  while  the  similar  color  from 
the  opal-glass  direct  system  was  responsible  probably  for  a  con- 
siderable portion  of  its  apparent  visual  superiority  over  the  pris- 
matic equipment.  Both  semi-direct  and  indirect  systems  took 
their  color  tone  to  a  marked  extent  from  the  ceiling  and  the 
harshness  of  the  tungsten  flux  was  somewhat  reduced  in  this  way. 
The  wide  variations  in  density  of  shadowgraph  films  obtained 
from  the  several  systems  with  identical  exposures  served  to  em- 
phasize the  effect  of  color  modification  in  those  systems  depend- 
ing largely  upon  ceiling  and  wall  reflections. 

Accuracy  of  Data. — The  usual  ratios  between  the  maximum, 
mean,  and  minimum  illumination  values  observed  on  the  30-inch 
plane  are  shown  in  columns  5,  6,  and  7  of  Table  I.  It  will  be 
noted  that  these  are  given  only  to  two  places  of  significant  figures, 
and  the  authors  wish  to  call  especial  attention  to  the  desirability  of 
thus  reducing  the  pretension  to  accuracy  found  in  many  illumin- 
ating data.  The  maximum  or  minimum  ratio  is  based  on  a  few 
readings  at  a  single  station  and  any  extended  experience  with 
the  portable  photometers  at  present  available  will  convince  the 
tester  that  there  is  little  probability  of  such  value  having  an  error 
less  than  5  per  cent,  while  even  in  careful  work  errors  of  10  per 
cent,  at  a  single  station  frequently  occur.  Furthermore  in  the 
present  state  of  lighting  a  10  per  cent,  variation  in  the  uniformity 
ratios  or  indeed  in  such  characteristics  as  mean  intensity  or  specific 
brightness  have  a  negligible  effect  on  the  excellence  of  the  in- 
stallation and  cannot  be  appreciated  by  the  most  experienced  en- 
gineer. Two  places  of  figures  thus  generally  carry  the  result 
beyond  the  point  of  uncertainty,  and  give  more  than  adequate 
numerical  precision. 


696     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Uniformity  of  Intensity. — The  uniformity  produced  on  the  30- 
inch  plane  by  the  five  systems  under  consideration  appeared 
largely  independent  of  the  system  used,  being  chiefly  determined 
by  the  spacing  and  suspension  height.  In  the  direct  system  using 
six  units  mounted  at  the  ceiling  the  maximum  intensity  was  but 
10  per  cent,  above  and  the  minimum  20  per  cent,  below  the  mean. 
With  the  indirect  and  dense  semi-direct  systems  the  maximum 
was  20  per  cent,  above  the  mean  and  the  minimum  30  per  cent, 
below  it.  This  last  variation  was  not  considered  excessive,  a 
high  mean  value  assuring  sufficient  illumination  at  all  points. 

Utilisation  Efficiency. — The  utilization  efficiencies  obtained  are 
given  in  column  10,  Table  I.  Those  for  the  direct  lighting  sys- 
tems are  open  to  some  question  on  account  of  the  necessity,  noted 
in  Appendix  I,  of  assuming  the  flux  generated  by  the  lamps  be- 
fore they  were  bowl  frosted;  but  as  the  means  of  six  units  are 
believed  to  be  fairly  reliable.  The  figures  for  the  semi-direct  and 
indirect  systems  were  computed  from  flux  values  based  on  actual 
photometric  measurements  and  should  have  high  accuracy. 

The  unusually  high  mounting  of  the  direct  units  adopted  in 
an  attempt  to  decrease  glare  and  shadow,  reduced  the  efficiency 
of  the  direct  systems,  while  the  exceptionally  low  absorption  of 
the  ceiling  and  walls  greatly  increased  the  efficiency  of  the  semi- 
direct  and  indirect  systems  as  compared  with  similar  tests  made 
in  other  offices. 

With  the  possible  exception  of  the  indirect  system,  there  was 
not  sufficient  difference  in  the  efficiencies  found  to  influence  the 
final  choice.  Indeed  utilization  efficiency  is  believed  to  be  of  far 
less  importance  with  the  higher-efficiency  lamps  and  if  the  losses 
of  generated  flux  are  expended  to  secure  better  diffusion  or  pre- 
ferred color,  the  increased  effectiveness  may  largely  overbalance 
the  cost  of  absorption. 

General  Conclusion  from  Preliminary  Tests. — The  superiority 
of  the  semi-direct  and  indirect  systems  over  the  direct  in  lessened 
eye  fatigue  and  in  harsh  shadow  elimination  seemed  to  the  light- 
ing committee  to  greatly  overbalance  the  decreased  utilization 
efficiency,  lessened  uniformity  and  increased  investment  costs  of 
these  more  diffusing  systems.  As  between  the  semi-direct  and 
indirect  system,  the  advertising  value  of  a  visible  light  source  in 


DURGIN  AND  JACKSON:    SEMI-DIRECT  OFFICE  LIGHTING      697 

the  offices  of  a  company  supplying  light,  a  more  ready  control  of 
flux  color  and  shadow  density,  and  a  somewhat  higher  utilization 
efficiency  led  to  the  recommendation  of  the  semi-direct  system, 
with  the  provision  that  semi-direct  and  indirect  units  of  closely 
similar  design  should  be  developed  and  that  each  department  head 
should  decide  which  was  to  be  installed  in  the  offices  under  his 
direction.  This  parallel  design  was  carried  out  and  the  indirect 
system  chosen  for  the  drafting  room,  where  all  agreed  that  the 
minimum  glare  on  tracing  cloth  made  it  ideal,  and  for  about 
5  per  cent,  of  the  offices.  This  represents  such  a  small  part  of 
the  total  floor  area,  however,  that  no  further  consideration  is 
given  the  indirect  system  in  the  present  paper. 

SEMI-DIRECT  LIGHTING  REQUIREMENTS. 

The  necessary  characteristics  of  a  satisfactory  semi-direct 
unit  were  considered  to  be:  (a)  Bowl  brightness  not  more  than 
three  times  that  of  the  ceiling,  (b)  Reasonably  high  overall  ef- 
ficiency. Hence  a  high  reflection  coefficient  for  the  bowl  interior 
and  little  interference  from  fixture  structure,  (c)  Color  modifi- 
cation of  tungsten  flux  to  a  warmer  tone,  (d)  Easy  cleaning  of 
bowl  and  lamps. 

Choice  of  Bowl. — The  first  requirement,  moderate  brightness 
of  bowl,  served  to  eliminate  a  large  proportion  of  the  glassware 
on  the  market.  Twelve  types  of  bowls  submitted  by  eight  manu- 
facturers were  equipped  with  three  100-watt  lamps  each  and  hung 
30  in.  (76  cm.)  from  the  ceiling  on  14  ft.  (4.3  m.)  centers  in  a 
long  office  some  n  ft.  (3.4  m.)  in  height.  An  indirect  fixture, 
similarly  equipped  and  hung  produced  a  maximum  ceiling  bright- 
ness, viewed  from  a  point  directly  below,  of  80  millilamberts. 
Assuming,  as  seemed  highly  probable,  that  no  semi-direct  equip- 
ment could  produce  higher  ceiling  brightness  under  these  con- 
ditions, the  desirable  bowl  brightness  was  limited  to  240  milli- 
lamberts. The  average  brightness  of  the  bottom  of  twelve  bowls 
tested  was  1,170  millilamberts  viewed  from  below,  and  the  aver- 
age side  brightness  at  the  8o°  angle  was  340  millilamberts.  One 
bowl  of  a  widely  used  glass  had  a  bottom  brightness  of  4,600 
millilamberts  and  several  a  side  brightness  of  over  500  milli- 
lamberts. Frequently  such  excessive  values  were  caused  by  the 
shape  of  the  bowl  placing  the  glass  too  near  the  lamps  when  their 


698     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

position  was  adjusted  to  bring  the  bulbs  below  the  top  plane  of 
the  fixture  ring;  but  it  is  believed  that  in  addition  to  too  shallow 
bowl  shapes  at  least  90  per  cent,  of  the  glassware  now  offered 
for  semi-direct  use  has  much  too  high  transmission. 

The  bowl  finally  chosen2  met  all  the  requirements  satisfactorily. 
The  bottom  was  about  2.7  times  as  bright  as  the  brightest  spot  in 
the  ceiling  and  the  side  of  practically  ceiling  brightness.  The 
depth,  6y2  in.  (16.5  cm.)  for  a  20  in.  (51  cm.)  bowl  and  5%  in. 
(13.3  cm.)  for  the  16  in  (41  cm.)  size,  conduced  to  this  result; 
but  the  density  of  the  triple-cased  glass  used  was  the  principal 
factor.  Measurements  made  in  the  office  shown  in  Fig.  4  gave 
the  values  of  Table  II. 

TABLE  II.— Brightness  Values  in  Office  Equipped  with 
Eight  Semi-Direct  Units. 

Millilamberts 

Mean  Maximum 

Bottom  of  bowl 150  190 

Side  of  bowl 60  90 

Ceiling  above  bowl 55  60 

Ceiling  at  center  of  four  unit  square 1.2  1.4 

Ceiling  at  middle  of  side  of  four  unit  square      2.8  3.0 

Side  wall  6  ft.  from  floor 2.6  2.6 

Side  wall  4  ft.  from  floor 1.8  2.2 

In  so  far  as  the  glassware  determined  the  efficiency  of  the  unit 
the  chosen  bowl  seemed  exceptionally  good,  the  interior  surface 
being  of  pure  white  highly  glazed  and  the  regular  and  simple 
curve  (see  Fig  2),  giving  a  moderately  wide  distribution.  The 
cased  glass  permitted  the  toning  of  the  transmitted  flux  to  an 
amber  of  approximate  visual  color  match  to  that  produced  by  a 
metallized  filament  lamp  at  96  per  cent,  rated  voltage,  while  the 
bowl  retained  when  not  lighted  an  appearance  of  iridescent  white. 
With  the  spectroscope  this  glass  was  found  to  absorb  in  trans- 
mission all  the  tungsten  lamp  spectrum  above  the  blue-green,  but 
in  reflection  from  the  interior  surface  the  spectral  composition  was 
entirely  unaffected.  The  high  interior  glaze  was  recognized  also 
as  of  marked  advantage  for  easy  cleaning. 

GLASS  AND  FIXTURE  SPECIFICATIONS. 
Purchase  of  Glassware  on  Specification. — To  secure  reasonable 
uniformity  in  separate  shipments  of  some  700  bowls  when  color 

2  Calcite. 


DURGIN  AND  JACKSON  :    SEMI-DIRECT  OFFICE  LIGHTING      699 

and  brightness  were  of  paramount  importance,  it  appeared  neces- 
sary to  closely  specify  these  qualities.  Previous  practise  offered 
no  published  precedent  and  in  consequence  the  specification 
shown  in  Appendix  II  was  proposed  and  submitted  to  the  manu- 
facturer. This  is  presented  not  as  a  finished  solution  of  the  ques- 
tion, but  as  a  focus  for  discussion  of  a  seemingly  neglected  means 
for  improvement  of  lighting  practise.  Even  after  conscientious 
inspection  of  each  bowl  by  the  manufacturer  for  compliance  with 
the  specification,  the  customer's  inspector  rejected  2.5  per  cent, 
of  the  shipped  bowls  for  size  and  6.5  per  cent,  for  uniformity  of 
color.  Without  specification  then,  no  approach  to  uniformity 
could  be  expected.  Experience  in  this  instance  showed  the  glass 
manufacturer  more  than  willing  to  cooperate  in  the  effort  to 
secure  better  product  and  although  the  rather  narrow  limits  im- 
posed lead  to  a  very  considerable  number  of  rejections  before 
shipment,  both  parties  are  convinced  of  the  benefit  of  the  plan. 
The  expense  to  the  customer  of  carefully  inspecting  each  bowl 
for  fit  in  a  gauge  ring,  design,  dimensions  and  quality  of  etching, 
for  appearance  when  lighted  with  lamps  grouped  as  in  the  com- 
pleted unit,  and  for  color  tone  as  compared  with  a  bowl  selected 
as  standard  was  less  than  7  cents  per  bowl. 

Fixture  Design. — The  principal  desiderata  in  the  fixture  were 
an  effect  of  substantial  and  simple  design,  small  interference  with 
generated  light  flux,  and  the  inclusion  of  a  double  ring  to  permit 
easy  cleaning.  In  the  specification  given  to  the  various  fixture 
houses  the  last  feature  was  covered  by  the  following  statement : 

"The  scheme  consists  of  a  double  ring,  one  ring  to  be  stationary  and 
to  carry  the  socket  equipment,  the  other  securely  hinged  to  the  first,  to 
be  so  arranged  as  to  be  dropped  easily  at  one  side  for  allowing  ready 
accesss  to  the  interior  of  the  bowl  for  cleaning.  The  hinge  must  be  at 
least  2  inches  wide  and  of  sufficient  strength  to  carry  bowl  weight  with- 
out wear.  Means  for  locking  the  two  rings  together  must  be  provided  at 
a  point  diametrically  opposite  from  the  hinge,  the  locking  scheme  to 
permit  quick  separation  of  the  bowls  but  to  be  of  ample  strength  to 
support  bowl  weight.  Means  for  securing  the  glass  bowl  in  the  lower 
ring  easily  and  permanently  also  must  be  arranged.  The  design  of  the 
two  rings  should  provide  a  rabbet  or  other  overlap  between  them  so  that 
no  leakage  of  light  is  possible." 

The  accepted  realization  of  these  ideas  is  well  shown  in  Fig.  2, 
a  and  b.    Two  strap-iron  rings  are  arranged  to  fit  concentrically. 
7 


yOO    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  outer  ring  carries  a  brass  spinning  to  give  the  exterior  finish 
and  provide  a  lip  for  supporting  the  bowl,  while  the  inner  ring 
carries  the  lamp  sockets  and  is  in  turn  carried  by  the  four  sup- 
porting rods.  Two  of  the  three  clips  arranged  to  retain  the  bowl 
are  shown  in  b,  and  the  spring  catch  which  holds  the  rings 
together  may  also  be  seen  at  the  lowest  point  of  the  outer  ring. 
This  arrangement  permits  the  bowl  to  be  lowered  in  a  few  sec- 
onds, exposing  both  sides  of  the  lamps  for  dusting  and  permitting 
the  interior  to  be  cleaned  with  a  single  sweep  of  a  cloth.  The 
entire  dusting  operation  can  be  performed  in  less  than  two 
minutes. 

Especial  attention  was  given  to  lamp  position,  the  socket  loca- 
tion being  specified  by  the  resulting  position  of  the  lamp  tips  as 
shown  in  Fig.  6.  This  figure  also  shows  the  details  of  canopy 
employed.  The  particular  point  to  be  noted  here  is  the  iron 
bridge  which  carries  the  stress  from  the  rod  rings  to  the  central 
hickey  and  by  means  of  a  nipple  and  lock  nut  supports  the 
fixture  when  the  canopy  shell  is  removed,  thus  permitting  the 
connection  of  wiring  after  the  fixture  is  permanently  in  place. 
This  construction  was  suggested  by  the  manufacturer  and  is  in 
more  or  less  common  use  in  fixtures,  but  is  emphasized  because 
of  its  strength  and  convenience. 

Each  fixture  was  inspected  after  hanging,  the  lamp  position 
checked  with  the  largest  specified  size  of  lamps  and,  where  neces- 
sary, altered  under  the  inspector's  direction  to  give  a  uniform 
illumination  of  the  entire  bowl.  As  will  be  noted  from  the  dimen- 
sions given  in  Fig.  6,  the  lamps  were  placed  higher  in  the  bowl 
than  usual.  This  arrangement  gives  a  breadth  of  distribution 
leading  to  a  bright  band  on  the  upper  part  of  the  side  wall  if  the 
unit  is  installed  less  than  6  feet  from  the  wall,  but  is  necessary, 
even  with  such  deep  bowls,  if  each  bowl  is  to  have  that  even 
gradation  of  brightness  and  freedom  from  spotting  which  is 
believed  to  be  one  of  the  most  pleasing  details  of  a  good  semi- 
direct  unit. 

Characteristics  of  Complete  Unit. — The  average  20  in.  (51  cm.) 
bowl  weighed  9  pounds  and  the  efficiency  of  the  unit  was  found 
to  increase  slightly  for  lighter  and  decrease  for  heavier  bowls 
due  to  corresponding  variations  in  transmitted  flux.    These  varia- 


Fig.  2.— (a)  Standard  semi-direct  unit:  (b)  20-in.  bowl  opened  for  cleaning. 


Fig.  3. — Shadowgraph  apparatus. 


Fig.  4.— Typical  Commonwealth  Edison  Co.  office  lighted  by  eight 
semi-direct  units  on  14  feet  centers. 


Fig.  5. — Office  of  Fig.  4.  with  units  converted  to  an  indirect  system. 


DURGIN  AND  JACKSON  :    SEMI-DIRECT  OFFICE  LIGHTING      701 

tions,  however,  were  not  more  than  1.5  per  cent,  from  the  mean 
unit  efficiency  of  80  per  cent.  A  standard  fixture  equipped  with 
a  bowl  weighing  8.7  pounds  and  three  100-watt  tungsten  lamps 
gave  the  distribution  curves  shown  in  Fig.  7,  and  summarized  in 
Table  III. 

TABLE  III.— Distribution  from  Semi-Direct  Unit. 

lumens  Per  cent. 

Generated  flux 2,875  100 

Absorbed  by  fixture 15  0.5 

Distributed  by   fixture   without  bowl  in 

lower  hemisphere 1,525  53 

Distributed  by  complete  unit 2,330  81 

Portion  of  complete  unit  flux,  in  lower 

hemisphere 260  1 1 

Portion  of  complete  unit  flux,   between 

1050  and  1800 1.930  83 

Curve  B  of  Fig.  7  is  of  especial  interest  as  it  indicates  the  pre- 
ponderance of  flux  in  the  lower  hemisphere  from  the  bare  lamps 
caused  by  the  downward  tip  of  the  bulb  axes  and  the  slight  ab- 
sorption from  the  fixture  structure.  Such  absorption  was  re- 
duced to  a  minimum  by  covering  the  interior  of  the  fixture  rings 
with  aluminum  paint  and  by  the  comparatively  light  supporting 
members  employed.  Photometer  readings  at  1700  and  1800 
could  not  be  obtained  with  the  apparatus  available,  hence  curve 
A  was  extrapolated  for  these  points  as  indicated  by  broken  line. 
This  procedure  should  introduce  a  negligible  error  in  the  flux 
values  as  the  zones  affected  are  of  small  area. 

In  curve  C  the  portion  of  curve  A  from  o°  to  900  is  redrawn 
at  an  enlargement  of  five  times  to  show  the  intensive  character 
of  the  distribution  in  the  lower  hemisphere. 

COMPLETED  OFFICE  INSTALLATIONS. 
The  office  floors  of  the  Edison  Building  are  arranged  on  three 
sides  of  an  oblong  court  60  by  120  ft.  (18  by  37  m.)  in  extent  and 
a  central  corridor  divides  a  considerable  part  of  each  floor  into 
an  inner  and  outer  space.  This  arrangement  leads  to  three 
groups  of  offices  approximating  20,  30  and  56  ft.  (6,  9  and  17  m.) 
in  width,  many  of  the  general  clerical  spaces  being  comparatively 
long  while  the  private  offices  average  15  ft.  (5  m.)  square.  The 
ceiling  height  varies  from  10  ft.  1  in.   (3.1  m.)  to  17  ft.  3  in. 


702     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

(5.3  m.),  44,000  sq.  ft.  (4,100  sq.  m.)  or  nearly  54  per  cent,  of  the 
total  floor  area  having  a  height  of  10  ft.  9  in.  (3.3  m.). 

The  considerable  range  in  width  of  offices  necessitated  a 
similar  variation  in  the  spacing  of  the  semi-direct  units.  14  ft. 
(4.3  m.)  between  centers  was  taken  as  the  maximum  and  this 
distance  may  be  considered  standard,  although  spacings  as  low 
as  8  ft.  (2.4  m.)  were  used  in  a  few  cases.  In  general  the  shorter 
spacings  were  employed  in  private  offices  and  units  with  16-in. 
(41  cm.)  bowls  installed  carrying  two  or  three  60  or  100- watt 
tungsten  lamps. 

The  complete  system  of  offices  required  250  of  these  16-in. 
(41  cm.)  bowl  units,  while  450  of  the  larger  units  equipped  with 
20-in.  (51  cm.)  bowls  were  used.  Most  of  these  carry  three 
100- watt  tungsten  lamps,  but  in  a  few  instances  60- watt  or  150- 
watt  lamps  are  necessary  to  produce  the  standard  mean  intensity. 

All  offices  were  decorated  with  the  cream  and  brown  tints  of 
calcimine  described  for  the  test  room  and  after  six  months  of 
use  the  reflection  coefficients  were  found  to  be  about  0.8  for  the 
ceilings  and  somewhat  above  0.7  for  the  walls. 

Taking  an  office  width  of  28  ft.  (8.5  m.),  a  ceiling  height  of 
10  ft.  9  in.  (3.3  m.),  a  spacing  distance  of  14  ft.  (4.3  m.)  and 
the  larger  or  20-in.  (51  cm.)  bowl  unit  with  the  upper  edge  of 
ring  30  in.  (76  cm.)  from  the  ceiling  as  representative  of  the  in- 
stallations, complete  illumination  tests  under  these  conditions 
were  made  in  two  rooms,  one  50  ft.  (15  m.)  and  the  other  100  ft. 
(30  m.)  in  length.  The  results  check  so  closely  that  all  data 
have  been  averaged  together  and  are  here  presented  as  applying 
to  any  of  the  group  of  long  offices  having  the  stated  width  and 
height.  The  end-wall  effect  is  to  decrease  the  average  illumina- 
tion about  10  per  cent,  in  a  strip  extending  some  8  ft.  (2.4  m.) 
from  the  wall  and  in  offices  approaching  a  square  plan  this  affects 
the  mean  values  to  a  small  extent  but  in  the  longer  offices  is 
practically  negligible.  End  walls,  therefore,  are  neglected  in  the 
following  discussion  and  the  computations  based  on  intensities 
obtained  in  the  middle  half  of  the  rooms. 

Illumination  Tests. — To  insure  accuracy,  checks  were  made 
simultaneously  by  two  observers  using  separate  Sharp-Millar  pho- 
tometers, one  of  standard  and  the  other  of  small  size.    In  those 


DURGIN  AND  JACKSON  :    SEMI-DIRECT  OFElCE  LIGHTING      703 
(a) 


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704    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

cases  where  results  failed  to  agree  the  data  were  rejected  or  only 
those  used  from  the  instrument  showing  no  change  on  recalibra- 
tion.  In  this  way  it  was  possible  to  obtain  mean  values  differing 
by  less  than  1  per  cent. 

The  unavoidable  variation  in  system  pressure  was  met  by 
taking  readings  from  side-wall  sockets  directly  on  the  distributing 
wiring,  correcting  for  the  measured  drop  to  the  fixture  sockets 
and  further  correcting  to  a  standard  mean  pressure  of  113  volts. 
As  there  was  some  question  of  the  relation  between  the  intensity 
of  the  amber  filtered  flux  and  pressure,  an  extended  series  of 
readings  was  taken  at  five  typical  stations  at  five  pressures  rang- 


Fig.  7.— Distribution  from  300-watt  semi-direct  unit.  {A)  Curve  when  equipped  with  20- 
in.  bowl.  (B)  Curve  when  equipped  with  lamps  but  no  bowl.  (3)  Portion  of  (A)  from 
o°  to  900,  enlarged  five  times. 


ing  from  108  to  117  volts.  These  data  were  obtained  for  both 
the  total  semi-direct  flux  and  for  the  indirect  component,  but 
when  plotted  showed  an  extreme  divergence  of  only  1  per  cent, 
from  the  accepted  curves  for  tungsten  lamps.  The  removal  of 
the  blue  rays,  therefore,  has  no  appreciable  effect  upon  the  estab- 
lished flux-pressure  relations. 

In  Figs.  4  and  5  two  views  are  presented  of  the  office  which 
is  50  ft.  (15  m.)  in  length.  This  room  is  equipped  with  eight 
units  and  Fig.  4  gives  a  close  representation  of  the  lively  char- 
acter of   the  illumination,    of   the  moderate   brightness   of   the 


DURGIN  AND  JACKSON:    SEMI-DIRECT  OFFICE  LIGHTING      705 

bowls,  and  of  the  absence  of  dense  shadows.  Fig.  5  presents  the 
method  used  for  separating  the  indirect  component  for  meas- 
urement and  suggests  faintly  the  resulting  flat  appearance  of  the 
lighting.  The  oil  cloth  covers  drawn  over  the  bowls  to  shut  off 
the  direct  component  were  grayish  white  on  the  outside  and  dull 
black  on  the  inside  thus  producing  minimum  interference  with 
the  normal  conditions  of  reflection  from  the  bowl  surfaces. 

Summarized  results  from  all  illumination  tests  on  clean  bowls 
and  new  lamps  are  given  in  Table  IV.  The  mean  semi-direct  in- 
tensity of  6.0  foot-candles  on  the  30-in.  (76  cm.)  plane  corres- 
ponds to  a  utilization  efficiency  of  42.5  per  cent,  with  115-volt, 
i-w.  p.  c.  lamps  operated  at  113  volts,  a  flux  of  2,770  lumens 
applying  to  an  area  14  ft.  (4.3  m.)  square.  The  corresponding 
mean  indirect  intensity  of  4.9  foot-candles,  or  a  utilization  ef- 
ficiency of  35  per  cent,  is  not  far  below  that  obtainable  with  the 
best  indirect  units  and  indicates  the  excellence  of  the  interior 
finish  and  shape  of  the  bowls. 

TABLE  IV.— Illumination  Values  from  Completed  Semi-Direct 

Installation. 

Intensities  in  foot-candles  Uniformity  ratio 

on  30  in.  plane  , < , 

/ " >  Max.  Max.  Min. 

Max.  Mean  Min.  Min.  Mean  Mean 

Semi-direct 8.0  6.0  4.2  1.9  1.3  0.7 

Indirect 5.6  4.9  3.7  1.5  1.1  0.8 

Direct 2.8  1.1  0.7  4.0  2.5  0.6 

The  mean  semi-direct  illumination  thus  contains  a  direct 
component  of  18  per  cent.,  which  although  it  is  somewhat  higher 
than  the  12  to  15  per  cent,  advocated  on  theoretical  grounds,2 
appears  eminently  satisfactory  in  affording  a  restful  contrast  and 
minimum  eye  fatigue.  It  should  be  noted  that  this  18  per  cent, 
of  illumination  is  given  by  11  per  cent,  of  the  generated  flux. 

In  Fig.  8  the  relation  of  the  three  components  are  shown,  the 
lower  group  of  curves  giving  the  relative  intensities  across  the 
room  on  a  line  30  in.  (76  cm.)  above  the  floor  directly  under  the 
units,  and  the  upper  group,  similar  intensities  midway  between 

2  Symposium  on  Indirect,  Semi-Indirect  and  Direct  Lighting:  Trans.  I.  E.  S.,  vol. 
VII,  p.  234;  1912. 


706     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

two  such  lines  of  units.  The  semi-direct  intensity  immediately 
beneath  the  bowl  is  taken  as  unity  and  all  other  intensities  plotted 
in  percentage  of  this  value.  Perhaps  the  uniformity  of  the  in- 
direct component  and  effect  of  the  direct  component  in  relieving 
the  flatness  are  the  most  notable  points  indicated.  The  drop  in 
intensity  toward  the  side  walls  is  also  well  shown.  This  pro- 
duces a  considerable  decrease  in  the  mean  intensity  and  since 
many  of  the  desks  are  placed  toward  the  center  line  of  these  long 
offices,  it  may  be  fairly  stated  that  an  intensity  of  7  foot-candles 
under  clean  units  is  being  used  by  a  majority  of  the  clerks  in 


1          1          1 

MIL  WAY   ■RET'rtEEtl    LIHCS 

Br 

OF 

JHITC 

40 

JiO 

0 

LIME 

rum 

60 

\ 

60 
40 

20 

i 

Feet 

Fig.  8. — Illumination  Curves  to  show  relation  of  indirect  and  direct  components 

to  total  flux  on  a  30  in.  plane. 

these  rooms.  Allowing  20  per  cent,  decrease  before  cleaning, 
the  average  value  of  the  intensity  for  these  desks  is  approximately 
6  foot-candles.  Wall  brightness  within  the  ordinary  field  of 
view  as  noted  in  Table  II  reaches  values  more  than  one-third  those 
produced  on  matt  paper  under  a  6  foot-candle  illumination  and 
would  seem  to  be  too  high  for  best  eye  efficiency.  As  yet,  how- 
ever, no  complaints  of  this  condition  have  been  received,  due 
perhaps  to  the  fact  that  a  large  part  of  the  wall  is  covered  by 
dark  mahogany  cases  and  that  these  high  brightness  values  only 
apply  to  small  areas  where  structural  limitations  have  brought 
units  close  to  an  end  wall.  The  greater  part  of  the  wall  has  z 
brightness  about  one  fourth  that  of  mat  paper  on  the  desks. 


DURGIN   AND  JACKSON  :     SEMI-DIRECT  OFFICE  LIGHTING      70J 

Dust  Factor. — Extra  care  was  used  in  securing  the  data  for 
the  dust  deterioration  curve,  Fig.  9,  and  the  plotted  points  from 
three  locations  representing  the  most  dusty  offices  in  the  building 
show  no  departure  from  a  straight-line  law  during  the  observation 
period  of  three  weeks.  As  the  absorption  had  increased  to  25 
per  cent,  at  that  time  the  further  performance  was  considered  of 
little  interest.  A  bi-monthly  cleaning  schedule  will  insure  an  il- 
lumination at  all  times  above  80  per  cent,  of  the  clean-bowl  con- 
dition.    Such  a  schedule  is  being  made  effective  and  although 


=  'C0 


SSD- 
,0 

£6C 


I  2  3 

WEEKS  Or  DUST  ACCUMULATION 


Fig.  9.— Dust  absorption  factor  of  standard  C  E.  Co.,  semi-direct 
office  installations. 

experience  is  not  yet  sufficient  to  permit  accurate  maintenance 
cost  figures,  the  fixture  design  bids  fair  to  reduce  cleaning  ex- 
pense to  a  very  nominal  amount. 

CONCLUSION. 

In  the  use  of  a  mean  intensity  above  6  foot-candles  and  of  a 
distinctly  amber  tone  of  effective  flux  the  office  lighting  in  the 
Edison  Building  of  Chicago  represents  an  experiment.  There  is 
no  question  as  to  the  immediate  popularity  of  the  results.  Clerks 
and  department  heads  agree  in  commendation.  But  the  element 
of  time  is  lacking  as  yet  and  only  extended  experience  can  show 
whether  high  intensities  and  filtered  flux  will  prove  a  permanent 
advance. 

The  low  value  of  bowl  brightness  and  the  fixture  design  em- 
ployed are  more  confidently  presented  as  realizations  of  generally 
accepted  but  rarely  applied  principles  and  the  dust  deterioration 
curve  will  give  definiteness,  it  is  hoped,  to  the  much  discussed 
question  of  semi-direct  lighting  maintenance. 

The  accumulation  of  data  for  this  paper  has  been  possible  only 
through  the  cordial  cooperation  of  Messrs.  G.  W.  Baker  and 
R.  E.  Powell  of  the  Commonwealth  Edison  testing  department 
and  to  them  the  authors  tender  their  hearty  thanks. 


708     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

APPENDIX  L— EQUIPMENT  AND  PROCEDURE  FOR 
PRELIMINARY  TESTS. 

Room. — Arranged  as  described  in  paper. 

Wiring. — A  system  of  metal  moulding  and  outlets  was  installed 
on  the  ceiling  whereby  a  symmetrical  2,  4,  6,  or  8  unit  system 
could  be  used.  To  insure  accurate  indication  of  the  voltage  ap- 
plied to  the  lamps  two  pressure  taps  were  arranged  directly  on 
the  ceiling  wiring.  Provision  was  also  made  for  measuring  the 
current  and  installing  a  controlling  rheostat  at  the  switch  cabinet. 

Steadiness  of  Supply. — Recording  voltmeter  charts  and  fre- 
quent readings  with  indicating  voltmeter  showed  the  day  pressure 
to  be  within  -f-  or  —  one  volt  of  the  mean  value  112  volts.  The 
average  during  each  test  was  computed  from  twenty  readings 
and  the  flux  corrected  to  this  value  using  National  Electric  Lamp 
Association  curve4  for  variation  of  candlepower  with  pressure. 

Lamps. — The  lamp  equipment  comprised: 

2  250-watt,  iT4-volt  clear  bulb  lamps  assumed  to  give 
standard  average  flux  (2  x  2,450  lumens)  at  114  volts. 

4  150-watt,  116-volt  clear  bulb  lamps  photometered  at  116 
and  1 13.5  volts  for  m.  h.  cp.  Flux  computed  using  re- 
duction factor  of  0.785. 

6  100- watt,  114-volt  clear  bulb  lamps  rated  at  114  volts 
for  m.  h.  cp.  and  total  flux  by  General  Electric  Co. 

6  100-watt,  114-volt  bowl  frosted  lamps  assumed  to  gen- 
erate standard  average  flux  (908  lumens)  at  114  volts 
before  frosting. 

6  60-watt,  114-volt  bowl  frosted  lamps  assumed  to  gen- 
erate standard  average  flux  (526  lumens)  at  114  volts 
before  frosting. 

6  60-watt,  114-volt  bowl  frosted  lamps  photometered  at 
112  volts  for  m.  h.  cp.  and  flux  computed  using  re- 
duction factor  of  0.785. 
Glassware  Equipment  and  Mounting  Heights. — 

1.  Prismatic  reflectors  X-I  100,  velvet  finish  used  with 
form  H  holder  mounted  at  9  ft.  9  in.  (3m.)  from  the 
floor  to  lower  edge. 

*  Engineering  Department,  National  Electric  Light  Association  Bulletin  13C,  p.  9; 
February  1,  1913. 


DURGIN  AND  JACKSON  :    SEMI-DIRECT  OFFICE  LIGHTING      709 

2.  Opal  glass  reflectors.    Sudan  No.  01213  8  in.  (20  cm.), 

Panalex  design,  dull  finish  used  with  form  H  holder. 
Mounted  9  ft.  9  in.  (3m.)  from  the  floor  to  lower 
edge. 

3.  Art  glass.    Monolux  No.  3,540  and  3,541.    Mounted  at 

8  ft.  o  in.  (2.4  m.)  from  floor  to  upper  edge. 

4.  Opal  glass  semi-indirect.     Calla  No.  1,215  J6  in.   (41 

cm.).  Mounted  8  ft.  o  in.  (2.4  m.)  from  floor  to  upper 
edge. 

5.  Totally  indirect.     X-Ray  No.  14,270  mounted  at  8  ft 

o  in.  (2.4  m.)  from  floor  to  upper  edge. 
Note. — XI  60  Prismatic  and  Sudan  No.  01213  7  in.  (18 
cm.)  reflectors  were  used  with  60- watt  bowl  frosted 
lamps  suspended  9  in.  (23  cm.)  from  ceiling  for  low 
intensity  direct  system  tests. 

Bye  Fatigue  Tests. — A  standing  desk  6  ft.  (1.8  m.)  long  by 
3  ft.  (0.9  m.)  wide  and  having  a  mean  height  of  44  in.  (1.1  m.) 
was  placed  facing  toward  the  center  of  the  room,  with  stool  in 
position  indicated.  By  arrangement  an  accountant  of  the  treasury 
department  did  regular  accounting  work,  principally  extensions 
of  books,  under  each  of  the  five  different  schemes  of  illumina- 
tion. His  working  day  averaged  about  seven  hours  and  he  used 
each  system  for  five  days.  Before  starting  work  and  at  the  close 
of  work  in  both  morning  and  afternoon  periods,  Ferree  tests 
were  made  on  his  eyesight  by  J.  R.  Cravath,  giving  two  pairs  of 
tests  per  day  or  ten  complete  visual  tests  under  each  system. 

Tests  of  Light  Direction  (Shadowgrams). — A  new  method 
was  developed  for  recording  shadows  photographically — shown 
in  Fig.  3.  A  plate  holder  loaded  with  Velox  transparency  film 
was  supported  in  a  30  in.  (76  cm.)  horizontal  plane  at  the  sta- 
tion to  be  investigated,  the  lights  turned  off,  the  film  exposed,  a 
round  vertical  rod  3/32  in.  (2.3  mm.)  in  diameter  and  i1/2  in. 
(3.8  cm.)  long  standing  on  circular  base  3/8  m-  (l  cm0  in  diam- 
eter placed  in  the  center  of  the  film  and  the  lights  turned  on  for 
30  seconds.  Shadows  thrown  by  the  rod  were  recorded  on  the 
film.  One  end  of  the  film  previously  protected  was  later  exposed 
in  the  laboratory  under  fixed  conditions,  the  tone  of  the  print 


7IO     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

from  this  end  serving  as  a  check  to  show  that  the  chemical  man- 
ipulation of  all  films  was  identical. 

Intensity  Measurements. — Eighty  stations  were  laid  out  mak- 
ing each  the  center  of  a  28^  in.  (73  cm.)  square.  As  preliminary 
surveys  on  a  plane  30  in.  {j6  cm.)  above  the  floor  showed  the 
four  quarters  of  the  room  to  be  practically  identical  in  horizontal 
illumination,  the  final  tests  were  confined  to  this  plane  and  to  the 
twenty  stations  in  a  single  quarter. 

A  Sharp-Millar  photometer  (standard  size)  was  used  exclu- 
sively. It  was  mounted  on  truck  for  quick  movement  from  sta- 
tion to  station,  storage  battery  supply  and  ammeter  reading  being 
used  to  insure  constancy  of  comparison  lamp.  The  instrument 
was  checked  against  standard  lamp  in  the  laboratory  every  two 
or  three  days  and  showed  fair  performance. 

In  the  actual  surveys  four  readings  were  taken  at  each  station 
and  the  mean  accepted  as  the  actual  value.  A  complete  set  of 
eighty  readings  could  be  taken  easily  in  one  half  hour. 

APPENDIX  II.— SPECIFICATION  COVERING   BOWLS 

FOR  SEMI-INDIRECT  LIGHTING  EQUIPMENT. 

Quantity. — 20-inch  bowls  and    16-inch  bowls 

are  to  be  furnished  under  this  specification  on  Commonwealth 
Edison  Company  purchase  requisition  No 

Material. — Bowls  are  to  be  of  special  grade  of  

glass  manufactured  by  the under  the  trade  name, 

Design. — Bowls  are  to  be  etched  with  special  Greek  fret  and 

central   web  as   shown  on  sketch   submitted  by    

The  upper  edge  of  Greek  border  is  to  be  2T/2  in.  below  bottom 
edge  of  rim,  and  over-all  width  of  border  is  to  be  2^  in.  on  20-in. 
bowls.  All  measurements  taken  over  the  curving  surface  of  the 
bowl.  Central  web  of  20-in.  bowls  to  be  7%  in.  in  diameter.  All 
three  dimensions  to  be  decreased  proportionately  for  16-in.  bowls. 

Etching  Detail. — All  etched  lines  to  be  smooth  and  of  uniform 
depth.  Greek  border  to  be  strictly  parallel  to  edge  of  bowl. 
Variation  in  distance  between  support  edge  of  bowl  lip  and  upper 
edge  of  Greek  border  to  be  not  more  than  1/16  in.  in  any  given 
bowl  and  variation  of  average  distance  between  support  edge  of 
bowl  lip  and  upper  edge  of  border  of  different  bowls  to  be  not 


DURGIN  AND  JACKSON  :    SEMI-DIRECT  OFFICE:  LIGHTING      711 

more  than  1/8  in.  Central  web  to  be  centered  within  1/8  in.  of 
center  of  circle  outlined  by  lower  edge  of  Greek  border. 

Etching  details  to  be  checked  by  measurement  and  inspection 
of  a  sample  from  each  shipment  comprising  5  per  cent,  of  lot  se- 
lected at  random. 

Surface  Finish. — External  surface  to  present  uniform  irides- 
cent texture,  free  from  scratches,  lines  or  other  blemishes.  In- 
ternal surface  to  be  highly  polished,  free  from  bubbles,  bunches 
or  other  irregularities. 

Twenty-inch  Bowls  (1.  Weight). — Weight  of  20-in.  bowls  on 
this  order  is  to  be  within  one  pound  of  the  average  weight  of  the 
lot,  that  is,  no  bowl  more  than  one  pound  heavier  or  one  pound 
lighter  than  the  average  will  be  accepted.  The  limits  of  maximum 
and  minimum  weight  thus  established  shall  apply  to  all  future 
orders  for  this  style  and  size  of  bowl. 

(2.  Over-all  Dimensions). — Each  bowl  to  fit  sample  ring  fur- 
nished.   Outer  diameter  of  lip  to  be  20  in.  plus  or  minus  Via  in- 

(3.  Thickness). — Thickness  of  any  given  bowl  to  be  so  uniform 
as  to  permit  even  color  tone  over  entire  bowl  when  lighted  by 
three  or  four  symmetrically  placed  100-  or  150-watt  Mazda 
lamps.  Variation  in  average  thickness  of  separate  bowls  to  be 
within  limits  necessary  to  give  close  color  tone  match  to  standard 

bowl  used  to  check  previous  shipments  of  20-in.  design 

bowls. 

(4.  Inspection  by  Customer.) — Compliance  of  shipment  with 
weight  specification  to  be  checked  by  weighing  all  bowls.  Com- 
pliance with  thickness  specification  to  be  checked  by  inspecting 
uniformity  of  color  of  each  bowl  when  lighted  by  three  100-watt 

lamps,  and  by  comparing  this  color  with  that  of  standard 

bowl. 

Sixteen-inch  Bowls. — These    bowls   to   be   of   quality 

agreeing  with  the  spirit  of  above  specification  for  20-in.  bowls, 
necessary  modifications  being  made  in  proportion  to  reduction  of 
diameter. 

(1.  Weight). — Average  to  be  specified  after  receipt  of  first 
one  dozen  bowls. 

(2.  Over-all  Dimensions). — Each  bowl  to  fit  sample  ring  fur- 
nished. 


712     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

(3.  Thickness). — Thickness  specification  identical  with  that  of 
20-in.  bowls  except  that  60-  and  100-watt  lamps  shall  be  used. 

(4.  Inspection  by  Customer). — As  outlined  under  20-in.  bowls. 

Rejection  of  Imperfect  Bowls. — If  checks  on  samples  as  out- 
lined above  show  breach  of  specification,  entire  shipment  to  be 
checked  for  detail  in  question  and  all  bowls  not  in  strict  com- 
pliance with  requirements  to  be  rejected. 

DISCUSSION. 

Mr.  F.  A.  Vaughn  :  I  am  anxious  to  utter  a  few  words  of 
commendation  for  work  of  this  kind,  especially  the  reference  to 
the  translucent  bowls  and  the  study  of  their  characteristics  and 
the  attempt  to  discover  luminous  bowls  which  will  satisfactorily 
meet  the  illuminating  engineering  requirements.  This  paper  is 
particularly  valuable,  not  only  in  its  technical  results  and  the 
highly  satisfactory  use  of  a  particular  type  of  glassware  in  a 
specific  office,  but  in  pointing  out,  as  the  authors  have  done,  the 
almost  utter  lack  of  bowls  which  are  satisfactory,  if  one  wishes 
to  have  a  choice.  The  choice  of  the  illuminating  engineer  is 
undoubtedly  restricted  very  greatly,  in  spite  of  the  very  great 
number  of  different  types  of  glassware  presented  to  him.  Most 
of  them  are  not  satisfactory  for  this  sort  of  work,  and  I  hope  that 
investigations  of  this  kind  will  spur  manufacturers  on  to  making 
more  dense,  more  esthetic  and  more  beautiful  glassware  so  that 
we  will  not  be  so  restricted  in  our  choice  of  units  of  this  character. 

Mr.  W.  R.  Moulton  :  The  authors  are  to  be  commended  for 
the  thoroughly  practical  data  and  information  presented  in  this 
paper.  It  is  of  special  value  to  the  practical  engineer  who  is 
daily  confronted  with  similar  problems. 

The  glass  manufacturer  is  usually  more  interested  in  the  pro- 
duction of  a  great  number  of  bowls  at  a  certain  profit,  than  in 
the  lighting  result  obtained  from  his  glassware.  This  work  in 
Chicago  has  impressed  this  particular  glass  manufacturer  with 
the  value  of  a  complete  study  for  the  application  of  his  product 
to  illumination  problems.  This  experience  will  undoubtedly 
improve  his  product  in  the  future,  and  in  turn  assist  in  raising 
the  general  standard  of  all  the  manufacturers. 

Fixture   construction   is   an   item   of   sufficient   importance  to 


SEMI-DIRECT   OFFICE   LIGHTING  713 

merit  the  engineer's  consideration.  Cooperation  of  the  engineer 
with  the  fixture  designer  and  manufacturer  should  result  in  a 
greatly  improved  product,  without  sacrificing  any  artistic  effect. 
The  work  done  by  the  authors  proves  this  conclusively. 

Mr.  J.  R.  Cravath  :  You  will  notice  that  the  authors  have 
given  figures  on  the  brightness  of  the  bowls  as  compared  with  the 
brightness  of  the  backgrounds  against  which  they  are  likely  to 
be  seen.  The  care  taken  to  keep  those  ratios  low  represent  some 
of  the  most  important  work  done  on  this  installation.  In  a 
report  that  has  already  been  filed  with  the  Council  by  this  year's 
Committee  on  Glare,  is  the  carefully  considered  statement  that  in 
the  opinion  of  the  committee  the  evidence  so  far  indicates  that 
contrasts  of  brightness  in  excess  of  from  1  to  100  to  1  to  200  are 
likely  to  produce  "glare,"  that  is  manifested  by  eye  fatigue  or 
annoyance.  You  will  notice  that  the  figures  given  in  the  paper 
are  well  within  that  range.  A  point  not  fully  appreciated  here- 
tofore, which  I  would  like  to  emphasize,  is  that  it  is  not  so  much 
the  absolute  value  of  the  brightness  of  the  globe  as  it  is  the 
brightness  compared  with  its  background  that  causes  glare. 

I  can  second  what  Mr.  Vaughn  has  said  as  to  the  difficulty  of 
getting  sufficiently  dense  semi-indirect  glassware.  Most  of  the 
semi-indirect  installations  heretofore  have  not  been  properly 
engineered,  if  engineered  at  all.  We  need  to  give  more  attention 
to  this  point,  the  brightness  of  our  semi-indirect  bowls. 

Mr.  R.  ff.  Pierce  :  This  paper  is  a  particularly  interesting 
one  to  me  because,  in  the  course  of  designing  glassware  fixtures 
for  a  line  of  semi-indirect  lighting  units  which  the  company  I 
am  connected  with  placed  upon  the  market  about  a  year  ago  for 
use  in  connection  with  horizontal  Bunsen  burners,  we  undertook 
practically  an  investigation  of  the  same  considerations  from  a 
purely  commercial  standpoint.  Mr.  Durgin  and  his  co-author 
have  been  fortunate,  possibly,  in  that  the  results  of  their  investi- 
gations were  not  required  to  be  passed  upon  and  endorsed  by  the 
general  public,  whereas  the  designs  upon  which  we  decided  were 
subjected  to  the  approval  of  the  purchasing  public;  in  other 
words,  they  were  manufactured  for  sale,  and  in  connection  with 
this  two  or  three  considerations  of  considerable  interest  arise. 
It  is  noteworthy  in  the  first  respect  that  the  design  finally  agreed 


714     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

upon  is  substantially  the  same  in  both  cases.  We  decided  upon  a 
bowl  for  lighting  which  has  substantially  the  same  characteristics 
of  distribution  as  the  one  displayed  here,  but  we  found  that  the 
general  public  demanded  higher  intensities, — higher  brightness  in 
the  bowl — than  was  exhibited  in  the  glassware  first  used.  In  other 
words,  people  have  not  succeeded  in  getting  it  out  of  their  heads 
that  there  is  anything  in  illumination  more  important  than  getting 
an  extremely  bright  piece  of  glassware,  and  that  has  been  the 
greatest  obstacle  we  have  to  overcome  in  raising  the  standard  of 
illumination  in  the  trade  which  we  sell.  The  general  public  de- 
mand much  higher  bowl-brightness  than  are  found  to  be  satis- 
factory to  discriminating  observers.  We  found,  for  example,  that 
those  bowls  which  gave  a  brightness  of  four  of  five  times  and 
eight  and  ten  times  the  brightness  which  we  had  fixed  upon,  were 
demanded  by  the  majority  of  the  consumers.  The  average  con- 
sumer seems  to  be  obsessed  with  the  idea  that  all  that  is  necessary 
to  make  a  semi-indirect  lighting  fixture  is  a  piece  of  glass  more  or 
less  opalescent  turned  upside  down.  In  some  previous  papers  pre- 
sented to  this  society,  Dr.  Ferree  presented  the  results  of  an  in- 
vestigation in  which  he  showed  that  with  orders  of  surface  bright- 
ness ranging  above  0.1  candlepower  per  square  inch,  diffusing 
glassware  of  any  character  whatever  was  practically  no  better 
than  a  bare  lamp,  and  with  that  in  view,  it  appears  to  me  that  the 
general,  broad  claim  that  any  type  of  semi-indirect  lighting  repre- 
sents an  improvement  over  unshaded  lamps  is  misleading.  Prob- 
ably the  indirect  lighting  systems  possess  a  degree  of  brightness 
which  makes  them  practically  no  better  than  bare  lamps  as  far  as 
the  fatigue  of  the  eye  is  concerned,  and  I  think  that  some  con- 
certed movement  to  limit  the  degree  of  brightness  to  something  of 
the  order  shown  in  this  sample  is  highly  desirable. 

Mr.  S.  B.  Burrows  :  There  is  one  point  in  this  paper  which 
appeals  to  those  of  us  who  are  interested  in  kilo-watt- 
hour  sales  as  well  as  the  application  of  the  principles  of  il- 
lumination, and  that  is  the  point  that  at  the  present  time  both  the 
central  station  and  dealer  talk  in  terms  of  candlepower. 

It  is  no  wonder  that  most  of  our  customers  are  in  the  frame  of 
mind  Mr.  Pierce  speaks  of,  for  there  are  any  number  of  jobbers 
and  electricians,  in  practically  every  town,  selling  gas-filled  tung- 


SEMI-DIRECT   OFFICE   UGHTING  715 

sten  units  indiscriminately  as  lamps,  rather  than  illumination, 
neglecting  accessories  which  would  conform  to  or  help  the  high 
intrinsic  brilliancy  of  the  unit.  There  is  a  field  here  which,  it 
seems  to  me,  for  engineers  is  the  biggest  we  have  seen  for  some- 
time, namely  increasing  lighting  sales  in  kilowatt-hours  by  push- 
ing the  sale  of  glassware  which  is  admittedly  best  for  the  eye, 
thereby  increasing  the  wattage  in  any  one  installation,  and  giving 
better  illumination. 

Those  of  us  who  are  not  only  illuminating  engineers  but  also 
salesmen  should  give  more  attention  to  the  semi-indirect  and  indi- 
rect fixtures  than  we  have  heretofore  given,  if  for  no  other  reason 
than  for  those  sales. 

Mr.  H.  Thurston  Owens:  The  sale  of  semi-indirect  fix- 
tures varies  inversely  with  the  size  of  the  bowl.  The  smaller 
bowls  are  cheaper  to  make  and  easier  to  sell,  and  as  this  condition 
is  at  variance  with  the  promotion  of  better  lighting  it  will  take  the 
concerted  action  of  the  whole  lighting  industry  to  change  the  situ- 
ation. Many  of  the  so-called  semi-indirect  units  are,  in  effect,  di- 
rect lighting  units  and  produce  a  glare  quite  as  objectionable  as 
the  older  forms  of  direct  lighting. 

Mr.  W.  A.  Durgin  (In  reply)  :  One  point  may  bear 
amplification.  We  advocate  a  dense  amber  bowl,  not  pri- 
marily because  it  has  high  absorption  and  hence  leads  to  the 
sale  of  more  energy.  We  advocate  it  because  we  believe 
that  the  amber  filtered  flux  gives  the  customer  increased  effective- 
ness of  lighting  far  more  than  in  proportion  to  the  decreased 
utilization  efficiency.  The  time  has  arrived  when  we  can  afford  to 
throw  away  a  part  of  the  generated  flux  in  order  to  secure  higher 
effectiveness  from  the  filtered  remainder.  The  customer  gets  the 
advantage  of  better  lighting  in  increased  business,  increased  pro- 
duction, improved  eye  hygiene  or  esthetic  satisfaction;  the  lamp 
manufacturer  sells  larger  lamps,  the  fixture  and  glassware  people 
sell  semi-direct  instead  of  small  direct  combinations  and  the  cen- 
tral station  maintains  output. 


yi6     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

THE  APPLICATION  OF  CROVA'S  METHOD  OF  COL- 
ORED LIGHT  PHOTOMETRY  TO  MODERN 
INCANDESCENT  ILLUMINANTS.* 


BY   HERBERT  E.   IVES  AND  E-   E.    KINGSBURY. 


Synopsis:  Crova's  method  of  colored  light  photometry,  which  con- 
sists in  the  observation  of  the  photometer  field  by  monochromatic  light 
of  a  selected  wave-length,  is  one  of  the  simplest  and  most  practical  means 
of  facing  the  problem  under  those  conditions  where  the  method  is 
applicable.  Practical  means  for  applying  the  method  are  here  developed 
for  the  ordinary  incandescent  electric  and  gas  illuminants.  Calibrations 
are  made  on  the  basis  of  the  authors'  luminosity  scale. 


Lord  Rayleigh1  suggested  in  1885  that  the  comparison  of  com- 
pound lights  of  somewhat  different  color  might  be  facilitated  by 
observing  them  by  monochromatic  light.  He  described  a  mono- 
chromatic telescope  to  be  used  for  this  purpose.  Crova,2  going 
a  step  further,  suggested  that  such  a  monochromatic  color  of  the 
spectrum  be  chosen  so  that  the  total  luminous  intensity  of  the 
lights  under  comparison  would  be  represented  by  their  relative 
intensity  at  this  wave-length.  He  showed  that,  in  the  case  of 
illuminants  possessing  continuous  spectra,  such  a  representative 
wave-length  could  be  found.3 

The  advantages  of  the  Crova  method  for  eliminating  color 
differences  in  photometric  comparison  are  very  real,  and  it  is  at 
first  sight  strange  that  it  has  not  been  more  generally  employed. 
The  reason  is  not  far  to  seek,  however.  Like  all  other  means  for 
eliminating  color  differences  at  the  photometer,  Crova's  method 
must  be  calibrated  in  terms  of  some  accepted  luminosity  scale. 
The  ability  to  make  a  perfectly  definite  setting  agreeing  with  the 
setting  of  any  other  observer  is,  in  the  majority  of  cases,  of  no 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing Society,  Washington,   D.   C,    September  20-23,    T9i5- 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 

1  Rayleigh,  A  Monochromatic  Telescope,  with  Application  to  Photometry  ;  Phil.  Mag., 
June,  1885. 

2  Crova  ;  Comples  Rendues,  93,  p.  512. 

3  Ives,  Note  on  Crova's  Method  of  Heterochromatic  Photometry ;  Physical  Review 
March,  1911. 


IVES   AND   KINGSBURY:     COLORED   LIGHT    PHOTOMETRY       717 

value  unless  one  knows  what  value  to  give  to  that  setting.  In 
the  case  of  Crova's  method  this  means  that  one  must  have  some 
definite  proof  that  the  wave-length  employed  is  the  representa- 
tive one  or  else  know  how  much  it  over  or  under-evaluates  the 
intensity  of  those  light  sources  which  are  of  interest. 

In  searching  for  the  most  practical  method  of  colored  light 
photometry  for  use  in  a  gas  photometric  laboratory,  we  have 
recently  experimented  with  Crova's  method  with  very  satisfac- 
tory results.  The  problems  of  gas  mantle  photometry  are  some- 
what peculiar.  There  exists  a  wide  range  of  color  in  mantles  of 
different  composition  and  structure,  added  to  which  are  smaller 
differences  caused  by  variations  of  adjustment  of  the  burner  and 
by  changes  in  the  kind  of  gas  used.  These  differences  cannot  be 
taken  care  of  by  the  mere  change  in  concentration  of  a  color- 
matching  solution,  as  in  the  case  of  the  Fabry  solutions  as  worked 
out  for  the  electrical  illuminants.4 

There  are  several  different  requirements  to  be  met  in  the  prac- 
tical development  of  means  for  carrying  out  Crova's  idea,  which 
are  in  partial  conflict.  The  dominating  practical  requirement  is 
that  the  means  for  securing  monochromatic  light  shall  not  be 
prohibitively  wasteful  of  light.  This  practically  means  that  a 
compromise  must  be  made  between  the  purity  of  the  monochro- 
matic light  and  the  working  illumination. 

A  second  point,  governed  in  part  by  the  one  just  emphasized, 
is  that  different  parts  of  the  spectrum  are  differently  suited  for 
securing  monochromatic  light  with  maximum  quantity.  Thus, 
the  hue  of  the  spectrum  changes  very  rapidly  in  the  yellow,  so 
that  there  a  very  narrow  band  must  be  chosen  in  order  to  elimi- 
nate color  differences.  On  the  other  hand,  in  the  green  region 
hue  change  is  slow,  and  a  comparatively  wide  band  of  the  spec- 
trum may  be  used,  with  consequent  increase  of  light.  Finally 
comes,  of  course,  the  restriction  that  the  true  representative  or 
Crova  wave-length  has  no  connection  with  the  luminosity  or  hue 
considerations.  It  actually  happens  that  the  Crova  wave-length 
lies  in  the  yellow,  where  hue  change  is  rapid.  Thus  there  is  as  one 
alternative  working  for  the  most  complete  elimination  of  color 
difference,  using  a  wave-length  in  the  green,  and  determining  its 

•  Ives  and  Kingsbury,  Experiments  with  Colored  Absorbing  Solutions  for  Use  in 
Heterochromatic  Photometry  i  Trans.  I.  E.  S.,  p.  795,  1914. 


718     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

calibration ;  and  as  another  alternative  working  for  perfection  of 
color  difference  elimination  in  favor  of  the  convenience  of  the 
true  Crova  wave-length.  Actually,  as  will  be  seen,  still  other 
considerations  have  had  a  say  in  our  particular  problem. 

To  obtain  monochromatic  light  Crova  used  a  solution  of  nickel 
nitrate  and  ferric  chloride,  placed  between  the  eye  and  the  photo- 
meter. After  some  study  of  colored  glasses  we  have  decided  in 
favor  of  the  use  of  a  solution,  similar  in  properties  to  the  one 
used  by  Crova,  as  being  more  definitely  reproducible  and  as  being 
more  nearly  monochromatic.  Our  first  work  was  done  upon  a 
monochromatic  green  solution,  which  had  been  developed  for 
another  purpose,5  our  idea  being  that  its  excellent  monochromatic 
quality  would  outweigh  its  non-agreement  with  the  Crova  wave- 
length.   The  transmission  of  this  solution,  whose  composition  is : 

CuCl    265.0  grams 

K2Cr207 2.5  grams 

HN03(i.o5  gr.) 26.5  c.c. 

Water  to  1  liter  of  solution  at  200  C. 

was  measured  in  a  thickness  of  one  centimeter,  against  a  clear 


\ 

\ 

--MAN1 

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ILLED 

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"EN 

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Fig.  1.— Transmission  of  monochromatic  green  solution  with  various  illuminants,  in 
times  of  its  transmission  of  the  light  of  a  "4-watt"  carbon  lamp. 

water  solution,  by  means  of  our  physical  photometer,6  which 
incorporates  the  characteristics  of  our  average  eye.  The  results 
with  various  illuminants,  all  expressed  in  terms  of  the  standard 

6  Ives  and  Kingsbury,  Flicker  Photometer  Measurements  by  a  Large  Group  of  Ob- 
servers on  a  Monochromatic  Green  Solution  ;  Physical  Review,  March,  1915,  p.  230. 

6  Ives  and  Kingsbury,  Physical  Photometry  with  a  Thermopile  Artificial  Eye ; 
Physical  Review,  1915. 


IVES   AND   KINGSBURY:     COLORED   LIGHT    PHOTOMETRY        719 

"4-watt"  carbon  lamp,  are  shown  in  Fig.  1.    The  abscissae  are 
watts  per  mean  spherical  candle,  in  the  case  of  the  electric  lamps, 
and  proportion  of  ceria,  in  the  case  of  the  mantles,  the  mantles  • 
used  being  of  a  representative  weave  and  weight. 

For  our  purposes  this  solution  was  decided  not  to  be  suitable, 
the  chief  reason  being  that  the  mantle  values  lie  on  a  line  which 
is  altogether  too  steep.  While  the  values  are  given  in  terms  of 
mantle  composition,  the  color  is  as  well  a  matter  of  weight  and 
weave  and  of  burner  adjustment.  Variations  of  any  of  these 
factors,  such  as  are  to  be  expected  in  miscellaneous  testing,  were 
found  to  be  equivalent  to  running  up  and  down  on  the  curve  by 
an  amount  of  several  per  cent. 

Our  experience  with  this  solution  led  us  to  formulate  a  new 
criterion  for  our  own  work  in  mantle  photometry,  namely,  that 
the  monochromatic  solution  to  use  is  one  which  has  as  nearly  as 
possible  the  same  transmission  for  all  the  ordinary  gas  mantles, 
irrespective  of  what  it  might  be  for  other  illuminants.  We  would 
then  be  as  free  as  possible  from  the  effects  of  the  variables 
peculiar  to  that  kind  of  photometry. 

Using  the  physical  photometer  a  process  of  trial  and  error  was 
gone  through  with  the  relative  proportions  of  the  two  coloring 
constituents  of  the  solution  being  gradually  changed  so  that  the 
equivalent  wave-length  moved  toward  the  yellow.  A  solution  was 
finally  obtained  which  answered  to  the  requirements,  whose  com- 
position is  as  follows : 

CuCl2 90.0  grams 

KjCrj07 30.0  grams 

HNO3  (x-°5  Sr-) 4°°  c-c- 

Water  to  1  liter  of  solution  at  200  C. 

This  solution  is  to  be  used  in  a  thickness  of  25  millimeters. 

A  calibration  of  this  solution  was  carried  through  with  the 
physical  photometer,  not  only  for  the  mantles  but  for  all  the 
common  electric  and  flame  illuminants.  This  calibration  is  shown 
in  Fig.  2,  by  the  crosses. 

Supplementary  to  this  a  partial  calibration  was  made  by  the 
visual  methods  developed  by  us ;  for  while  we  have  established 
the  agreement  of  the  visual  and  physical  methods  with  great  care 
it  was  thought  worth  while  to  take  this  opportunity  to  make  a 
further  check.    We  first  made  a  set  of  observations  by  the  flicker 


720     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

method,  under  the  standard  conditions,  selecting  our  observers 
according  to  the  scheme  recently  described  before  the  Society.7 
The  procedure  was  to  have  each  observer  make  a  set  of  readings 
with  an  ordinary  Lummer-Brodhun  head,  interposing  the  Crova 
solution  between   eye  and   eye-piece.     The  eye-piece  was  then 


1.10 

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PHYSICAL   PHOTOMETER    * 

FLICKER 

YELLOW  SOLUTION  o 


Fig.  2.— Transmission  of  Crova  solutions  in  times  of  transmission  with  "4-watt' 
lamp.    Upper— gas  solution  ;  lower— electric  solution. 


removed  and  the  nicker  photometer  attachment8  put  in  its  place, 
and  another  set  of  readings  made.  Both  sets  were  made  against 
a  "4-watt"  lamp.  Under  these  conditions  all  questions  of  the 
slight  change  of  transmission  of  the  solution  with  temperature, 
etc.,  are  ruled  out.  The  flicker  photometer  points  are  shown  by 
dots. 

In  addition  to  the  flicker  settings  a  check  was  made  upon  the 
electric  illuminants  by  the  use  of  the  Fabry  yellow  solution 
recently  described,9  whose  calibration  was  done  by  the  same  flicker 
method,   but  by   a   different   group   of   observers.     The   values 

1  Ives  and  Kingsbury,  On  the  Choice  of  a  Group  of  Observers  for  Heterochromatic 
Measurements;  Trans.  I.  E.  S.,  No.  3,  p.  203,  1915. 

8  Kingsbury,  E.  F.,  A  Flicker  Photometer  Attachment  for  the  Lummer-Brodhun 
Photometer   Head;  Journal  of  the  Franklin  Institute,  August,  1915. 

9  Ives  and  Kingsbury,  Experiments  with  Colored  Absorbing  Solutions  for  Use  in 
Heterochromatic  Photometry,  Trans.  I.  E.  S.,  p.  795,  1914. 


IVES   AND   KINGSBURY:     COLORED   EIGHT    PHOTOMETRY       J2I 


assigned  to  the  Crova  solution  by  the  Fabry  solution  are  shown  by 
the  circles. 

It  is  evident  that  our  various  means  of  calibration  are  in  excel- 
lent agreement,  and  that  we  have  a  solution  meeting  our  criterion, 
that  the  incandescent  gas  mantles  should  measure  alike. 

Upon  the  completion  of  the  work  on  the  mantle  solution,  it 
seemed  worth  while  to  determine  what  solution  would  answer  the 
same  purpose  for  the  incandescent  electric  illuminants.  By  a 
slight  change  of  the  relative  proportions  of  the  constituents  such 
a  solution  was  found,  as  follows : 

CuCl2 86  grains 

K2Cr207 60  grams 

HNO3  ( 1.05  gr.) 40  c.c. 

Water  to  1  liter  of  solution  at  200  C. 

The  calibration  of  this  solution  was  carried  out  entirely  with 

THREADED    RINGn^ 
GLASS- 


Fig.  3. — Cell  for  holding  Crova  solution. 

the  aid  of  the  Fabry  yellow  solution.  It  is  shown  in  Fig.  2 
(lower  diagram).  The  transmission  is  practically  the  same  over 
the  whole  range  of  lamp  colors  from  the  color  of  the  pentane 
flame  to  that  of  the  high  efficiency  nitrogen-filled  tungsten. 

For  the  practical  use  of  these  solutions  we  have  devised  a  small 
absorption  cell  which  slips  into  the  eye-piece  of  the  Lummer- 
Brodhun  photometer  head.  It  is  shown  in  section  in  Fig.  3.  The 
solution  is  held  in  a  glass  cell  consisting  of  a  section  of  glass 
tubing  on  which  plane  glass  ends  are  fastened  with  paraffin.  This 
cell  is  then  imbedded  in  the  brass  casing  with  plaster  of  Paris, 
the  excess  being  squeezed  out  when  the  threaded  ring  is  screwed 
into  place.  We  have  thus  far  had  no  trouble  with  any  leakage 
from  these  cells. 

The  procedure  in  using  the  solutions  is  quite  simple.  In  our 
laboratory  the  gas  solution  is  of  course  used,  except  in  special 
work.    Every  photometer  head  is  permanently  equipped  with  its 


722     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

solution  cell.  All  the  standard  lamps  have  their  efficiencies  tabu- 
lated on  a  card  near  the  photometer,  beside  which  is  a  blue-print 
of  Fig.  2.  The  operations  are  exactly  as  in  ordinary  photometry, 
but  the  resultant  values  are  to  be  reduced  in  accordance  with  the 
ratio  indicated  by  the  chart.  We  have,  however,  introduced  a 
still  further  simplification  by  tabulating  the  "Crova  solution 
value"  of  each  standard,  which  is  simply  the  value  to  be  assigned 
to  it  in  order  that  the  readings  on  the  mantles  shall  be  in  their 
correct  values  as  obtained.    The  Crova  value  of  a  4.85  w.  p.  s.  c.  p. 

carbon  standard,  for  instance,  is  — —  X  its  true  value. 

1.065 

In  the  case  of  the  electric  solution  no  correcting  values  are 
necessary;  observations  are  made  and  recorded  as  though  no 
solution  were  present.  Its  use  is,  however,  restricted  to  incan- 
descent electric  illuminants. 

Our  experience  thus  far  with  this  method  has  been  very  satis- 
factory. The  very  slight  color  difference  which  remains  we  find 
to  give  no  trouble,  while  the  loss  of  light  (the  transmission  is 
about  10  per  cent.)  is  taken  care  of  by  more  careful  shielding  of 
the  observer's  eye,  and  taking  greater  care  to  avoid  looking  at 
the  light  source.  The  precision  of  setting  is  practically  the  same 
as  in  ordinary  photometry  of  lights  of  the  same  color.  The 
greater  convenience  of  this  method  over  those  requiring  a  change 
of  absorbing  medium  with  each  change  of  illuminant  makes  it  by 
far  the  most  practical  laboratory  means  for  eliminating  color 
differences. 

The  calibrations  here  given  are  in  terms  of  the  luminosity  scale 
developed  and  used  in  our  laboratory.  Should  any  other  con- 
sistent scale  be  ultimately  adopted,  slight  changes  in  the  relative 
proportions  of  the  constituents  of  these  solutions  would  fit  them 
to  perform  the  same  function  in  conformity  with  such  scale. 

Fig.  4  shows  the  spectral  transmission  of  the  two  solutions,  and 
in  Fig.  5  these  same  transmissions  are  shown  multiplied  by  the 
energy  distribution  of  a  tungsten  lamp  and  by  the  luminosity 
curve  of  the  eye.  The  resultant  curves  show  (by  calculations  of 
their  centers  of  gravity)  that  the  equivalent  wave-lengths  are 
approximately  0.573/*  for  the  mantle,  and  0.577/i  for  the  elec- 
tric solution. 


IVES  AND   KINGSBURY:     COLORED   LIGHT    PHOTOMETRY       723 


While  we.  have  obtained  our  monochromatic  light  by  the  use 
of  absorbing  media  it  is  worthy  of  note  that  a  very  elegant  method 
would  be  by  the  use  of  a  spectroscopic  eye-piece,  similar  in  prin- 
ciple to  Lord  Rayleigh's  monochromatic  telescope,  to  take  the 
place  of  the  ordinary  photometer  eye-piece.  Such  a  device  would 
permit  the  variation  of  the  wave-length  used  and  also,  by  vary- 
ing the  width  of  the  slit,  of  the  amount  of  light,  to  suit  the  con- 


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Fig.  4.— Spectral  transmission  of  Crova  solutions. 

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Fig.  5.— Spectral  transmission  of  Crova  solutions,  multiplied  by  typical  illuminant 
energy  distribution  and  visual  luminosity  curve. 

ditions.  The  calibration  of  this  kind  of  instrument  could  not  be 
done  at  present  with  the  physical  photometer,  which  would  not  be 
sensitive  enough,  but  the  alternation  of  the  flicker  attachment  and 
a  spectroscopic  attachment  in  the  manner  described  in  connection 
with  the  Crova  solution,  furnishes  an  excellent  means  for  cali- 
brating such  an  eye-piece.  It,  of  course,  involves  the  use  of  a 
group  of  observers,  but  with  the  equivalent  wave-length  closely 
determined  by  the  present  work,  the  labor  of  finding  this  exactly 
should  not  be  great. 


724     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

DISCUSSION. 

Dr.  P.  G.  Nutting  :  If  it  is  in  order,  I  would  like  to  ask  a  few 
questions  about  the  method  rather  than  the  matter  presented  here. 
Do  I  understand,  Dr.  Ives,  that  you  are  entirely  independent  of 
the  observer?  Are  your  intensities  read  as  deflections  of  a  gal- 
vanometer needle  ?  I  should  also  like  to  ask  what  the  sensibility 
of  the  method  is,  the  amount  of  probable  error,  etc ;  what  is  the 
range  over  which  it  is  applicable  under  the  conditions  described? 

Dr.  C.  E.  K.  MeES  :  I  should  like  to  ask  Dr.  Ives  what  the  sta- 
bility of  the  solution  is,  and  what  means  he  takes  to  check  it.  It 
strikes  one  who  has  been  trained  as  a  chemist,  off  hand,  that  a  bi- 
chromate and  nitric  acid  would  form  a  powerfully  oxidizing  solu- 
tion, and  if  there  is  any  possibility  of  its  oxidizing  anything  it  will 
do  it ;  so  it  would  be  necessary  to  obtain  some  analytical  check  on 
the  solution. 

M.  Luckiesh  :  I  should  like  to  ask  Dr.  Ives  if  he  has  had  an 
opportunity  to  test  the  permanency  of  this  solution  over  a  period 
of  a  few  months  or  more.  If  it  is  permanent  it  will  be  of  consid- 
erable advantage. 

Dr.  H.  E.  Ives:  Regarding  stability, — strictly  speaking,  the 
answer  depends  upon  the  time  more  than  upon  any  definite  evi- 
dence we  can  offer.  We  simply  say  this,  that  the  constituents 
were  the  same  as  ones  used  in  a  previously  developed  solution, 
on  which  many  tests  for  permanency  were  made,  and  that  during 
the  time  that  this  work  was  continued,  we  watched  very  carefully 
and  made  photometric  checks  of  one  sort  and  another  which 
would,  we  believe,  have  revealed  any  change  in  composition  or 
behavior.  Now  if  you  will  note,  from  the  figure  showing  the  con- 
struction of  the  containing  cell,  the  solution  is  in  contact  with 
nothing  except  glass,  with  the  possibility  of  a  very  thin  edge  of 
paraffin,  so  that  the  possibility  of  its  doing  any  oxidizing  is 
negligible.  The  cells  have  not  shown  any  leakage.  I  think 
now  it  is  about  four  or  five  months  since  our  set  of  tanks  was  put 
in  use.  We  very  recently  made  a  check  of  the  results  obtained  by 
their  use,  against  our  physical  photometer,  and  the  check  was  ab- 
solute. We  have  noticed  some  temperature  coefficient  of  change 
of  transmission,  and  thought  we  noticed  some  reversible  photo- 
chemical change.     For  instance,  we  did  part  of    the  work    with 


COLORED   LIGHT    PHOTOMETRY  725 

large  tanks  which  were  exposed  directly  to  radiation  from  the 
light  source.  We  obtained  some  results  which  seemed  to  indi- 
cate that  if  this  solution  were  exposed  to  light  continuously  for  a 
long  time,  its  transmission  would  alter  somewhat.  On  being  let 
alone  in  the  dark  for  a  few  hours,  the  solution  returned  to  its 
original  state.  In  all  the  later  work  the  solution  was  used  ex- 
clusively in  the  eyepiece,  where  the  intensity  of  incident  radiation 
is  very  small,  and  any  change  would  effect  both  sides  of  the  field 
practically  the  same. 

Mr.  Mees  :    Does  it  get  yellower  ? 

Dr.  Ives:  Yes,  it  probably  did.  I  do  not  remember  exactly, 
but  all  these  changes  which  we  have  suspected  are  minimized  in 
their  action  by  the  method  of  use.  If  there  is  a  change  in  the 
total  transmission  without  a  shift,  both  illuminants  are  affected 
equally.  If  there  were  a  very  large  shift,  that  would  be  serious, 
but  we  have  not  found  any.  I  realize  that  this  is  not  an  adequate 
answer  to  the  general  question  of  stability.  If  we  had  had  these 
in  use  for  two  or  three  years,  we  could,  of  course,  give  more 
definite  information,  but  I  will  say  that  we  have  found  them 
satisfactory  and  perfectly  consistent  with  such  checks  as  we  have 
made  by  going  around  the  complete  circle  at  various  periods. 

In  regard  to  Dr.  Nutting's  question,  whether  the  method  is  in- 
dependent of  the  observer — of  course,  if  we  had  an  absolutely 
monochromatic  solution  or  used  a  spectroscopic  attachment  with 
a  sufficiently  narrow  band  of  transmission,  we  would  be  quite  in- 
dependent of  the  observer.  (The  transmission  of  a  solution 
much  more  monochromatic  than  the  one  described  would  prob- 
ably be  prohibitively  low.)  On  a  recent  test  of  some  incandescent 
lamps  which  I  mentioned  a  minute  ago,  in  abstracting  the  paper, 
we  deliberately  chose  two  observers  from  our  laboratory,  one  of 
whom  I  think  is  the  most  blue  sensitive  of  any  we  have,  and  a 
rather  red  sensitive  one.  These  two  observers  made  the  observa- 
tion and  there  were  no  systematic  differences  of  any  sort.  I  think 
I  am  justified  in  saying  that  unless  a  very  abnormal  observer  is 
used,  the  method  is  independent  of  the  observer. 

Dr.  P.  G.  Nutting  :  You  do  measure  light  rather  than  energy. 

Dr.  Ives  :  Yes ;  this  is  a  visual  method.  Now  as  to  precision : 
using  the  photometer  as  we  do  writh  laboratory  voltmeters,  and 


726     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

as  a  common  battery  we  are  working  to  probably  less  precision 
than  that  of  a  laboratory  such  as  the  Bureau  of  Standards,  where 
they  may  have  a  whole  storage  battery  for  one  particular  investi- 
gation, and  it  is  very  probable  that  the  effect  of  even  the  slight 
color  difference  still  present  would  show  itself  on  a  long  series  of 
tests  in  somewhat  lower  precision.  But  for  our  purposes,  the 
precision  is  all  that  could  be  desired.  The  range  of  applicability 
is  just  so  far  as  shown  on  these  curves.  It  may  be  further,  but  we 
do  not  so  state. 


SHARP   AND   LITTLE:     COMPENSATED   TEST-PLATE  727 

COMPENSATED    TEST-PLATE    FOR    ILLUMINATION 
PHOTOMETERS.* 


BY   CLAYTON    H.    SHARP  AND   W.    F.    LITTLE. 


Synopsis:  The  errors  of  illumination  test-plates  due  to  their  devia- 
tion from  the  theoretical  cosine  law  have  been  studied  experimentally 
(Tables  I,  II,  III,  IV,  Figs.  1  and  2).  The  most  important  cause  for  the 
deviation  of  test-plates  from  the  cosine  law  is  shown  to  be  the  increasing 
reflection  with  increasing  incidence  according  to  Fresnel's  law  (Fig.  3). 
Test-plates  may  be  compensated  for  the  deficiency  in  brightness  with 
light  at  large  angles  of  incidence  by  admitting  light  to  the  posterior  side 
of  the  plate  in  sufficient  quantities.  Transmitting  test-plates  are  mounted 
on  flashed  opal  rings  of  suitable  width  and  light  at  900  is  cut  off  by 
a  metal  screen  (Figs.  4  and  5).  Reflecting  test-plates  are  constructed  as 
in  Fig.  6.  The  results  of  this  method  of  compensating  plates  are  shown 
in  Tables  V  and  VI  and  are  summarized  in  Fig.  7.  The  results  of  a 
test  of  illumination  with  compensated  and  uncompensated  test-plates  are 
given  in  Table  VII.  The  possible  application  to  the  integrating  sphere  is 
noted. 


The  only  essential  difference  between  a  photometer  for  the 
measurement  of  illumination  and  a  photometer  for  the  measure- 
ment of  candlepower  is  that  the  illumination  photometer  is  pro- 
vided with  a  photometric  surface  or  test-plate  which  should  vary- 
in  brightness  as  the  cosine  of  the  angle  of  incident  light.  The 
test-plate,  which  serves  as  a  device  for  integrating  the  luminous 
flux  falling  upon  it,  is  the  distinguishing  feature  of  the  illumin- 
ation photometer.  Any  failure  on  the  part  of  the  test-plate  to 
integrate  correctly  is  reflected  in  corresponding  errors  in  the  re- 
sults of  the  illumination  measurements.  This  paper  contains  a 
discussion  of  errors  encountered  in  existing  forms  of  test-plates 
due  to  departure  from  Lambert's  cosine  law,  and  a  description 
of  a  method  of  compensating  the  test-plates  in  order  to  avoid 
such  error. 

Classification  of  Test-plates. — Test-plates  may  be  divided  into 
two  general  classes  according  to  the  method  of  their  use : 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,   Washington,   D.   C,   September  20-23,    I9I5- 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


728     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

(a)  Transmitting  (usually  attached  to  the  photometer). 

(b)  Reflecting  (usually  detached  from  the  photometer). 
Transmitting  plates  are  made  of  diffusing  glass  usually  de- 
polished  on  the  exposed  surface.     Reflecting  plates  may  be  of 
opaque  material  having  a  diffusing  surface,  or  they  also  may  be 
of  depolished  white  glass. 

Historical. — Unfortunately  there  is  no  known  substance  nor 
method  of  constructing  a  surface  which  obeys  the  theoretical 
cosine  law  of  Lambert.  Wright,  some  fifteen  years  ago,  suc- 
ceeded in  making  surfaces  of  compressed  powders  which  came 
very  near  it;  but  evidently  this  form  of  construction  would  not 
lend  itself  to  the  practical  requirements  of  photometry.  There- 
fore photometrists  in  measuring  illumination  have  been  obliged 
to  content  themselves  with  test-plates  which  were  known  to  give 
erroneous  results  under  conditions  of  high  angle  of  incidence. 
The  comforting  thought,  however,  was  always  present  that  prob- 
ably in  the  great  majority  of  cases  the  light  flux  incident  at  high 
angles  represented  so  small  a  percentage  of  the  total  flux  that  an 
error  in  measuring  it  was  relatively  of  little  consequence.  Never- 
theless, the  test-plate  error  has  been  by  all  means  the  largest  in- 
trinsic or  unavoidable  error  in  illumination  measurements,  and 
the  knowledge  of  its  existence  has  been  a  thorn  in  the  flesh  of 
photometrists.  Therefore  no  little  study  has  been  given  to  the 
question  of  a  practical  method  of  its  avoidance. 

The  idea  of  replacing  a  material  surface  by  an  imaginary  one, 
such  as  a  clear  aperture  in  an  opaque  body,  undoubtedly  has 
occurred  to  more  than  one  worker  in  this  field.  Such  an  aperture 
would  evidently  transmit  light  in  accordance  with  the  cosine  law, 
but  unfortunately  it  would  require  some  auxiliary  arrangement 
to  diffuse  this  light.  A  small  aperture  in  the  surface  of  an  in- 
tegrating sphere  would  admit  flux  of  light  proportional  to  the 
cosine  of  the  angle  of  incidence,  and  the  flux  density  at  a  point 
in  the  interior  of  the  sphere,  which  is  shielded  from  the  aperture, 
would  measure  the  flux  admitted.  Evidently  such  an  arrange- 
ment must  have  its  limitations  in  practise,  because  of  the  prac- 
tical limits  of  the  size  of  the  sphere  and  because  the  loss  of  light 
involved  in  the  multiple  reflections  required  in  diffusing  the  light, 
will  be  so  great  that  the  field  viewed  in  the  photometer  will  be  of 


SHARP   AND   LITTLE:     COMPENSATED   TEST-PLATE  729 

relatively  feeble  intensity.  A  construction  along  these  lines,  the 
details  of  which  however  are  not  entirely  clear  from  the  meager 
account  at  hand,  has  been  described  by  Bechstein1  before  the 
German  Illuminating  Engineering  Society.  He  states  that  with 
the  aperture  in  the  sphere  one  forty-sixth  as  large  as  the  surface 
of  the  sphere  itself,  the  cos  i  error  at  70  °  incidence  is  —6  per. 
cent.,  and  the  brightness  of  the  field  is  one  third  as  great  as  that  of 
a  plaster  of  Paris  plate  with  the  same  illumination.  Evidently  if 
the  advantages  so  noted  are  not  over-borne  by  disadvantages 
which  are  not  mentioned,  this  style  of  test-plate  marks  a  decided 
improvement. 

W.  D'A  Ryan  patented  a  form  of  test-plate  some  five  years 
ago  which  was  intended  to  obviate  the  cos  i  error.  This  test- 
plate  consisted  of  a  block  of  diffusing  glass  with  a  dome-shaped 
upper  surface  for  the  reception  of  the  illumination.  Surround- 
ing this  surface  was  a  low  circular  screen  notched  at  the  top  in 
such  a  way  that  the  shadow  cast  by  it  on  the  surface  was  suffi- 
cient to  maintain  the  diffused  flux  of  light  in  the  interior  of  the 
block  at  its  right  value  with  i  approaching  900.  The  dome-shaped 
upper  surface  evidently  tended  to  correct  the  deficiency  of  bright- 
ness at  high  angles  by  presenting  a  larger  surface  to  illumination 
at  those  angles.  This,  of  course,  gave  a  lopsided  distribution  of 
light  on  the  test-plate,  but  the  thickness  of  the  plate  was  such 
that  the  flux  was  undoubtedly  fully  diffused  before  it  reached  the 
photometric  field.  It  would  seem  that  there  must  have  been  a 
very  serious  loss  of  light  in  passing  through  this  thick  diffusing 
test-plate.  The  device  was  incorporated  by  Mr.  Ryan  in  an 
illumination  photometer. 

Study  of  Test-plate  Errors.— It  may  be  advisable  next  to  study 
the  errors2  of  existing  test-plates  such  as  are  commonly  used  in 

1  Zeitschriftfur  Beleuchtungswesen,  March  15,  1915,  p.  31. 

2  The  apparatus  used  in  the  study  of  test-plates  was  as  follows:  The  telescope  was 
removed  from  a  spectrometer  and  to  the  arm  of  the  spectrometer  a  light  tubular  sup- 
port was  attached,  carrying  at  its  outer  end  an  incandescent  lamp  enclosed  except  for  a 
slit  in  front,  by  a  metal  screen.  The  radius  of  the  circle  in  which  the  lamp  moved  was 
about  one  meter.  Transmitting  test-plates  to  be  studied  were  fixed  to  a  portable  photo- 
meter and  adjusted  at  the  center  of  rotation.  Reflecting  test-plates  were  entirely  de- 
tached from  the  photometer  which  then  was  set  up  at  such  a  distance  that  the  arm  carry- 
ing the  lamp  could  be  moved  in  front  of  it.  The  angles  were  accurately  read  on  the 
divided ^circle  of  the  spectrometer.  With  high  angles  of  incidence  it  is  necessary  that  the 
angle  shall  be  measured  quite  accurately  inasmuch  as  the  values  of  the  cosine  are  chan*- 
mg  rapidly.  5 


730     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

order  to  inform  ourselves  as  to  how  serious  they  are.  In  Table  I 
are  given  variations  from  the  theoretical  values  shown  by  two 
transmitting  test-plates  of  white  glass  with  the  surfaces  de- 
polished.  It  will  be  seen  that  while  the  error  is  of  relatively 
small  magnitude  up  to  about  400,  yet  beyond  that  point  it  becomes 
quite  serious. 

TABLE  I.— Errors  of  Transmitting  Test-Plate  with 

Depolished  Surface. 

Plate  numbers 5  220 

Thickness  (inches) 0.0718  (1.82  mm.)  0.055  (1.4  mm.) 

Angle  of  Errors,  per  cent. 

incidence  , ' » 


O0  OO 

IO°  +0.5  ,         +  0.5 

20°  O  O 

30°  —  1-5  —  2-5 

40°  —  5  —  4-5 

500  -  8  -  7 

6o°  —  8  —10 

700  —13  —13 

8o°  — 24  — 29 

85°  -33  -37 

In  the  use  of  reflecting  test-plates  a  complication  enters  which 
is  not  present  with  transmitting  test-plates,  and  which  arises 
from  the  fact  that  the  reflecting  test-plates  are  usually  detached 
from  the  photometer,  and  the  angle  at  which  the  photometer 
views  the  plate  is  not  fixed ;  nor  is  the  position  of  the  photometer 
with  respect  to  the  direction  of  the  principal  flux  of  light  reach- 
ing the  test-plates ;  i.  e.,  the  angle  of  azimuth.  Hence  a  double 
dissymmetry.  A  transmitting  test-plate  attached  to  the  pho- 
tometer is  viewed  normally ;  hence  the  brightness  of  the  plate 
must  be  independent  of  the  azimuth  of  the  incident  light.  The 
same  thing  is  true  of  the  reflecting  test-plate,  provided  the  grains 
of  its  upper  diffusing  surface  are  indifferently  arranged  and 
provided  the  plate  is  viewed  normally.  Ordinarily  such  test- 
plates  are  viewed  with  the  photometer  held  in  the  hand,  and  the 
angle  of  view  may  differ  from  the  normal  by  a  considerable 
amount,  while  the  azimuth  is  determined  by  the  convenience  of 
the  operator.  The  arrangement  therefore  is  not  symmetrical 
with  respect  to  the  photometer. 


SHARP   AND   LITTLE:     COMPENSATED   TEST-PLATE  731 

The  data  on  reflecting  test-plates  here  presented  do  not  repre- 
sent a  complete  investigation  but  are  sufficient  for  the  purpose  of 
showing  some  of  the  peculiarities  encountered.     Table  II  shows 

TABLE  II.— Errors  of  Reflecting  Test-plate  of  Depolished 
White  Glass. 

In  plane  of  incidence 


Vngle  of  view 

.     .    0° 

30° 

45° 

Angle  of 
Incidence 

Same 
side 

Opposite 
side 

Same 
side 

Opposite 
side 

Errors  per  cent. 

o° 

0 

O 

O 

0 

O 

io0 

—0.5 

+0.5 

0 

-0.5 

O 

20° 

— I 

0 

+  1 

0 

+    I 

30° 

— 2 

0 

0 

+0.5 

+   8.5 

40° 

—  2 

0 

+  1 

— I 

+  9 

50° 

—  2 

-0-5 

+0.5 

— c-5 

+  12 

6o° 

—4-5 

—  I 

+  2 

0 

4-20 

700 

—7-5 

+  0.5 

+  1 

—0.5 

+29 

8o° 

—9 

—6 

+7 

— 12 

+44 

850 

—  11 

—7 

+19 

—15 

+59 

the  errors  of  a  depolished  white  glass  reflecting  test-plate  when 
viewed  at  o°,  that  is  normally,  at  300  and  at  450  all  in  the  plane 
of  incidence  of  the  light.  It  will  be  noted  that  at  o°,  which  is  the 
symmetrical  position,  the  error  at  70  °  is  — 7.5  per  cent.  When  the 
angle  of  view  is  changed  to  300,  a  surprising  thing  is  seen; 
namely  that  in  the  plane  of  incidence  the  errors  of  such  a  plate 
are  small  all  the  way  to  8o°.  And  this  is  true  irrespective  of 
whether  the  source  of  light  illuminating  the  plate  is  on  the  side 
toward  the  photometer  or  on  the  side  away  from  it.  When  the 
angle  of  view  is  increased  to  45 °,  this  symmetry  vanishes.  As  in 
the  former  case,  from  o°  incidence  to  900  incidence  on  the  side 
toward  the  photometer,  the  errors  are  negligibly  small.  On  the 
opposite  side,  however,  the  errors  mount  rapidly  after  200  is 
passed  until  at  700  the  error  is  -f2§  Per  cent-  (see  Fig.  1). 
This  indicates  a  condition  of  specular  reflection,  which  enters 
when  the  angle  of  view  is  as  large  as  45  ° ,  which  is  necessarily 
no  factor  when  the  light  is  on  the  side  of  the  plate  toward  the 
photometer.  In  order  to  investigate  this  effect  of  the  angle  of 
view  more  closely,  the  readings  shown  in  Table  III  and  in  Fig.  2 
were  taken.  Here  the  angle  of  incidence  of  the  light  was  main- 
tained at  6o°  and  the  angle  of  view  of  the  photometer  was  varied, 
o 


732     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


il 

/ 

-D 

/ 

/ 

r 

> 

/ 

-jp 

r< 

.... 

' 

1?  "^ 

A. 

"^r*5^ 

- 

KA 

( 

r 

i 

j 

I 

j 

3 

It 

4 

0 

s 

a 

i 

;> 

70 

80 

90 

angle:  of  incidence: 

Fig.  i.— Reflecting  test-plate,  viewed  in  plane  of  incidence.  A.  Viewed  at  450;  lamp  on 
side  toward  photometer.  B.  Viewed  at  450;  lamp  on  side  away  from  photometer. 
C.  Viewed  at  300;  lamp  on  side  toward  photometer.  D.  Viewed  at  300;  lamp  on 
side  away  from  photometer. 


20  30 

ANGLE  OF  VIEW 


Fig.  2.— Reflecting  test-plate  viewed  in  plane  of  incidence.  Angle  of  incidence  =  6o°.  The 
upper  branch  of  the  curve  beyond  300  shows  the  errors  when  the  lamp  is  on  the  side 
opposite  to  the  photometer.  On  the  same  side  as  the  photometer  the  errors  are  prac- 
tically zero. 


SHARP   AND   LITTLE:     COMPENSATED   TEST-PLATE  733 

It  will  be  seen  that  the  arrangement  shows  symmetry  up  to  300 

angle  of  view  and  that  at  25 °  and   300  angle  of  view,  the  error 

is  zero.    Above  this  point  the  errors  increase  when  the  lamp  is  on 

the  side  opposite  to  the  photometer,  whereas  when  the  lamp 

is  on  the  same  side  the  errors  remain  negligibly  small. 

TABLE  III.— Errors  of  Reflecting  Test-Plate  of  Depolished 

White  Glass  with  Constant  Angle  of  Incidence  and 

Varying  Angle  of  View. 

Angle  of  incidence  =  6o°. 

Angle  of  view  •  •       o°         150       250     300       32. 50        350        450 

Errors 

Same  side — 4.5      — 0.5      o      — 1       —0.5  o  o 

Opposite  side  ..   — 4.5  o  o       +2       +5-°       —  II       +24 

TABLE  IV.— Errors  of  Reflecting  Test-Plates. 

In  plane  of  incidence  At  right 

angles 


Angle  of  view o°  150  300  3oc 


Same         Opposite 
side  side 


Angle  of  Errors,  per  cent, 

incidence 


0 

0 

0 

0 

0 

—  2.5 

0 

—  0.5 

—  0.5 

+  0.5 

—  3-5 

0 

+  0.5 

0 

0 

—  3 

0 

0 

0 

0 

-  6.5 

-  0.5 

—  1 

—   1 

+  0.5 

—  9 

—  2 

—  1 

—  0.5 

—  1 

— 11 

—  2.5 

0 

0 

—  6 

—15 

—  7 

—  7 

0 

—  7 

—23 

—13 

—  14 

3 

—  S 

oa 

IO° 
2O0 
30° 
40° 
50° 

6o° 
700 
8o° 
850  —25         —20  —24  -  3  —18 

Data  on  tests  of  a  commercial  test-plate  of  other  manufacture 
than  the  one  given  above  are  shown  in  Table  IV.  Here  again 
the  errors  are  smaller  with  an  angle  of  view  of  300  than  they  are 
at  o°  or  1 50.  In  a  further  study  of  this  plate  the  photometer 
was  placed  so  that  its  angle  of  view  should  be  300  to  the  plate 
at  right  angles  to  the  plane  of  incidence  to  the  light.  The  errors 
under  this  condition  are  given  in  the  last  column  of  Table  IV. 
In  these  data  as  well  as  in  the  data  of  the  preceding  two  columns, 
one  finds  a  very  good  argument  for  the  proposition  that  a  test- 
plate  of  this  character  should  be  viewed  at  an  angle  of  about  300. 
A  certain  amount  of  dissymmetry  is  evident  but  it  occurs  at  such 
high  angles  that  it  may  not  be  a  very  important  factor. 


734     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


Causes  of  Deviations  from  Cosine  Law. — It  will  be  noted  from 
the  foregoing  that  in  all  cases  where  the  test-plate  is  viewed  from 
a  symmetrical  position,  that  is,  along  the  normal,  the  test-plate 
errors  are  negative  at  the  higher  angles.  The  light  incident  at 
higher  angles  does  not  bring  the  brightness  of  the  plate  up  to  its 
theoretical  value.  More  light  is  needed  for  this.  It  is  interesting 
to  inquire  into  the  cause  for  it. 


o° 


20 


30  40  50  60 

ANGLE  OF  INCIDENCE 


70 


80" 


Fig.  3.— A.  Reflection  from  polished  glass,  n  =  1.5,  reduced  to  zero  reflection  at  normal. 
B.  Errors  of  polished  white  glass  test-plate.  C.  Errors  of  polished  white  glass  test- 
plate.    D.  Errors  of  depolished  white  glass  test-plate. 

All  the  light  incident  on  a  test-plate  is  either  reflected,  absorbed 
or  transmitted.  In  the  case  of  a  transmitting  test-plate  the  bright- 
ness evidently  cannot  obey  the  cosine  law,  even  if  the  glass  itself 
is  a  perfect  diffuser,  unless  the  loss  by  reflection  is  constant  for 
all  angles.  The  endeavor  is  made  by  depolishing  the  glass  to 
attain  this  condition.  The  reflection  of  a  polished  glass  surface 
at  various  angles  of  incidence  is  shown  in  Fig.  3,  curve  A,  in 
such  a  way  that  the  values  are  comparable  with  test-plate  errors 
in  the  tables ;  that  is,  all  values  are  diminished  by  the  percentage 
reflected  at  normal  incidence,  4  per  cent.  If  we  were  to  use 
as  a  transmitting  test-plate  a  disk  of  polished  white  glass,  there 
would  evidently  be  an  error  of  30  per  cent,  at  8o°  due  to  surface 


SHARP   AND   LITTLE:     COMPENSATED  TEST-PLATE  735 

reflection,  quite  apart  from  any  failure  of  the  glass  to  diffuse  the 
light  penetrating  it.  The  actual  errors  of  test-plates  made  of 
polished  instead  of  depolished  glass  are  shown  for  comparison 
in  Fig.  3,  curves  B  and  C.  These  curves  are  evidently  what 
would  be  expected  if  an  imperfectly  diffusing  surface  were  over- 
laid with  a  smooth  glass  surface.  The  lack  of  diffusion  is 
evidently  less  important  as  a  source  of  error,  than  the  variable 
loss  by  reflection. 

In  curve  D  of  Fig.  3  are  shown  graphically  the  errors  of  de- 
polished  plate  No.  220.  It  will  be  seen  that  the  effect  of  rough- 
ening the  surface  of  the  glass  is  to  diminish  the  loss  of  light  at 
the  higher  angles  and  hence  to  improve  the  plate  at  these  angles. 
That  a  variable  loss  by  reflection  still  plays  a  part,  however,  is 
demonstrated  by  the  fact  that  the  light  reflected  at  about  the 
polarizing  angle  (560)  still  shows,  when  examined  through  an 
analyzer,  a  considerable  percentage  of  polarization.3  It  would 
appear  therefore  that  the  loss  by  reflection,  following  the  theoret- 
ical law  of  Fresnel,  may  be  considered  as  the  chief  cause  for  the 
deficiency  of  test-plate  brightness  at  high  angles. 

PRINCIPLE  OF  COMPENSATION. 

If  additional  light  could  be  introduced  to  the  plate,  so  pro- 
portioned as  to  be  zero  at  normal  incidence  and  to  increase  rapidly 
from  500  on,  this  deficiency  might  be  overcome  and  the  test-plate 
caused  to  give  a  correct  result.  It  is  this  idea  which  underlies 
the  compensated  test-plate,  forming  the  subject  of  this  paper. 
The  construction  is  a  very  simple  one.  In  the  transmitting  test- 
plate  the  ordinary  glass  plate  instead  of  being  mounted  on  the 
end  of  a  metal  tube  is  mounted  on  a  little  diffusing  (opal)  glass 
ring.  The  brightness  of  the  test-plate  with  o°  incidence  is  not 
altered  by  the  presence  of  the  opal  ring  except  by  internal  reflec- 
tions, but  as  the  incidence  increases,  a  larger  and  larger  amount 
of  light  falls  upon  the  ring,  and  by  it  is  diffused  in  such  a  way  as 
to  add  a  certain  illumination  to  the  under  surface  of  the  test-plate. 

8  It  is  clear  that  in  measuring  partially  polarized  light  (e.  g.,  skylight)  the  error  of  the 
test-plate  will  depend  on  the  relation  of  the  plane  of  polarization  to  the  plane  of  inci- 
dence. This  may  be  important  in  the  case  of  reflecting  test-plates.  Furthermore,  pho- 
tometers operating  on  the  polarization  principle  may  give  erroneous  results  with  a  reflect- 
ing test-plate  of  depolished  glass  or  similar  material  such  as  celluloid.  Such  an  error 
may  be  eliminated  by  taking  settings  with  the  polarizing  apparatus  in  two  positions  at 
right  angles  to  each  other. 


736     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

By  properly  proportioning  the  transmission  of  the  test-plate  and 
the  transmission  and  diffusion  of  the  ring,  together  with  the  width 
of  the  latter,  a  compensation  for  the  deficiency  in  brightness  of 
the  test-plate  at  high  angles  may  be  obtained. 

It  is  evident  that  if  the  arrangement  as  described  were  used, 
light  coming  at  900  of  incidence,  which  would  produce  no  illumin- 
ation whatever  on  the  upper  side  of  the  plate,  would  pass  through 
the  opal  glass  ring  and  illuminate  the  under  side  of  the  plate. 
Light  coming  from  angles  even  greater  than  90 °  might  have  the 
same  effect.  Evidently  this  light  must  be  cut  off  and  this  is  done 
by  the  interposition  of  a  saucer-shaped  screen  with  the  edge  of  the 
saucer  in  line  with  the  top  of  the  aperture  in  the  opal  ring.  The 
construction  used  is  shown  in  half -section  in  Fig.  4,  and  the 
actual  test-plate  as  attached  to  a  photometer  is  shown  in  Fig.  5. 


Fig.  4.— Compensated  transmitting  test-plate.  P.  Test-plate  of  polished  white  glass.  R. 
Ring  of  opal  glass.  C.  Opaque  shield.  A.  Clear  aperture  in  ring  for  admission 
of  light.    S.  Screen  to  cut  off  light  at  900  incidence. 


It  has  been  found  that  if  the  light  is  admitted  to  the  opal  ring 
close  to  the  test-plate,  the  compensating  illumination  is  not  uni- 
formly distributed  over  the  test-plate,  so  that  at  high  angles  of 
incidence  the  field  is  irregular.  On  this  account  the  aperture  in 
the  ring  is  placed  well  below  the  test-plate.  The  portion  of  the 
opal  ring  through  which  light  should  not  pass  is  covered  up  by  a 
metal  band,  the  width  of  which  determines  the  width  of  the 
aperture  in  the  compensating  ring  and  hence  the  amount  of  com- 
pensating light. 


SHARP   AND   LITTLE:     COMPENSATED   TEST-PLATE 


737 


Evidently  the  amount  of  compensating  light  has  to  be  accur- 
ately proportioned  to  fit  the  peculiarities  of  the  test-plate.  If  the 
test-plate  is  quite  thin  and  transparent,  a  larger  amount  of  com- 
pensating light  is  required  than  if  it  is  relatively  dense.  The 
more  perfect  the  diffusing  qualities  of  the  test-plate,  the  less 
compensating  light  is  required.  It  has  been  found  in  practise  that 
the  opal  ring  may  be  optically  quite  thin ;  that  is  it  may  be  clear 
glass  with  a  light  flashing  of  opal.  A  ring  of  this  character  asso- 
ciated with  a  polished  test-plate  gives  a  combination  which  is  quite 


Fig.  5.— Compensated  test-plate  in  practical  form. 

readily  adjusted  by  varying  the  width  of  the  annular  aperture  in 
the  ring  to  conform  with  the  cosine  law  even  at  very  high  angles 
of  incidence. 

Polished  Versus  Depolished  Plates. — There  are  very  consider- 
able advantages  accruing  from  the  use  of  polished  test-plates 
rather  than  depolished  ones.  In  the  first  place  a  polished  plate  is 
more  uniform  in  its  characteristics  than  the  depolished  one  and 
hence  is  more  easily  compensated  for  its  error.  The  depolished 
plate  varies  according  to  the  means  used  in  removing  the  polished 
surface  whereas  the  polished  plate  is  not  subject  to  this  source  of 


738     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

irregularity,  provided  the  polish  is  made  sufficiently  good. 
Furthermore  depolished  plates  are  very  difficult  to  clean ;  minute 
quantities  of  dirt  become  embedded  in  the  irregular  surface  and 
cannot  be  removed,  while  polished  plates  offer  no  difficulties 
whatever  in  this  respect. 

Results  of  Compensation. — In  Table  V  are  given  the  results 

TABLE  V. — Transmitting  Test-phase  of  Polished  Glass  without 
and  with  Compensating  Ring  of  Flashed  Opal. 


Plate  B 
uncom- 
pensated 

Plate  B  un- 
dercompen- 
sated W32  in. 
^4.0  mm.) 
aperture 

Plate  B 

com- 
pensated 

3/ie  in- 
(4.8  mm.) 
aperture 

Plate  A 
uncom- 
pensated 

Plate  A 

com- 
pensated 

Plate  A 
compen- 
sated in 
permanent 
mounting 

Angle  of 

Error,  per  cent. 

Lncidencc 
o° 

0 

O 

O 

O 

O 

O 

IO° 

+   0.5 

—   0.3 

+  0.5 

O 

O 

O 

2O0 

+   0.5 

O 

O 

O 

O 

O 

30° 

+   0.5 

—  0.5 

—0.5 

—   1-5 

—0.5 

+   0.5 

40° 

+   0.5 

—  0.5 

+0.5 

—  4 

+0.5 

+    1.5 

50° 

—  3-5 

+   0.5 

—0.5 

-  6.5 

—0.5 

+    I.O 

6o° 

— 11 

O 

O 

—  13-5 

—0.5 

+    1.5 

700 

—20.5 

—  2.5 

+  1 

—  15 

—  I 

O 

8o° 

-44 

—13 

+  1 

-48 

—1-5 

—   O.5 

85° 

—72 

— II 

+6 

— 

—4 

—  II 

obtained  in  compensating  two  different  plates.  In  the  first  column 
are  shown  the  errors  of  an  uncompensated  polished  plate ;  in  the 
second  column  are  shown  the  errors  when  this  plate  is  under- 
compensated, the  aperture  in  the  opal  ring  being  too  narrow.  In 
the  next  column  are  shown  the  results  of  a  perfect  compensation 
with  the  opening  in  the  aperture  of  the  ring  only  1/32  in.  (0.8 
mm.)  wider  than  in  the  preceding  case.  In  the  next  column  an- 
other uncompensated  plate  is  shown  followed  by  results  of  the 
same  plate  compensated.  In  the  last  column  are  shown  the  errors 
of  a  compensated  test-plate  in  practical  form  for  using  on  the 
photometer.  Remembering  that  measurements  made  at  85  °  of 
incidence  are  subject  to  large  errors  due  to  the  great  effect  of 
small  inaccuracies  in  the  measurement  of  the  angle  and  to  the 
relative  darkness  of  the  field,  it  may  be  said  that  in  all  cases  the 
outstanding  errors  are  within  the  errors  of  observation. 

Compensated  Reflecting  Test-Plate. — The  construction  where- 
by reflecting  test-plates  may  be  compensated  in  accordance  with 
the  above-mentioned  principles  is  quite  as  simple  as  that  of  the 


SHARP   AND   LITTLE:     COMPENSATED   TEST-PLATE 


739 


transmitting  test-plate.     The  reflecting  test-plate  proper  is  made 

of  a  disk  of  depolished  white  glass;  parallel  with  this  disk  is 

placed  another  similar  disk.    A  similar  opaque  screen  is  used  for 

shielding  the  upper  disk  from  light  coming  at  angles  of  900  and 

TABLE  VI.— Compensated  Reflecting  Test-Plate. 
Viewed  Normally. 

Angle  of  incidence  Error,  per  cent 

o°  o 

lo°  _  0.5 

2°°  -   1-5 

30°  -    1.5 

40°  —  2.0 

5°°  —  0.5 

60°  _  0.5 

7°°  +  4 

8o°  +  2 

85°  -12 

greater.  Compensation  is  affected  by  the  light  reflected  from  the 
lower  disk  which  passes  through  the  upper  disk  and  adds  a  suf- 
ficient amount  to  the  brightness  of  the  test  surface.  This  con- 
struction is  shown  in  section  in  Fig.  6.    Table  VI  shows  the  re- 


.•11  •  in  1  1  111,, — 1 r0 — r 


1        bmbjmJimm .*-">' 


Fig.  6.— Half  section  of  compensated  reflecting  test-plate.  P.  Test-plate  of  depolished 
white  glass.  C  Compensating  diffuser  of  depolished  white  glass.  S.  Screen  for  cut- 
ting off  light  at  go°. 

suits  obtained  with  this  form  of  construction.  The  angle  of  view 
of  the  photometer  was  normal  to  the  plate.  Here  again  the  re- 
sults of  the  compensation,  while  not  quite  so  good  as  in  the  case 
of  the  reflecting  plate,  are,  for  practical  purposes,  about  as 
good  as  could  be  desired.  It  should  be  noted,  however,  that  the 
reflecting  plate  suffers  under  the  disadvantage  that  in  order  to 
give  these  results,  the  angle  of  view  must  be  normal  to  the  plate. 
There  does  not  seem  to  be  any  way  of  obviating  this  disadvantage. 
Also,  the  reflecting  plate  is  considerably  more  cumbersome  than 
the  transmitting  plate  on  account  of  its  dimensions.     Evidently, 


740     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

the  plate  itself  must  be  of  sufficient  size  to  cover  the  entire 
field  of  the  photometer  when  the  photometer  is  placed  at  the  de- 
sired distance  from  it.  The  shading  ring  surrounding  it  must  be 
large  enough  so  that  it  does  not  begin  to  cast  a  shadow  on  the 
lower  plate  at  too  small  an  angle  of  incidence,  for  otherwise  the 
compensation  at  high  angles  of  incidence  will  be  incomplete.  In 
the  construction  investigated  the  test-plate  had  a  diameter  of 
5  in.  (12.7  cm.)  and  the  entire  apparatus  a  diameter  of  10  in. 
(25.4  cm.). 

The  results  of  a  number  of  the  above  tests  are  for  convenience 
summarized  in  the  curves  of  Fig.  7. 

RESULTS  OF  ILLUMINATION  TEST. 

In  order  to  form  an  idea  of  the  magnitude  of  the  errors  which 
may  be  introduced  into  the  results  of  illumination  measurements 


►IU 

. 4 

► . 

U 

' 

^ 

- 

_ — 

^ 

L-             -- 

---i 

—A 

VI 

D 

•10 

s 

E 

\ 



\  i 

20 

V 

\ 

30 

\ 

A 

\ 
\ 

\ 

B 

\ 

- — - 

1 

y 

1 

u 

i 

0 

3 

0 
1 

4 

0 

or  T 

0 

NCI 

b 
JEN 

0 

ce: 

7 

0 

B 

0 

H 

0 

11 

0 

Fig.  7. — Errors  of  various  test-plates  viewed  normally.  A.  Depolished  transmitting  plate. 
B.  Polished  transmitting  plate.  C  Depolished  glass  reflecting  plate.  D.  Compen- 
sated transmitting  plate.    E.  Compensated  transmitting  plate. 

through  test-plate  deficiencies,  an  actual  test  of  the  illumination 
in  a  room  at  the  Electrical  Testing  Laboratories  was  made.  The 
results  with  a  compensating  test-plate  were  taken  as  standard  and 
the  others  compared  with  them.  The  system  of  illumination  was 
semi-indirect  and  may  be  taken  as  fairly  typical  of  good  modern 
practise. 

The  results  as  given  in  Table  VII  show  a  deficiency  of  5.5  per 
cent,  in  the  values  yielded  by  the  uncompensated  transmitting 
test-plate  and  of  13.5  per  cent,  in  the  values  of  the  reflecting  test- 


SHARP   AND   LITTLE:     COMPENSATED   TEST-PLATE 


741 


plate,  which  was  viewed  normally.  The  value  13.5  for  the  error 
of  the  reflecting  test-plate  is  much  larger  than  would  be  expected 
from  the  test  results  of  such  plates  given  above.  The  discrepancy 
may  properly  be  ascribed  to  the  light  cut  off  from  the  plate  by 
the  photometer  and  the  operator.  However,  this  source  of  error 
is  rarely,  if  ever,  absent  in  using  reflecting  test-plates  in  interiors 
where  the  light  is  well  diffused,  and  constitutes  a  serious  disad- 
vantage of  the  reflecting  test-plate  as  compared  with  the  trans- 
mitting type. 

TABLE  VII.— Comparison  of  Test-Plates  in  Measuring  Illumina 

tion  in  a  Room. 


Uncompensated  transmitting 


Uncompensated  reflecting 
test-plate  viewed  normally* 


Test 

transmitting 

Per  cent,  of 

Per  cent,  of 

station 

Foot-candles 

Foot-candles 

compensated 

Foot-candles 

compensated 

I 

12. 1 

11. 7 

97 

10.9 

90 

Check  after  test 

12.2 

11. 7 

96 

II. O 

91 

2 

9-1 

9-°5 

99 

8.15 

89 

3 

5-05 

4.69 

93 

4-03 

80 

4 

2.6l 

2-53 

97 

2.25 

86 

5 

6-35 

5-85 

92 

5-5 

87 

6 

4.50 

4.04 

90 

3-69 

82 

7 

2.64 

2-57 

97 

2.18 

83 

8 

9-35 

9-i 

98 

8.6 

92 

9 

4.68 

4.90 

95 

4.24 

86 

10 

2.68 

2.48 

93 

2.38 

89 

11 

12.9 

12.5 

97 

12. 1 

94 

12 

8-95 

8.55 

95 

8.05 

90 

13 

4.90 

4-45 

9i 

4.27 

88 

14 

2.71 

2.58 

95 

2.26 

83 

15 

5-95 

5.65 

95 

5-4 

9i 

16 

4-33 

4.02 

93 

3-58 

83 

17 

2-59 

2-34 

90 

2. 11 

82 

18 

9.8 

9-15 

94 

8.25 

84 

19 

4.83 

4.70 

97 

4.16 

86 

20 

2.76 

2-55 

93 

2.15 

78 

21 

12.9 

12.8 

99 

11. 8 

92 

Mean 

illumination  • 

•  5.21 

4-95 

4-5i 

Percentage 

of 

compensated . 

94-4 

85.5 

*  Errors  due  in  part  to  shadow  of  observer  and  of  photometer. 


If  the  5  per  cent,  error  as  shown  by  the  uncompensated  trans- 
mitting plate  be  taken  as  typical,  it  will  be  seen  that  in  all  prob- 


742     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ability  test-plate  errors  have  not  been  a  very  serious  matter  from 
a  practical  standpoint,  but  it  must  likev/ise  be  conceded  that  to 
eliminate  them  entirely  is  very  'desirable. 

Application  to  the  Integrating  Sphere. — In  the  theory  of  the 
integrating  sphere  the  assumption  is  made  that  the  window,  the 
brightness  of  which  is  observed,  is  a  perfect  diffuser.  Experi- 
mental work  is  now  in  progress  looking  to  the  adaptation  of  the 
compensation  idea  to  these  plates  with  a  view  to  attaining  a  higher 
accuracy  in  sphere  work. 

APPENDIX. 

Brightness  of  Test-plates  as  Seen  in  the  Photometer  when 

Measuring  an  Illumination  of  One  Lumen  Per 

Square  Foot. 

Apparent  lumens 
Cp.  per  sq.  in.  emitted  per  sq.  ft. 

Depolished,  transmitting 0.00049  0.22 

Polished,  transmitting 0.00056  0.25 

Thick  white  flashed  opal 0.00048  0.22 

Thin  greenish,  flashed  opal 0.00123  0.56 

Depolished  glass,  reflecting 0.0180  0.81 

The  above-given  figures  represent  the  results  of  test  of  one 
plate  only  of  each  kind  and  are  to  be  taken  only  as  approximately 
indicative  of  the  performance  of  the  various  classes.  In  the 
measurement  of  feeble  illumination  particularly,  the  plates  having 
a  relatively  large  brightness  permit  photometric  settings  to  be 
made  more  easily. 

DISCUSSION. 

Ward  Harrison  :  One  redeeming  feature  of  the  test-plate  er- 
ror is  that  if  the  photometer  measures  3  foot-candles  it  can  be 
confidently  asserted  that  more  than  that  is  being  obtained  rather 
than  less.  Its  worst  characteristic  is  that  it  usually  tends  to 
magnify  variations  in  intensity  of  illumination.  For  example,  in 
a  photometric  survey,  the  measurements  taken  near  the  side  walls 
of  a  room  will  indicate  a  much  lower  intensity  than  in  the  cen- 
tral portion.  The  illumination  is  generally  somewhat  lower  any- 
way, but  since  most  of  the  light  falls  obliquely  on  the  test  plane  at 
these  stations,  the  test-plate  error  becomes  a  considerable  factor 
and  the  photometer  reading  is  still  further  reduced.  The  illumina- 
tion on  a  desk  in  this  portion  of  an  office  is  often  much  more 
satisfactory  than  would  be  indicated  by  a  foot-candle  reading. 


COMPENSATED   TEST-PLATE  743 

Again,  in  the  case  of  industrial  plants  the  fact  has  just  been 
emphasized  that  illumination  measurements  should  be  made  with 
at  least  one  lamp  shaded.  A  man  working  at  his  machine  will 
often  shade  his  work  from  the  lamp  placed  directly  above  him,  or 
nearly  so,  and  if  the  residue  of  the  illumination  is  measured,  one 
may  be  unnecessarily  startled  at  the  low  values  obtained.  It  is 
simply  another  case  of  oblique  lighting  and  the  actual  intensity 
may  be  easily  20  per  cent,  greater  than  the  quantity  measured. 

Perhaps  the  most  glaring  of  all  cases  of  this  error  is  that  en- 
countered when  one  attempts  to  measure  horizontal  illumination 
in  a  street  lighting  installation.  Five  and  one-half  per  cent,  has 
been  given  as  the  average  error  due  to  the  use  of  an  ordinary  test- 
plate  as  determined  in  an  illumination  survey  of  a  room  equipped 
with  a  semi-indirect  system.  We  have  made  several  investiga- 
tions where  the  error  of  the  old  type  of  plate  appeared  to  be  con- 
siderably greater  than  this.  The  magnitude  of  the  error  depends 
of  course  upon  the  character  of  distribution  from  the  light 
sources ;  units  which  emit  most  of  their  light  at  angles  near  the 
vertical  will  give  rise  to  a  much  less  error  in  an  illumination  test 
than  will  units  having  a  wide  distribution  of  light.  In  the  case  of 
a  semi-indirect  installation  the  portion  of  the  light  which  is  re- 
flected from  the  ceiling  has  a  circular  or  concentrated  distribu- 
tion and  the  same  is  also  often  true  of  the  portion  of  the  light 
which  is  supplied  by  the  bowl  itself.  With  a  system  of  direct 
lighting  units  having  an  extensive  distribution,  it  has  been  found 
that  the  error  in  mean  intensity  runs  as  high  as  10  or  12  per  cent. 

In  conclusion  I  wish  to  express  my  appreciation  of  the  work  of 
Dr.  Sharp  and  Mr.  Little  in  producing  this  new  test-plate.  It  will 
certainly  afford  a  great  degree  of  mental  satisfaction  to  all  who 
have  occasion  to  make  illumination  surveys ;  from  a  practical 
standpoint  the  satisfaction  is  much  increased  by  the  fact  that  the 
test-plate  has  a  polished  surface.  It  is  therefore  not  so  liable  to 
the  very  common  error  due  to  dust  which  is  especially  serious 
where  an  instrument  is  calibrated  in  one  place  and  at  a  later  date 
operated  in  another. 

G.  H.  Stickney:  This  paper  apparently  confirms  the  distrust 
which  I  have  held  for  many  tests  made  with  the  reflecting  type  of 
test-plate.     I  have  never  used  such  test-plates  to  any  extent,  but 


744    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

I  have  noted  the  very  optimistic  use  of  them  by  others.  How- 
ever, it  must  be  recognized  that  such  test-plates  are  exceedingly 
valuable  for  certain  classes  of  measurements  and  when  properly 
used  give  very  useful  results. 

At  the  Boston  Convention  in  1907  (see  Transactions  1907, 
pages  559,  562  and  571)  some  mention  was  made  of  an  illumina- 
tion photometer  developed  under  the  direction  of  Mr.  W.  D'A. 
Ryan,  with  which  I  had  something  to  do.  As  Dr.  Sharp  says,  this 
photometer  was  not  particularly  suitable  for  very  low  intensity 
measurements.  It,  however,  met  quite  well  the  requirements 
in  the  class  of  problems  which  we  were  then  meeting.  It  was 
never  claimed  for  this  photometer  that  it  was  suitable  for  all  sorts 
of  illumination  measurements.  It  had  the  advantage  over  all 
other  existing  photometers  in  giving  the  proper  value  of  light  fall- 
ing at  all  angles.  In  view  of  the  fact  that  the  discrepancy  was 
then  realized,  it  is  somewhat  surprising  that  up  to  the  present  no 
device  has  been  in  common  use  to  effect  a  similar  correction. 

The  arrangement  described  in  the  present  paper  seems  to  me  to 
be  an  exceedingly  important  one,  which  should  be  applied  as  far 
as  possible  in  all  measurements  taken  in  interiors  where  there  is  a 
large  component  of  side  light,  either  from  reflecting  walls  or 
otherwise.  The  new  device  seems  to  embody  some  of  the  same 
fundamental  principles  of  Mr.  Ryan's  photometer,  although  the 
method  of  mixing  the  light  is  of  course  quite  different. 

I  believe  we  frequently  encounter  serious  error  in  illumination 
measurements  in  undervaluating  the  diagonal  light  which  often  is 
most  valuable  in  securing  good  illumination.  For  example,  in  this 
room  at  the  present  time,  with  the  daylight  coming  in  at  the  side 
windows,  an  ordinary  photometer  plate  would  not  properly  meas- 
ure the  light  on  the  chairman's  table,  although  it  would  more  cor- 
rectly measure  the  artificial  illumination.  I  do  not  think  this 
would  be  a  happy  instance  to  illustrate  the  excellence  of  the  meas- 
uring qualities  of  an  ordinary  plate  as  commonly  used  in  illumina- 
tion photometers. 

Mr.  P.  S.  Milear:  There  have  been  two  conditions  surround- 
ing the  use  of  erroneous  test-plates  which  have  tended  to  reduce 
the  ill  effects  of  such  errors.  First,  most  surfaces  which  have 
been  viewed  in  practise  depart  from  the  cosine  law  in  the  same  di- 


COMPENSATED   TEST-PLATE  745 

rection  as  do  inaccurate  test-plates.  Second,  the  error  has  been 
more  or  less  a  systematic  one  applying  in  a  general  way  to  all 
photometric  results  and  therefore  less  misleading  than  it  might 
have  been  if  applied  to  comparative  results. 

In  spite  of  these  conditions  users  of  portable  photometers  have 
been  uneasy  regarding  the  test-plate  error  which  has  affected 
much  of  their  work.  It  is  accordingly  very  gratifying  to  know 
that  we  are  in  a  fair  way  to  eliminate  such  errors  and  I  want  to 
express  my  appreciation  of  the  work  of  Dr.  Sharp  and  Mr.  Little 
in  making  available  a  practical  device  with  which  this  last  remain- 
ing systematic  error  can  be  removed  from  illuminating  photo- 
meters. 

Dr.  C.  H.  Sharp  (In  reply)  :  One  speaker  quite  properly  call- 
ed attention  to  the  fact  that  the  reflecting  test-plate,  when  prop- 
erly used,  apparently  is  inherently  less  in  error  than  the  trans- 
mitting plate.  I  believe,  however,  that  because  it  can  be  viewed  at 
pretty  much  any  angle  and  is  liable  to  be  so  placed  that  the  body 
of  the  observer  or  instrument  will  cut  off  some  of  the  light  which 
it  ought  to  get,  it  has  disadvantages  as  compared  with  the  test-plate 
rigidly  attached  to  the  photometer,  which  in  practise  renders  it 
less  reliable.  I  think  Mr.  Stickney  has  answered  very  well  the 
question  of  the  value  of  the  light  at  80  degrees.  Very  often  it  is 
not  very  important,  and  then  again  it  may  be  very  important,  and 
when  it  is  important,  we  surely  want  to  be  able  to  measure  it.  As 
to  the  area  of  the  field  in  the  apparatus  illustrated,  the  diameter 
of  the  field  is  only  about  half  the  diameter  of  the  transmitting 
test-plate.  In  a  reflecting  test-plate,  the  area  of  the  field  depends 
upon  the  distance  of  the  photometer  away.  There  has,  however, 
been  no  practical  difficulty  due  to  an  irregular  field  caused  by  an 
irregular  distribution  of  the  compensating  light;  the  field  is 
regular  to  a  satisfactory  degree.  I  perhaps  should  have  said 
more  in  presenting  the  paper  regarding  Mr.  Ryan's  instrument. 
Ryan's  compensated  test-plate,  for  that  is  what  it  was,  was  a  very 
ingenious  thing.  It  was  an  endeavor  to  meet  a  difficulty  which, 
even  at  that  relatively  early  day,  was  well  recognized,  and  it  is 
probably  a  misfortune  that  it  was  not  followed  up. 


746     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

PRESENT  PRACTISE  IN  THE  LIGHTING  OF 

ARMORIES  AND  GYMNASIUMS  WITH 

TUNGSTEN  FILAMENT  LAMPS.* 


BY  A.  E.  POWELE  AND  A.  B.  ODAY. 


Synopsis:  The  general  requirements  for  lighting  are  here  discussed 
from  a  practical  viewpoint.  Typical  installations  are  pictured  and  briefly 
described;  and  data  covering  a  considerable  number  of  buildings  are  pre- 
sented in  tabular  form,  giving  dimensions,  spacing,  hanging  height  and 
size  of  lamps,  type  of  reflector,  equipment,  etc.  From  this  data  average 
values  of  power  consumption  per  unit  of  area  (watts  per  square  foot)  are 
obtained. 


INTRODUCTION. 

A  careful  search  through  the  Transactions  of  the  society  and 
of  technical  literature  reveals  but  little  data  on  this  field  of  light- 
ing. It  is  true  that  the  lighting  of  these  buildings  is  a  relatively- 
simple  proposition,  yet  the  engineer  who  is  about  to  design  a  new 
system  usually  desires  to  have  available  data  with  which  to  check 
his  calculations.  The  authors  of  the  paper  were  in  a  position  to 
examine  a  considerable  number  of  typical  installations  and  cor- 
relate the  material.  They  make  no  pretense  of  originality  of 
design  as  the  lighting  of  but  comparatively  few  of  the  buildings 
inspected  was  planned  by  them. 

The  method  of  procedure  in  preparing  the  paper  was  to  visit 
representative  armories  and  gymnasiums  located  within  a  con- 
venient radius  of  New  York  City,  and  note  the  facts  as  enumer- 
ated in  the  text;  and,  next,  from  observation  and  experience,  to 
outline  the  principles  involved  in  the  lighting,  as  far  as  possible 
include  these  with  the  data. 

Illumination  tests  were  conducted  in  only  a  few  instances  as 
the  time  and  expense,  which  would  have  been  involved,  would 
not  have  been  warranted,  for  the  illuminating  efficiency  of 
standard  equipments  is  now  fairly  well  known  or  can  be  estimated 
quite  closely  from  similar  cases.  For  checking  calculations,  the 
watts  per  square  foot  of  floor  area,  with  the  proper  modifications 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,    September  20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


POWELL  AND  ODAY:    ARMORY  AND  GYMNASIUM  LIGHTING      747 

deduced  from  experience,  proves  very  useful.  In  each  case  the 
actual  watts  per  square  foot  are  given,  but  since  the  efficiency  of 
the  lamps  found  in  service  varies  from  0.6  to  1.05  watts  per  hori- 
zontal candlepower,  a  table  headed  "Comparative  watts  per  square 
foot"  based  on  i  watt  per  candle  or  approximately  10  lumens  per 
watt  is  also  included. 

ARMORIES. 

When  one  thinks  of  an  armory,  the  drill  shed  alone  is  usually 
pictured;  yet  some  of  these  structures  are  very  elaborate  indeed, 
having  also  a  gymnasium,  theatre,  rifle  ranges,  bowling  alleys, 
billiard  room  and  the  like.  The  subject  therefore  may  be  sub- 
divided as  given  below. 

Drill  Shed. — This  is,  of  course,  the  most  important  part  of  the 
armory  and  should  receive  the  most  attention.  As  a  general 
proposition  the  usual  form  is  a  large  open  space  with  an  arched 
roof.  The  size  of  those  investigated  varied  from  600  ft.  x  300  ft. 
(182.88  x  91.44  m.)  (180,000  sq.  ft.)  x  100  ft.  (30.48  m.)  high, 
to  76  x  92  (23.16  x  28.04  m0  (7,ooo  sq.  ft.)  (n.58  m.)  38  ft. 
high.  The  roof  is  often  partly  glass  to  admit  daylight  and 
usually  the  iron  work  is  exposed. 

Many  drill  sheds  have  balconies  for  the  seating  of  spectators, 
necessitating  special  lighting  below  to  prevent  dense  shadows 
which  would  result  if  only  the  general  lighting  was  provided. 
The  floor  varies  considerably  depending  on  the  branch  of  service, 
cavalry  having  a  very  dark  brown  tanbark;  infantry,  light  hard 
wood.  Naturally  the  character  of  the  floor  has  a  marked  effect 
on  the  quantity  of  light  which  must  be  supplied. 

On  account  of  the  simplicity  of  operation  and  maintenance,  the 
high  efficiency  of  light  production,  the  pleasing  color  of  light,  the 
steadiness  and  adaptability  to  reflectors  giving  any  desired  distri- 
bution of  light,  the  gas-filled,  tungsten  filament  lamp  has 
become  practically  the  standard  illuminant  for  lighting  drill  sheds 
in  the  territory  investigated.  The  large  areas  permit  the  use  of 
high  candlepower  units  and  the  lofty  ceilings  give  hanging  heights 
such  that  lamps  are  always  well  out  of  the  ordinary  angle  of 
vision,  overcoming  any  objection  which  might  be  raised  on  the 
question  of  intrinsic  brightness.  The  wide  range  of  sizes  avail- 
able make  it  possible  to  select  a  unit  fitting  any  chosen  spacing 


748    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

giving  the  desired  watts  per  square  foot  or  foot-candles.  In- 
expensive fixtures,  holders,  sockets  and  reflecting  devices  are 
all  standardized,  thus  avoiding  the  added  cost  of  special  designs 
which  are  sometimes  attendant  on  propositions  of  these  mag- 
nitudes. 

The  uses  to  which  the  drill  hall  is  put  are  somewhat  varied. 
The  drilling  of  raw  recruits  takes  place  on  only  a  portion  of  the 
floor  and  does  not  require  the  entire  area  to  be  lighted ;  battalion 
and  regimental  drills  and  reviews  necessitate  full  illumination 
for  ease  of  manoeuvres  and  inspection;  gun  drills  in  the  coast 
defense  and  artillery  sometimes  need  all  lights  out ;  or  the  armory 
is  often  rented  to  charitable  organizations  and  the  like  for  fairs 
and  bazaars,  which  demand  brilliant  lighting  as  well  as  special 
decorative  or  spectacular  effects.  In  any  event  sufficient  light 
must  be  provided  in  all  parts  of  the  room  to  meet  the  most  ex- 
acting conditions. 

Type  of  Unit. — Appearance  is  one  of  the  factors  which  must 
be  given  consideration,  as  the  general  effect  of  the  room  must  be 
attractive,  particularly  if  used  for  other  than  regimental  purposes. 
Efficiency  must  also  be  considered  as  there  are  large  areas  to 
be  illuminated  and  an  extravagant  fixture  would  make  the  cost  of 
proper  lighting  prohibitive. 

Eye  protection  must  be  assured  as  glare  in  such  work  as  gun 
training  would  materially  reduce  the  effectiveness  of  the  unit. 

Since  the  ceilings  are  usually  broken  by  trusses  and  often  quite 
dark,  as  a  general  proposition  direct  lighting  is  essential. 

In  most  cases  it  is  advisable  to  use  either  a  translucent  re- 
flector or  a  unit  which  permits  some  of  the  light  to  escape  above 
the  horizontal,  for  if  the  ceiling  is  totally  dark  ones  attention  is 
involuntarily  attracted  and  the  room  seems  unpleasant.  Occas- 
ionally, however,  the  floor  is  light  enough  to  reflect  sufficient 
light  back  to  the  ceiling  even  if  opaque  bowl  reflectors  are 
employed. 

The  type  of  distribution  will  vary  with  conditions.  If  the  side 
walls  are  quite  dark  a  unit  giving  a  wide  curve  is  inadvisable  as 
far  too  much  flux  will  be  wasted  by  wall  absorption.  With  light 
walls,  however,  the  diffuse  reflection  will  assist  in  the  general 
illumination  and  concentration  of  the  light  is  not  as  necessary. 


Fig.  I. — Night  photograph  7th  Regiment  Armory  X.  G.  X.  Y.,  lighted  by  1,000-watt  gas- 
filled  tungsten  lamps  in  two-piece  prismatic  enclosing  globes ;  average  illumination 
3.3  feet  candles. 


F'g-  2.— Xight  photograph  71st  Regiment  Armory  X.  G.  X.  Y.,  lighted  by  soo-watt  gas- 
filled  tungsten  lamps  in  bowl  prismatic  reflectors. 


Fig.  3.— Night  photograph  Troop  C  Armory  N.  G.  N.  Y.,  lighted  by  750-watt  gas-filled  tung- 
sten lamps  in  deep  bowl  dense  opal  reflectors,  average  illumination  3.24  foot-candles. 


Fig.  4.— Night  photograph  22nd  Regiment  Armory  N.  G.  N.  Y.,  lighted  by  1000-watt 
gas-filled  tungsten  lamps  with  deep  bowl  enameled  steel  reflectors. 


POWELL  AND  ODAY  I    ARMORY  AND  GYMNASIUM  LIGHTING      749 

Ease  of  Cleaning  and  Renewals. — On  account  of  the  high 
hangings  employed,  some  sort  of  a  lowering  device  should  be 
provided.  Most  of  the  single  unit  fixtures  weigh  so  little  that  a 
simple  steel  cable  will  safely  support  them ;  a  cut-out  hanger  with 
lowering  rope  or  wire  simplifies  this  phase  of  building  main- 
tenance. In  some  cases  the  cut-out  is  omitted  and  the  cable 
passes  through  a  pulley,  then  down  the  sides  of  the  room,  the 
current-carrying  wires  hanging  in  loops. 

Convenience  of  Control. — Although  often  not  considered,  this 
is  an  important  point ;  for  instance,  in  the  coast  defense  armories 
when  practising  with  the  guns  it  is  often  desirable  to  hurriedly 
turn  off  any  group  of  lamps.  In  the  Brooklyn  armories  remote 
control  is  employed.  The  man  in  charge  of  the  entire  floor  has 
a  board  with  pilot  lights  and  switches.  At  each  gun  are  a  num- 
ber of  push  buttons,  so  that  when  the  squads  are  firing  the  officer 
in  charge  of  the  firing  can  at  once  signal  for  any  group  of  lamps 
to  be  extinguished.  The  whole  armory  can  be  thrown  in  dark- 
ness in  an  extremely  short  time.  With  the  system  of  lighting 
formerly  employed  it  required  twelve  men  for  this  work  with 
the  attendant  delay. 

Intensity  of  Illumination  Desirable. — From  general  consider- 
ation the  cavalry  and  field  artillery  armories  would  require  less 
light  than  those  of  the  other  branches  of  service,  as  they  are 
not  likely  to  be  used  for  social  purposes.  This  is  counteracted, 
however,  by  the  fact  that  the  tanbark  or  loam  floor  absorbs  a 
great  deal  of  light  and  makes  the  place  appear  abnormally  dark. 

Average  Figures. — The  actual  average  watts  per  square  foot 
for  15  drill  halls  with  wood  floors  was  0.39;  comparative  0.58  ;x 
for  the  6  armories  with  loam  and  tanbark,  actual  0.34 ;  compara- 
tive 0.52. 

Rifle  Range. — The  satisfactory  illumination  of  this  part  of  the 
building  is  too  large  a  subject  to  be  treated  with  any  degree  of 
completeness  in  a  paper  of  this  nature.  In  fact  the  British  Il- 
luminating Engineering  Society  devoted  their  entire  May  meeting 
to  this  phase  of  the  art.  A  very  valuable  paper,  by  Mr.  A.  P. 
Trotter,  and  interesting  discussion  is  reported  in  their  June 
Transactions.2 

1  i.  e.  with  lamps  at  10  lumens  per  watt. 

2  See  Illuminating  Engineer,  (L,ondon)  June,  1915. 


750     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

So  many  facts  enter  into  the  problem,  such  as  glare,  contrast, 
intensity,  uniformity,  surface  brightness,  type  of  sight  employed 
and  so  on,  that  it  seems  advisable  to  avoid  all  attempts  at  out- 
lining the  proper  practise.  Those  interested  can  study  the  above 
reference. 

However  as  an  indication  of  the  American  practise  a  descrip- 
tion is  given  of  two  indoor  ranges,  the  first  rather  elaborate  and 
the  second  simple. 

There  are  two  rifle  ranges  at  the  69th  Regiment  N.  G.  N.  Y. 
Armory,  each  120  yards  (109.72  m.)  in  length:  in  brief,  they 
consist  of  two  tunnels  approximately  10  ft.  (3.04  m.)  high  and 
14  ft.  (4.26  m.)  wide,  walls  of  brick  and  the  ceiling  of  concrete. 
General  illumination  is  provided  in  the  firing  room  by  small  lamps 
and  diffusing  glassware.  Across  the  tunnel  at  both  the  50  and 
75-yard  (45.72  and  68.58  m.)  points  are  placed  mirrored  trough 
reflectors12  pointing  downward,  with  16  25-watt  clear  lamps 
each.  A  short  distance  above  and  in  front  of  the  targets  (which 
are  2  ft.  x  3  ft.  0.60  x  0.91  m.  in  size)  is  placed  a  third  mirrored 
trough12  reflector  giving  an  asymmetrical  distribution.  In  this 
25-watt  lamps  are  placed  on  8  in.  (20.32  cm.)  centers.  Heavy 
crystal  glass  plates  are  set  in  the  floor  in  front  of  each  target  and 
the  direct  light  from  the  reflectors  passes  through  these  and  serves 
to  illuminate  the  telephones  and  enables  the  scorers  in  the  butts 
to  prepare  fresh  targets.  The  night  view  in  Fig.  6  was  taken 
at  the  60-yard  mark  or  approximately  midway  between  the  two 
sets  of  lights  in  the  gallery. 

Princeton  University  has  a  short  range  with  four  targets  which 
are  controlled  from  the  shooting  position  by  means  of  a  con- 
tinuous wire  and  hand  wheel.  Above  each  target  position  is 
located  a  60-watt  clear  lamp  in  a  45  °  angle  aluminum  finish  steel 
reflector13  12  in.  (30.48  cm.)  in  front  of  and  18  in.  (45.72  cm.) 
above.  The  average  illumination  on  the  targets  is  approximately 
12  foot-candles  and  is  quite  even. 

Offices,  Board  and  Company  Rooms. — These  are  in  fact  club 
rooms  with  uses  similar  to  those  of  the  residential  living  room. 
Decorative  yet  comfortable  lighting  should  be  provided;  the  in- 
tensity must  be  fairly  high  and  illumination  even,  owing  to  the 
diversified  requirements ;  for  cards,  reading  or  writing  in  any 


POWELL  AND  ODAY:    ARMORY  AND  GYMNASIUM  LIGHTING      75 1 

part  of  the  room,  piano  playing  and  singing.  There  seems  to  be  a 
tendency  to  decorate  the  rooms  with  dark  finishes  which,  of 
course,  detract  from  the  apparent  brightness  of  the  room.  The  fur- 
nishings of  some  of  these  rooms  are  very  elaborate ;  for  instance, 
over  $8,000  was  expended  on  the  quarters  shown  in  Fig.  9. 
Yet  in  many  such  cases  but  little  attention  has  been  paid  to  the 
lighting  system  and  its  decorative  qualities  have  been  neglected. 
The  fixtures  used  are  often  quite  commercial,  whereas  an  ex- 
cellent field  is  offered  for  special  designs  in  etched  and  colored 
glassware  and  appropriate  metal  work.  One  can  conceive  how 
the  artist  could  work  into  the  glass  decoration,  the  company 
letter,  U.  S.  A.  monogram,  or  the  eagle  in  a  similar  manner  to 
those  emblem  bowls  designed  for  lodge  rooms  with  the  elk's  head, 
square  and  compases,  etc.  Diffused  semi-indirect  lighting  with 
appropriate  fixtures  seems  to  be  one  logical  method  of  treating 
this  part  of  the  building. 

A  view  of  the  quarters  of  Company  K,  71st  Regiment  N.  G. 
N.  Y.,  20  x  45  ft.,  lighted  by  36  25-watt  tungsten  filament  lamps 
in  prismatic  enclosing  globes  '* and  *s  on  "shower"  fixtures  and 
three  arm  brackets,  is  shown  in  Fig.  8.  This  rather  high  wattage 
is  necessitated  by  the  finish  of  walls  and  ceiling. 

Company  Locker  Rooms.— Utility  of  equipment  is  essential 
here  with  lamps  located  between  rows  of  lockers  and  fitted  with 
efficient  reflectors.  Somewhat  higher  illumination  should  be  pro- 
vided in  the  neighborhood  of  the  mirrors  to  facilitate  dressing. 

Company  Store  Rooms.— The  accoutrements  and  spare  supplies 
are  placed  on  racks  or  shelves  and  must  be  fairly  well  illuminated 
for  inspection  and  ease  of  locating  a  given  article.  Efficient 
equipment,  so  placed  that  an  even  intensity  will  be  produced  over 
the  shelves,  should  be  used.  The  work  bench,  which  is  often  lo- 
cated in  this  room,  should  have  one  or  two  well  shaded  localized 
lamps;  for  minor  repairs  and  cleaning  of  arms  and  other  ap- 
paratus are  carried  on  here. 

Offices.— The  lighting  requirements  of  the  private  office  have 
already  been  discussed  before  the  society,  and  the  practise  is 
fairly  well  established.  The  regimental  officers'  rooms  present  no 
especial  problem. 

Corridors.— A  low  intensity  of  light  is  sufficient  here;  in  the 


752     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

less  frequented  parts  of  the  building  there  should  be  sufficient 
light  to  prevent  stumbling;  but  the  main  corridors  should  have 
enough  illumination  to  readily  distinguish  a  passerby,  and  to  avoid 
any  danger  of  accident  in  the  event  of  a  crowded  condition. 

The  band  room,  quartermasters'  and  armorers'  departments 
offer  no  especial  problems  beyond  that  of  the  average  interior. 

Stables. — The  stables  for  the  cavalry  horses  are  often  located 
in  the  basement  of  the  armories ;  comparatively  little  light  is  re- 
quired and  the  lamps  should  be  of  low  candlepower,  so  that  they 
can  be  placed  at  fairly  frequent  intervals  without  excessive  energy 
being  consumed.  The  ceilings  are  usually  low  and  if  too  wide 
spacing  is  used  some  of  the  stalls  will  be  in  deep  shadow.  A 
fairly  satisfactory  arrangement  is  that  of  Squadron  A,  New 
York  City.  There  is  an  aisle  approximately  15  ft.  (4.57  m.)  wide 
between  rows  and  stalls.  Two  rows  of  25-watt  clear  lamps  are 
used  in  each  aisle  without  reflectors  close  to  the  whitewashed 
ceiling,  one  in  front  of  every  second  stall.  This  gives  plenty  of 
light  for  harnessing,  cleaning  and  feeding  the  horses,  and  the 
passageway  is  well  illuminated. 

GYMNASIUMS. 

As  in  the  case  of  the  armory,  the  subject  must  be  divided  into 
several  sections  the  first  of  which  is  the 

Main  Exercising  Floor. — This  is  usually  rectangular  in  shape 
with  a  moderate  height  of  ceiling.  The  arrangement  most  fre- 
quently used  has  the  running  track  as  a  balcony  6  to  8  ft.  wide 
around  all  four  sides  of  the  room.  In  the  center  of  the  main 
floor  are  the  principal  pieces  of  apparatus,  horses,  bucks,  jump- 
ing standards  and  parallel  bars,  while  the  flying  rings  and  hor- 
izontal bars  hang  from  the  main  ceiling.  These  can  usually  be 
pushed  aside  or  drawn  up  out  of  the  way  for  basketball,  indoor 
baseball  and  wrestling,  matches  or  practise.  Below  the  balcony 
are  found  the  exercisers  of  the  various  types  and  racks  for  wands, 
dumb-bells  and  Indian  clubs. 

The  center  part  of  the  space  requires  even  illumination  of  a 
moderate  intensity  with  lamps  so  located  that  the  hanging  appar- 
atus will  not  cause  dense  shadows.  Particular  attention  should 
be  paid  to  the  shielding  of  the  eye  from  the  lamp  filament,  for  one 
is  forced  to  look  upward  a  great  deal  when  playing  basketball. 


75-2- 


*             I       F    r  Hi  r , 

J  ^J      ^    :        ■     IBB 

lair  rrKOL 

Fig.  5.— Night  photograph  U.  S.  Naval  Academy,  Annapolis,[lighted  by  1000-watt  gas- 
filled  tungsten  lamps  with  enameled  steel  reflectors^andjdiffusing  globes. 


Fig.  6.— Night  photograph  rifle  range 
69th  Regiment  N.  G.  N.  Y. 


Fig.  7. — Night  photograph  rifle  range 
Princeton  University. 


Fig.  8.— Night  photograph,  Club  Room  Company  K,  71st  Regiment  N.  G.  N.  Y. 


Fig.  9.  — Night  photograph  main  exercising  room  Princeton  University  gymnasium 

lighted  by  250-watt  bowl-frosted  tungsten  lamps  in  dome 

shaped  enameled  steel  reflectors. 


powell  and  oday:  armory  and  gymnasium  lighting    753 

If  possible  a  slightly  higher  intensity  should  be  provided  in  the 
neighborhood  of  the  basket  to  facilitate  shooting. 

The  illumination  on  the  apparatus  attached  to  the  side  wall 
below  the  track  need  not  be  as  high  as  in  the  open  space,  yet  in 
many  cases  it  is  necessary  to  provide  a  few  outlets  here  with 
small  lamps  properly  shaded  to  prevent  dense  shadows. 

The  general  discussion  on  choice  of  a  unit  given  under  armories 
applies  here  also. 

It  is  a  regretable  fact  that  in  over  50  per  cent,  of  the  gymnas- 
iums examined  an  old  type  of  equipment  was  employed.  This 
consisted  of  a  3,  4,  6  or  12-lamp  cluster  body  with  a  white  glass 
or  enameled  steel  flat  reflector  about  12  or  15  in.  (30.48  or  38.1 
cm.)  in  diameter;  in  most  every  instance  these  were  placed  close 
against  the  ceiling  and  surrounded  by  wire  cages  or  guards.  This 
device  is  unsightly,  gives  a  poor  distribution  of  light,  is  inefficient, 
as  light  from  one  lamp  must  pass  through  the  adjacent  bulbs,  and 
finally  the  whole  of  the  filament  is  exposed  to  the  eye.  It  would 
require  too  much  space  to  tabulate  the  detailed  data  on  all  of  these 
installations  so  the  average  figures  are  alone  presented. 

TABLE  I. — Average  Data  on  Gymnasiums  Lighted  by  Tungsten 
Filament  Lamps  in  Clusters. 


High  Schools 

Colleges 

Y 

.  M.  C  A. 

Number  examined,  19 

Number  examined,  6 

Number  examined,  5 

Min. 

Max. 

Avg. 

Min. 

Max. 

Avg. 

Min. 

Max. 

Avg. 

Area  in  sq.  ft  • 

640 

8,200 

3.56o 

800 

7,600 

3,340 

1,650 

5,600 

3,IOO 

Ceiling  height 

9 

31 

17 

12 

30 

19 

15 

25 

23 

No.  outlets  •  •  • 

3 

43 

15 

3 

5 

4 

4 

18 

9 

No.  lamps .... 

12 

252 

73 

20 

32 

30 

16 

108 

54 

Total  watts. .. 

300 

5,800 

1,635 

500 

3,000 

1,200 

960 

2,700 

1,880 

Watts  per  sq.  ft, 

Actual    

O.26 

1. 1 

0.65 

O.  IO* 

I. OO 

0.63 

0.48 

0.85 

0.62 

Comparative 

O.25 

1.05 

0.63 

O.O95 

0.95 

0.60 

0.46 

O.90 

o.59 

*  It  seems  unfortunate  that  the  minimum  watts  per  sq.  ft.  was  found  in  a  university 
of  first  rank. 

As  examples  of  more  modern  practise  the  following  table  is 
given,  classified  as  to  the  type  of  reflecting  device  employed.  (See 
Appendix  No.  2.) 

Space  is  not  available  for  photographs  showing  all  the  dif- 
ferent types  of  equipment  in  use.  Fig.  9  illustrates  the  use  of 
the  dome  shaped  steel  reflector16  in  the  Princeton  University 
gymnasium.  An  illumination  test  conducted  on  this  floor  showed 
the  following  results.  The  lamps  are  spaced  closer  to  the  center 
than  ordinarily,  as  it  was  desirable  to  have  the  basketball  court  of 


754     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

a  higher  intensity  than  the  sides  of  the  room.  The  minimum  read- 
ing on  a  30-in.  (76.2  cm.)  horizontal  plane  in  the  court  was  2.7 
foot-candles,  the  maximum  3.25  with  an  average  of  2.95.  Read- 
ings close  to  the  wall  apparatus  indicated  an  illumination  of  about 
1  foot-candle  on  the  horizontal  plane. 

Fig.  10  shows  the  Union  College  gymnasium  as  it  appears  by 
night;  a  rather  large  white  enameled  reflector  with  concentric 
corrugations  to  break  up  striations  is  used  above  the  lamps  and 
a  medium  density  opal  deep  bowl  hangs  below,  shielding  the  eye 
and  diffusing  the  light.    Detailed  data  is  given  in  Appendix  No.  2. 

Two  other  installations  of  those  described  should  have  slight 
additional  explanation.  In  the  Columbia  University's  main  gym- 
nasium the  ceiling  above  the  basketball  court  is  largely  openwork 
for  ventilation.  There  are  fifteen  sections,  each  of  which  is 
further  divided  into  nine  squares.  The  metal  work  of  the  center 
square  in  each  section  was  removed  and  250-watt  lamps  in  deep 
mirrored  glass  reflectors19  are  set  with  the  mouth  flush  with  the 
ceiling.  This  directs  a  strong  light  downward  and  the  lamps  are 
not  visible  unless  one  looks  directly  upward. 

Below  the  running  track  or  balcony,  the  under  side  of  which  is 
23  ft.  (7.01  m.)  from  the  floor,  are  placed  14  150-watt  lamps  in 
deep  bowl  medium  density  opal  glass  reflectors.28  These  provide 
good  illumination  on  the  side  wall  apparatus  and  at  the  same 
time  give  some  light  in  the  horizontal  direction,  overcoming  the 
"dead"  effect  which  would  result  if  only  the  strongly  directional 
light  was  employed. 

In  the  Northwestern  University  gymnasium  deep  bowl  mir- 
rored reflectors1"  are  also  used  for  direct  lighting,  but  to  prevent 
the  ceiling  being  dark  these  units  are  placed  on  sheet  iron  cases 
and  two  small  mirrored  reflectors29  with  25-watt  lamps  are  used 
at  each  outlet  for  indirect  illumination.  The  sides  of  the  casing 
are  cut  away  and  art  glass  inserts  reveal  the  monograms  of  the 
university  in  color. 

For  the  twenty-two  buildings,  the  data  regarding  which  are 
given  in  Appendix  No.  2,  the  average  watts  per  sq.  ft.  is  actual 
0.78,  comparative  0.90. 

Swimming  Pool. — These  rooms  are  usually  rectangular  in 
shape  with  white  tile  walls  and  ceiling,  in  fact  from  a  lighting 


Fig.  10.— Xight  photograph  main  floor  Union  College  gymnasium  lighted  by  400-watt 
tungsten  lamps  with  enameled  steel  reflectors  and  diffusing  bowls. 


Fig.  1 1. —Night  photograph  swimming  pool  Princeton  University,  lighted  by  250-watt 
bowl-frosted  tungsten  lamps  and  dome  shapped  enameled  steel  reflectors. 


Fig.  12. — Xight  photograph  swimming  pool  Union  College,  lighted  by  150-watt  bowl- 
frosted,  tungsten  lamps  and  bowl  shaped  light  density  opalescent  glass  re- 
flectors. 


Fig.  13.— Night  photograph  gymnasium  locker  room,  lighted  by  60-watt  tungsten 
lamps  and  flared  prismatic  glass  reflectors. 


POWELL  AND  ODAY:    ARMORY  AND  GYMNASIUM  LIGHTING      755 

standpoint  they  are  practically  modified  Ulbrich  spheres.  The 
type  of  reflecting  device  employed  makes  but  very  little  difference 
in  the  illumination. 

The  following  data  were  obtained  from  examination  of  eight 
pools  with  various  reflecting  devices;  viz.,  prismatic  glass  bowl, 
opalescent  glass  bowl,  mirrored  glass  bowl,  cluster  body,  flat 
white  glass  shade  and  enameled  steel  flat  dome. 

TABLE  II.— Illumination  Data  Indoor  Swimming  Pool. 

Min.  Max.  Avg. 

Area  in  sq.  ft.  760  4,600  2,400 

Ceiling  height 9  24  13.5 

Total  watts    400  3,150  1,140 

Watts  per  sq.  ft.: 

Actual 0.31  0.70  0.47 

Comparative  0.30  0.78  0.50 

The  swimming  pool  at  Princeton  University  is  approximately 
35  x  130  ft.  (9.14  x  39.62  m.)  and  is  lighted  by  seven  250-watt 
bowl- frosted  lamps  in  enameled  steel  dome-shaped  reflectors16 
located  in  a  row  down  the  center  of  the  room  between  girders.  By 
means  of  a  temporary  bridge  illumination  readings  were  taken 
on  the  surface  of  the  water,  giving  an  average  of  1.7  foot-candles. 
It  is  to  be  noted  how  clearly  visible  is  the  floor  of  the  pool  al- 
though containing  from  4  to  10  ft.  of  water.     (See  Fig.  11.) 

The  pool  at  Union  College,  Schenectady,  as  it  appears  by  night 
is  pictured  in  Fig.  12;  150  watt  bowl-frosted  lamps  are  used  in 
light  density  opalescent  glass  reflectors,  bowl  shaped  10  in.  in 
diameter,30  placed  in  three  rows,  on  equal  spacings.  The  dimen- 
sions are  45  x  100  ft.  (13.71  x  30.48  m.)  giving  0.70  watt  per 
sq.  ft.  Here  also  the  lanes  marked  on  the  bottom  of  the  pool  are 
clearly  visible. 

Shower  Room. — These  present  no  especial  problem  in  regard 
to  the  lighting,  but  on  account  of  the  high  percentage  of  vapor 
present  in  the  air  it  is  advisable  that  moisture-proof  electric  fit- 
tings be  employed. 

Locker  Rooms. — Double  rows  of  lockers,  with  aisles  between 
in  most  cases,  extend  to  the  ceiling.  The  athletes  dress  in  these 
aisles.  Mirrors  are  ordinarily  placed  at  the  ends  of  rows  on  the 
main  aisle.  Low  ceilings  of  light  color  make  practical  the  use  of 
low  candlepower,  all-frosted  lamps  without  reflectors,  with  sock- 


756     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

ets  set  flush.  In  a  number  of  the  installations  examined  25-watt 
lamps  are  used  on  8  ft.  centers.  Larger  lamps  with  suitable  re- 
flectors localized  near  the  mirrors  on  the  main  aisle  are  essential. 
A  60-watt  lamp  with  bowl-shaped  dense  opal  reflector  between 
pairs  of  mirrors  proves  satisfactory. 

The  night  view  in  Fig.  13  shows  a  locker  room  with  single  tier 
lockers  in  which  general  illumination  is  provided.  The  finish  is 
dull  gray  throughout.  Sixty-watt  clear  tungsten  filament  lamps 
in  flared  prismatic  reflectors22  are  placed  close  to  the  11  ft. 
3.35  m.)  ceiling  on  8  x  14  ft.  (2.43  x  4.26  m.)  centers,  giving  one 
half  watt  per  sq.  ft. 

Running  Track. — In  most  cases  this  extends  around  the  main 
exercising  room,  but  the  one  at  Columbia  University  is  some- 
what longer  than  the  average  and  the  major  portion  is  in  the 
form  of  a  rather  low  tunnel  10  ft.  high  by  11  ft.  wide.  Glaring 
light  sources  would  prove  very  objectionable  here  so  60-watt 
clear  tungsten  filament  lamps  are  used  in  12  in.  opalescent  glass 
semi-indirect  dishes31  on  28- ft.  (8.53  m.)  centers. 

Wrestling,  Boxing  and  Fencing  Rooms. — The  finish  is  fre- 
quently light  and  the  ceiling  smooth ;  the  room  is  often  decorated 
with  prizes,  pennants,  etc.,  so  the  decorative  element  of  the  light- 
ing becomes  of  more  importance.  The  indirect  systems  are  quite 
applicable. 

A  description  of  the  fencing  room  at  Columbia  University  will 
illustrate  a  typical  case;  the  dimensions  are  26  x  38  ft.  with  a 
14  ft.  white  ceiling;  two  outlets  are  provided  and  400  watt  gas- 
filled  tungsten  filament  lamps  in  leaded  white  glass  semi-indirect 
dishes32  20  in.  in  diameter  furnish  very  satisfactory  illumination. 
The  energy  consumption  is  0.8  watt  per  sq.  ft.  actual  compara- 
tive 1. 14. 

Medical  Director's  Office. — This  room  has  the  ordinary  require- 
ments for  office  lighting,  providing  plenty  of  light  in  all  parts  of 
the  room  for  physical  examinations.  Totally  indirect  lighting 
is  employed  in  quite  a  number  of  the  installations  visited,  averag- 
ing approximately  one  watt  per  square  foot. 

Squash  Court. — These  are  usually  rectangular  in  shape  and  ap- 
proximately 15  x  30  ft.  (4.57  x  9.14  m.)  in  size.  Many  have 
white  ceilings  which  will  permit  the  use  of  totally  indirect  or 


POWELL  AND  ODAY:    ARMORY  AND  GYMNASIUM  LIGHTING      757 

semi-indirect  lighting.  Since  the  walls  are  finished  in  dark  red, 
an  imitation  of  mahogany,  quite  a  high  wattage  will  be  required 
with  either  of  the  above  systems.  The  Squash  Club  of  New 
York  is  experimenting,  at  the  present  time,  with  semi-indirect 
bowls  and  gas  filled  tungsten  filament  lamps.  The  courts  at  the 
Yale  Club  are  equipped  with  porcelain  enameled  totally  indirect 
fixtures.  It  is  quite  important  to  avoid  glare  and  reflections  from 
the  varnished  surfaces. 

Handball  Court. — The  board  must  be  well  lighted,  and  a  rather 
high  component  of  illumination  on  imaginary  vertical  planes  cov- 
ering the  whole  area  of  play  should  be  provided,  as  it  is  necessary 
to  see  the  ball  in  its  travel.  The  angle  type  reflector  meets  these 
conditions  excellently,  completely  shielding  the  eye,  for  the  player 
is  always  looking  forward.  The  courts  at  Columbia  University 
are  24  x  21  ft.  (7.31  x  6.40  m.)  with  a  13  ft.  white  ceiling.  Two 
250-watt  lamps  are  placed  on  each  court  close  to  the  ceiling  in 
angle  type  porcelain  enameled  steel  reflectors,33  giving  slightly 
over  one  watt  per  sq.  ft.  for  the  effective  area. 

In  the  Newark  Y.  M.  C.  A.  the  board  is  located  below  the 
running  track  and  is  especially  lighted  by  25  watt  lamps  in  half 
hand  metal  shades  on  the  under  side  of  the  track,  spaced  on  4-ft. 
centers.  The  general  illumination  of  the  room  is  adequate  when 
one  is  playing  back. 

Trophy  Room. — This  is  usually  quite  elaborate  and  decorative 
lighting  systems  are  desirable.  On  account  of  the  variety  of 
decoration,  it  is  inadvisable  to  present  any  average  figures. 

ACKNOWLEDGMENT. 

The  authors  express  their  appreciation  of  the  assistance  in  the 
compilation  of  the  paper  rendered  by  the  members  of  the  De- 
partment of  Water  Supply,  Gas  &  Electricity  of  the  City  of  New 
York,  Mr.  G.  B.  Nichols,  chief  engineer  of  the  New  York  State 
Architect's  Office  and  Messrs.  G.  H.  Stickney,  R.  E.  Harrington 
and  E.  F.  Carrington  of  the  Edison  Lamp  Works. 


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POWELL  AND  ODAY  :    ARMORY  AND  GYMNASIUM  LIGHTING      759 

APPENDIX  III. 
i.  Holophane  Realite  06260  V.  S. 

2.  Holophane  prismatic  reflector  XE-500. 

3.  Holophane  prismatic  reflector  XL250. 

4.  Benjamin  fixture  6158. 

5.  Holophane  Sudan  reflector  1224-16". 

6.  Holophane  prismatic  reflector  XE-100. 

7.  Benjamin  fixture  6124. 

8.  G.  E.  Novalux  form  1  157078. 

9.  Benjamin  fixture  6179. 

10.  Benjamin  fixture  6199. 

11.  Wheeler  multiple  Mazda  fixture  2702. 

12.  Frink  mirrored  reflectors,  marketed  by  the  H.  W.  Johns-Manville  Co. 

13.  Ivanhoe  metal  reflector  AL-60. 

14.  Holophane  pendant  ball  3063. 

15.  Holophane  Stalactite  3354. 

16.  Ivanhoe  metal  DED-250. 

17.  Benjamin  flat  cone  5503. 

18.  Ivanhoe  metal  DED-150. 

19.  National  X-Ray  Beehive  765. 

20.  Ivanhoe  metal  BEI-500. 

21.  Luna  reflector  14,  made  by  the  H.  Northwood  Glass  Co. 

22.  Holophane  distributing  reflector  6072. 

23.  Doric  hemisphere  1234,  marketed  by  the  Lighting  Studios  Co. 

24.  Ivanhoe  promotion  fixture  758. 

25.  Holophane  prismatic  reflector  XE-150. 

26.  Holophane  glass  reflector  2633. 

27.  Mazda  Monolux  diffuser  unit  1329. 

28.  Holophane  Sudan  glass  reflector  01225-10". 

29.  National  X-Ray  reflector  E-60. 

30.  Holophane  Druid  glass  reflector  3024-10". 

31.  Camia  dish,  marketed  by  the  Opalux  Co. 

32.  Mazda  Monolux  fixture  3320. 

33.  Ivanhoe  metal  REL-250. 


760     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

DISCUSSION. 

Mr.  G.  B.  Nichols  :  Mr.  Powell's  paper  on  armory  and  gym- 
nasium lighting  appears  to  have  come  before  this  Society  at  a 
very  opportune  time,  in  that  probably  within  the  next  year  there 
will  be  a  large  number  of  armories  started  throughout  the  coun- 
try, following  up  the  movement  of  increasing  the  facilities  of  the 
armories,  which  has  been  advocated  since  the  European  War. 
This  paper  I  believe  to  be  very  complete  in  obtaining  the  latest 
data  on  the  armories  throughout  the  East,  in  which  the  latest 
equipment  has  been  installed.  The  paper  will  also  be  of  consid- 
erable interest  in  designing  the  equipment  for  the  new  Eighth 
Regiment  Coast  Artillery,  referred  to  in  the  paper  as  being  the 
armory  with  180,000  square  feet  of  floor  area  in  the  drill  shed, 
which  is  probably  the  largest  armory  that  will  be  constructed  in 
this  country  for  a  considerable  period.  The  size  of  this  armory 
can  be  conceived,  when  we  say  it  is  three  and  one  half  times  the 
size  of  Madison  Square  Garden. 

In  the  lighting  of  armories,  as  brought  out  in  the  paper,  con- 
siderable attention  should  be  paid  to  the  character  of  the  floor, 
for  in  armories  designed  for  calvary  use,  generally  some  form 
of  tan  bark  is  installed  and,  on  account  of  the  absorbing  qual- 
ities of  this  material,  double  the  foot-candle  intensity  will  be  re- 
quired to  obtain  the  same  lighting  effect.  Up  to  four  years  ago 
the  majority  of  armories  of  New  York  State  were  lighted  by 
incandescent  and  gas  lamps  and,  in  a  few  cases,  by  arc  lights.  At 
this  time  considerable  study  was  carried  on,  particularly  in  New 
York  City,  to  determine  the  advisability  of  installing  flame  arcs 
and  a  number  of  installations  were  made  at  that  time.  It  is  to 
be  regretted  that  these  installations,  which  have  been  in  use  such 
a  short  period,  should  now  be  supplanted  with  incandescent 
lamps  of  the  gas-filled  type. 

One  of  the  armories  mentioned  in  the  paper,  namely,  Troop  C 
Armory  in  Brooklyn,  which  is  one  of  the  newer  armories  in  New 
York,  during  the  last  four  years  has  had  three  different  types  of 
lighting  units  installed  in  the  riding  ring.  Originally  there  were 
114  enclosed  arc  lamps.  Three  years  ago  this  installation  was 
changed  to  flaming  arcs,  14  having  a  total  wattage  of  approxi- 
mately   18,000   watts   being   installed.      In   this   installation   the 


ARMORY   AND   GYMNASIUM    LIGHTING  761 

average  foot-candle  intensity  for  the  entire  room  was  3.6;  the 
maximum  was  5.5,  and  the  minimum  1.2.  The  1.2  readings, 
however,  were  at  the  very  outer  edge  of  the  riding  ring  and  are 
of  slight  importance.  The  watts  per  square  foot  figure  was  0.093. 
The  estimated  cost  of  lighting  for  this  armory  for  one  year,  in- 
cluding maintenance  for  this  installation  was  $1,348.55. 

A  year  ago  this  installation  of  flame  arcs  was  removed  and 
gas-filled,  incandescent  lamps  were  installed,  which  installation 
is  the  one  mentioned  in  Mr.  Powell's  paper  as  having  a  total 
wattage  of  22,500  watts.  Photometric  readings  showed  the  fol- 
lowing intensities:  average  3.24,  maximum  4,  minimum  1.82. 
Watts  per  square  foot  0.129.  The  estimated  total  cost  of  lighting, 
including  maintenance  per  year  and  lamps  replaced,  is  $1,235.23, 
being  a  slight  decrease  from  that  of  the  flame  arc  installation. 

On  comparing  the  two  systems,  the  slight  difference  in  annual 
cost  is  very  little  importance,  the  main  feature  being  to  decide 
the  relative  merits  of  the  two  installations.  The  consensus  of 
opinion  was  that  the  gas-filled  lamps  are  preferable  to  flame  arcs 
for  the  following  reasons : 

1.  Colors  are  not  distorted  to  such  an  extent  under  the  gas- 
filled  lamps.  This  is  particularly  objectionable  where  the  arm- 
ories are  used  for  dress  occasions,  where  there  is  considerable 
objection  to  having  the  colors  of  the  uniforms  very  much  dis- 
torted. 

To  add  to  the  information  given  in  the  schedule,  I  would  state 
that  photometric  tests  have  been  made  on  the  following  armories : 

Troop  C,  3.24  foot-candles;  10th  Regiment  Armory,  Albany, 
2.32  foot-candles;  47th  Regiment,  small  shed,  1.46  foot-candles. 
It  appears  that  the  47th  Regiment  lighting  should  be  increased,  as 
this  installation  was  not  designed  for  the  equipment  now  in- 
stalled. 

I  would  also  call  to  your  attention  the  State  Armory  at  Albany, 
mentioned  in  the  paper,  which  is  typical  of  what  might  be  done 
in  an  armory  already  lighted  by  incandescent  lamps.  At  this 
armory,  two  gas-filled  lamps  were  installed  in  place  of  a  lighting 
fixture  containing  eight  250-watt  tungsten  lamps.  The  old  fix- 
tures were  simply  taken  down  and  new  ones  installed  in  their 
place,  with  two  lamps  at  each  outlet,  the  fixtures  simply  being 


762     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

suspended  by  wire  cables  from  the  overhead  trusses,  making  a 
very  inexpensive  outfit.  This  change  could  be  made  at  almost 
any  armory  at  a  slight  extra  expense,  which  would  probably  be 
saved  during  the  first  year. 

Considerable  improvement  I  believe  is  possible  in  the  method 
of  trimming.  At  the  present  time  the  most  practical  way  seems 
to  be  to  trim  by  extension  ladders,  which  is  done  with  consider- 
able difficulty,  the  lamps  being  generally  about  35  feet  from  the 
floor.  As  yet  no  successful  lowering  device  of  moderate  cost  has 
been  developed. 

In  reference  to  gymnasium  lighting,  I  would  state  that  in  my 
judgment  the  values  given  in  the  paper  are  the  minimum  rather 
than  the  average  for  good  lighting.  In  discussing  this  form  of 
lighting  with  gymnasium  instructors,  it  appears  to  be  the  con- 
sensus of  opinion  that  the  illumination  should  be  very  high  and 
well  distributed,  on  account  of  the  vast  work  being  carried  on. 
In  some  gymnasiums  the  foot-candle  intensities  run  as  high  as 
6,  which  is  not  excessive. 

Would  it  not  be  possible  to  reach  the  lighting  equipment  in  an 
armory  from  a  walk-way  constructed  in  the  trusses  in  the  roof 
and  thus  eliminate  the  necessity  of  lowering  the  lamps  ?  It  would 
seem  that  the  girder  construction  and  wide  spacing  of  a  few 
large  units  would  make  this  not  only  possible,  but  probably  most 
advisable.  I  believe  the  Colesium  in  Chicago  has  such  an  ar- 
rangement, with  a  main  walk-way  lengthwise  of  the  building, 
protected  by  a  pipe  hand-rail  on  either  side  and  branch  walk- 
ways crosswise  the  building. 

Mr.  L.  C.  Porter  :  Reference  has  been  made  in  this  paper  to 
the  lighting  of  rifle  ranges.  This  is  a  subject  which  warrants  a 
great  deal  more  study  than  has  been  given  to  it.  The  ultimate 
aim  of  this  indoor  practise  is  to  teach  a  man  to  shoot  out-of- 
doors,  to  handle  a  rifle,  to  load,  to  pull  the  trigger,  to  properly 
sight,  etc.  In  most  rifle  ranges  the  conditions  are  vastly  differ- 
ent from  what  they  are  out-of-doors.  It  is  very  common  to  have 
the  target  highly  lighted  and  the  space  between  the  targets  and 
the  shooter  entirely  dark;  sometimes  there  is  enough  light  to  en- 
able the  shooter  to  load  the  gun.  Experiments  which  have  been 
undertaken  seem  to  indicate  that  it  may  be  better  practise  to  have 


ARMORY   AND  GYMNASIUM    LIGHTING  763 

some  illumination  between  the  man  and  the  target,  thus  at  least 
approximating  a  little  more  closely  outdoor  conditions. 

One  method  that  has  been  successfully  tried  to  accomplish  this 
is  by  the  use  of  flood  lighting,  by  projecting  a  beam  of  light  from 
behind  the  shooter  onto  the  target.  There  will  be  enough  stray 
light  to  give  some  illumination  the  entire  length  of  the  gallery.  Of 
course,  in  this  case  care  must  be  taken  that  the  target  does  not 
reflect  the  light  specularly  back  to  the  shooter. 

Mention  has  been  made  of  the  Yale  gymnasium ;  being  a  Yale 
man  myself  I  have  done  some  work  in  that  gymnasium  and  I 
think  that  one  word  of  caution  should  be  given  to  those  who  are 
working  on  gymnasium  lighting.  It  seems  to  me  that  it  is  neces- 
sary to  have  light  of  high  intensity  in  gymnasiums,  especially  in 
ring  work  and  bar  work.  However,  it  is  of  extreme  importance 
to  have  it  well  diffused ;  under  no  circumstances  should  a  glaring 
light  source  be  used.  There  are  many  times  when  a  man  is  fac- 
ing the  ceiling  and  the  light  source,  and  in  tumbling  and  ring 
work,  as  has  been  mentioned,  it  is  necessary  for  him  to  see  very 
quickly,  to  catch  the  flying  ring.  In  such  cases  glaring  light 
sources  may  result  in  serious  accidents. 

Mr.  R.  B.  Ely  :  I  should  like  to  ask  Mr.  Powell  as  to  his  ex- 
perience with  lamps  used  over  swimming  pools,  whether  he  ever 
uses  enclosing  globes.  I  think  enclosing  globes  would  take  care 
of  and  eliminate  the  danger  of  exploding  and  broken  lamps.  The 
broken  glass  may  be  the  cause  of  accidents. 

I  know  of  a  case  where  a  man  brought  suit  for  having  one  of 
his  patrons  cut  by  a  piece  of  glass  in  the  bottom  of  the  swimming 
pool,  and  another  instance  where  a  young  man  started  to  fool 
with  a  lamp  and  accidentally  touched  the  base  and  was  killed. 

Mr.  A.  L.  Powell  :  One  of  the  gentlemen,  who  has  discussed 
the  paper,  mentioned  that  the  intensity  of  illumination  in  the  23rd 
Regiment  Armory,  Brooklyn,  was  somewhat  low.  An  examina- 
tion of  the  data  presented  shows  this  to  be  undoubtedly  true,  for 
there  is  but  0.25  watt  per  sq.  ft.,  whereas  the  average  value  is 
approximately  0.5  watt  per  sq.  ft.  using  the  gas-filled  tungsten 
lamps.  This  average  value,  we  believe,  will  give  satisfactory 
results  under  ordinary  conditions. 

It  was  suggested  that  a  platform  or  run-way  be  built  among  the 


764     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

roof  trusses,  from  lamp  to  lamp,  instead  of  providing  lowering 
devices.  One  speaker  pointed  out  the  greatly  increased  invest- 
ment necessary  to  build  a  platform  strong  enough,  and  the  safety 
factor  must  also  be  very  carefully  considered,  for  in  most  in- 
stances the  iron  work  is  from  50  to  100  ft.  above  the  ground. 

Floodlighting  may  be  of  use  for  those  rifle  ranges  with  no  ob- 
structions, but  in  some  galleries  the  construction  is  such  that  this 
type  of  lighting  would  be  impracticable.  These  particular  cases 
are  arranged  so  that  but  one  target  can  be  seen  from  the  gun  posi- 
tion. This  is  done  by  placing  partitions  or  shields  at  points  along 
the  gallery,  with  apertures  in  the  line  of  the  target  acting  in  the 
same  manner  as  the  light  screens  on  a  standard  photometer  bar. 
One  has  to  be  directly  in  line  with  these  series  of  holes  in  order 
to  see  the  target,  else  all  that  is  visible  is  the  black  shield  (see 
Fig.  6.)  A  projector  unit  would  not  serve  in  this  case  unless 
there  were  one  for  each  target. 

Other  speakers  called  attention  to  the  fact  that  data  were  pre- 
sented on  a  number  of  gymnasiums  which  were  far  from  very 
well  illuminated,  as  indicated  in  the  minimum  values  given.  This 
is  indeed  too  true,  particularly  in  reference  to  those  exercising 
rooms  listed  in  Table  1,  and  as  is  stated  in  the  paragraph  above 
this  table,  it  is  to  be  hoped  that  these  conditions  will  be  remedied. 
There  is  a  large  field  open  for  improvement  in  this  class  of  light- 
ing. It  can  be  seen  that  quite  a  number  of  gymnasiums  were 
visited  and  those  described  under  Appendix  2  represent  the  best 
conditions  met  as  far  as  proper  equipment  and  suitable  intensity 
of  light  are  concerned.  Even  in  this  table  there  are  but  few  ex- 
amples of  what  might  be  termed  the  best  lighting. 

The  authors'  attention  has  never  been  called  to  the  danger  of 
broken  glass  from  the  lamps  about  swimming  pools  and  in  locker 
and  wash  rooms.  In  none  of  the  gymnasiums  visited  was  there 
any  special  provision  made  to  protect  the  lamp  from  water 
and  to  prevent  glass  falling  to  the  floor.  It  does  not  seem  that 
there  should  be  any  more  appreciable  danger  in  walking  about 
these  rooms  in  one's  bare  feet  than  in  walking  about  the  bath 
room  in  the  home  which  is  ordinarily  lighted  by  a  standard  type 
of  fixture  and  incandescent  lamp. 

Mr.  G.  B.  Nichols:     In  reference  to  the  breakage  of  lamps 


ARMORY   AND  GYMNASIUM    LIGHTING  765 

and  globes  in  swimming  pools,  this  breakage  has  not  been  of  any 
great  importance,  unless  in  swimming  pools  where  games  are 
carried  on,  which  are  likely  to  break  the  globes.  In  these  in- 
stances, it  seems  preferable  to  install  some  form  of  wire  cage 
over  the  fixture.  I  believe,  however,  that  these  conditions  can 
be  met  to  a  considerable  extent  by  using  some  form  of  metal  re- 
flector; the  breakage  of  the  lamps  is  not  a  serious  matter. 


766     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

PRACTICAL  HINTS  ON  THE  USE  OF  PORTABLE 
PHOTOMETERS.* 


BY  W.  F.  LITTLE. 


Synopsis:  This  paper  outlines  a  desirable  procedure  in  the  conduct 
of  photometric  tests  with  portable  apparatus.  It  discusses  the  planning 
of  a  survey;  a  description  of  the  condition  of  the  installation  and  pre- 
cautions which  should  be  taken  to  make  the  results  useful;  a  method  of 
testing  candlepower,  illumination  intensity  and  brightness;  good  practise 
in  the  maintenance  of  photometric  apparatus ;  photometric  errors  inhering 
in  photometers  and  accessories,  together  with  means  of  avoiding  them; 
photometric  accuracy  and  test  results. 


In  the  use  of  portable  photometers  the  same  photometric  prin- 
ciples prevail  as  in  the  operation  of  stationary  or  laboratory  types 
of  photometers ;  indeed,  a  portable  photometer  is  no  more  than 
a  stationary  photometer  reduced  in  size  and  with  a  test-plate  sub- 
stituted for  one  of  the  photometric  surfaces.  The  only  principle 
peculiar  to  the  use  of  portable  photometers  is,  therefore,  that  of 
the  cosine  law  as  applied  to  the  test-plate. 

The  practise  of  photometry  as  applied  to  portable  photometers 
differs  radically  from  that  followed  with  stationary  photometers, 
in  that  the  conditions  of  use  are  not  standardized,  the  purpose 
and  the  method  of  test  are  usually  not  so  definitely  indicated,  and 
the  practitioner  is  often  less  experienced.  Also,  the  auxiliary 
instruments  used  in  connection  with  portable  photometers  are 
frequently  less  accurate  than  those  used  with  stationary  pho- 
tometers. 

These  differences,  in  combination,  contribute  to  surround  the 
use  of  portable  photometers  with  a  liability  to  error  which  is 
greater  than  that  experienced  in  the  use  of  stationary  photometers. 
The  successful  use  of  portable  photometers  demands  more  exer- 
cise of  good  judgment,  and  a  more  general  knowledge  of  photo- 
metric principles  and  practise  than  is  usually  required  of  the 
photometrist  in  routine  laboratory  work.  In  view  of  these  facts 
it  has  been  thought  desirable  to  present  the  results  of  the  writer's 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,    September  20-23,    I9I 5- 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


LITTLE:     USE  OF   PORTABLE   PHOTOMETERS  767 

experience  in  the  use  of  portable  photometers,  making  it  avail- 
able to  others  who  may  engage  in  this  class  of  testing. 

AN  ILLUMINATION  SURVEY. 
In  the  conduct  of  an  illumination  test  the  first  fundamentally 
important  consideration  is  to  arrive  at  a  correct  understanding 
of  the  purpose  of  the  lighting  installation  and  of  the  purpose  of 
the  test.  It  is  then  important  to  determine  whether  the  installa- 
tion tested  is  representative  and  whether  the  samples  or  sample, 
if  only  a  portion  of  the  installation  is  tested,  are  typical  of  the 
whole.  The  test  should  be  so  planned  and  described  that  there 
shall  be  a  minimum  of  danger  that  any  incorrect  conclusions  will 
be  drawn.  These  statements,  though  generalities,  may  be  applied 
in  specific  cases  and  when  applied  will  contribute  to  the  useful- 
ness of  the  data  obtained  through  illumination  tests. 

DESCRIPTION  OF  INSTALLATION  AND  CONDITIONS. 

The  photometrist's  note-book  should  contain  a  full  description 
of  the  important  features  of  the  installation  including  the  con- 
dition of  pressure  or  voltage  and  consumption,  the  condition  of 
illuminants  and  other  accessories  with  special  references  to  their 
suitability  for  the  service,  their  cleanliness  and  age;  variables 
affecting  the  test  as,  for  example,  pressure  fluctuations  with  arti- 
ficial illuminants,  change  in  sky  brightness  in  daylight  tests,  etc. ; 
description  of  the  environment  including  dimensions,  finish  and 
location  of  light  sources  in  indoor,  and  corresponding  descriptions 
in  outdoor  tests.  The  refinement  to  which  this  description  is 
carried  must,  of  course,  depend  upon  the  nature  and  purpose  of 
the  survey.  When  the  measurments  are  of  illumination  inten- 
sity or  brightness,  the  description  should  include  a  statement  of 
the  total  flux  and  of  the  distribution  characteristic  of  the  light 
source. 

The  description  should  give  very  specifically  the  location  of 
the  installation  under  test  so  that  it  may  be  readily  identified  and 
conditions  duplicated  at  any  time.  It  should  have  in  view  the 
purpose  of  affording  a  basis  for  intelligent  discussion  of  results 
after  the  tests  are  complete. 

OPERATING  DATA. 
It  is  important  to  measure  the  pressure  and  consumption  values 


768     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

of  the  illuminants.     From  such  data  deviations  from  standard 
initial  operating  conditions  can  be  allowed  for. 

TESTS  OF  CANDLEPOWER. 

Location  of  Photometer. — It  is  to  be  presumed  that  in  measure- 
ments of  candlepower  a  certain  angle  or  series  of  angles  in  a  ver- 
tical plane  is  stipulated  for  investigation.  It  is  important  to 
know  whether  or  not  the  source  tested  has  symmetrical  distribu- 
tion at  such  angles.  If  not,  care  should  be  taken  to  select  a  di- 
rection in  which  the  intensity  is  the  mean  for  the  angle  investi- 
gated. If  this  is  not  feasible  the  tests  should  be  made  in  a  num- 
ber of  directions.  It  is  good  practise  where  a  second  photometer 
is  available  to  make  simultaneous  tests  on  opposite  sides  of  the 
illuminant. 

Stray  Light. — An  important  step  which  should  be  taken  in 
preparing  for  measurements  of  candlepower  is  the  proper  screen- 
ing of  the  photometer  against  stray  light.  A  portable  photometer 
is  likely  to  be  used  in  the  measurements  of  candlepower  else- 
where than  in  a  well  equipped  laboratory  where  all  proper  ar- 
rangements are  provided.  The  conditions  for  the  test  are  likely 
to  be  improvised  and  the  need  for  proper  precaution  against  stray 
light  is,  therefore,  the  greater.  It  is  important  to  look  from  or 
through  the  photometer  toward  the  light  source  and  make  certain 
that  no  other  light  source  illuminates  the  test-plate,  and  that  no 
surface  reflects  an  appreciable  amount  of  light  upon  it.  A  sim- 
ple procedure  is  to  introduce  a  suitable  lens  between  the  pho- 
tometer device  and  the  light  source  which  will  enlarge  the  field  of 
view  permitting  the  easy  examination  of  the  entire  field.  Most 
portable  photometers  are  equipped  with  one  or  more  screens 
near  the  test-plate  which  limit  the  area  to  which  the  test-plate 
is  exposed.  Frequently,  however,  additional  screens  are  neces- 
sary to  cut  off  all  stray  light. 

Alignment  of  Photometer. — The  tubes  carrying  the  test-plate 
of  the  photometer,  and  the  screens,  limit  the  light  falling  on  the 
test-plate,  so  that  the  photometer  can  be  aimed  directly  at  the 
lamp.  If  the  test-plate  employed  is  placed  across  the  angle  of 
the  tube  so  that  the  rays  fall  upon  it  at  45 °,  the  position  of  the 
test-plate  is  particularly  important.  Unless  suitable  facilities  are 
provided,  much  time  may  be  consumed  in  properly  aligning  a 


little:   use;  of  portable  photometers  769 

photometer  in  candlepower  measurements.  A  method  which  ex- 
perience has  shown  to  be  convenient  consists  in  the  use  of 
the  elbow  tube  of  the  photometer  with  a  simple  telescope  and 
cross  hairs  described  elsewhere.  With  a  protractor  and  plumb 
bob  attached  to  such  a  telescope  a  ready  means  of  determining  the 
height  of  the  lamps  is  at  hand,  also  its  distance  from  the  photom- 
eter may  be  determined.  The  protractor  also  affords  a  quick  and 
accurate  measurement  of  the  angle  between  the  vertical  and  the 
direction  of  light,  without  the  necessity  of  accurately  leveling  the 
photometer. 

Test-plate. — Both  reflecting  and  transmitting  test-plates  are 
used  in  candlepower  measurements.  As  the  subject  of  test-plates 
is  to  be  discussed  before  this  convention  in  another  paper1  the  dis- 
cussion in  this  connection  will  be  limited.  The  test-plate  set  at 
45°  to  the  rays  of  light  suffers  under  the  disadvantages  of  requir- 
ing more  accurate  alignment,  but  has  the  advantage  of  being  more 
easily  screened  and  of  rendering  a  brighter  field. 

Calculations. — In  the  conduct  of  candlepower  tests  it  is  of 
course  necessary  to  know  the  angle  of  measurement  and  the  dis- 
tance between  the  lamp  and  the  photometer. 

Computations  may  be  based  upon  the  following : 


C.P.  =F.C.X</21 

d2  =  A2  +  b2 


d- 


b    \2  \  Fi§- 


Vsina/  J 


LAMP 


PHOTOM 

To  determine  h  where  the  height  cannot  be  measured  directly, 
a  base  may  be  laid  off  and  from  the  angle  determined,  h  can  be 
computed. 


LAMP 


h  =  a  Tan.  /?     Fig.  2. 

"*  AT 

The  photometer  may  be  located  so  as  to  measure  any  angle  by 

1  Sharp,  C  H.,  and  Little,  W.  F.,  A  compensated  illumination  test-plate. 


770     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

first  determining  the  height  and  then  laying  off  the  proper  base. 

Tan.  a 
b=— IT 

In  all  computations  it  is  to  be  remembered  that  the  distances 
are  measured  vertically,  and  horizontally,  and  they  are  determined 
with  respect  to  the  test-plate  and  not  the  floor  or  street  level. 

Means  of  determining  street  grades  and  exact  location  of 
lamps  are  discussed  later. 

The  signs  and  tangents  are  used  in  the  above  formula  as  they 
may  be  read  directly  from  a  slide  rule. 

ILLUMINATION  MEASUREMENTS. 

It  is  obvious  that  illumination  measurements  should  be  made 
in  a  plane,  the  illumination  of  which  is  the  principal  purpose  of 
the  installation.  This  refers  to  height  of  horizontal  plane  or  to 
inclination  of  other  planes  which  may  be  studied.  In  some  cases 
it  may  be  desirable  to  determine  the  flux  density  of  the  light 
incident  on  a  surface  inclined  to  the  horizontal.  As  in  the  case 
of  the  study  of  the  illumination  of  school  desks,  show  windows, 
machinery,  etc. 

During  the  test  it  is  very  essential  to  record  service  conditions 
simultaneous  with  the  photometer  readings;  for  example,  the 
voltage  should  be  noted  for  each  reading  or  the  averaging  voltage 
for  a  series  of  readings.  With  the  data  and  the  characteristic 
curves  of  the  illuminants  the  measurements  may  be  corrected  to 
the  standard  condition  (Fig.  3). 

Selection  of  Test  Stations. — Practise  in  the  selection  of  test 
stations  falls  into  two  general  classes :  in  the  one  the  purpose  is 
to  determine  the  total  flux  of  light  on  a  given  plane  and  to  employ 
this  value  to  determine  the  illumination  efficiency  of  the  installa- 
tion. In  the  other  the  purpose  is  to  determine  the  flux  density  at 
important  points  without  the  intention  of  making  a  compete  study 
of  the  installation.     Each  practise  has  its  own  field  of  usefulness. 

If  irregular  or  special  locations  for  test  stations  are  selected 
it  is  usually  impracticable  to  arrive  at  a  figure  for  the  illumination 
efficiency. 

In  the  writer's  work  it  has  usually  been  desirable  to  make  the 
more  complete  study  of  an  installation  from  which  the  efficiency 
may  be  determined,  and  the  practise  has  been  to  select  syste- 


LITTLE :     USE   OF    PORTABLE    PHOTOMETERS 


771 


matically  arranged  test  stations,  and  to  supplement  them  by  such 
measurements  as  may  be  desired,  at  points  of  special  significance. 
In  such  practise  it  is  customary  to  divide  the  floor  space  beneath 
the  illuminants  into  equal  areas,  the  illuminants  being  over  the 
intersection  of  boundary  lines  of  such  areas  rather  than  over  the 
centers  of  the  areas.  Fig.  4  illustrates  such  a  layout  for  a  bay 
illuminated  by  four  lamps).  The  numerical  average  of  the  hori- 
zontal illumination  intensities  for  test  stations  so  disposed  will  be 
the  mean  flux  density  for  the  entire  plane  if  a  sufficient  number 
of  test  stations  are  selected.     For  the  construction  of  illumination 


95     96     97      96     99     100     101      102    103     104-    105 


curves,  and  for  further  information  regarding  the  uniformity 
of  the  lighting,  it  is  usually  desirable  to  supplement  these  regu- 
larly spaced  test  stations  by  other  measurements  made  perhaps 
directly  beneath  lamps,  at  points  where  a  minimum  intensity  is 
anticipated,  and  at  other  points  of  special  interest.  Measure- 
ments directly  beneath  the  lamps  also  afford  some  indication  as  to 
the  rating  and  the  uniformity  of  the  lamps. 

Photometer  Test-Plate. — As  has  been  indicated  the  test-plate 
is  the  one  elemental  feature  which  differentiates  the  portable 
photometer  from  the  stationary  photometer,  or  the  illumination 
photometer  from  the  candlepower  photometer.  It  is  also  the  one 
feature  of  a  photometer  in  which  a  known  systematic  error  has 
existed.    The  reference  is  to  the  departure  of  the  brightness  char- 


772     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


acteristic  of  the  test-plate  from  Lambert's  cosine  law.  This 
error  has  been  tolerated  because  no  simple  and  adequate  means 
of  avoiding  it  have  been  available.  In  the  compensated  test- 
plate  described  in  another  paper1  this  error  is  eliminated. 

The  error  of  the  transmitting  test-plate  differs  from  that  of 
the  reflecting  test-plate  in  that  for  a  given  angle  it  is  constant  for 
all  directions  of  incident  light  because  the  surface  is  always 
viewed  normally.  The  error  of  the  reflecting  test-plate  likewise 
varies  with  the  angle,  and  for  any  given  angle  may  vary  with  the 
azimuth  or  the  direction  of  light.  In  the  cases  where  the  reflect- 
ing test-plate  is  viewed  normally  one  of  these  variables  is 
eliminated. 


Fig.  6.— Plumb-bob  suspended  from  center  of  an  opaque  ring. 

With  the  transmitting  test-plate  the  photometer  and  the  ob- 
server may  be  located  below  the  plane  of  illumination  and  may, 
therefore,  avoid  shadows  upon  the  plane.  When  a  reflecting  test- 
plate  is  employed  it  usually  is  difficult  to  avoid  casting  shadows 
upon  the  plate.  The  obvious  procedure  is  to  choose  the  direction 
of  view  which  will  minimize  the  obstruction  of  light  on  the  plate, 
by  the  photometer  and  observer,  having  due  regard  to  the  selection 
of  the  angle  of  view  which  will  avoid  large  errors  due  to  the  de- 
parture from  cosine  law. 

The  reflecting  test-plate  may  be  used  to  good  advantage  in 
inaccessible  places,  such  as  show  cases,  walls,  ceilings,  shelves, 
packing  cases,  letter  files,  etc. 

In  the  extended  study  of  illumination  on  a  given  plane  it  is 

i  Trans.  I.  E-  S.,  No.  8,  vol.  X,  1915. 


• 


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x^  : 

x- 

y*  : 

x?  : 

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Nei*>\^ 


Fig.  7.— A  self-leveling  test-plate. 


"**  '  Fig.  8.— Protractor,  plumb-bob  and  level.  Fig.  5.— Ammeter  rheostat  and  dry  cells. 


LITTLE:     USE   OF   PORTABLE   PHOTOMETERS  773 

necessary  to  establish  a  level  for  the  test-plate  and  maintain  it. 
This  is  a  simple  matter  in  interiors  where  a  level  floor  may  be 
relied  upon.  In  other  cases,  such  as  street  lighting  where  the 
level  has  to  be  re-established  at  each  station,  and  a  reflecting 
test-plate  is  employed,  a  self -leveling  test-plate  is  a  great  con- 
venience. 

Associated  Candlepower  Measurements. — Where  a  complete 
knowledge  of  the  facts  is  desired,  an  intelligent  discussion  of 
results  is  impracticable  if  the  light  flux  produced  by  the  sources 
is  unknown. 

BRIGHTNESS. 

Many  installations  may  prove  thoroughly  satisfactory  in  that 
the  intensity  is  all  that  is  required,  and  the  uniformity  good, 
but  there  may  be  objects  reflecting  specularly  or  brightly  il- 
luminated areas  within  the  immediate  line  of  vision,  which 
make  the  result  objectionable  and  fatiguing  to  the  eyes.  It 
is  frequently  found  of  considerable  aid  in  studying  an  installation 
to  measure  the  brightness  of  the  various  objects  within  the  ordi- 
nary line  of  vision.  It  is  sometimes  advisable  to  measure  the 
same  object  in  the  plane  of  incident  light,  and  in  a  direction 
900  removed  from  the  plane  of  incident  light;  in  other  words, 
measure  the  brightness  in  the  direction  of  highest  intensity 
and  lowest  intensity.  The  percentage  difference  will  afford  some 
indication  of  the  potentialities  for  glare  due  to  specular  reflection 
from  objects,  such  as  a  polished  top  desk,  glossy  paper,  etc. 

The  brightness  of  the  glassware  surrounding  the  illuminant 
and  ceiling  or  wall  against  which  it  is  viewed  can  be  measured, 
and  the  data  obtained  may  represent  the  characteristics  of  the 
installation  from  the  standpoint  of  great  and  annoying  contrasts. 

The  approximate  reflecting  qualities  or  any  mat  surface  can 
be  ascertained  by  comparing  the  brightness  of  the  surface  with 
the  brightness  of  a  reflecting  test-plate.  The  reflection  coefficient 
of  the  test-plate  is  known,  therefore,  the  reflection  coefficient  of 
the  surface  may  be  computed. 

Brightness  Measurements. — To  make  brightness  measurements 
with  a  portable  photometer  the  plate  is  eliminated  and  the  surface 
to  be  measured  is  viewed  directly.  In  other  words,  the  surface 
to  be  measured  is  one  of  the  photometric  surfaces  to  be  compared 
with  the  standard  surface  in  the  photometer.     The  brightness  of 


774     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

a  uniformly  illuminated  surface  as  indicated  by  the  photometer 
scale  is  independent  of  the  distance  between  the  photometer  and 
the  surface.  This  is  obvious  as  the  brightness  of  a  surface  does 
not  vary  with  distance.  Also  as  the  distance  between  the  photom- 
eter and  the  surface  increased  so  does  the  area  viewed  in  the 
photometer  increase. 

Brightness  may  be  expressed  in  Lamberts.2 

L  =  Lamberts 

F  =  Flux 

S  =  Area  in  sq.  cm. 

MAINTENANCE  OF  PHOTOMETER. 

The  photometrist  should  satisfy  himself  as  to  the  correctness 
of  the  constants  of  the  photometer  before  employing  it  in  serious 
work.  The  adjustment  of  the  comparison  lamp,  the  transmis- 
sion of  the  absorbing  screens,  and  the  accuracy  of  the  scale 
throughout  its  entire  range  should  command  his  particular  atten- 
tion. This  cannot  be  done  unless  there  is  available  an  adequate 
equipment  for  verifying  the  instrument.  Such  an  equipment  is 
essential  not  only  for  a  first  check  of  the  instrument  but  must 
be  on  hand  if  maintained  accuracy  is  to  be  had  throughout  the 
life  of  the  instrument.  Comparison  lamps  will  change  and  the 
optical  parts  of  an  instrument  may  become  dusty  through  inatten- 
tion. The  only  efficient  safeguard  is  to  provide  independent 
means  of  verifying  the  photometer. 

Among  means  for  verifying  photometers  are  small  standard- 
izing attachments  for  the  simple  check  of  the  instrument  in  ser- 
vice at  one  point  on  the  scale.  Such  a  check  is,  however,  quite 
incomplete  unless  an  independent  means  is  employed  for  the 
electrical  measurements.  To  use  the  same  electrical  instruments 
for  the  photometer  lamp  is  not  good  practise.  For  a  verification 
of  the  other  constants  of  the  instrument  more  elaborate  means 
must  be  provided. 

The  absorbing  screens  may  be  checked  approximately  at  any 
one  time  during  a  test  by  finding  some  point  where  a  fairly  con- 
stant illumination  can  be  had  of  such  intensity  that  it  may  be 

2  See  1915  report  of  the  Committee  on  Nomenclature  and  Standards  of  the  I.  E.  S. 


UTTLE:     USE  OF   PORTABLE   PHOTOMETERS  775 

read  both  with  and  without  the  screen.  In  case  of  the  use  of 
two  or  more  screens  a  darker  screen  can  be  verified  by  securing 
some  other  illumination  which  may  be  read  with  first  the  light 
screen  and  then  the  dark,  thus  securing  the  values  for  one  screen 
in  terms  of  the  other. 

ACCESSORIES. 
There  are  a  number  of  accessories  to  a  portable  photometer 
some  of  which  are  necessary,  others  simply  convenient  or  con- 
ducive to  greater  accuracy.  A  few  of  these  accessories  are  cited 
below,  divided  into  two  groups,  essentials,  and  those  conducive 
to  greater  accuracy. 

Essentials  Aids  to  convenience  or  accuracy 

Note-book  Standardizing  equipment 

Batteries  or  other  supply  Self  leveling  test-plate 

Electrical  instrument  Color  screens 

Tripod  Telescope  and  cross-hairs 

Plumb-bob  Protractor,  plumb-bob  and  level 

Tape  Slide  rule 

Chalk 

Note-Book. — The  keeping  of  a  photometrist's  note-book  is  very 
important,  as  in  many  cases  the  small  details  which  are  often 
overlooked  are  of  vital  importance  in  the  discussion  of  results. 
An  aid  to  this  end  is  a  blank  form  divided  into  numerous  head- 
ings and  to  be  filled  in  during  the  test.  The  following  is  a  sheet 
from  a  photometrist's  note-book  (see  Fig.  4).  The  note-book 
page  should  be  ruled  in  cross  section  as  an  aid  in  making  maps. 

Electrical  Instrument. — All  modern  portable  photometers  em- 
ploy electric  comparison  lamps.  They  must  be  kept  at  the  stand- 
ardization values  if  the  work  is  to  be  accurate.  It  is  a  character- 
istic of  the  tungsten  filament  lamp  that  1  per  cent,  variation  in  the 
impressed  voltage  occasions  a  change  in  candlepower  of  about 
5  per  cent.,  and  1  per  cent,  change  in  the  current  occasions  a 
change  in  candlepower  of  about  10  per  cent.  Errors  in  indicating 
electrical  instruments  used  with  photometers  are  therefore  mul- 
tiplied by  large  factors  in  the  resultant  photometric  values.  Thus 
precision  in  the  electrical  instrument  becomes  very  important. 
Unfortunately,  it  is  the  current  practise  to  employ  with  portable 
photometers  electrical  instruments  which  in  themselves  are  either 
of  insufficient  precision  or  which  in  their  use  are  not  handled  with 


776     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

sufficient  care  to  obtain  proper  precision.  It  is  to  be  feared  that 
many  illumination  measurements  suffer  in  consequence  of  this. 
It  is  conservative  to  say  that  an  accuracy  of  0.2  per  cent,  ought 
to  be  attained  in  voltmeters  or  ammeters  used  in  portable  work. 
Most  portable  voltmeters  and  ammeters  are  not  compensated 
for  temperature  changes  sufficiently  for  work  where  extremes  of 
temperature  prevail.  If  photometric  equipment  is  to  be  used  in 
such  cases  the  temperature  of  the  indicating  electrical  instrument 
should  be  determined  and  the  corrections  should  be  applied.  An- 
other source  of  error  encountered  through  the  use  of  electrical 
instruments  is  that  due  to  the  influence  of  stray  fields  or  the 
shunting  of  the  instrument  field.  Care  should  therefore  be  taken 
to  avoid  placing  the  instrument  on  or  near  magnetic  metals,  such 
as  resting  the  meter  on  the  floor  or  sidewalk  over  iron  beams. 
With  the  usual  portable  voltmeter  and  ammeters  0.2  per  cent, 
accuracy  can  be  obtained  only  if  the  error  of  the  instrument  is 
known  and  the  instrument  is  handled  and  read  most  carefully. 

Different  portable  photometers  require  different  potentials  for 
their  operation,  but  the  majority  use  a  low  volt  comparison  lamp 
(3-6  volts)  which  may  be  operated  on  either  a  small  storage  bat- 
tery or  on  dry  cells.  If  the  lamp  does  not  require  more  than  0.2 
to  0.3  ampere  dry  cells  will  be  found  very  satisfactory,  and  for 
convenience  the  screw  top  cell  is  preferable.  As  a  measuring 
instrument  a  well  compensated  ammeter  is  preferable  to  a  volt- 
meter as  the  photometer  leads  can  be  as  long  or  as  short  as  con- 
venience requires  without  changing  the  electrical  values  in  the 
lamp,  Fig.  5.  In  some  photometers  the  regulation  of  a  compari- 
son lamp  is  accomplished  by  means  of  a  Wheatstone  bridge.  The 
resistance  of  a  tungsten  filament  varies  with  the  temperature. 
With  three  fixed  arms  in  the  bridge  and  the  lamp  for  the  fourth, 
the  bridge  will  balance  only  when  the  lamp  is  at  the  proper  resis- 
tance or  the  proper  current  is  passing  through  the  lamp.  This 
device  may  be  used  as  an  accessory  or  part  of  the  instrument.  If 
as  an  accessory  it  must  be  attached  to  the  photometer  so  that  there 
is  a  minimum  of  wire  of  low  resistance  between  the  device  and  the 
lamp,  thus  obviating  errors  due  to  change  in  temperature  of  the 
leads.  A  low  resistance  galvanometer  or  low  resistance  high 
sensibility  telephone  may  be  used  with  excellent  results  as  an  in- 


LITTLE:     USE  OF    PORTABLE    PHOTOMETERS  JJJ 

dicator  for  securing  a  balance.  With  sensitive  galvonometer 
changes  in  current  may  be  detected  to  less  than  0.01  of  I  per  cent. 

Tripod. — A  great  deal  of  the  work  in  which  a  portable  photo- 
meter is  required  is  done  with  the  photometer  mounted  on  a 
tripod,  the  measurements  being  made  in  a  given  plane.  As  the 
photometer  is  moved  from  station  to  station  it  is  not  convenient 
to  re-level  each  time.  Therefore  a  tripod  with  rigid  legs  is  most 
convenient.  For  street  work  with  uneven  surfaces,  however,  it 
is  essential  that  the  legs  be  adjustable. 

Plumb-bob. — In  any  photometric  measurements  where  it  is 
essential  to  establish  test  stations  having  a  definite  location  with 
reference  to  the  light  source,  it  is  necessary  to  establish  accurately 
a  point  immediately  beneath  the  source.  A  quick  method  is  the 
use  of  a  plumb-bob  suspended  from  the  center  of  an  opaque  ring. 
To  determine  the  point  directly  beneath  the  light  source  the  plumb- 
bob  must  fall  in  the  center  of  the  illuminated  area  of  light  falling 
through  the  ring  or  at  the  center  of  the  shadow  of  the  ring  (see 
Fig.  6). 

Tape. — For  computations  a  tape  divided  in  tenths  and  hun- 
dredths of  feet  is  found  very  helpful. 

AIDS  TO  CONVENIENCE  AND  ACCURACY. 

Standardising  Equipment. — As  previously  stated  photometers 
must  be  frequently  verified,  and  a  small  standardizing  equipment 
for  portable  photometers  furnishes  a  verification  during  test. 
This  equipment,  of  course,  must  be  verified  itself,  but  as  it  is  used 
for  only  a  small  fraction  of  the  time  that  the  photometer  is  used, 
it  should  remain  constant  for  a  long  period.  These  standardizing 
equipments  may  be  either  self-contained,  using  the  Wheatstone 
bridge  principle,  or  may  make  use  of  the  energy  supply  and  meter 
used  for  the  photometer.  This  later  method  has  the  disadvantage 
of  rendering  inaccurate  results,  if  there  is  any  change  in  the  in- 
dicating instrument. 

Self -Leveling  Test-Plate. — For  horizontal  illumination  values 
where  a  level  floor  or  street  are  not  available  the  self -leveling  test- 
plate  proves  a  great  time  saver.  In  case  of  high  winds  this  de- 
vice is  equipped  with  a  lock,  but  when  the  lock  is  used  care  should 
be  taken  to  relevel  the  test-plate  at  each  station.     Fig.  7. 

Color  Filters. — Photometric  accuracy  depends  largely  upon  a 


778     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

close  color  match  between  the  test  and  comparison  field  and  an 
aid  in  promoting  accuracy  in  measuring  illuminants  of  a  different 
color  than  the  comparison  lamp  is  a  set  of  color  filters.  While  it 
is  difficult  to  match  every  light  source,  an  approximate  match 
can  be  secured  with  a  few  filters.  The  transmission  values  of 
these  filters  should  be  determined  by  comparison  with  standard- 
ized filters,  and  wherever  practicable  the  filters  should  be  placed 
between  the  comparison  lamp  and  the  photometer  head.  Thus 
a  known  flux  of  light  is  allowed  to  pass  regardless  of  the  color 
components  of  the  test  source.  The  objection  to  the  use  of  color 
filters  on  the  test  side  of  a  photometer  however  is  more  theoreti- 
cal than  practical. 

Telescope. — Cross  Hairs. — A  simple  short  focus  telescope  with 
cross  hairs  forms  a  convenient  apparatus  for  aligning  the  photom- 
eter. This  can  be  made  either  a  part  of  the  photometer  optical 
system  or  be  mounted  adjacent  and  parallel  to  the  optical  system. 

Protractor  and  Plumb-Bob  and  Level. — The  convenience  of 
this  device  has  been  discussed  in  the  determination  of  angles  for 
candlepower  measurements.  It  is  also  an  aid  in  establishing 
street  levels  and  street  grades  as  well  as  securing  building  heights, 
tree  heights,  etc.  (Fig.  8). 

DISCUSSION  OF  RESULTS. 

When  a  survey  has  been  completed  and  the  time  comes  to  draw 
conclusions  from  the  test  data  there  are  a  number  of  consider- 
ations which  it  is  well  to  remember.  In  the  first  place  the  purpose 
of  the  survey  should  be  kept  clearly  in  mind  and  the  photometrist 
should  be  satisfied  that  the  measurements  are  such  in  number  and 
time  as  will  accomplish  this  purpose.  It  is  important  to  be  sure 
that  the  measurements  have  been  made  in  the  plane  or  planes 
whose  illumination  is  important;  that  the  installation  is  typical 
of  any  installations  which  the  conclusions  may  affect;  that  the 
operating  conditions  are  typical  and,  in  general,  that  there  is 
no  reason  why  the  indications  of  the  test  should  not  be  taken  at 
their  face  value. 

Test  results  invariably  are  subject  to  errors  or  to  deviation 
from  absolute  accuracy.  Each  element  which  contributes  to  the 
final  result  possess  liability  to  error.  The  photometer,  the  elec- 
trical instrument,  the  observer,  each  departs  from  absolute  ac- 


LITTLE:     USE   OF    PORTABLE    PHOTOMETERS  779 

curacy,  and  the  individual  errors  combine  to  constitute  the  error 
of  the  final  result.  The  procedure,  therefore,  is  to  ascertain  or 
estimate  the  extent  of  such  individual  errors,  and  to  make  certain 
that  no  errors  are  present  in  the  final  results  which  are  large 
enough  to  vitiate  the  conclusions.  Before  results  are  accepted 
the  accuracy  of  the  indication  of  the  photometer  with  the  instru- 
ment with  which  it  has  been  used  should  be  determined  to  a 
certainty,  and  it  is  good  practise  to  recalibrate  the  photometer 
with  its  electrical  instruments  after  as  well  as  before  the  test, 
in  order  to  obtain  assurance  on  this  score. 

In  work  of  this  class  there  are  so  many  possibilities  of  error 
that  all  reasonable  means  ought  to  be  availed  of  to  check  the 
results.  No  opportunity  should  be  neglected  to  compare  measure- 
ments with  those  obtained  with  another  equipment.  Experience 
with  tests  in  similar  installations  should  be  brought  to  bear  to 
ascertain  if  the  results  appear  reasonable.  Where  the  flux  pro- 
duced by  the  lamps  has  been  ascertained,  and  illumination  meas- 
urements have  been  made  on  a  particular  plane,  the  ratio  of 
flux  delivered  to  flux  produced  should  be  computed  in  order  to 
determine  if  the  ''efficiency  of  utilization"  appears  to  be  reason- 
able. 

Finally  when  accuracy  has  been  assured  and  conclusions  are 
drawn  from  a  test,  it  is  important  to  confine  such  conclusions  to 
the  particular  test  under  discussion.  All  that  can  be  said  without 
qualification  is  that  the  result  and  the  conclusions  as  obtained 
apply  to  a  particular  installation,  a  particular  set  of  operating 
conditions,  and  a  particular  time.  Before  the  conclusions  may  be 
assumed  to  be  applicable  to  any  other  installation,  any  other  set 
of  operating  conditions  or  any  other  time,  assurance  must  be  had 
that  no  differences  exist  which  would  alter  the  results  in  any 
particular  capable  of  changing  the  conclusions. 

DISCUSSION. 

Mr.  W.  A.  Durgin  :  Those  of  us  who  are  more  or  less  in  the 
business  of  selling  illumination  which  shall  be  permanently  satis- 
factory are  very  glad  to  have  this  sort  of  paper  published.  Illum- 
ination questions  are  much  befogged  by  assertions  and  discussions 
based  on  readings  made  by  some  inexperienced  person  with  a 
portable  photometer  borrowed  over  night  from  a  central  station 


780     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

company  or  other  unwilling  accomplice.  It  is  to  be  hoped  that 
this  paper  will  give  much  publicity  to  the  need  of  specialized  ex- 
perience and  skill,  if  data  of  any  real  value  is  to  be  secured. 

A  few  accessories  not  mentioned  in  the  paper  have  been  found 
helpful. 

First  in  importance  is  a  small  truck  similar  to  that  shown  in 
Fig.  3  in  Messrs.  Harrison  and  Anderson's  paper1  which  is  to  be 
read  at  this  convention.  We  have  used  such  a  truck  with 
smaller  casters  for  some  time  in  all  interior  and  side  walk  tests 
and  recommend  it  especially  for  the  ease  with  which  cross  wires 
on  the  base  can  be  used  to  quickly  fix  the  location  at  stations. 
The  arrangement  is  much  more  convenient  than  the  usual  swing- 
ing plumb-bob. 

Improved  absorption  screens  offer  another  convenience.  These 
are  available  in  sets  having  definite  coefficients  of  0.1,  0.0 1  and 
0.001  transmission  accurate  to  x/i  per  cent.;  a  notable  advance 
over  the  haphazard  coefficients  generally  in  use. 

In  standardizing  the  photometer,  we  obtain  more  consistent 
results  by  leaving  the  current  adjustment  unchanged  and  deter- 
mining from  time  to  time  the  constant  factor  to  be  applied  to  the 
foot-candle  readings.  The  use  of  a  factor  presents  another  ad- 
vantage since  in  important  work  we  find  it  necessary  to  use 
duplicate  equipment  with  two  sets  of  observers  and,  with  cor- 
rection factor  standardization,  the  two  sets  of  uncorrected  ob- 
servations are  sufficiently  different  to  prevent  bias  in  reading. 

Some  discussion  of  the  means  of  checking  brightness  co- 
efficient perhaps  would  add  to  the  great  value  of  the  paper. 
There  is  considerable  doubt  in  many  testers'  minds  as  to  just 
what  brightness  constant  means  at  the  photometer  screen  and  as 
to  whether  the  same  calibration  correction  constant  applies  to  it 
as  to  the  foot-candle  reading. 

Mr.  L.  C.  Porter:  Mr.  Little  calls  attention  to  the  necessity 
of  accurate  measurement  of  the  current  in  standard  lamps,  and 
I  think  that  that  should  be  emphasized  a  little  more.  We  find 
in  our  work  that  one  of  the  great  sources  of  error  is  in  not  getting 
the  standard  lamp  in  our  photometer  to  operate  at  exactly  the 
proper  current  value.     Some  tests  which  I  have  made  indicate 

1  Trans.  I.  E.  S.,  No.  9,  vol.  X,  1915. 


USE   OF    PORTABLE    PHOTOMETERS 


78l 


that  a  change  of  about  one  one-hundredth  of  an  ampere  through 
the  standard  lamp  will  result  in  something  like  a  20  per  cent, 
change  in  foot-candles  read  on  our  photometer.  The  accompany- 
ing curve  shows  a  calibration  test  run  on  one  lamp. 


"92       94        96       98        100       I0Z       104      106      108 
PERCENT.  NORMAL  AMPERES  ON  PHOTOMETER  LAMP 

Calibration  curve  of  a  portable  photometer. 

We  have  found  that  it  is  hardly  practicable  to  hold  the  voltage 
on  the  photometer  lamp.  The  voltmeter  leads  are  soldered  to 
the  lamp  socket  and  even  with  correct  voltage  there  the  lamp  may 
not  be  operating  correctly,  due  to  contact  resistance  between  the 
lamp  base  and  the  socket.  It  is  more  accurate  to  read  amperes, 
and  in  order  to  do  that  we  use  a  mirrored  needle  milli-voltmeter 
with  a  scale  divided  into  150  divisions,  and  a  six-tenths  ampere 
shunt.  In  that  way  we  can  obtain  a  very  accurate  current  value, 
and  changing  the  leads  used  does  not  entail  a  voltage  drop,  con- 
tact resistance,  etc. 

Speaking  of  the  use  of  dry  batteries— we  use  dry  batteries  a 
great  deal  for  working  portable  photometers,  but  find  that  almost 
every  time  the  batteries  are  moved  we  have  to  re-set  the  milli- 
voltmeter.  After  the  lamp  has  burned  a  short  time,  the  batteries 
seem  to  hold  fairly  steady  for  a  considerable  length  of  time,  if 
not  moved,  but  if  the  batteries  are  moved,  it  seems  to  affect  the 
current  and  we  have  to  make  readjustments. 


782     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Another  field  in  which  portable  photometers  are  being  used  to 
a  considerable  extent  is  the  measuring  of  searchlights,  floodlights, 
stereopticons,  motion  picture  machines,  etc. ;  in  fact,  any  pro- 
jected light.  That  is  very  easily  accomplished  by  two  methods: 
a  searchlight  may  be  set  on  a  table  which  can  be  rotated  ac- 
curately; and  the  photometer  held  in  one  position  or  one  may 
draw  an  arc  of  a  circle  and  measure  off  stations  about  a  foot 
apart  across  the  beam  of  the  searchlight  and  move  the  photom- 
eter across  the  beam.  In  doing  that,  it  is  well  to  make  sure  that 
the  tube  of  the  photometer  points  directly  at  the  searchlight.  It 
can  be  easily  located  by  taking  off  the  diffusion  plate  on  the  end 
of  the  tube  and  centering  the  searchlight  in  the  photometer  (one 
can  see  it  in  the  center  of  the  mirror  very  clearly  and  can  center 
it  in  that  way)  then  replace  the  diffusing  glass  and  read  the  foot- 
candle  value.  Multiplying  that  by  the  square  of  the  distance 
from  the  light  source  to  the  photometer,  one  obtains  the  beam 
candlepower  of  the  searchlight. 

Mr.  Earl  A.  Anderson  :  The  discussion  of  the  precautions 
necessary  in  performing  illumination  tests  with  a  portable  pho- 
tometer as  given  in  this  paper  is  of  special  value  for,  as  Mr.  Dur- 
gin  has  suggested,  very  often  portable  photometers  have  been 
used  by  individuals  unacquainted  with  the  necessary  precautions. 
Perhaps  the  first  essential  in  reliable  photometric  work  is  careful 
and  frequent  standardization  of  the  comparison  lamp.  Where 
stationary  photometers  are  used,  means  for  accomplishing  this 
are  provided  as  a  matter  of  course  and  for  portable  photometers 
repeated  calibration  is  even  more  necessary  on  account  of  the 
more  delicate  nature  of  the  apparatus  and  lamp,  and  the  un- 
avoidable jars  and  disturbances  in  carrying  the  instrument  about. 

Recognizing  the  importance  of  facilitating  checks  of  the  port- 
able instruments  the  engineering  department  of  the  National 
Lamp  Works  of  the  General  Electric  Company  at  Nela  Park  has 
found  it  desirable  to  fit  up  a  special  photometric  bench  for  this 
purpose.  A  standard  125  in.  bar  is  arranged  with  a  device  for 
readily  clamping  into  a  fixed  position  at  one  end  the  illuminom- 
eter  which  is  to  be  checked.  Standard  lamps  of  high  and  low 
candlepower  are  provided  and  the  illumination  can  be  conven- 
iently varied  over  a  wide  range  by  altering  the  position  of  the 


USE  OP   PORTABLE   PHOTOMETERS  783 

standard  lamp  carriage.  Calculations  are  simplified  by  the  use 
of  a  distance  scale  calibrated  to  read  directly  in  foot-candles  upon 
the  test-plate. 

A  bench  of  this  kind  with  the  proper  indicating  instruments 
in  place  enables  the  operator  to  take  the  number  of  observations 
necessary  for  complete  standardization  of  his  instrument  in  a 
very  short  period  of  time.  In  addition  to  the  large  saving  in  time 
introduced,  a  permanent  routine  method  for  checking  the  port- 
able photometer  eliminates  the  doubt  existent  in  test  results 
where  standardization  must  be  made  with  a  temporary  set-up. 

Mr.  S.  L.  E.  Rose:  It  seems  to  me  that  one  of  the  most  im- 
portant things  here  is  the  note-book  and  data  taken  during  the 
test.  It  is  easy  enough  to  watch  the  operator  while  he  is  in  the 
laboratory  calibrating  his  instruments,  and  I  don't  think  Mr. 
Little's  paper  probably  intended  to  cover  the  work  done  in  the 
laboratory;  but  when  the  operator  gets  outside,  it  has  been  our 
experience  that  he  will  often  come  back  with  insufficient  data  to 
properly  interpret  the  results,  and  it  is  very  advisable  to  have  a 
data  sheet  calling  for  what  is  wanted,  and  then  all  the  operator 
has  to  do  is  to  fill  in  these  blanks  and  when  he  gets  back  it  is  easy 
enough  to  interpret  the  results.  Another  thing  Mr.  Little  has 
called  attention  to,  which  is  important,  is  the  experience  neces- 
sary to  pick  out  the  proper  representative  sections  in  the  lighting 
installation  under  test.  Anyone  with  ordinary  intelligence  and 
some  instruction  can  take  readings  on  a  portable  photometer; 
but  to  go  out  and  get  the  data  properly  noted  down  so  that  one 
can  have  all  the  required  conditions  has  been  the  greatest  fault 
we  have  found  with  the  operator.  Another  great  aid  which  we 
have  often  used  and  which  we  have  found  advisable  is,  where 
possible,  to  take  a  photograph  of  the  installation.  This  will  often 
give  a  lot  of  data  possibly  not  called  for,  and  the  operator  has  not 
thought  to  jot  down. 

Mr.  G.  H.  Stickney:  From  my  experience  and  observation 
of  tests  made  with  illumination  photometers,  I  believe  much  data 
is  gathered,  and  some  is  published,  in  which  indeterminate  errors 
exist.  Such  errors  may  render  data  worse  than  valueless,  in 
making  it  misleading. 

I  am  somewhat  apprehensive  of  tests  made  in  interiors,  especi- 


784     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ally  with  reflecting  side  walls,  when  the  opaque  test-plate  is  used, 
since  such  plates  must  be  observed  from  above.  Even  though  the 
observer  may  not  cast  a  direct  shadow  on  the  test-plate,  it  is  often 
impracticable  to  tell  whether  or  not  an  appreciable  amount  of 
light,  reflected  from  side  walls  or  other  objects,  is  being  inter- 
cepted. 

Another  source  of  error  which,  though  small,  may  under  some 
conditions  be  sufficient  to  give  misleading  results,  is  the  failure  of 
most  test-plates  to  adequately  evaluate  light  falling  at  angles  ap- 
proaching the  horizontal.  It  has  sometimes  seemed  to  me  that 
this  error  has  been  responsible  in  the  past  for  the  tendency  of  il- 
lumination tests  to  favor  lighting  units  in  which  a  large  part  of 
the  flux  is  delivered  at  steep  angles. 

Illumination  tests  made  by  amateurs  are  often  of  little  value 
because  conditions  are  not  made  definite  or  are  not  properly  re- 
corded. For  example,  the  observers  may  be  careless  as  to 
whether  all  the  lamps  in  the  installation  are  of  the  designated 
rating,  whether  they  are  old  or  new,  clean  or  dirty,  or  are  oper- 
ated at  the  correct  voltage. 

I  quite  agree  that,  on  account  of  convenience  and  simplicity, 
too  much  weight  has  been  given  to  the  intensity  in  a  horizontal 
reference  plane.  Often  the  intensity  in  some  particular  oblique 
plane,  or  rather  a  number  of  such  planes,  is  a  more  correct  meas- 
ure of  the  value  of  the  illumination.  To  take  care  of  such  con- 
ditions we  have  sometimes  supplemented  readings  in  the  refer- 
ence planes  by  a  measurement  of  the  illumination  falling  on  par- 
ticular surfaces  where  strong  illumination  is  especially  required. 

In  a  way  brightness  measurements,  which  are  becoming  more 
and  more  common,  carry  out  the  same  idea,  with  the  additional 
value  of  including  the  effect  of  the  surface. 

The  importance  of  illumination  and  brightness  measurements 
in  connection  with  certain  problems  is  so  great  that  every  effort 
should  be  made  to  avoid  any  discrediting  of  such  measurements 
due  to  careless  or  imperfect  work. 

In  measuring  the  beam  candlepower  of  projected  light — say, 
from  a  parabolic  reflector — it  is  important  that  the  observing 
stations  should  be  far  enough  away  from  the  reflector  to  insure 
homogeneity  of  the  beam.    In  this  connection  it  is  well  to  specify 


use  of  portable;  photometers  785 

the  distances  at  which  measurements  are  made  in  giving  the  data. 
Where  practicable  it  is  preferable  to  measure  it  at  a  distance  cor- 
responding approximately  to  the  principal  use  of  the  light. 

Norman  Macbeth  :  It  hardly  seems  possible  that  among  all 
the  papers  presented  before  this  Society,  that  this  is  the  first 
paper  on  this  most  important  subject.  I  know  of  no  one  better 
qualified  by  experience  than  Mr.  Little,  and  I  only  regret  that 
these  results  were  not  on  record  several  years  ago.  I  am  not  alto- 
gether in  agreement  with  Mr.  Little  on  some  of  the  points 
brought  up  in  discussions  of  this  kind  from  time  to  time,  and 
particularly  on  what  I  feel  is  an  over-capitalization  of  the  il- 
lumination measurements  taken  to  secure  the  so-called  utiliza- 
tion efficiencies.  That  this  consideration  is  uppermost  is  due  very 
largely  to  the  general  use  in  the  past  of  the  transmitting  test-plate 
and  very  largely  also  because  in  the  investigations  which  Mr. 
Little  has  been  required  to  make  these  values  were  desired.  I 
have  always  felt  that  the  largest  field,  by  far,  for  the  portable 
photometer  or  illuminometer  is  in  investigations  of  the  bright- 
ness of  the  various  surfaces  with  which  we  have  to  deal  in  all 
lighting  installations. 

The  apparatus  which  he  has  perfected  should  be  considered  as 
part  of  the  regular  equipment  as  it  is  all  very  valuable  and  neces- 
sary. The  manufacturers  of  photometers  should  include  some 
such  devices  with  every  instrument  sold. 

The  telescope  plum-bob  and  protractor  illustrated  in  Fig.  8  is 
especially  interesting.  A  couple  of  years  ago  in  the  development 
of  an  illuminometer  I  designed  somewhat  similar  parts,  but  be- 
fore the  construction  was  completed  we  found  that  a  clinometer 
made  by  an  English  concern  would  do  all  we  hoped  for  and  cer- 
tainly at  a  cost  much  less  considering  the  greater  number  of  clino- 
meters made  as  compared  with  the  more  limited  market  for  a 
special  instrument  to  be  made  for  use  with  an  illuminometer.  This 
instrument  was  a  beautiful  piece  of  work  and  required  but  a 
slight  addition  to  adapt  it  to  our  work.  Furthermore,  its  cost — 
twenty  to  twenty-five  dollars — is  considerably  less  than  it  could 
be  produced  for  in  limited  quantities. 

Mention  is  made  of  a  standardizing  equipment.  I  believe  that 
a  device  for  this  purpose  is  most  important ;  and  in  my  experience 


786     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

I  know  of  no  other  device  as  comforting  and  tending  to  save  time 
and  generally  facilitate  illumination  measurements  and  without 
the  incident  worry  as  to  whether  the  working  standard  lamp  is 
in  an  unknown  condition. 

This  paper  will  be  especially  valuable  in  the  Transactions.  The 
matter  is  of  the  greatest  importance  and  has  been  covered  in  an 
authoratative  detailed  manner  which  can  only  result  in  a  better 
understanding  of  this  subject.  Now  that  we  have  received  full 
sanction  of  that  necessary  brightness  unit,  the  lambert,  I  hope  to 
see  papers  before  this  association  having  to  do  with  illumination 
measurements  on  the  surfaces  which  are  of  the  greatest  im- 
portance— those  surfaces  encountered  by  the  eye  in  an  interior — 
and  with  data  on  their  brightness  range  we  will  have  more  real 
information  as  to  what  constitutes  good  illumination  than  is  pos- 
sible with  our  present  data  where  only  test-plate  measurements 
have  been  taken.  The  test-plate  values  help  in  working  back- 
wards to  repeat  a  given  result  where  all  other  conditions  of 
installation  are  similar.  As  this  is  an  almost  impossible  combina- 
tion, we  should  look  forward  to  the  day  of  more  general  recogni- 
tion for  illumination  measurements  of  surfaces  as  they  are  in 
daily  use. 

Mr.  Little  says  that  "It  is  obvious  that  illumination  measure- 
ments should  be  made  in  a  plane,  the  illumination  of  which  is  the 
principle  purpose  of  the  installation.  This  refers  to  height  of 
horizontal  plane  or  to  inclination  of  other  planes  which  may  be 
studied.  In  some  cases  it  may  be  desirable  to  determine  the  flux 
density  of  the  light  incident  on  a  surface  inclined  to  the  hori- 
zontal. As  in  the  case  of  the  study  of  the  illumination  of  school 
desks,  show  windows,  machinery,  etc."  I  should  like  to  ask,  inas- 
much as  Mr.  Little  has  stated  the  necessity  of  measurements 
taken  with  the  operator  below  the  test-plate,  if  he  would  also  con- 
sider, that  in  all  cases  of  school  desks,  etc.  that  the  observer 
should  occupy  the  same  position  as  a  pupil  at  a  desk  or  a  man 
working  at  machinery.  We  do  not  live  in  unfurnished  rooms,  and 
most  of  the  illumination  measurements  here  described  were  in- 
vestigations tending  to  bring  out  the  utilization  efficiency  of 
lamps,  not  the  effectiveness  of  the  lighting  installation  with 
people  in  the  rooms.  It  is  particularly  in  measurements  of 
this  kind  that  the  body  of  the  operator  should  occupy   the  same 


USE   OF   PORTABLE    PHOTOMETERS  787 

position  as  an  average  occupant  of  a  room  or  operator  at  a 
machine. 

Mr.  P.  S.  Millar:  The  novice  in  photometry  rarely,  if  ever, 
considers  himself  capable  of  undertaking  a  photometric  test  util- 
izing well  designed  set-up  laboratory  apparatus.  It  is  one  of  the 
unfortunate  things  about  portable  photometers  that  this  same 
novice  approaches  their  use  with  all  kinds  of  confidence  in  his 
ability  to  make  a  photometric  test  and  in  the  reliability  of  the 
results  which  he  obtains.  Because  the  instrument  is  smaller  and 
less  elaborate  in  appearance  than  laboratory  apparatus,  and  be- 
cause it  is  a  simple  matter  to  go  through  certain  perfunctory 
motions  and  to  get  an  indication  on  a  scale,  there  is  a  tendency  to 
assume  that  such  process  constitutes  a  photometric  test.  Those 
of  us  who  are  familiar  with  the  facts  appreciate,  as  the  author 
has  stated,  that  the  requirements  for  care  and  the  exercise  of 
common  sense  in  the  use  of  these  instruments  probably  surpass 
that  which  the  ordinary  practising  photometrist  is  called  upon  to 
exercise  in  routine  work  under  established  conditions. 

This  paper  and  discussion  have  made  it  evident  that  there  are 
two  points  of  view  regarding  the  use  of  portable  photometers. 
The  author's  viewpoint  is  that  of  one  who  is  engaged  in  testing 
work;  his  principal  aim  is  to  obtain  accurate  results  from  an 
engineering  survey,  the  report  of  which  is  rendered  to  a  client. 
He  therefore  avails  himself  of  every  practisable  means  of  verify- 
ing the  test  and  the  results.  When  practicable  he  prefers  to  as- 
certain the  total  flux  of  light  on  some  plane  because  the  exper- 
ienced photometrist  or  illuminating  engineer  can  usually  estimate 
fairly  well  what  the  average  intensity  of  light  on  a  given  plane 
should  be  in  any  particular  installation;  and  if  the  result  is  not 
in  accord  with  such  estimate,  the  reason  for  the  difference  must 
be  ascertained.  He  makes  it  a  point  to  obtain  a  measure  of  the 
light  produced  by  the  illuminants  as  a  part  of  his  attempt  to  tie 
together  all  the  data  of  the  installation  into  one  consistent  whole. 
When  a  test  of  this  kind  is  completed  the  photometrist  feels 
fairly  certain  that  his  results  are  reasonably  correct,  and  this 
certainty  arises  not  only  from  his  knowledge  that  he  has  exercised 
care  and  intelligence  in  the  conduct  of  the  test  but  also  from  his 
knowledge  that  the  various  data  of  the  installation  are  in  a 
proper  and  consistent  relation  with  one  another. 


788     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

This  point  of  view  by  no  means  eliminates  interest  in  and  need 
for  measurements  at  arbitrarily  selected  points  both  of  illumina- 
tion intensity  and  brightness.  It,  however,  requires  that  these 
measurements  be  supplemented  by  the  other  measurements,  which 
ought  not  to  be  eliminated  if  a  definite  engineering  report  is  to 
be  had  on  an  installation. 

The  other  point  of  view  is  that  of  a  man  who  is  doing  illum- 
ination work.  With  a  minimum  of  bother  and  in  the  shortest 
possible  time  he  wants  to  know  in  general  what  the  lighting  con- 
ditions are.  He  wants  to  know  the  high  and  low  extremes  of 
intensity  and  brightness  and  gets  a  few  values  of  the  light  here 
and  there  where  he  is  particularly  concerned  with  the  conditions. 
The  difficulty  with  such  a  survey  is  that  the  photometrist  has  no 
adequate  means  of  verifying  his  determinations  and  conclusions. 
His  results  may  be  and  often  are  quite  erroneous,  while  there  is 
nothing  to  indicate  that  such  is  the  case.  In  such  a  survey  the 
photometer  may  be  wrongly  calibrated,  lamps  which  are  pro- 
viding the  light  may  be  operating  at  the  wrong  voltage  and 
various  features  of  the  installation  may  be  improper.  The 
photometrist  will  not  know  the  facts  and  his  conclusions  based 
on  his  results  may  be  unwarranted. 

If  we  could  only  compel  every  man  who  uses  a  portable 
photometer  to  go  through  the  more  extensive  testing  routine  as 
well  as  to  make  the  occasional  haphazard  measurements  at  points 
of  special  interest,  photometric  errors  would  be  reduced  and  per- 
haps eliminated,  because  that  man  would  soon  learn  the  real 
fundamentals  of  photometric  testing.  It  was  not  long  ago  that 
we  had  occasion  to  use  a  photometer  whose  absorption  screens 
were  erroneously  calibrated  by  10  to  20  per  cent.  Unless  some 
of  the  precautions  advocated  in  this  paper  had  been  taken,  we 
would  not  have  known  that  the  instrument  was  erroneously  cali- 
brated. 

Another  reason  favoring  a  systematic  study  of  illumination  in- 
stallations is  that  only  in  that  way  can  strict  comparison  be  made 
between  different  lamps,  different  lighting  equipments,  etc. 
Where  matters  of  commercial  importance  hinge  on  the  results, 
it  is  very  important  that  photometric  tests  reveal  the  facts,  and  a 
systematic  study  of  the  installation  along  the  lines  laid  down  in 
this  paper  is  essential  to  correct  conclusions  in  such  cases. 


USE  OF   PORTABLE   PHOTOMETERS  789 

One  speaker  has  suggested  that  the  photometrist  may  be  sub- 
stituted for  a  workman  in  respect  to  the  shadow  cast  upon  the 
work  during  a  photometric  test.  In  testing  work  it  is  a  funda- 
mental principle  to  separate  as  many  variables  as  possible  and  to 
examine  each  from  the  influence  of  the  other.  Shadows  consti- 
tute a  very  important  variable  and  ought  to  be  studied  as  shadows. 
The  distribution  of  light  in  a  room  and  its  intensity  should  be 
measured,  and  then  to  determine  the  influence  of  shadows  one 
should  study  those  shadows  with  respect  to  direction  and  density 
under  actual  working  conditions.  It  would  be  the  simplest  thing 
in  the  world  for  a  photometrist  either  to  draw  improper  conclu- 
sions regarding  shadows  while  turning  to  arrive  at  the  correct 
ones,  or  to  purposely  create  improper  conditions  if  the  shadows 
were  created  by  himself  during  the  course  of  his  testing. 

Mr.  A.  H.  Taylor:  I  would  like  to  call  attention  to  a  few 
things  which  we  have  found  in  practise  at  the  Bureau  of  Stand- 
ards to  be  very  fertile  sources  of  error.  One  of  these  is  in  setting 
the  voltage  or  current  to  its  proper  value.  In  practise  it  is  best 
to  use  a  meter  with  which  you  have  practically  full  scale  de- 
flection for  the  proper  setting  of  the  lamp  in  the  photometer. 
Some  small  meters,  as  you  know,  have  no  mirror  backing,  and 
it  is  possible  with  these  to  make  a  very  appreciable  error  due  to 
parallax.  Another  source  of  error  is  in  estimating  a  fractional 
scale  division.  Instead  of  trying  to  get  the  setting  of  the  needle 
to  give  the  proper  balance  of  photometer,  it  would  be  better  to 
set  the  needle  on  the  nearest  even  scale  division,  making  necessary 
the  application  of  a  small  correction  factor  to  the  results.  This 
factor  could  be  incorporated  in  the  calculations  in  the  laboratory 
after  measurements  have  been  made,  and  would  eliminate  this 
source  of  error.  A  method  which  we  have  used  with  success,  one 
which  does  away  with  the  necessity  for  application  of  a  correction 
factor  to  results,  is  the  use  of  a  temporary  scale  line.  When  the 
photometer  is  standardized  in  the  laboratory,  and  proper  meter 
setting  has  been  determined,  a  piece  of  gummed  paper,  having 
two  fine  ink  lines  ruled  on  opposite  sides,  so  that  one  line  is 
directly  opposite  the  other,  is  pasted  on  the  glass  of  the  meter.  It 
is  so  placed  that  the  line  on  the  paper,  the  needle,  and  the  mir- 
rored images  of  the  needle  and  line  on  under  side  of  paper  are 


790     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

in  line.  If  the  lines  are  ruled  fine,  meter  adjustments  can  be  made 
quickly  and  very  accurately,  and  difference  between  observers  in 
estimating  fractional  divisions  are  entirely  eliminated.  In  using 
this  method,  however,  it  is  evidently  necessary  to  be  certain  that 
the  meter  casing  is  rigidly  fastened  so  that  there  can  be  no  rela- 
tive movement  between  casing  and  scale.  Additional  ease  of 
setting  may  be  obtained  by  the  use  of  a  reading  glass  fixed  in 
position  over  the  scale. 

In  the  initial  standardisation  of  the  photometer  it  is  desirable 
to  make  not  less  than  ten  to  twenty  photometer  settings  at  the 
determined  voltage,  since  the  average  of  that  number  may  be 
quite  different  from  the  average  of  only  three  or  four  readings. 
The  additional  readings  are  so  easily  made  that  the  increased 
accuracy  amply  justifies  the  trouble. 

In  many  portable  photometers  the  field  is  far  from  uniform  in 
intensity.  Some  observers  say  that  they  balance  the  whole  field, 
and  really  do  get  very  consistent  results,  even  when  the  field  is 
not  uniform.  However,  with  the  same  photometer,  observers 
who  confine  their  attention  to  a  small  portion  of  the  field  get 
differences  in  their  readings  by  making  balances  at  different  parts 
of  the  field.  Sometimes  there  is  as  much  difference  as  5  to  10 
per  cent,  in  settings  taken  at  opposite  sides  of  the  photometer 
field.  The  observer  who  is  to  read  the  photometer  should  have 
this  definitely  in  mind,  and  if  he  is  reading  only  a  small  part  of 
the  field,  as  is  sometimes  the  case,  that  is  the  part  of  the  field 
which  should  be  observed  in  standardizing  the  instrument. 

Mr.  W.  F.  Little  (In  reply)  :  Mr.  Durgin  has  referred  to 
the  caster  truck  for  the  photometer  tripod.  If  a  rigid  tripod  is 
used  the  test-plate  may  be  located  over  one  of  the  legs  at  the  be- 
ginning of  the  test.  Thus  the  photometer  may  be  quickly  and 
accurately  located  over  the  test  station  without  a  plumb-bob  and, 
as  the  equipment  is  light,  little  time  is  lost  in  lifting  it  from  station 
to  station. 

A  sufficient  number  of  check  readings  will  under  ordinary  con- 
ditions prove  sufficient  to  establish  the  representative  values  with- 
out a  duplication  of  apparatus. 

Applying  a  factor  to  the  scale  reading  instead  of  changing  the 
current  on  the  photometer  lamp  to  secure  true  values  makes  un- 


USE   OF   PORTABLE   PHOTOMETERS 


791 


necessary  computation  work.  If  the  photometer  is  standardized 
and  found  to  read  incorrectly,  the  characteristic  curve  of  the 
comparison  lamp  may  be  consulted  and  the  current  changed.  A 
second  series  of  readings  at  the  new  current  value  will  produce 
a  double  check,  and  the  calibration  should  be  that  much  more 
accurate. 

Calibration  for  brightness  is  quite  difficult  outside  of  a  well- 
equipped  photometric  laboratory;  therefore,  it  was  not  discussed 
in  detail  in  this  paper.    It  is,  however,  done  as  follows : 

Standardize  the  photometer  in  foot-candles  using  a  reflecting  test- 
plate,  then  illuminate  the  test-plate  (preferably  from  the  rear  to  eliminate 
stray  light)  to  a  definite  intensity  (probably  50  foot-candles)  and  measure 
the  illumination  produced  by  it  at  a  given  distance  (at  least  five  times 
the  plate  diameter  distance).  From  the  distance  and  the  illumination, 
compute  brightness  per  unit  area. 

Once  having  standardized  the  photometer,  a  transmitting  test-plate 
may  be  used  as  a  secondary  standard  by  measuring  the  brightness  of  its 
under  surface  with  a  known  illumination  produced  on  the  outer  surface. 


.100 

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1 

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200    Y, 

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180    ° 

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IG 

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a    112    11 

Characteristic  curve  of  1.5- volt  photometer  lamp. 


792     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Mr.  Porter  speaks  of  the  necessity  of  accurately  holding  the 
current  of  the  photometer  lamp.  An  examination  of  the  char- 
acteristic curve  of  the  lamp  will  further  emphasize  this  point. 
The  measuring  instrument  used  for  this  purpose  should  have  a 
long  mirrored  scale,  and  a  shunt  such  that  the  meter  indication 
is  well  toward  the  top  of  the  scale.  Long  leads  to  the  batteries 
obviate  the  necessity  of  frequent  changes  in  their  location. 

Mr.  Anderson  refers  to  the  process  of  standardization  of  the 
photometer.  A  quick  and  accurate  method  which  has  proved 
very  satisfactory  is  to  use  a  standard  lamp  of  sufficient  candle- 
power  to  produce  16  foot-candles  on  the  transmitting  test-plate 
at  a  distance  of  at  least  two  feet  and  with  the  use  of  rotating 
sector  disks  the  complete  range  of  scale  can  be  covered,  includ- 
ing the  absorption  glasses. 

Mr.  Taylor  has  spoken  of  errors  caused  by  an  insufficient 
number  of  readings  and  inaccuracies  in  reading  the  electrical 
instrument.  These  and  many  other  errors  (as  mentioned  in  the 
paper)  creep  into  portable  photometry.  Experience  alone  will 
suffice  to  place  them  in  their  order  of  importance,  and  the  pho- 
tometer operator  should  use  judgment  and  discretion  in  the  per- 
formance of  the  work. 


SPAULDING  AND  POTTER :    GAS  AND  ELECTRIC  COMPANIES      793 

HOW  CAN  GAS  AND  ELECTRIC  COMPANIES  UNDER 

ONE  MANAGEMENT  RENDER  THE 

BEST  LIGHT  SERVICE?* 


BY  A.  B.  SPAULDING  AND  N.   H.  POTTER. 


Synopsis:  This  paper  treats  from  the  commercial  standpoint  only 
the  subject  of  service  to  the  customer  by  gas  and  electric  companies 
under  one  management.  It  emphasizes  the  importance  of  service  to  the 
customer,  and  outlines  the  question  of  service  from  a  practical  standpoint. 
In  discussing  the  selling  force  necessary  for  the  proper  handling  of 
lighting  business,  the  authors  recommend  the  employment  of  specialists 
on  gas  illumination  and  specialists  on  electric  illumination.  The  educa- 
tion of  the  salesmen  is  considered  and  a  successful  local  educational 
course  outlined.  The  education  of  the  customer  is  discussed  from  the 
standpoints  of  the  manufacturer  of  appliances  and  the  lighting  company. 
The  relation  between  the  representative  and  the  customer  is  of  special 
importance  and  particular  stress  is  laid  on  the  matter  of  maintenance  of 
lighting  units,  which  maintenance  is  in  reality  the  "keynote  of  service." 


One  of  the  important  subjects  to-day  among  gas  and  electric 
companies  is  "How  can  the  best  service  be  given  ?"  The  engineer- 
ing phases  of  this  question  have  received  marked  attention,  and 
the  improvement  in  design  and  operation  of  gas  and  electric 
plants  has  increased  the  confidence  of  the  public  in  the  efficiency 
of  these  plants. 

This  paper  deals  with  the  rendering  of  service  after  the  product 
is  delivered,  or  beyond  the  meter.  There  are  differences  of 
opinion  as  to  how  this  can  best  be  done. 

Among  the  trio  of  products  of  gas  and  electric  companies — 
light,  heat  and  power — light  has  always  received  the  first  place. 
Upon  the  selling  of  this  product  depended  the  initial  success  of 
all  gas  and  electric  companies ;  and  the  early  history  of  both  in- 
dustries is  bound  up  inseparably  with  the  development  of  their 
lighting  business. 

There  has  been  a  radical  change  in  the  methods  and  personnel 
of  the  selling  force.  Heretofore  gas  and  electric  energy  were  the 
points  of  discussion  with  the  consumer;  but  now  illumination  is 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing Society,  Washington,   D.   C,   September  20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


794     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

the  topic.  Instead  of  so  many  cubic  feet  of  gas  or  watts  of 
energy,  illumination  is  being  sold. 

On  account  of  this  advancement  the  illuminating  engineer  has 
developed,  and  the  Illuminating  Engineering  Society  is  an  out- 
come of  the  desire  of  gas  and  electric  companies  and  manufac- 
turers to  render  the  public  a  service  by  united  effort  toward  im- 
proved illumination. 

The  present  estimate  of  the  work  of  any  man  must  be,  "How 
much  does  he  produce,"?  and  if  any  representative,  no  matter 
what  his  printed  title  may  be,  does  not  produce,  he  is  not  efficient. 

Selling  and  service  should  be  synonymous,  and  service  has 
various  phases.  In  order  to  render  it  intelligently  it  is  essential, 
first,  that  the  representative  be  capable  of  laying  out  and  super- 
vising a  lighting  installation;  second,  that  the  consumer  be  edu- 
cated to  appreciate  the  difference  between  proper  and  improper 
lighting,  insofar  as  the  value  of  proper  lighting  to  his  business  is 
concerned. 

Service  does  not  necessarily  mean  the  reduction  of  bills ;  it  may 
and  often  does  result  in  an  increase  in  the  amount  of  business 
with  customers.  Proper  illumination  is  desired  and  must  be  the 
primary  factor  in  the  discussion  of  cost,  not  only  of  electricity 
and  gas  supplied,  but  of  fixtures  and  first  installation.  Service, 
therefore,  means  the  providing  of  the  illumination  best  suited 
to  each  customer  at  minimum  cost. 

Both  the  representative  of  lighting  companies  and  the  public 

must  be  educated  to  the  value,  use  and  maintenance  of  a  lighting 

installation. 

GAS  AND  ELECTRIC   SPECIALISTS  ON  THE  SALE  OF 
ILLUMINATION. 

The  writers  believe  that  with  gas  and  electric  companies  under 
one  management  specialists  on  gas  illumination  and  specialists  on 
electric  illumination  are  productive  of  the  best  results,  particularly 
as  regards  service  to  the  customer.  This  method  is  in  reality 
intensive  selling  and  each  man  becomes  an  expert  in  either  gas  or 
electric  illumination.  Both  men  are  selling  the  same  thing,  viz., 
illumination ;  and  unconsciously  perhaps,  each  man  picks  out  the 
most  likely  prospects. 

It  would  seem  that  there  is  no  good  reason  for  a  gas  or  electric 
company  under  one  management  adopting  a  policy  which  en- 


SPAULDING  AND  POTTER:    GAS  AND  ELECTRIC  COMPANIES      795 

courages  only  one  source  of  supply.  The  duty  of  such  a  company 
is  not  to  pre-determine  what  source  to  sell,  but  to  give  the 
customer  the  benefit  of  the  best  advice  and  leave  to  him  the 
decision. 

That  two  sources  are  better  than  one  is  certain  where  gas  and 
electric  units  are  installed  for  general  illumination.  The  units 
should  harmonize  with  each  other  and  with  their  sur- 
roundings. The  only  question,  which  might  influence  the  in- 
stallation of  a  single  source,  would  be  its  adaptability. 

The  argument  has  been  advanced  that  by  having  one  man  sell 
both  gas  and  electric  illumination,  the  selling  force  could  be  cut 
in  half.  This  is  not  true  if  the  business  is  to  be  taken  care  of 
properly. 

It  has  been  contended  that  the  consumer  is  confused  by  having 
two  men  advising  different  sources  of  supply.  This  may  be  true 
where  companies  are  under  separate  management  and  competition 
dictates  a  policy  of  "Get  business  anyway, — but  get  it,"  rather 
than  a  policy  of  real  service  to  the  consumer.  With  a  company 
under  one  management  the  consumer  is  not  confused  by  having 
information  on  both  gas  and  electric  illumination  from  different 
men. 

The  customer  should  be  credited  with  common  sense  and  have 
the  privilege  of  choice.  By  having  both  sides  advanced  to  him  by 
experts  he  is  able  to  consider  economy,  convenience,  safety,  etc., 
and  in  the  end  be  sure  that  he  is  getting  that  method  of  illumina- 
tion best  suited  to  his  needs. 

Summing  up  we  find  that  separate  gas  and  electric 
lighting  representatives  are  in  the  end  no  more  expensive  than 
combination  representatives.  There  is  absolutely  no  question 
that  this  separation  does  stimulate  the  trade  in  a  healthy  manner. 
Each  salesman  becomes  more  proficient  in  the  art  of  gas  or  elec- 
tric illumination  as  the  case  may  be.  He  has  cooperative  com- 
petition and  will  necessarily  have  to  watch  his  installations  more 
closely.  He  is  also  forced  to  make  proper  installations  and  to 
render  proper  service  after  installation  is  made ;  otherwise  he  is 
likely  to  have  "lost  business"  charged  up  against  him,  and  he 
keeps  in  closer  touch  with  improvements  in  his  particular  line. 

A  man  selling  both  gas  and  electricity  is  too  prone  to  follow 
the  path  of  least  resistance  and  to  think,  "If  I  don't  sell  gas,  I  will 
13 


796     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

sell  electricity,"  with  the  result  that  a  desire  for  better  illumin- 
ation is  not  created  and  therefore  the  best  service  is  not  given. 
EDUCATION  OF  SALESMEN. 

Lighting  representatives  should  have  good  appearance,  per- 
sonality, and  selling  ability,  together  with  a  knowledge  of  the 
principles  of  illumination.  The  salesman  should  make  a  general 
survey  of  his  territory  and  become  familiar  with  its  conditions. 
He  should  make  periodic  tours  after  dark  in  the  store  section. 
He  can  then  pick  out  the  improperly  lighted  stores  and  by  one 
night's  work  of  this  sort  obtain  sufficient  leads  to  keep  him  busy 
for  several  days.  The  writers  know  of  several  instances  where 
salesmen  living  out  of  town  had  never  seen  their  territory  illum- 
inated. After  making  night  inspections  and  following  up  leads 
thus  obtained,  the  volume  of  store  business  from  their  particular 
sections  showed  a  marked  increase,  and  improved  installations 
also  resulted. 

The  representative  should  visit  other  districts  than  his  own 
and,  where  possible,  other  cities  and  towns,  thus  acquainting  him- 
self with  conditions,  perhaps  different  than  those  in  his  territory, 
which  will  enable  him  to  handle  more  successfully  new  and  similar 
problems  as  they  arise. 

The  lighting  representative  should,  if  he  expects  to  become 
more  valuable  to  his  company,  do  everything  in  his  power  to 
increase  his  knowledge  of  illumination  and  other  branches  of  the 
business.  This  can  be  brought  about  by  his  becoming  a  member 
of  the  Illuminating  Engineering  Society,  National  Electric  Light 
Association  and  National  Commercial  Gas  Association,  through 
which  he  obtains  at  first  hand,  knowledge  of  all  advancements  in 
the  art  of  illumination  as  well  as  other  subjects,  particularly  so 
if  he  take  advantage  of  the  correspondence  courses  now  offered 
by  the  last  two  societies.  If  he  be  fortunate  enough  to  have  a 
local  section  of  any  of  these  associations  in  his  vicinity,  he  will 
derive  great  benefits  by  attending  all  its  meetings  and  taking  an 
active  part  in  the  discussions.  In  addition  he  will  become  ac- 
quainted with  other  men  in  the  same  line,  receive  the  benefits  of 
their  personal  knowledge  and  experience,  and  be  able  to  recipro- 
cate. 

There  are  other  means  at  hand  of  increasing  one's  knowledge 
and  keeping  abreast  of  the  times,  viz.,  reading  periodicals  dealing 


SPAULDING  AND  POTTER  \    GAS  AND  ELECTRIC  COMPANIES      797 

with  all  branches  of  illumination  and  theadvertisingliteraturesent 
out  by  manufacturers,  which  contains  an  education  in  itself.  This 
literature  should  be  studied,  not  merely  read ;  for  here  is  a  fruit- 
ful field  of  knowledge.  Up-to-date  data  can  be  obtained  by 
having  one's  name  placed  on  the  mailing  lists  of  manufacturers. 

The  sales  manager  in  charge  of  these  men  should  hold  regular 
meetings  for  the  discussion  of  illuminating  problems.  Arrange- 
ments should  be  made  for  visits  to  places  like  the  testing  labora- 
tories and  various  fixture  and  lamp  works.  When  some  particu- 
larly fine  installation  has  been  made  in  the  vicinity,  a  party  should 
be  made  up  to  inspect  and  discuss  it  when  it  is  lighted. 

The  company  itself  has  a  duty  to  perform  in  the  education  of 
its  representatives.  It  should  encourage  the  men  to  study  and 
show  that  their  efforts  are  appreciated. 

The  Public  Service  Gas  Company  and  the  Public  Service  Elec- 
tric Company  of  New  Jersey  have  given  courses  to  develop  the 
desire  for  further  knowledge  on  the  part  of  the  men. 

The  following  course  has  been  given  by  the  Public  Service 
Electric  Company. 

( i )  "The  Central  Station  Salesman ;  His  Duties,  Troubles 
and  Needs." 

(2)  "Lamps;    Their    Manufacture   and    Characteristics." 

(Lecture  by  representative  of  a  lamp  company, 
and  visit  to  factory.) 

(3)  "Light:   Its  Production;  Its  Properties.    Some  Laws 

of  Light." 

(4)  "Measurement  of  Light  and  Illumination."      (Visit 

to  testing  laboratories.) 

(5)  "Reflectors,  Shades  and  Diffusing  Globes;  Their  Use 

and  Abuse." 

(6)  "Direct  and  Semi-indirect  Illumination." 

(7)  "Location  of  Units:    General  Consideration." 

(8)  "Residence  Lighting." 

(9)  "Store  Lighting." 

(10)  "Industrial  Lighting." 

(11)  "Electrical  Advertising." 

(12)  "Kw-h.  Sales  and  New  Business." 

(13)  "Wiring."     (By  a  contractor.) 

(14)  "Review." 


798     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

EDUCATION  OF  THE  CUSTOMER. 

The  main  object  of  a  storekeeper  for  instance  is  to  sell  mer- 
chandise; he  has  no  desire  to  become  an  illuminating  engineer; 
but  he  is  desirous  of  having  his  store  and  windows  properly  il- 
luminated, provided  of  course,  he  is  an  up-to-date  merchant.  In 
the  event  of  his  being  behind  the  times — and  there  are  many  of 
that  kind — in  fact,  they  are  the  ones  who  make  up  the  best  list  of 
prospects — he  should  be  taught  that  a  properly  lighted  store  and 
window  are  absolutely  necessary  for  success  in  selling  merchan- 
dise. 

The  desire  to  have  a  properly  lighted  window,  store,  factory 
or  home  lies  dormant  in  every  man,  and  under  stimulus  he  wilL 
unconsciously  start  a  course  of  self -education  by  asking  questions 
and  observing  other  installations  and  perhaps  reading. 

The  company  should  send  advertising  literature  acquainting 
him  with  the  proper  method  of  using  lighting  units.  For  ob- 
vious reasons  this  literature  should  be  absolutely  non-technical. 
It  should  be  attractive  in  appearance  and  so  written  that  it  will 
hold  the  attention  from  cover  to  cover. 

The  manufacturer's  representative  should  present  the  subject 
of  illumination  first,  and,  secondly,  the  wares  he  is  selling.  The 
architect,  builder,  electrician  and  gas  fitter  should  be  educated  by 
both  the  company  and  the  manufacturer  in  order  that  they  may 
in  turn  do  their  part  toward  the  education  of  the  prospective 
customer. 

With  these  three  different  sources  of  information  for  the  cus- 
tomer properly  co-ordinated,  there  would  be  little  or  no  reason 
for  the  absence  of  good  lighting  installations. 

RELATION  OF  REPRESENTATIVE  AND  CUSTOMER. 

As  has  been  stated,  the  first  consideration  in  this  relation  is  the 
impressing  upon  the  consumer  the  value  of  proper  illumination. 
Poor  installations  have  been  made  in  every  town  and  one  of  the 
present  difficulties  is  to  have  the  customer  realize  the  importance 
of  a  good  installation. 

If  the  manufacturers  of  lamps  and  accessories  were  to  deal  en- 
tirely through  the  gas  and  electric  company  whose  sole  idea  is 
proper  illumination,  or  at  least  submit  for  the  approval  of  these 
companies  the  unit  or  accessory  which  is  to  be  installed  for  a 
customer,  relations  with  the  consumer  would  be  much  improved- 


SPAULDING  AND  POTTER  :    GAS  AND  ELECTRIC  COMPANIES      799 

Cheap  and  inefficient  gas  and  electric  units  have  caused  the 
gas  and  electric  companies  much  trouble.  Such  units  are  often 
sold  with  an  argument  to  the  effect  that  the  gas  or  electric  com- 
pany is  robbing  the  consumer  and  will  not  sell  such  units  because 
they  reduce  the  company's  revenue.  On  account  of  such  con- 
flicting suggestions  to  the  customer  it  has  been  found  advisable  to 
demonstrate  the  correctness  of  recommendations  made.  The 
Public  Service  Electric  Company  has  been  using  for  some  time 
very  successfully  window  demonstration  sets.  These  are  made 
up  in  portable  form  and  consist  of  4- ft.  (1.23  m.)  sections  of  pipe 
with  five  outlets.  Twenty-five,  40,  or  60  watt  lamps  with  proper 
reflectors  may  be  connected  and  in  the  case  of  large  windows 
several  sets  may  be  hung  in  line.  The  sets  are  hung  by  the  repre- 
sentatives in  a  few  minutes  by  the  use  of  screw  eyes  and 
picture  wire,  and  connections  made  by  lamp  cord  to  any  available 
lamp  socket.  As  may  be  seen  the  outfit  is  very  flexible  and  may 
be  made  to  fit  almost  any  window  condition.  It  may  be  advisable 
to  change  these  outfits  to  accommodate  the  gas-filled  lamp  on  ac- 
count of  its  better  color  value  and  increased  efficiency. 

The  demonstration  not  only  shows  the  display  to  better  ad- 
vantage, but  the  merchant  gives  more  attention  to  the  dressing  of 
his  windows,  which,  combined  with  good  lighting,  results  in  in- 
creased sales  of  his  merchandise,  thereby  bringing  the  company 
and  customer  closer  together,  the  latter  realizing  that  the  com- 
pany has  rendered  real  service.  By  advising  customers  both  as 
to  lighting  and  dressing  of  their  windows,  it  has  been  possible  to 
have  more  light  used  not  only  for  illumination,  but  as  part  of 
merchandise  displays.  For  instance,  a  customer  who  operates  a 
piano  store  desired  a  special  dressing  for  his  window  and  the  dis- 
play installed  was  a  reproduction  of  a  painting  entitled  "Just  a 
Song  at  Twilight."  A  reproduction  of  the  original  painting  was 
placed  in  the  window  and  properly  lighted.  In  one  corner  of 
the  window  was  a  woman  playing  a  baby  grand  piano  and  on  the 
other  side  a  fireplace,  in  front  of  which  the  husband  sat  holding 
a  child  in  his  arms.  At  one  side  of  the  room  was  a  window 
through  which  was  projected  light  approximating  moonlight. 
From  the  fireplace  was  projected  light  of  a  ruddy  hue.  Alter- 
nately the  lighting  of  the  window  itself  was  flashed  on,  then  the 
effect  as  noted. 


800     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Since  the  installation  of  this  window  the  Public  Service  Electric 
Company  has  been  requested  many  times  to  dress  other  windows, 
and  in  every  case  where  this  has  been  done,  the  number  of  ob- 
servers of  the  window  has  been  more  than  doubled,  and  in  the 
case  of  the  window  mentioned  the  observers  were  increasd  1,200 
per  cent,  between  5  and  11  o'clock  at  night. 

These  installations,  which  are  allowed  to  remain  about  a  week, 
usually  convince  customers  of  their  value  and  lead  to  the  in- 
stallation of  permanent  outfits. 

Factory  lighting  may  be  handled  in  the  same  way.  Demon- 
strations of  either  gas  or  electric  lighting  have  been  in  many  cases 
the  closing  arguments  for  the  sale  of  better  lighting. 

After  the  installation  is  laid  out,  it  is  necessary  that  the  repre- 
sentative should  closely  follow  the  development  in  the  work  to  see 
that  the  suggestions  of  the  electrician  or  plumber  are  not  such 
as  to  spoil  the  desired  results.  It  often  occurs  that  the  customer 
accepting  advice  on  changes  in  position  of  outlets  and  accessories 
secures  an  incorrect  installation  and  blames  the  representative  for 
whatever  unsatisfactory  result  may  ensue. 

The  representative's  responsibility  does  not  end  with  the  demon- 
stration. It  is  his  duty  to  lay  out  the  proper  units,  supervising 
their  installation  and  see  that  prompt  service  is  rendered. 

At  this  point  the  real  service  in  lighting  installations  begins. 
Once  connected  to  the  company's  supply,  service  to  the  customer 
never  ends,  and  that  all  important  question  of  maintenance  begins. 

In  the  case  of  electric  lighting,  maintenance  is  more  or  less  a 
matter  of  education.  The  customer  should  be  taught  first  that 
electric  lamps  have  a  useful  life  and  that  after  a  certain  period  it 
is  economy  to  throw  away  old  and  purchase  new  lamps.  Sec- 
ondly, reflectors  decrease  in  efficiency  with  the  accumulation  of 
dust,  and  like  the  plate  glass  window  in  the  store  must  be  cleaned 
periodically. 

The  customer  usually  promises  to  attend  to  these  details  which 
are  in  reality  a  part  of  his  regular  house  cleaning,  but  the  drop 
in  efficiency  of  the  loss  in  illumination  is  by  such  small  steps,  that 
it  is  never  noticeable  from  day  to  day,  and  the  customer  being 
intent  on  selling  goods,  gives  little  or  no  attention  to  the  import- 
ance of  maintenance. 


SPAULDING  AND  POTTER  :    GAS  AND  ELECTRIC  COMPANIES      801 

The  lighting  salesman  may  continue  rendering  service  by  calling 
attention  to  any  blackened  lamps,  dirty  reflectors,  etc.  By  stating 
to  the  customer  that  this  is  his  (the  salesmen's)  installation,  that 
he  is  proud  of  it,  but  that  it  cannot  come  up  to  his  guarantee 
unless  properly  cared  for,  the  customer  is  usually  awakened  to 
his  responsibility  in  the  matter  and  the  habit  of  periodic  inspection 
and  cleaning  is  formed. 

In  the  case  of  a  gas  installation,  maintenance  is  also  a  very 
important  matter.  Thoughtlessness  or  carelessness  is  the  reason 
for  depreciation  in  lighting  value.  Again  the  daily  change  or 
drop  in  efficiency  is  so  small  as  to  be  unnoticeable.  Many  cus- 
tomers through  not  having  time  or  not  appreciating  this  drop  in 
efficiency  continue  using  old  or  broken  mantles  with  the  result 
that  very  poor  service  is  obtained  from  the  unit. 

Gas  companies  have  been  trying  for  years  to  educate  cus- 
tomers to  give  proper  attention  to  their  lighting  units,  but  in  many 
cases  it  is  almost  a  hopeless  task,  with  the  result  that  in  many 
instances  companies  have  launched  maintenance  departments  to 
do  for  the  customer  what  he  does  not  seem  to  care  to  do  for  him- 
self. Probably  the  day  is  not  far  off  when  all  gas  companies  will 
have  to  maintain  all  customer's  lighting  installations  in  order  to 
insure  proper  illumination. 

At  this  point  the  writers  desire  to  mention  a  system  of  resi- 
dence maintenance  service  by  which  customers  receive  periodic 
inspections  of  all  lighting  units.  This  service  includes  cleaning  of 
glassware  and  adjustment  of  burners  without  any  charge.  The 
men  engaged  in  this  work  also  carry  samples  of  the  latest  types 
of  lamps  and  a  full  line  of  repair  parts  and  accessories.  If  new 
material  is  sold  to  replace  that  which  is  broken,  no  charge  is  made 
other  than  the  regular  selling  price  of  such  material.  By  this  plan 
the  company  is  enabled  to  attend  to  all  complaints  received  before 
3  p.  m.  the  same  day.  This  plan  is  being  tried  out  by  the  Public 
Service  Gas  Company  in  one  city  in  New  Jersey  with  such  good 
results  that  in  a  very  short  time  it  is  expected  that  the  sale  of  re- 
pair parts  and  additional  units  will  alone  make  this  department 
self  sustaining,  not  to  mention  the  increased  satisfaction  on  the 
part  of  the  consumer  nor  the  added  consumption  derived  by  hav- 
ing more  units  in  good  working  order.  This  department  is 
productive  of  many  sales  and  materially  strengthens  the  selling 


802     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

organization  of  the  company.  The  aforementioned  plan  is  similar 
to  the  so-called  Toronto  Plan  with  which  many  of  you  are  no 
doubt  familiar. 

It  is  the  opinion  of  the  writers  that  in  order  that  a  gas  and 
electric  company  under  one  management  may  give  the  best  light- 
ing service,  separate  representatives  who  are  specialists  in  the 
application  of  each  lighting  source  should  be  employed.  These 
representatives  should  be  encouraged  to  keep  in  touch  with  the 
science  of  illuminating  engineering  and  the  most  advanced  thought 
in  modern  salesmanship.  The  company  should  lead  the  customer 
to  an  intelligent  appreciation  of  proper  illumination  and  by  the 
adoption  of  a  maintenance  service  should  make  him  feel  that  the 
company  is  genuinely  interested  in  his  continued  satisfaction. 

DISCUSSION. 

Mr.  Preston  S.  Millar:  I  think  the  work  of  electric  and  gas 
supply  companies,  their  engineering  and  operation  up  to  the 
meter,  is  likely  to  be  much  better  standardized  in  the  several  com- 
munities than  are  the  conditions  in  the  consumers'  premises  be- 
yond the  meter ;  all  sorts  of  policies  obtain  among  such  compan- 
ies in  regard  to  the  treatment  of  the  consumer  in  his  own  in- 
stallation. The  service,  whether  gas  or  electricity,  is  translated 
into  illumination  by  lamps  and  fixtures. 

Gas  lamps  are  in  general  not  what  they  ought  to  be  in  residence 
lighting.  Open  flame  burners  are  still  used  very  largely  and  the 
possibilities  of  gas  for  illuminating  purposes  are  not  being  real- 
ized. 

I  have  recently  had  the  privilege  of  conducting  a  survey  to 
obtain  what  condition  the  electric  lamps  are  in  when  they  are 
offered  to  central  station  customers.  A  great  many  tungsten 
filament  lamps  are  distinctly  inferior  to  the  standard.  The  con- 
dition of  some  lamps  that  are  offered  to  the  consumer  by  repu- 
table dealers  and  contractors,  and  by  other  selling  agencies  rang- 
ing down  to  the  five  and  ten  cent  store,  is  such  as  ought  to  com- 
mand the  attention  of  every  central  station.  Unless  care  is  taken 
by  the  central  station  as  to  the  quality  of  lamps  that  are  sold  to 
their  consumers,  electric  lighting  is  likely  to  get  into  some  of  the 
difficulties  that  gas  lighting  is  laboring  under. 


GAS   AND   ELECTRIC    COMPANIES  803 

In  the  matter  of  fixtures  I  have  often  wondered  if  gas  and 
electric  supply  companies  could  not  do  a  great  deal  in  the  way  of 
cultivating  good  public  opinion,  pleasing  the  customer  and  pro- 
moting the  sale  of  gas  and  electricity  by  making  pleasing  fixtures 
available  on  attractive  terms.  I  think  that  men  should  be  em- 
ployed to  select  and  design  artistic  fixtures  which  will  give  pleas- 
ing effects,  fixtures  that  will  bring  out  the  decorations  of  the 
room  to  the  best  advantage,  diffuse  and  tint  the  light  so  that  it 
will  be  pleasing  to  the  eye  and  comfortable.  In  so  doing  there 
may  be  an  increase  in  the  customer's  bill,  but  this  will  not  be 
objectionable  to  the  customer  if  the  lighting  pleases  him.  The 
experience  I  have  had  indicates  that  once  the  lighting  is  im- 
proved in  a  house  in  the  manner  I  have  indicated,  the  customer 
is  willing  to  pay  a  larger  monthly  bill  because  he  has  more  pleas- 
ing lighting  and  he  would  not  go  back  to  the  lower  bill  and  the 
inferior  lighting  for  anything.  I  know  of  very  little  that  is 
being  done  in  the  way  of  cultivating  in  this  way  the  opportunities 
which  are  offered. 

Finally  I  want  to  compliment  the  authors  of  the  paper ;  it  seems 
to  me  that  it  is  just  the  kind  of  a  paper  that  the  Illuminating 
Engineering  Society  wants  to  see  brought  to  the  attention  of  the 
gas  and  electric  supply  companies  throughout  the  country  and  I 
would  like  to  recommend  that  the  paper  be  printed  for  general 
distribution  among  gas  and  electric  companies ;  I  think  it  would 
do  a  great  deal  of  good. 

Mr.  R.  B.  Ely:  I  believe  the  lighting  companies  are  more 
inclined  to  the  belief  of  selling  a  service  rather  than  gas  or 
wattage  and  with  that  in  view  they  are  trying  to  furnish  all,  that 
their  advertising  departments  are  talking  about,  such  as  proper 
illumination  and  upkeep  of  system  to  obtain  the  maximum  re- 
sults at  a  minimum  cost.  I  would  like  to  inquire  as  to  how  far 
the  Public  Service  Company  has  gone  in  checking  up  the  recom- 
mendations of  their  representatives,  whether  they  follow  the 
recommendations  up  with  any  tests,  and  to  what  extent  they  are 
going  in  the  matter  of  demonstration,  the  demonstration  of  fix- 
tures for  the  interior  of  stores,  both  gas  and  electric,  and  the 
period  of  time  of  such  demonstrations.  I  would  also  like  to  in- 
quire whether  the  men  on  this  particular  end  of  the  work,  the 


804     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

lighting  service  work  look  after  the  commercial  conditions,  such 
as  contracts,  to  see  that  their  consumers  are  receiving  the  best 
possible  rate  and  whether  the  small  repairs  that  may  be  necessary 
are  noted  and  taken  care  of  by  this  department. 

Mr.  H.  T.  Owens  :  The  illuminating  engineers  of  the  United 
States  are  the  fixture  salesmen ;  they  have  more  to  do  with  light- 
ing than  all  the  rest  of  the  illuminating  people  put  together.  The 
salesmen  in  retail  fixture  stores  never  come  to  the  meetings  of  the 
Society  and  they  don't  use  the  title,  but  they  have  more  to  do  with 
lighting  than  the  members  of  this  Society.  The  paper  by  Mr. 
Spaulding  and  Mr.  Potter  tells  how  things  could  be  done  and  not 
how  they  are  done.  I  know  of  no  company  that  has  two  illumin- 
ating engineers.  In  the  eastern  part  of  this  country  there  is  more 
good  gas  than  electric  lighting  for  the  reason  that  the  gas  com- 
panies handle  fixtures  and  sell  them  and  the  type  of  fixture  they 
sell  on  the  average  furnishes  better  lighting  than  the  kind  of  fix- 
ture that  the  small  electrical  contractor  sells. 

Mr.  W.  R.  Moulton  :  In  Baltimore  it  has  been  found  advis- 
able for  the  central  station  to  not  only  give  advice  regarding  il- 
lumination, but  also  sell  and  install  the  proper  fixtures  at  a  fair 
price  to  the  consumer.  By  so  doing  it  is  possible  to  actually  give 
better  service  to  customers  and  at  the  same  time  increase  the  in- 
come. I  do  not  believe  there  is  another  large  central  station  work- 
ing on  this  basis. 

Referring  to  the  paragraph  where  the  authors  suggest  that  the 
salesman  handling  a  prospect  be  allowed  to  lay  out  the  entire  in- 
stallation. This  is  no  doubt  advisable  for  simple  installations,  but 
when  the  problem  is  completed  it  should  be  referred  to  the  de- 
partment head,  or  someone  else  who  is  capable  of  giving  special 
advice. 

It  is  true  one  can  often  increase  the  energy  consumption 
of  a  customer's  installation  and  at  the  same  time  have  that  cus- 
tomer pleased.  For  example,  he  may  be  spending  $6.00  a  month 
for  electricity  or  gas,  and  may  be  receiving  poor  illumination, 
poor  service,  poor  return  for  his  money.  With  proper  equipment 
installed  to  give  him  the  correct  result,  his  energy  bill  or  gas  bill 
may  increase  to  $10.00  per  month,  but  if  at  the  same  time  the  ser- 
vice and  lighting  is  thoroughly  satisfactory,  the  customer  will  not 
object  to  the  increase  in  operating  cost. 


GAS  AND   ELECTRIC   COMPANIES  805 

It  would  certainly  be  inadvisable  to  leave  the  selection  of  the  il- 
luminant  to  the  customer,  as  in  few  cases  would  he  be  capable  of 
selecting  what  is  most  suitable  to  his  conditions.  By  studying  his 
present  conditions  and  service  and  being  familiar  with  results 
possible  with  the  different  methods  of  lighting,  one  can  definitely 
recommend  a  form  of  lighting  that  would  be  best  for  the  cus- 
tomer's special  case.  The  gas  salesmen  and  the  electric  salesmen 
should  not  be  allowed  to  compete  for  his  business,  as  they  are 
only  liable  to  confuse  him  as  to  the  best  method  of  lighting  his 
establishment. 

It  would  be  well  for  lighting  salesmen  to  study  the  results  of 
different  types  of  installations  at  night.  There  is  a  broad  educa- 
tion to  be  obtained  by  studying  and  analyzing  different  lighting 
installations,  both  as  to  a  judgment  of  the  present  results  and  a 
possible  change  that  would  result  in  improved  lighting  conditions, 
necessitating  only  a  slight  expenditure  in  revising  the  installation. 

As  the  central  station  and  its  representatives  give  recommenda- 
tions for  lighting,  why  should  they  not  also  follow  these  with  the 
actual  sale  and  installation  of  the  necessary  equipment.  They  can 
then  be  absolutely  certain  that  the  result  will  be  satisfactory  and 
forestall  the  possibility  of  unsatisfactory  results  that  often  come 
about  when  the  instructions  are  turned  over  to  some  other  con- 
cern to  carry  out.  Such  a  method  of  handling  business  keeps  the 
entire  responsibility  just  exactly  where  it  belongs,  namely  with 
the  central  station,  who  has  not  only  recommended,  but  installed 
the  equipment  to  give  best  results. 

Chairman,  C.  A.  LittlEField:  A  great  deal  has  been  said 
this  morning  about  education.  A  special  man  or  a  man  holding  a 
managerial  position  is  highly  developed,  not  alone  in  his  particu- 
lar field,  but  in  the  general  line  of  his  business.  But  it  is  not  so 
much  of  him  I  wish  to  speak  as  of  the  man  who  is  out  on  the 
street — the  average  salesman.  It  is  not  an  over-easy  matter  to 
get  a  good  salesmen;  some  people  are  naturally  salesmen,  they 
are  born — not  made.  But  it  is  sometimes  possible  to  improve 
even  this  man  by  giving  him  a  broader  educational  foundation 
upon  which  he  may  base  his  selling  problems.  Some  people  can 
sell  anything  from  a  domino  to  a  dynamo.  But  as  we  study  this 
paper  by  Messrs.  Spaulding  and  Potter,  we  cannot  help  but  be 
impressed  with  the  fact  that  even  these  successful  salesmen  have 


806     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

something  to  learn.  I  presume  there  is  not  a  manager  of  a  single 
corporation — large  or  small — who  is  not  constantly  striving  to 
improve  the  calibre  of  his  men,  and  it  is  this  fact  that  is  causing 
such  a  widespread  interest  in  the  general  subject  of  the  education 
of  salesmen.  We  see  this  in  the  National  Commercial  Gas  As- 
sociation, the  National  Electric  Light  Association,  and  other  as- 
sociations of  larger  and  smaller  sizes  that  are  conducting  courses 
of  education.  It  is  really  astonishing  to  see  the  results  that  are 
being  achieved  by  these  several  organizations  and  the  eager  re- 
sponses that  are  being  made  to  the  advertised  courses,  not  only 
by  the  companies  for  their  men,  but  by  the  men  themselves,  who 
are  paying  for  these  courses  out  of  their  own  pockets,  with  the 
sole  object  of  making  themselves  better  and  broader  men.  Men 
themselves  are  beginning  to  realize  that  their  positions  are  much 
more  secure  the  higher  they  are  developed,  and  in  the  proportion 
as  they  themselves  strive  to  improve  their  mental  capacities  do 
they  improve  their  position  as  employees  of  successful  corpora- 
tions. I  think  that  altogether  too  little  has  been  said  on  this  most 
important  subject.  Speaking  personally,  I  am  very  glad  indeed 
that  this  paper  has  been  brought  before  this  convention.  I  should 
like  you  to  think  this  over  seriously,  and  if  you  are  in  a  man- 
agerial position  yourself  to  put  into  effect  the  many  recommenda- 
tions of  this  excellent  paper.  But  whether  your  position  is  that 
of  a  manager  or  otherwise,  I  trust  that  you  will  bring  it  to  the  at- 
tention of  the  executives  of  your  company  on  your  return  home. 
Is  there  any  further  discussion? 

Mr.  Z.  M.  Hyer:  I  think  a  salesman  can  do  better  work 
if  he  has  ony  one  commodity  to  sell.  For  myself  I  doubt  if  I 
could  go  out  and  conscientiously  recommend  gas,  having  sold 
electricity  for  a  number  of  years.  I  could  not  do  this  unless  I 
were  employed  by  a  gas  company  that  was  not  handling  electric 
products  and  I  feel  that  the  gas  salesman  would  be  in  the  same 
position :  he  could  not  conscientiously  talk  up  electricity  after 
having  sold  gas.  It  is  natural  that  a  man  would  feel  a  certain 
loyalty,  have  a  certain  feeling  about  the  commodity  that  he  is 
selling;  he  has  to  have  confidence  in  it,  and  faith  in  it,  and  if 
he  has  that  I  do  not  see  how  he  could  offer  another  form  of 
illumination  as  a  substitute.  I  think  both  illuminants  have  their 
special  uses,  but  for  illuminating  purposes  I  think  electricity  has 


GAS   AND   ELECTRIC   COMPANIES  807 

many  advantages  over  gas  and  I  don't  feel  that  I  could  go  out 
and  recommend  gas  to  a  customer  for  all  purposes ;  I  could  not 
go  out  and  be  unbiased  in  my  judgment. 

Mr.  Norman  Macbeth  :  The  paper  is  valuable  in  calling  at- 
tention to  a  serious  situation  existing  in  many  territories  served 
by  combination  companies.  The  lack  of  reasonably  aggressive 
sales  methods  and  the  policy  of  waiting,  often  results  in  letting  in 
the  gasoline  isolated  plant.  At  the  bottom  of  the  second  page 
there  is  the  following  statement :  "It  would  seem  that  there  is  no 
good  reason  for  a  gas  or  electric  company  under  one  management 
adopting  a  policy  which  encourages  only  one  source  of  supply. 
The  duty  of  such  a  company  is  not  to  predetermine  what  service 
to  sell,  but  to  give  the  customer  the  benefit  of  the  best  advice 
and  leave  to  him  the  decision."  It  is  true  that  there  are  a  great 
many  factors  entering  into  an  installation  with  which  the  cus- 
tomer is  more  familiar  than  the  representative  of  a  utility  com- 
pany. Given  the  right  information  about  rates,  costs  and  load 
factor  conditions  he  quickly  decides  whether  he  will  have  gas 
or  electric  service ;  there  is  very  little  opportunity  for  argument, 
provided,  of  course,  that  the  information  given  the  customer  is 
as  unbiased  as  it  should  be. 

Toward  the  end  of  the  paper  it  is  stated,  "It  is  the  opinion 
of  the  writers  that  in  order  that  a  gas  and  electric  company 
under  one  management  may  give  the  best  lighting  service,  sep- 
arate representatives  who  are  specialists  in  the  application  of 
each  lighting  source  should  be  employed."  It  has  never  appeared 
to  me  that  it  is  necessary  to  have  separate  representatives.  The 
extent  of  the  information  sought  by  the  consumer  is  not 
difficult  to  secure,  nor  should  it  be  involved  as  to  require 
separate  specialists.  The  average  commercial  installation  to  a 
specialist  presents  nothing  difficult ;  the  possibilities  of  the  avail- 
able gas  and  electric  sources  have  been  so  thoroughly  studied  and 
their  limitations  are  so  well  known  that  many  of  the  installations 
required  are  simple  problems.  A  plain  presentation  of  the  facts 
regarding  the  gas  or  electric  service  available  for  a  particular 
purpose  is  sufficient  to  enable  the  consumer  to  reach  a  decision. 

There  is  just  one  more  question.  How  are  the  men  paid ; 
are  they  given  a  regular  salary  or  do  they  work  on  a  commission 


8o8     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

basis ;  and  also  how  many  hours  a  day  do  they  work  ?  I  have 
known  cases  where  men  have  worked  on  a  commission  basis 
where  they  could  not  limit  their  work  to  the  ordinary  nine  to 
five  day.  Their  interest  in  the  work  and  the  necessity  of  seeing 
their  customers  at  night  required  that  they  work  until  ten  o'clock 
at  night.  How  do  you  arrange  the  day's  period  and  compen- 
sation ?    What  are  your  working  hours  ? 

Mr.  T.  J.  LiTLE,  Jr.  :  Relative  to  the  sale  of  both  gas  and  elec- 
tric units  by  combination  companies,  I  would  like  to  say  that  there 
are  certain  corporations  in  this  country,  such  as  large  department 
stores,  which  are  coming  to  believe  that  for  their  own  protection 
no  one  system  of  illumination  should  be  entirely  depended  on. 
They  believe  that  for  continuous  illumination  in  their  store  it 
is  advisable  to  have  both  forms  of  lighting.  Now  I  am  not 
speaking  in  a  general  way;  I  have  in  mind  several  instances 
where  these  great  corporations  operate  both  systems  continu- 
ously, not  just  for  an  emergency  to  be  used  in  case  of  accident, 
but  as  a  continuous  system,  operated  simultaneously.  Now  the 
combination  company  in  serving  a  community  has  an  advantage 
that  the  separate  company  does  not  have,  and  it  seems  to  me 
that  broad  minded  empolyees  of  such  a  company  should  bear 
that  in  mind.  I  understand  and  feel  myself  that  the  illuminating 
engineer  is  either  in  favor  of  electric  or  gas  illumination,  but 
if  he  is  connected  with  a  combination  company  he  should  sell 
both  products  and  I  don't  think  there  should  be  a  single  large 
department  store  in  this  country,  nor  any  large  building,  in  which 
a  great  number  of  people  assemble,  in  which  the  single  system 
should  be  installed ;  some  auxiliary  system  should  be  provided 
and  this  should  provide  continuous  illumination.  Take,  for  in- 
stance, the  basements  in  the  large  department  stores.  If  any- 
thing happens  to  the  lighting  system,  a  general  panic  is  likely 
to  occur  and  there  will  be  a  scramble  for  the  exits  and  accidents 
are  sure  to  happen ;  and  I  think  that  these  stores  should  provide 
an  auxiliary  system  just  to  meet  such  emergencies.  There  are 
local  ordinances  that  provide  for  this  in  armories  and  other 
large  buildings  where  a  number  of  people  are  gathered  and  I 
think  the  lighting  companies  themselves  should  provide  for  the 
use  of  some  auxiliary  system. 


GAS   AND   ELECTRIC   COMPANIES  809 

Mr.  Z.  M.  HyEr:  I  might  give  a  little  information  that  would 
be  of  interest,  relative  to  the  dual  lighting  in  New  York  City. 
We  have  done  away  with  dual  lighting  in  large  buildings  to  a 
large  extent.  This  is  due  to  the  fact  that  the  city  authorities 
compelled  the  electric  lighting  companies  to  put  in  two  distinct 
services.  Our  company  has  developed  an  apparatus,  an  auto- 
matic switch,  by  which  it  is  possible  to  switch  the  current  from 
one  service  to  the  other  automatically.  If  the  service  goes  off 
on  one  circuit  the  switch  operates  which  immediately  cuts  in  the 
other  circuit.  We  are  the  only  company  that  I  know  of  that 
use  a  switch  of  this  kind.  I  had  an  experience  only  a  short  time 
ago:  the  electrical  contractors  of  New  York  City  has  an  outing 
on  Staten  Island  and  were  going  to  have  a  vaudeville  entertain- 
ment in  the  evening.  We  assembled  in  the  hall  and  when  the 
first  number  was  put  on  the  electric  lights  all  went  out;  in  fact 
they  went  out  all  over  that  section  of  the  island.  They  had  a 
dual  system  of  lighting  installed  in  the  building  and  the  porter 
came  along  with  a  step  ladder  and  matches  to  light  the  gas 
lamps.  The  first  fixture  he  went  to  had  four  jets  on  it  and 
after  about  15  minutes  he  succeeded  in  getting  one  of  them 
lighted ;  the  delay  was  due  to  the  fact  that  he  had  to  renew  all  the 
mantles.  We  were  an  hour  waiting  for  him  to  get  all  the  gas 
fixtures  in  proper  shape  and  by  the  time  he  did  the  electric  lamps 
were  in  operation  again,  so  the  gas  was  not  needed. 

Mr.  L.  C.  Porter  :  I  would  like  to  bring  out  the  point  that  gas 
when  used  as  an  emergency  system  usually  consists  of  a  few 
open  flame  jets  without  any  means  of  lighting  them,  unless  some- 
body goes  down  in  his  pocket  and  gets  a  match ;  and  then  possibly 
the  key  to  the  fixture  can  not  be  found,  which  is  as  bad  as  if  there 
were  no  fixture  there.  I  do  not  call  that  a  dual  system  at  all. 
The  dual  system  that  is  built  along  lines  as  nearly  identical  as 
possible  and  both  controlled  by  the  same  switchboard  is  the  only 
kind  of  a  system  to  install.  The  point  was  brought  up  about 
glassware  being  developed  for  gas  lighting  that  will  give  the  same 
appearance  as  the  electric  lighted  glassware.  I  think  the  manu- 
facturers of  mantles  can  get  the  desired  color  in  a  measure  by 
using  an  amber  light  mantle  and  also  I  think  the  electric  man 
should  do  his  part ;  he  should  use  a  lamp  with  a  very  white  light, 
possibly  a  gas  filled  tungsten  lamp,  and  I  think  it  could  be  worked 


8lO     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

and  developed  so  that  one  could  not  detect  the  difference  between 
the  sources  either  when  lighted  or  unlighted. 

Mr.  T.  J.  Litle,  Jr.  :  I  would  like  to  say  one  more  word. 
Some  people  argue  that  there  is  no  necessity  for  a  dual  system  as 
they  have  never  had  occasion  to  use  it,  but  you  might  as  well  say 
that  there  is  no  necessity  to  have  fire  escapes  on  a  certain  build- 
ing because  you  have  never  had  a  fire  there.  I  think  a  dual 
system  is  absolutely  necessary  in  halls  and  buildings  where  a 
large  number  of  people  are  apt  to  congregate.  Some  of  the 
larger  corporations  have  insisted  that  the  illuminating  company 
themselves  do  this  work  and  I  know  of  several  cases  where  an 
illuminating  company,  supplying  only  one  system,  was  compelled 
even  though  they  had  to  buy  the  gas,  to  put  in  the  dual  system. 
In  a  combination  company,  of  course,  this  would  not  be  necessary. 

Mr.  G.  B.  Nichols:  In  reference  to  the  question  of  dual 
lighting  systems,  I  believe  that  this  is  somewhat  a  question  of 
locality,  depending  on  the  class  of  service  furnished.  In  first- 
class  cities  generally,  where  the  service  is  of  such  a  nature  that 
interruptions  are  very  seldom,  if  any,  and  particularly  those 
cities  where  all  of  the  wires  are  underground  and  where  on  large 
installations  dual  systems  of  electric  feeders  are  extended  into 
the  building,  it  appears  unnecessary  for  two  classes  of  service. 
In  cities,  however,  where  the  electric  service  is  maintained  by 
overhead  lines  and  particularly  those  fed  from  water  power 
plants  at  a  considerable  distance,  a  dual  system  undoubtedly 
would  be  of  some  advantage. 

Mr.  F.  A.  Vaughn  :  I  can  see  where  the  independent  con- 
sulting engineer  has  considerable  advantage  over  some  of  you.  I 
think  he  can  look  at  the  problem  without  any  bias  from  either 
side.  The  remarks  of  a  previous  speaker  remind  me  of  a  system 
which  has  been  installed  in  two  department  stores  in  Milwaukee 
where  it  was  felt  decidedly  necessary  to  have  an  emergency  gas 
installation.  Instead  of  having  the  additional  gas  units  out  of 
symmetry,  the  gas  unit  was  made  as  nearly  identical  as  possible 
with  the  electric  unit;  its  apearance  was  almost  identical,  even  to 
the  extent  of  carrying  out  the  chain  effect.  A  rigid  hollow  chain 
was  made,  which  would  allow  the  gas  to  flow  to  the  mantle.  To 
the  customer,  the  store  appeared  to  be  lighted  by  electricity — by 


GAS    AND   ELECTRIC    COMPANIES  8ll 

only  one  form  of  illumination —  and  in  case  of  accident  to  either 
system  there  would  be  sufficient  light  available  to  illuminate  the 
counters.  This  installation  was  not  only  to  guard  against  acci- 
dent in  case  of  panic,  but  also  against  theft,  which  is  a  large 
factor  at  such  a  time.  The  details  were  carried  out  a  little  further 
by  providing  push  buttons  for  lighting  the  gas ;  these  were  on  the 
same  gang  as  the  electric  push  buttons  and  the  clerks  did  not 
know  which  unit  they  were  turning  on,  gas  or  electric.  This 
made  a  complete  continuous  auxiliary  system  as  an  emergency 
equipment.  The  ordinary  emergency  equipment  is  sometimes 
difficult  to  get  on  in  time  to  prevent  a  panic. 

Mr.  N.  H.  Potter  :  Mr.  Macbeth  mentioned  the  combination 
man  versus  the  special  man  selling  both  kinds  of  energy.  He 
brought  out  the  only  strong  argument  in  favor  of  one  man  selling 
both  kinds  of  energy,  namely,  gas  and  electricity.  Naturally  there 
is  a  difference  of  opinion  regarding  which  is  the  best  plan  to 
adopt,  but  as  stated  in  the  paper,  we  think  that  special  men  are 
better  than  the  combination  man.  A  combination  man  is  too 
prone  to  follow  the  lines  of  least  resistance;  he  naturally  thinks 
that  he  will  get  the  installation  for  either  gas  or  electricity ;  hence 
he  may  not  advise  the  best  installation. 

Regarding  the  number  of  men  employed  by  our  company,  there 
are  four  specialists  on  gas,  and  eight  on  electric  lighting,  besides 
fourteen  solicitors  who  sell  gas  lighting  units  throughout  resi- 
dential and  business  sections.  These  men  are  educated  to  such 
an  extent  that  they  are  competent  to  properly  advise  a  customer 
as  to  the  best  installation  for  his  particular  requirements. 
Strictly  speaking,  they  are  not  technical,  but  practical  men,  and 
they  are  forced  to  meet  conditions  as  they  find  them. 

In  a  majority  of  cases  their  work  consists  principally  of  trying 
to  correct  mistakes  that  were  made  in  the  layout  of  the  original 
installation,  regarding  location  of  outlets,  etc.  They  come  in 
contact  with  many  conditions  of  this  character.  If  a  customer 
has  insufficient  or  improperly  placed  outlets  in  a  store,  the  only 
thing  to  do  is  to  extend  the  line,  place  an  additional  outlet  or 
change  the  location  of  the  existing  outlets  and  then  install  the 
best  fixture  for  his  particular  requirement. 

Mr.  Ely  spoke  of  the  men  in  the  house  lighting  maintenance 
14 


8l2     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

department.  I  think  this  is  a  more  important  proposition  in  a 
gas  company  than  in  the  electric  company.  We  furnish  the 
repairs  and  the  lamps  in  good  condition  free,  but  charge  for  the 
material  used  in  putting  the  lamp  in  perfect  condition.  This, 
however,  is  a  new  department  and  is  in  an  experimental  stage,  but 
promises  to  be  a  very  good  addition  to  our  present  organization. 

Mr.  Owens  touched  on  the  gas  company  advising  a  good  type 
of  fixture,  and  installing  them.  I  take  it  that  he  means  the  com- 
pany would  install  the  fixtures.  We  have  tried  to  place  some 
semi-indirect  lighting  in  homes  and  stores,  but  the  main  disad- 
vantage we  have  to  contend  with  is  that  the  customer  is  inclined 
to  look  at  the  unit  itself,  thereby  considering  the  intensity  of 
the  source  instead  of  noting  the  effect  and  the  utilization  of 
the  light  to  a  better  advantage.  This  is  due  to  a  lack  of  edu- 
cation on  the  part  of  the  general  public,  a  condition  which  will 
take  some  time  to  entirely  overcome,  and  accounts  for  the  higher 
intensity  units  meeting  favor. 

Mr.  Moulton  said  that  the  representative  should  consult  the 
department  head,  that  he  should  not  be  allowed  to  lay  out  the 
installation,  and  that  he  should  consult  the  engineer.  This  is 
done  in  our  company  if  the  salesman  is  at  all  in  doubt.  The 
sales  manager  also  instructs  the  man  regarding  just  what  are 
considered  good  installations  for  different  cases  and  how  to  install 
them.  Of  course  the  longer  a  man  is  with  the  company  the  more 
proficient  he  becomes,  but  we  cannot  always  have  men  with  ex- 
perience filling  these  positions.  It  is  therefore  necessary  to 
employ  from  time  to  time  new  men,  who  are  instructed  as  soon 
as  possible.  It  is  better  that  men  should  be  competent  to  handle 
the  average  case  instead  of  bringing  every  installation  to  the 
attention  of  the  department  head. 

If  the  manufacturers  of  glassware  would  adopt  some  measures 
by  which  they  could  make  a  bowl  which  when  illuminated  by  gas 
would  give  the  same  color  as  a  bowl  illuminated  by  elec- 
tricity, such  a  scheme  would  be  a  great  improvement  toward 
perfecting  the  appearance  of  dual  installations.  At  present  there 
is  a  noticeable  difference  in  the  color  of  the  glassware  when 
lighted  by  these  two  agents.  The  glassware  lighted  by  gas  retains 
nearly  the  same  color  when  lighted  as  when  extinguished,  while 
electric  light  imparts  an  orange  or  pink  tint  to  the  glassware. 


GAS  AND  ELECTRIC   COMPANIES  813 

The  elimination  of  this  condition  can  only  be  accomplished  by 
development  of  glassware  by  manufacturers  of  glassware. 
Manufacturers  of  fixtures  do  not  appear  to  give  enough  attention 
to  the  design  and  construction  of  good  combination  fixtures. 

All  the  electric  solicitors  are  on  a  salary.  The  gas  solicitors 
are  on  a  salary  with  an  addition  of  a  bonus  system.  Our  solicitors 
work  from  8  a.  m.  until  5  p.  m.  unless  the  men  wish  to  work 
after  hours  in  order  to  inspect  lighting  conditions  after  dark,  or 
keep  appointments  after  hours.  All  solicitors  do  this  more  or 
less,  especially  those  who  have  a  desire  to  get  all  the  business 
possible. 


814     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

LIFE  TESTING  OF  INCANDESCENT  LAMPS  AT  THE 
BUREAU  OF  STANDARDS.* 


BY  G.  W.  MIDDLEKAUEE,  B.   MULLIGAN  AND  J.  E.  SKOGLAND. 


Synopsis:  The  method  employed  by  the  Bureau  of  Standards  in  the 
inspection  and  life  testing  of  incandescent  lamps  for  the  federal  govern- 
ment is  outlined  and  a  description  of  the  power  plant,  the  life  racks,  and 
the  photometer  is  given.  Particular  attention  is  directed  to  the  special 
equipment  of  the  photometer.  This  includes  a  watts-per-candle  computer 
and  a  recording  device  by  which  observed  values  of  candlepower,  watts, 
watts  per  candle,  and  actual  life  are  recorded  on  a  separate  card  for  each 
lamp.  These  records  are  made  in  such  a  way  that  life  at  forced  efficiency 
is  corrected  to  life  at  normal  without  computation  or  reference  to  tables 
of  factors.  The  procedure  in  actual  measurement  and  testing  is  described 
with  considerable  detail. 


CONTENTS. 

Introduction 816 

Purposes  of  a  Life  Test 817 

1.  General   818 

2.  Special  Purposes  of  Bureau  of  Standards  Tests 819 

Selection  of  Life  Test  Lamps 820 

Measurement  of  Life  Test  Lamps 821 

1.  The  Life  Test  Photometer 821 

a.  General  Construction 821 

b.  Instruments  and  Candlepower  Scales 822 

c.  Wiring  and  Special  Resistances 823 

d.  The  Watts-per-candle  Computer. 824 

e.  The  Recording  Device 825 

f.  Features  of  the  Record 827 

a.    Detection  and  Compensation  of  Errors    827 

p.    Increased  Accuracy  in  Life  Values 828 

2.  Methods  of  Measuring  and  Recording  Observed  Values  829 

a.  Rating  of  Lamps  for  Life  Test 829 

b.  Details  of  a  Photometric  Run 829 

The  Life  Test 832 

1 .  Design  of  the  Installation 832 

a.  Wiring  and  Voltage  Adjustment 833 

b.  Voltage  Regulation 834 

c.  Current  Generator  and  Voltage  Transformers  • .  •   835 

d.  The  Life  Test  Racks 835 

e.  Measurement  of  Lite  Test  Periods 836 

2.  Records  Taken  During  Life  Test 836 

Summaries  of  Life  Values 836 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,   Washington,   D.   C,   September  20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


MIDDLEKAUFF,  MULLIGAN,  SK0GLAND:    TESTING  OF  LAMPS      815 

INTRODUCTION. 

The  first  edition  of  "Standard  Specifications  for  the  Purchase 
of  Incandescent  Electric  Lamps,"1  issued  in  1907,  was  the  result 
of  concerted  action  on  the  part  of  the  federal  government  de- 
partments, representative  lamp  manufacturers,  the  Electrical 
Testing  Laboratories,  and  the  Bureau  of  Standards.  The  pur- 
pose of  these  specifications  was  to  establish  such  standard  methods 
of  initial  inspection  and  life  testing  as  would  permit  their  adoption 
by  the  government  and  make  them  available  to  the  general  public ; 
so  that  all  purchasers  of  incandescent  lamps,  by  including  these 
specifications  in  contracts,  might  realize  the  benefits  of  their  use. 

Application  of  these  specifications  necessitates  careful  initial 
inspection  and  reliable  life  tests.  The  specified  life  test  procedure 
is  so  exacting  and  the  quantity  of  lamps  to  be  tested  on  any  con- 
siderable contract  so  large  that  the  purchaser,  unless  his  facili- 
ties for  testing  are  complete,  must  of  necessity  refer,  at  least,  the 
life  test  work  to  some  reputable  testing  laboratory.  It  was,  there- 
fore, the  natural  outcome  that  the  Bureau  of  Standards  should 
be  sought  and  recognized  by  departments  of  the  government  as 
the  authority  on  life  tests.  Initial  inspection  is  so  closely  related 
to  life  test  procedure  and  its  efficiency  so  pronounced  in  the  ef- 
fect on  the  results  of  life  test  that  the  Bureau,  almost  of  necessity, 
undertook  this  part  of  the  work  as  well. 

The  design  of  a  life  test  installation  was  therefore  begun  early 
in  1908.  This  was  developed  by  Messrs.  E.  P.  Hyde,  F.  E.  Cady, 
C.  F.  Sponsler,  and  H.  B.  Brooks,  under  the  direction  of  Dr. 
E.  B.  Rosa,  chief  of  the  Electrical  Division  which  included  the 
photometric  section.  A  lamp  inspector  was  appointed  in  July  and 
the  plant  was  put  into  operation  in  October  of  the  same  year 
(1908).  About  this  time  Dr.  Hyde  and  Mr.  Cady  left  the  service 
of  the  Bureau  and  the  work  has  since  been  carried  on  and  de- 
veloped mainly  by  the  authors  of  the  present  paper,  under  the 
direction  of  the  chief  of  the  electrical  division. 

The  whole  life  test  equipment  was  originally  installed  in  the 
mechanical  building  which  houses  the  power  plant  of  the  Bureau. 
In  191 3  the  life  racks,  transformers,  and  photometric  apparatus 
were  removed  to  two  adjoining  rooms  on  the  third  floor  of  the 

1  These  specifications  are  issued  by  the  Bureau  of  Standards  as  Circular  No.  13,  which 
has  been  revised  from  time  to  time  and  is  now  in  the  seventh  edition. 


8l6     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

new  electrical  building  which  was  then  nearing  completion.  Al- 
though some  parts  of  the  equipment  are  differently  arranged  in 
the  new  building,  the  general  plan  has  remained  the  same  as  orig- 
inally designed. 

The  introduction  of  new  classes  of  lamps,  however,  rendered  it 
advisable  to  make  considerable  changes  in  the  original  photo- 
metric equipment  and  in  the  details  of  the  method  of  testing. 
These  changes  have  been  made  from  time  to  time  by  those  who 
have  been  most  intimately  associated  with  the  work.  The  equip- 
ment as  it  now  stands  and  the  present  method  of  the  Bureau's 
life  testing  procedure  in  all  its  details  are,  therefore,  the  result  of 
a  gradual  development  in  which  various  persons  have  been  of 
assistance. 

From  the  beginning  the  magnitude  of  the  work  of  inspection 
and  life  testing  has  been  constantly  increasing  year  by  year  in 
consequence  of  the  natural  growth  of  the  government's  pur- 
chases of  incandescent  lamps.  Fortunately,  however,  the  quality 
of  the  lamps  supplied  has,  in  most  cases,  been  fairly  uniform  and 
also  above  the  requirements  of  the  specifications,  so  that  full  and 
reliable  data  on  the  lamps  supplied  by  each  manufacturer  have 
been  obtained  by  submitting  to  life  test  a  yearly  total  of  not  over 
five  thousand  lamps  which  represent  about  one  and  a  quarter  mil- 
lions of  inspected  lamps. 

Since  inspections  and  tests  are  made  primarily  for  departments 
of  the  government,  outside  tests  are  accepted  only  "when  special 
circumstances  make  the  test  of  more  than  usual  importance."  A 
specified  fee  is  charged  for  work  of  this  kind.2 

In  the  following  description  of  apparatus  and  methods  of  life 
test,  an  attempt  is  made  to  indicate  the  essential  features  of  this 
work  and  the  manner  in  which  the  testing  is  at  present  actually 
conducted. 

PURPOSES  OF  A  LIFE  TEST. 

General. — A  life  test  may  be  run  for  any  one  of  several  rea- 
sons. For  example,  a  manufacturer  who  desires  quick  results  in 
order  to  test  the  effect  of  some  modified  construction  or  change 
in  material  may  choose  to  burn  the  lamps  selected  at  a  voltage 

2  Fees  for  Electric,  Magnetic,  and  Photometric  Testing;  Bureau  of  Standards  Circular 
No.  6,  p.  26,  1914. 


MIDDLEKAUFF,  MULLIGAN,  SKOGLAND :    TESTING  OF  LAMPS      817 

greatly  in  excess  of  that  employed  in  normal  operation  thus  caus- 
ing the  lamps  to  fail  in  a  few  hours.  Unwarranted  confidence  is 
sometimes  placed  in  tests  of  this  kind  for  other  purposes,  and 
attempts  are  made  to  evaluate  life  at  normal  voltage  from  the  test 
results,  whereas  no  known  constants  for  these  life  corrections 
will  apply  in  all  cases.  Although  relative  results  may  be  of  some 
value,  they  often  point  to  conclusions  not  at  all  in  agreement  with 
those  which  might  be  drawn  from  a  test  at  a  voltage  correspond- 
ing more  nearly  to  rated  efficiency. 

Comparative  tests  of  greater  value  may  be  run  at  or  near 
normal  operating  efficiency,  even  on  a  line  of  uncertain  voltage 
regulation,  by  placing  both  tests  side  by  side  on  the  same  circuit. 
However,  the  voltage  applied  to  the  lamps  of  each  test  must  be 
such  that  the  average  efficiency  of  the  two  groups  is  the  same,  or, 
if  differently  rated  and  burned  at  one  voltage,  correction  factors 
must  be  applied  to  reduce  the  test  results  of  one  group  to  their 
equivalent  life  at  the  efficiency  of  the  other  group.  In  all  cases 
the  initial  (test)  efficiency  must  be  known,  if  test  results  are  to 
be  correctly  interpreted.  It  should  be  emphasized  that  relative 
results  only  are  obtained  by  such  a  test,  unless  the  voltage  regu- 
lation is  that  indicated  in  the  specifications  under  which  the  lamps 
are  tested. 

In  contradistinction  to  these  rough  tests  are  those  in  which 
actual  values  of  life  at  normal  efficiency  are  obtained  for  any 
group  of  lamps.  This  necessitates  great  care  in  initial  rating  and 
constancy  of  voltage  at  which  the  lamps  are  operated  on  the  life 
test.  By  choosing  test  efficiencies  within  a  range  through  which 
factors  for  life  correction  have  been  fully  established,  the  time 
necessary  to  complete  the  tests  may  be  materially  shortened. 
Life  tests  at  the  Bureau  of  Standards  are  of  this  kind. 

2.  Special  Purposes  of  Bureau  of  Standards  Tests. — Although 
the  chief  concern  of  departments  of  the  government  in  connec- 
tion with  tests  under  Standard  Specifications  is  to  secure  reason- 
ably prompt  delivery  of  lamps  which  meet  the  specified  require- 
ments, a  consideration  almost  equal  in  importance  is  the  determin- 
ation from  the  life  tests  of  the  relative  standing  of  the  various 
manufactures  as  regards  quality  of  output.     The  relative  quality 


8l8     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

thus  determined  is  referred  to  and  given  due  weight  in  deciding 
upon  future  awards  of  contract. 

The  evaluation  of  a  lamp  life  to  as  high  a  degree  of  accuracy 
as  is  possible  in  testing  a  large  quantity  of  lamps  has  no  doubt 
guided  the  manufacturers  to  some  extent  in  their  improvements 
of  efficiency  ratings,  notably  in  the  tungsten  lamp.  Consequently 
manufacturers  and  purchasers  receive  all  available  service  and 
assistance  not  only  from  the  actual  test  results  but  from  con- 
clusions drawn  therefrom. 

SELECTION  OF  LIFE  TEST  LAMPS. 

The  Standard  Specifications,  in  accordance  with  which  all 
Bureau  tests  of  lamps  for  the  government  are  made,  recognize  the 
importance  of  a  proper  selection  of  samples  for  life  test.  It  is 
assumed  that  no  lamp  can  accurately  represent  the  life  of  a  group 
unless  it  accurately  represents  the  group  in  other  respects.  Hence 
great  care  is  exercised  in  the  selection  of  the  samples  for  life 
test,  and  no  sample  is  taken  unless  the  lamps  have  first  passed 
the  prescribed  initial  tests. 

These  initial  tests  are  made  by  Bureau  inspectors3  at  the  factory 
of  the  manufacturer,  and  regular  factory  apparatus  is  used.  Such 
testing  equipment  as  is  required  in  the  work  of  inspection  is  usually 
assembled  in  an  inspection  department,  so  that  factory  work  is  not 
interfered  with.  In  the  larger  factories,  where  initial  tests  under 
specifications  are  made  for  a  number  of  purchasers,  certain  opera- 
tors are  employed  most  or  all  of  the  time  in  the  inspection  de- 
partment. It  is  their  duty  to  render  the  inspectors  such  assistance 
as  may  be  required  in  making  initial  tests.  Besides  one  or  more 
photometers  this  department  contains  vacuum  test  equipment, 
special  sockets  supplied  with  current  for  lighting  up  the  test  lamps, 
and,  in  factories  manufacturing  tungsten  lamps,  racks  for  sea- 
soning or  "aging"  the  lamps  selected.  This  last-named  equip- 
ment has  been  introduced  as  required  by  Standard  Specifications, 
because  of  the  new  process  of  exhaust,  which  produces  a  ductile 
filament,  not,  however,  stable  in  its  electrical  characteristics ;  so 
that  a  certain  amount  of  burning  is  necessary  before  the  current 
and  candlepower  reach  values  sufficiently  steady  for  accurate 
measurement. 

3  One  inspector  is  employed  continuously  and  another  is  sent  out  to  assist  him  when 
necessary. 


MIDDLEKAUFF,  MULLIGAN,  SKOGLAND :    TESTING  OF  LAMPS      819 

The  quantity  of  lamps  selected  for  initial  tests  is  specified 
as  5  per  cent,  of  the  total  of  a  lot  including  only  lamps  of  the 
same  size,  class,  and  voltage  range,  and  not  less  than  ten  lamps 
from  any  one  lot.  The  number  of  lamps  to  be  included  in  a  lot  is 
left  to  the  judgment  of  the  inspector. 

The  lamps  must  conform  to  certain  specified  requirements  as 
regards  bulbs,  bases,  filaments,  and  vacuum.  Lamps  which  pass 
these  requirements  are  then  run  on  the  photometer,  and  in  de- 
termining their  acceptability,  tables  of  allowable  limits  of  watts 
and  candlepower  or  of  watts  per  candle,  as  given  in  the  specifica- 
tions, are  applied.  In  calibrating  the  photometer  for  these  tests 
the  inspector  uses  standards  which  have  been  certified  by  the 
Bureau  for  candlepower  and  current.  A  lot  of  lamps  is  accepted 
if  the  number  of  defective  lamps  on  either  test  is  below  the  speci- 
fied percentage  of  the  total. 

The  next  step  is  to  compute  from  the  records  of  the  photom- 
etric test  the  mean  values  of  individual  groups  of  test  lamps 
representing  not  more  than  250  lamps  from  any  one  lot.  The 
lamp  nearest  the  mean  value  of  each  group  is  selected,  labeled, 
and  sent  to  the  Bureau  to  represent  the  group  on  life  test. 

MEASUREMENT  OF  LIFE  TEST  LAMPS. 

In  order  to  facilitate  the  photometric  measurement  of  the  life 
test  lamps  and  still  secure  a  permanent,  accurate,  and  as  nearly 
as  possible,  automatic  card  record  of  each  lamp  tested,  certain 
modifications  and  additions  have  been  made  to  the  photometer 
used  in  this  work.  As  these  features  are  decidely  special  and  not 
found  elsewhere,  their  construction  and  use  are  fully  explained 
in  what  follows,  not  only  that  the  method  of  measurement  de- 
scribed later  may  be  better  understood  but  also  that  the  equip- 
ment may  be  duplicated  by  anyone  desiring  to  use  it. 

1.  The  Life  Test  Photometer. — (a)  General  Construction. — 
The  general  construction  of  the  life  test  photometer  is  shown  in 
Fig.  1.  A  Lummer-Brodhun  contrast  photometer  head  is  mounted 
upon  a  movable  carriage  between  the  test  lamp  and  comparison 
source,  the  distance  between  the  last  two  mentioned  being 
250  cm.  The  comparison  lamp,  a  100-watt  tungsten,  is  placed 
in  a  mirror-backed  box  fronted  by  a  ground  glass  window.  This 
window  presents  an  approximately  uniformly  illuminated  surface 


820     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

to  the  photometer,  so  that  the  glass  plate  acts  as  the  effective  light 
source  and  is  so  considered.  The  mirrors  within  the  box  are 
employed  to  increase  the  illumination  of  the  window  to  a  practical 
working  value,  the  effective  area  of  the  window  being  adjusted  by 
means  of  a  variable  diaphragm  or  shutter,4  this  adjustment 
being  used  in  calibrating  the  photometer.  By  the  screening  sys- 
tem used,  stray  light  is  so  effectively  excluded  from  the  photom- 
eter screen  that  measurements  are  made  in  a  curtained  booth  about 
8  feet  high  under  conditions  which  might  be  denned  as  approxi- 
mately "semi-daylight." 

The  standard  lamp  socket  may  be  rotated  in  a  direction  depend- 
ing upon  the  position  of  a  knee  switch  which  reverses  the  current 
in  the  armature  of  the  motor;  so  that  lamps  may  be  rapidly  turned 
in  or  out  of  the  socket  and  may  be  rotated  during  measurements. 

Current  and  voltage  leads  are  joined  to  the  lamp  rotator  by 
means  of  mercury  cup  connectors.  Storage  battery  current  is 
used  in  all  measurements  and  available  line  voltage  is  adjusted 
by  means  of  end-cell  switches. 

(b)  Instruments  and  Candlepower  Scales. — Current  through 
the  standard  or  test  lamp  is  read  on  a  millivoltmeter  connected 
across  a  separate  shunt.  Standard  or  test  lamp  voltage  is  read 
on  a  Brooks  deflection  potentiometer.5  On  this  instrument  the 
balanced  portion  of  the  e.  m.  f .  is  read  from  the  dial  which  is 
arranged  in  steps  of  two  volts.  The  unbalanced  portion  produces 
current  in  the  galvanometer  circuit  with  consequent  motion  of  a 
pointer  over  a  scale  calibrated  in  o.i  volt  divisions  through  a 
range  of  1.5  volts  above  and  below  the  dial  setting;  so  that  0.01 
to  0.02  volt  is  the  smallest  readable  deflection,  and  the  pre- 
cision of  any  setting  is  within  these  limits.  In  practise  a  null 
method  is  used  and  voltages  corresponding  to  dial  settings  are 
chosen  in  the  measurement  of  all  test  lamps.  Certain  modifica- 
tions described  later  have  been  made  in  the  connections  of  this 
instrument  to  facilitate  the  convenient  handling  of  large  quantities 
of  lamps. 

Several  candlepower  scales  are  mounted  on  a  brass  drum  which 

4  This  arrangement  of  the  comparison  lamp  and  of  a  special  resistance,  described 
later,  were  introduced  by  Ives  and  Woodhull,  who,  for  a  short  time,  were  associated  with 
this  work.    See  Bulletin  of  Bureau  of  Standards,  vol.  5,  p.  555. 

5  Brooks,  H.  B.,  A  New  Potentiometer  for  the  Measurement  of  Electromotive  Force 
and  Current;  Bulletin  of  the  Bureau  of  Standards,  vol.  2,  p.  225, 1906. 


MIDDLEKAUEF,  MULLIGAN,  SKOGLAND :    TESTING  OE  LAMPS      821 

fits  within  the  front  tube  of  the  track.  The  normal  scale  is  used 
when  the  photometer  receives  unmodified  light  from  both  test  and 
comparison  lamps.  The  choice  of  other  scales  depends  upon  the 
opening  of  the  sectored  disk8  or  the  transmission  of  the  glass 
screen  used  and  upon  whether  these  auxiliaries  are  used  on  the 
test  or  on  the  comparison  side  of  the  photometer.  In  routine  work 
these  scales  are  used  only  in  calibrating  the  photometer,  because 
the  equipment  installed  eliminates  all  reference  to  actual  values 
on  the  scales. 

(c)  Wiring  and  Special  Resistances. — As  shown  in  Fig.  3,  the 
test  and  the  comparison  lamps  are  wired  in  separate  circuits  in 
order  to  permit  a  wide  voltage  range  on  the  former  without  af- 
fecting the  voltage  on  the  latter.  In  the  comparison  lamp  circuit, 
besides  the  adjustable  rheostat  R2,  there  are  two  special  resis- 
tances designated  by  R3  and  R4,  respectively.  The  purpose  of 
these  special  resistances  is  to  maintain  the  comparison  lamp  at 
certain  definite  colors  and  still  permit  a  precise  calibration  of  the 
photometer  in  terms  of  the  group  of  standards  used  without 
making  tedious  experimental  adjustments  of  resistance. 

With  the  resistance  R3  all  in  circuit  the  comparison  lamp 
operates  at  the  color  of  carbon  test  lamps.  With  a  fixed  amount 
of  R3  short-circuited  by  the  switch  SW,  a  color  used  in  the 
measurement  of  tungsten  lamps  is  obtained.  When  the  standards 
are  operated  at  the  same  color  as  the  test  lamps,  a  color  match 
with  the  comparison  lamp  is  obtained  by  placing  a  blue  glass 
screen  (the  percentage  transmission  of  which  need  not  be  known) 
on  the  comparison  side  of  the  photometer.  This  is  done  in 
order  that  the  comparison  lamp  may  be  operated  at  a  compara- 
tively low  efficiency  and  thus  prolong  its  useful  life.  In  case  it  is 
desired  to  run  test  lamps  at  an  efficiency  higher  than  that  which 
would  be  safe  for  the  standards,  a  glass  screen  of  known  trans- 
mission must  be  used  with  the  comparison  lamp  while  measuring 
the  test  lamps,  but  in  calibrating  the  photometer  the  screen  is 
replaced  by  the  sectored  disk  so  set  that  the  percentage  opening 
is  equal  to  the  coefficient  of  the  screen.  In  this  way  the  standards 
are  operated  at  the  unmodified  color  of  the  comparison  lamp 
and  the  test  lamps  at  any  desired  color  for  which  a  color  screen  of 

*  For  all  work  on  this  photometer  an  adjustable  sectored  disk  is  used. 


822     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  proper  density  for  color  match  with  the  comparison  lamp  is 
selected. 

The  potentiometer  button  2.,  to  which  the  galvanometer  is 
switched  in  setting  the  comparison  lamp,  is  connected  to  contact 
P  on  the  slide-wire  resistance  R4  which  will  be  described  pres- 
ently. In  the  position  shown  it  is  evident  that  the  drop  from  P 
across  the  portion  of  R3  in  circuit  is  measured.  This  drop  is 
proportional  to  the  current  in  the  comparison  lamp  circuit,  and 
hence  by  a  proper  choice  of  resistance  R3  (which  is  large  in 
comparison  with  R4)  the  exact  current  in  the  comparison  lamp 
for  carbon  color  is  obtained.  As  the  voltage  on  the  standards  or 
test  lamps  is  set  with  the  switch  lever  on  button  I,  a  check  can  be 
kept  on  the  current  in  the  comparison  lamp  without  disturbing  the 
potentiometer  setting  by  simply  switching  the  lever  to  a  button  2. 
Any  necessary  adjustment  in  the  current  is  made  by  means  of 
resistance  R2  to  bring  the  galvanometer  pointer  back  to  zero. 

In  calibrating  the  photometer  the  adjustment  of  the  comparison 
source  is  easily  made  to  within  1  or  2  per  cent,  in  candlepower 
by  means  of  the  adjustable  shutter  on  the  ground  glass  window. 
The  final  adjustment  is  made  by  moving  contact  P  along  the 
slide-wire  resistance  R4  a  distance  corresponding  to  the  desired 
small  change  in  candlepower  as  read  from  a  scale  of  candlepower 
differentials  placed  under  the  wire.  The  changes  of  current  pro- 
duced by  moving  P  are  small,  so  that  the  changes  in  color  of 
the  comparison  lamp  thus  produced  are  entirely  negligible.  Ives 
and  Woodhull7  made  use  of  an  adjustable  resistance  but  the  null 
method  made  possible  by  the  modified  potentiometer  connections 
and  the  calibrated  slide- wire  resistance  just  described  was  in- 
troduced later. 

(d)  The  Watts- per-Candle  Computer. — Two  sets  of  special 
scales  are  used  in  connection  with  this  photometer.  One  set  is 
used  in  computing  watts-per-candle  from  the  observations  while 
the  other  set  is  used  in  connection  with  a  recording  device.  The 
w.  p.  c.  computer,  which  operates  on  the  principle  of  an  ordinary 
slide  rule,  consists  of  an  ampere  scale  and  a  w.  p.  c.  scale  both 
logarithmic  and  calculated  on  the  same  base.8    These  are  placed 

7  .See  note  5,  p.  7. 

8  The  base  of  a  common  logarithmic  scale  is  the  distance  from  1  to  10,  10  to  100,  etc., 
on  the  scale. 


MIDDLEKAUFF,  MULLIGAN,  SKOGLAND :    TESTING  OF  LAMPS      823 

parallel  to  the  photometric  axis  between  the  photometer  head 
and  the  carriage,  the  w.  p.  c.  scale  (showing  white  in  Fig.  1)  being 
attached  to  the  carriage  so  as  to  move  with  it. 

The  design  of  the  computer  is  based  upon  the  fact  that  a 
logarithmic  scale  may  be  constructed  which  practically  coincides 
with  the  candlepower  scale  over  a  range  extending  from  one-half 
to  double  the  candlepower  reading  at  the  middle  of  the  scale. 
The  base  of  such  a  logarithmic  scale  for  a  250  cm.  photometer  is 
71.25  cm.  and  the  maximum  differences  of  a  scale  so  constructed 
from  the  true  candlepower  scale,  the  middle  division  of  which  is 
20  candlepower,  are  only  0.08  cm.  corresponding  to  about  0.25 
per  cent,  in  candlepower  and  occurring  at  approximately  the  14 
and  28  candlepower  divisions.  These  differences,  even  at  the 
points  of  maximum  value,  are  entirely  negligible  for  the  purposes 
of  this  photometer  and  the  advantages  gained  by  employing  the 
logarithmic  scale  fully  offset  the  small  errors  introduced. 

The  two  parts  of  the  computer  are  logarithmic  scales  con- 
structed in  this  manner,  but  the  divisions  are  labeled  amperes  and 
w.  p.  c.  respectively,  instead  of  candlepower. 

Now,  it  is  evident  that,  with  the  photometer  set  to  a  given  can- 
dlepower, the  ampere  scale  may  be  moved  horizontally  to  a  point 
where  for  a  given  voltage  the  corresponding  w.  p.  c.  will  appear 
under  any  chosen  value  of  current  (which  then  corresponds  to  the 
wattage),  and  that  after  this  setting  the  correct  w.  p.  c.  value  will 
appear  under  the  corresponding  current  at  all  points  of  the  scale. 
Now  if  a  lamp  is  run  at  this  same  voltage  and  the  photometer  is 
moved  to  the  point  of  balance  the  correct  w.  p.  c.  will  still  appear 
under  the  observed  current,  because  the  w.  p.  c.  scale  attached  to 
the  photometer  carriage  has  been  moved  in  its  relation  to  the 
ampere  scale  by  a  distance  corresponding  to  the  change  in  can- 
dlepower. The  ampere  scale  must  be  reset  for  every  change  of 
voltage  but  by  proper  grouping  of  lamps  a  large  number  may  be 
run  in  succession  at  one  voltage,  so  that  these  changes  are  infre- 
quent during  any  single  run. 

(e)  The  Recording  Device. — The  recording  device  consists  of 
a  stamping  magnet,  a  cylinder  carrying  a  number  of  scales,  and  a 
car  for  holding  the  record  cards.  The  magnet  and  cylinder  are 
attached  to  the  photometer  carriage  and  therefore  move  with  it. 


824    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

The  cylinder  is  mounted  normal  to  the  photometric  axis  and 
carries  three  lorarithmic  scales  running  parallel  to  its  length,  one 
being  an  hour  scale,  the  other  two  being  w.  p.  c.  scales  for  use  in 
measuring  tungsten  and  carbon  lamps,  respectively.  The  magnet 
is  supported  by  a  rod  placed  parallel  to  the  cylinder,  so  that  the 
pointer  carried  by  the  magnet  may  be  set  at  any  division  on  any 
one  of  the  three  scales,  the  desired  scale  being  presented  by  turn- 
ing the  cylinder. 

The  car  may  be  moved  on  a  track  parallel  to  the  photometric 
axis  but  is  held  at  any  one  of  a  number  of  nearly  equally  spaced 
points  by  means  of  a  pin  placed  in  a  corresponding  hole  in  the 
track.  The  distance  between  any  two  adjacent  holes  corresponds 
to  half  the  distance  from  100  per  cent,  to  80  per  cent,  candle- 
power  as  read  from  the  true  candlepower  scale.  These  holes  are 
labeled  with  two  series  of  the  same  letters,  one  series  being  printed 
in  red,  the  other  in  black,  the  letters  of  the  red  series  being  placed 
two  spaces  nearer  the  comparison  lamp  than  the  corresponding 
letters  of  the  series  in  black.  The  use  of  these  letters  will  be 
described  presently. 

The  observations  are  recorded  as  points  stamped  on  plain  white 
cards  approximately  12.5  cm.  by  20  cm.,  there  being  one  card  for 
each  lamp  (see  Fig.  4).  These  are  placed  in  the  car  with  their 
long  dimension  normal  to  the  photometric  axis  and  therefore 
parallel  to  the  scales  on  the  cylinder.  Now  it  is  evident  that  the 
short  dimension  of  the  card  may  be  looked  upon  as  a  candle- 
power  scale  and  the  long  dimension  as  an  hour  scale  or  a  w.  p.  c. 
scale  depending  upon  which  of  these  two  quantities  is  to  be  meas- 
ured and  recorded.  The  position  for  the  card  on  the  photometer 
is  so  chosen  at  the  initial  measurement  that  the  candlepower 
record  will  be  made  sufficiently  high  to  permit  all  values  during 
the  life  of  the  lamp  to  fall  on  the  card.  This  is  regarded  as  the 
normal  position  of  the  card  and  is  designated  by  the  correspond- 
ing black  letter  which  is  then  written  on  the  card.  The  card  is 
placed  in  this  position  during  all  but  the  initial  measurements, 
the  reason  for  this  exception  being  given  in  the  following  section. 

The  two  most  important  quantities  to  be  recorded  are  the 
initial  (test)  w.  p.  c.  and  the  life.  The  latter  is  defined  as  the 
number  of  hours  required  for  a  lamp  to  reduce  to  80  per  cent,  of 


Fig.  i. — The  life  test  photometer. 


Fig.  2.— Transformers,  switchboard  and  life  racks. 


*4 


WIMVWWMAA — £ 


Potentiometer 


From  storage  Battery 


y 


iv 


'\/V\UvV\M/WVWMWAMWvv\AMWV\MMM/\A\M 


-<r 


I? 


Fig.  3. — Wiring  diagram  of  the  life  test  photometer. 


[Cord  Position  on  Photomt ter Bench) 


'^Ill-flour  Readings) 


'AZI  -//our  Readings] 
'•(/S7-//our  Readings) 


(liJeTesl  Lot/Co) 

[Test  /oils) 

471    120 


(M>th)~° 


(Candlepo^'.  (,nde*  of //our  Scale), 

3  hours        4  5  S\7        0       3       iJJ 

Record  of  Test  Vpc) 

'II     / 
■^-V  (80-/.  C/> Line) 

(Lamp  Wo) 

38N4310 


/  1 

(Life  at  loo  ¥/>c  -  7S7firs)     \ 

1 

(Test  Life -SOS Urs) 


z                              J    Hours       4 
(Mean  Test  Wpc  -0.3467) 1  — 


5  6,7         691 


k/at/s  Per  Candle 


Fig.  4.— Completed  test  record  on  a  lamp  card  showing  the  scales  used  in  placing  the 
record  points  and  in  evaluating  corrected  life. 


MIDDLEKAUFF,  MULLIGAN,  SKOGLAND :    TESTING  OF  LAMPS      825 

its  initial  candlepower,  or  to  burn  out,  if  within  that  period. 
Now  it  is  evident  that,  so  far  as  making  the  record  is  concerned, 
motion  of  the  card  toward  higher  candlepower  on  the  photometer 
is  equivalent  to  moving  the  photometer  in  the  opposite  direction. 
If,  therefore,  during  the  initial  measurement  of  candlepower  the 
card  be  set,  not  at  its  normal  (black  letter)  position,  but  at  that 
designated  by  the  corresponding  red  letter,  the  record  point  of  the 
observed  candlepower  will  fall  at  a  position  corresponding  to  80 
per  cent,  of  the  value  observed.  This  point  therefore  establishes 
on  the  record  the  limiting  line  of  life  as  defined  by  the  specifi- 
cations. 

As  the  record  of  the  initial  measurement  does  not  include  the 
element  of  time,  it  may  be  made  at  any  point  along  the  80  per 
cent.  line.  Hence,  if  the  stamping  magnet  be  set  at  the  point  on 
the  w.  p.  c.  scale  (which  scale  for  tungsten  lamps  is  reproduced 
under  the  card  in  the  figure)  corresponding  to  observed  initial 
w.  p.  c,  not  only  80  per  cent,  of  the  initial  candlepower  but  also 
the  initial  w.  p.  c.  as  well  may  be  recorded  by  the  same  point.  To 
distinguish  these  initial  points  from  the  rest  of  the  records,  they 
are  stamped  in  red  (indicated  by  -f-  in  the  figure)  while  all  the 
others  are  stamped  in  black.  For  all  but  the  initial  measurements 
the  card  is  set  at  the  black  letter  position  and  the  magnet  is  set 
at  a  point  on  the  hour  scale  (which  scale  is  also  reproduced  under 
the  card  in  the  figure)  corresponding  to  the  total  number  of 
hours  the  lamp  has  burned.  The  candlepower-hour  record  points 
are  stamped  in  succession  across  the  card  as  many  times  as  neces- 
sary, the  hour  scale  reading  for  each  succeeding  series  being  ten 
times  the  value  it  had  in  the  series  next  preceding.  The  complete 
record  thus  obtained  on  any  card  graphically  represents  the  per- 
formance of  the  corresponding  lamp  and  the  actual  test  life  is 
indicated  by  the  point  of  intersection  of  the  curve  of  candlepower 
performance  with  the  80  per  cent,  candlepower  line. 

So  far  as  obtaining  a  record  is  concerned,  any  scale  might  have 
been  adopted  for  use  on  the  cylinder  in  recording  test  life  and 
initial  w.  p.  c,  but  the  scales  here  employed  have  been  so  chosen 
in  respect  to  their  relative  lengths  and  relative  position  on  the 
cylinder  as  to  permit  the  evaluation  of  corrected  life  from  test 
w.  p.  c.  to  rated  w.  p.  c.  directly  from  the  card  record  without 


826     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

computation  or  reference  to  tables  of  factors.  This  arrangement 
was  based  upon  the  following  considerations. 

It  has  been  shown  that  within  certain  limits  the  relation  be- 
tween life  and  w.  p.  c.  may  be  expressed  by  the  formula, 

Life  ratio  =  (w.  p.  c.  ratio)  m (1) 

in  which  m  has  been  found  to  have  a  value  of  about  7.4  for 
tungsten  lamps  and  5.83  for  carbon  lamps.  From  equation  (1) 
is  derived 

log  life  ratio  =  m  log  w.  p.  c.  ratio (2) 

analogous  to  the  equation 

y  =  mx (3) 

which  is  the  equation  of  a  straight  line.  Hence  a  logarithmic 
hour  scale  and  a  similarly  constructed  w.  p.  c.  scale  with  a  base 
equal  to  m  times  the  base  of  the  hour  scale  may  be  used  together 
as  a  slide  rule  for  making  life  corrections  from  one  efficiency 
to  another.  Life  in  hours  on  the  one  scale  is  set  opposite  the 
corresponding  w.  p.  c.  on  the  other,  and  life  at  any  other  w.  p.  c, 
not  exceeding  the  limits  through  which  m  has  a  constant  value,  is 
read  by  referring  to  the  corresponding  w.  p.  c.  division. 

The  hour  scale  on  the  cylinder  of  the  recording  device  was 
plotted  to  a  base  of  20  cm.  (equal  to  the  approximate  length  of 
the  record  cards)  with  divisions  from  1  to  10,  as  in  all  slide- 
rule  scales,  and  hence  the  base  taken  for  the  w.  p.  c.  scale  for 
tungsten  lamps  was  7.4  X20=  148.0,  and  for  carbon  lamps, 
5.83  X  20=  1 16.6. 

Life  requirements  in  the  specifications  are  expressed  in  hours 
as  rated  w.  p.  c.  As  rated  w.  p.  c.  is  not  the  same  for  all  sizes  of 
lamps  of  any  class  and  is  subject  to  change  from  year  to  year,  it 
was  considered  best,  in  constructing  this  device,  to  arrange  for 
life  correction  to  a  certain  chosen  w.  p.  c.  value  for  each  class  of 
lamps,  and  by  means  of  equation  (1)  compute  for  all  sizes  of 
the  same  class  the  required  life  at  this  chosen  w.  p.  c.  Accord- 
ingly 1. 00  w.  p.  c.  was  chosen  for  tungsten  lamps  and  3.05  w.  p.  c. 
for  carbon  lamps.  The  life  of  any  lamp,  or  the  mean  life  of  any 
group  of  lamps  of  the  same  size,  is  then  expressed  in  per  cent,  of 
the  required  life. 


MIDDLEKAUFF,  MULUGAN,  SKOGLAND :    TESTING  OF  LAMPS      827 

The  logarithmic  hour  and  w.  p.  c.  scales  constructed  as  above 
described,  were  then  so  placed  on  the  cylinder  that  the  1.00  w.  p.  c. 
division  of  the  tungsten  scale  was  in  line  with  the  1,000-hour  di- 
vision of  the  hour  scale,  as  shown  in  Fig.  4,  and  the  3.05  w.  p.  c. 
division  of  the  carbon  scale  in  line  with  the  450-hour  division. 
The  w.  p.  c.  points  on  the  card  are  thus  recorded  on  a  logarithmic 
scale  and  in  a  definite  relation  to  the  hour  scale.  Now  if  the  1,000- 
hour  division  of  the  scale  in  the  case  of  tungsten  lamps,  orthe450- 
hour  division  in  the  case  of  carbon  lamps,  be  taken  as  an  index  and 
a  duplicate  of  the  hour  scale  be  placed,  as  shown  in  Fig.  4,  with 
the  proper  index  on  the  mean  of  the  w.  p.  c.  points  of  the  record 
and  with  its  reading  edge  on  the  80  per  cent,  line,  the  test  life, 
corrected  to  the  chosen  w.  p.  c,  may  be  read  at  the  intersection  of 
the  scale  and  the  candlepower  performance  curve. 

In  case  a  lamp  burns  out  above  80  per  cent,  of  its  initial  candle- 
power  value,  a  vertical  line  is  drawn  across  the  80  per  cent,  line 
at  the  proper  point  as  determined  by  the  life  test  log  and  the 
hour  scale,  but  the  procedure  in  obtaining  corrected  life  is  the 
same  as  in  the  case  of  lamps  which  have  burned  to  80  per  cent. 

For  lamps  having  other  than  the  specified  mean  spherical  re- 
duction factors,  the  index  may  be  so  chosen  that  the  correspond- 
ing difference  is  made  in  the  corrected  life.  Certain  special 
lamps,  for  example  lamps  in  tubular  and  round  bulbs,  are  thus 
evaluated. 

(/)  Features  of  the  Record. — (a)  Detection  and  Compensa- 
tion of  Errors. — One  characteristic  of  these  record  points  of  the 
initial  readings  of  w.  p.  c.  and  candlepower  (Fig.  4)  is  of  interest 
and  importance  in  that  it  serves  as  a  visual  check  upon  the  cor- 
rectness of  the  records.  Rarely  do  two  observers  on  the  photom- 
eter check  each  other  exactly,  but  the  precision  of  electrical  in- 
struments and  the  constancy  of  electric  lamps  during  the  rela- 
tively short  time  they  are  in  circuit  on  the  photometer  are  such 
that  the  ampere  reading  is  usually  repeated  to  within  0.001.  Sup- 
pose now  that  at  the  same  current  the  second  observer  reads  a 
candlepower  value  higher  than  that  recorded  by  the  first.  The 
w.  p.  c.  computer  will,  consequently,  indicate  a  lower  value,  since 
the  candlepower  is  higher  for  the  same  watts.  Referring  to  Fig. 
4  it  will  be  seen  that  the  second  point  will  be  placed  above  and  to 
15 


828     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  left  of  the  first.  For  a  candlepower  reading  lower  than  the 
first,  the  current  remaining  the  same,  the  point  will  be  placed 
below  and  farther  to  the  right.  Supose,  now,  that  one  or  other  of 
the  ampere  readings  is  in  error,  the  second  being  appreciably 
higher  than  the  first.  The  apparent  w.  p.  c.  of  the  second  observa- 
tion is  then  higher  than  it  should  be,  regarding  the  first  as  correct, 
and  the  effect  is  to  change  the  slope  of  the  line  connecting  the  rwo 
observations.  Displacements  may  occur  also  in  case  of  errors  in 
transfer  to  the  record  card  or  as  combination  of  errors. 

Now  it  is  evident  that  the  equation 

Watts  =  cp.  X  w.p.c.  =  constant (4) 

expresses,  for  a  steady  lamp,  the  condition  for  correct  reading. 
This  is  the  equation  of  an  equilateral  hyperbola.  Although  some- 
what modified  by  the  logarithmic  scale  of  the  recording  equipment, 
it  is  closely  approximated  in  form  by  correctly  recorded  points 
under  conditions  of  constant  watts ;  so  that  the  slope  of  the  line 
connecting  the  initial  w.  p.  c.  points  may  be  used  as  an  indication 
of  their  precision,  and  any  considerable  deviation  from  the  correct 
slope  indicates  that  some  error  has  been  made.  Any  lamps,  the 
records  of  which,  show  such  deviations  are,  therefore,  re-photom- 
etered. 

Another  interesting  feature  of  the  card  record  of  a  normal  lamp 
is  that  the  slope  of  the  candlepower-life  curve  between  its  last 
two  points  is  often  very  nearly  the  same  as  that  of  the  line  join- 
ing the  two  initial  w.  p.  c.  points ;  consequently  in  these  cases  com- 
paratively large  differences  in  distance  between  initial  points 
effect  no  considerable  change  in  corrected  life,  which  may  be 
evaluated  with  small  error  from  any  point  in  the  line  connecting 
the  w.  p.  c.  points.  Observational  errors  in  initial  readings  are 
therefore  always  compensated  for  to  some  extent  by  the  fact  that 
the  candlepower-life  and  initial  w.  p.  c.  curves  always  slope  in  the 
same  general  direction.  It  is  doubtful  if  any  other  than  this 
system  of  photometry  and  recording  posesses  these  advantages. 

(/?)  Increased  Accuracy  in  Life  Values. — In  evaluating  lamps 
which  have  burned  to  80  per  cent,  a  straight  line  is  drawn 
between  the  last  two  points  on  the  record  cards,  one  of  which 
is  above  and  other  below  the  80  per  cent,  candlepower  line 
(Fig.  4).     If  this  line  be  transferred  to  rectangular  co-ordinates 


MIDDLEKAUFF,  MULLIGAN,  SKOGLAND :    TESTING  OF  LAMPS      829 

it  will  be  found  that  it  is  slightly  curved,  being  convex  downward 
toward  the  life  axis.  As  this  is  characteristic  of  a  true  candle- 
power-life  curve,  this  method  gives,  on  an  average,  a  closer 
approximation  to  the  actual  time  of  crossing  the  80  per  cent,  line 
than  that  obtained  by  direct  interpolation. 

2.  Methods  of  Measuring  and  Recording  Observed  Values. — 
(a)  Rating  of  Lamps  for  Life  Test. — Two  methods  are  in  com- 
mon use  in  rating  lamps  for  life  test.  The  first  distinguishes 
two  voltages,  namely,  "photometer"  voltage,  which  usually  cor- 
responds to  rated  voltage,  and  "rack"  voltage.  Rack  voltage  is 
computed  from  photometer  voltage  and  the  corresponding  w.p.c. 
by  the  characteristic  equation  expressing  the  relation  of  volts 
to  w.  p.  c.  By  this  method  the  lamps  are  always  run  on  the 
photometer,  both  initially  and  during  life  test,  at  photometer 
voltage.  They  are  operated  on  life  test  at  rack  voltage,  which  of 
course  correspond  to  test  w.  p.  c.  within  the  desired  limits.  By 
the  second  method  the  lamps  are  photometered  and  operated  on 
life  test  at  rack  voltage.  In  the  case  of  vacuum  tungsten  lamps, 
the  characteristics  of  which  are  well  known,  either  method  may 
be  used.  Advocates  of  the  first  method  claim  advantages  for  it 
in  the  greater  certainty  of  candlepower  observations  made  at  or 
near  a  color  match  with  the  standards.  These  are  no  doubt  real 
advantages,  as  there  is  now  practically  no  uncertainty  introduced 
by  computations  based  on  well  established  values  within  certain 
limits  of  w.  p.  c.  for  normal  lamps. 

The  Bureau,  however,  employs  the  second  method.  Although 
this  method  was  adopted  before  the  characteristics  of  tungsten 
lamps  were  as  well  known  as  they  now  are,  it  is  still  used  be- 
cause it  introduces  no  uncertainties  due  to  possible  failure  of  any 
lamps  to  conform  to  the  characteristic  relations.  Although  an 
extra  scale  for  reading  rack  voltage  could  easily  be  added  to  those 
above  described,  thus  permitting  measurements  at  photometer 
voltage,  a  careful  investigation  of  the  possible  added  advantages 
thus  secured  as  weighed  against  a  somewhat  greater  complexity 
of  apparatus  and  consequent  added  liability  of  error  would  first 
have  to  be  made,  if  a  change  to  the  first  method  should  ever  be 
contemplated. 

(b)  Details  of  a  Photometric  Run. — As  a  Lummer-Brodhun 


83O     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

photometer  is  used,  all  measurements  are  made  at  as  nearly  a 
color  match  as  possible.  By  the  method  at  present  in  use,  the 
photometer  is  always  calibrated  by  six  tungsten  standards  se- 
lected at  random  from  a  much  larger  group.  The  values  of 
candlepower  and  current  for  the  individual  lamps  of  this  group, 
over  a  wide  range  of  voltage  (and  color),  are  tabulated  on  a 
card  within  view  of  the  electrical  operator  and  in  what  follows 
these  are  designated  as  "certified"  values.  The  comparison  lamp 
is  adjusted  in  current  so  as  to  give  the  proper  color  to  match  the 
lamps  to  be  tested,  this  being  done  by  simply  balancing  the  po- 
tentiometer against  the  voltage  drop  across  resistance  R3  (Fig.  3), 
the  small  adjustment  necessary  being  made  by  means  of  resis- 
tance R2.  Switch  SW  is  open  or  closed,  depending  upon  whether 
carbon  or  tungsten  lamps  are  to  be  measured.  The  first  standard 
is  then  placed  in  the  socket  and  adjusted  in  voltage  to  match  the 
modified  or  unmodified  color  of  the  comparison  lamp  depending 
upon  the  efficiency  at  which  the  test  lamps  are  to  be  measured 
(see  p.  821). 

After  the  color  adjustment,  the  certified  candlepower  value 
of  the  standard,  at  the  voltage  to  which  adjustment  was  made, 
is  called  off  by  the  electrical  operator,  and  the  photometer  oper- 
ator so  adjusts  the  shutter  on  the  ground  glass  window  which 
fronts  the  comparison  lamp-box  that  a  balance  is  secured  at 
approximately  the  certified  value  as  read  on  the  candlepower 
scale.  After  this  approximate  calibration,  a  stamped  record  of 
about  ten  individual  settings  is  made  for  each  of  the  six  stand- 
ards. After  the  observed  values  of  a  standard  are  recorded,  the 
certified  value  is  called  off  by  the  electrical  operator  and,  with 
the  photometer  set  at  this  point  on  the  scale,  this  value  also  is 
stamped  on  the  card.  A  copy  of  a  short  section  of  the  candle- 
power  scale  is  used  to  read  off  the  algebraic  differences  between 
the  certified  and  the  observed  candlepower  values.  In  this  man- 
ner the  difference  between  observed  and  certified  values  of  all  the 
standards  are  determined  and  the  mean  difference  is  computed. 
Correction  for  this  mean  difference  is  then  made  by  moving  the 
sliding  contact  P  of  the  resistance  R4  (p.  822)  the  proper  number 
of  scale  divisions.  This  necessitates  a  small  adjustment  of  the 
comparison  lamp  current  which  is  now  made  by  means  of  re- 


MIDDLEKAUFF,  MULLIGAN,  SKOGLAND :    TESTING  QF  LAMPS      83I 

sistance  R2.  The  electrical  operator  has,  in  the  meantime,  com- 
pared the  observed  current  with  the  certified  current  and  deter- 
mined a  mean  correction  for  ammeter  readings ;  or,  in  case  lamps 
whose  ampere  readings  are  considerably  different  from  that  of 
the  standards  are  to  be  run,  the  proper  ampere  standard  is  selected 
from  a  group  of  seasoned  lamps  used  only  for  this  purpose,  and 
the  mean  ampere  correction  thus  established  is  applied  throughout 
the  run.  The  standard  check  is  the  last  direct  reference  made  to 
actual  values  on  the  candlepower  scale. 

Having  determined  by  trial  the  even  voltage,  {e.  g.,  118,  120, 
etc.)  corresponding  to  a  dial  setting  on  the  potentiometer  at  which 
the  first  test  lamp  falls  within  the  desired  range  of  test  w.  p.  c, 
the  ampere  scale  is  set  to  a  point  corresponding  to  this  voltage 
(see  p.  823).  Opposite  the  ampere  value  called  off  by  the  elec- 
trical operator  is  read  the  test  w.  p.  c.  With  the  card  so  placed 
that  the  value  to  be  recorded  will  be  at  least  two-thirds 
of  the  way  down  the  card,  the  index  carried  by  the  stamping 
magnet  is  set  at  the  observed  w.  p.  c,  the  circuit  through  the 
magnet  is  closed  by  pressing  a  button,  thus  making  the  record 
of  the  w.  p.  c.  and  also  80  per  cent,  of  the  candlepower  as  a 
single  point  in  red.  The  red  letter  indicating  the  card  position  is 
noted  and  a  card  bearing  this  letter  is  selected  from  the  file 
within  reach  and  placed  face  down  on  the  photometer  bench,  the 
first  record  card  being  turned  over  and  placed  upon  it.  As  the 
different  lamps  are  photometered  the  corresponding  lamp  cards 
and  position  cards  are  added  in  regular  order.  The  same  voltage 
is  applied  to  each  lamp  in  succession  until  one  is  reached  which 
requires  a  change  of  voltage,  when  the  ampere  scale  is  reset  to 
correspond  to  this  voltage.  Readings  are  continued  at  this  new 
voltage  to  a  point  where  another  change  of  voltage  is  required, 
etc.  "Information  cards"  designating  voltage,  disk  opening, 
card  position,  etc.  are  introduced  in  the  proper  place  to  indicate 
the  changes  to  be  made  in  succeeding  measurements. 

The  photometer  calibration  is  checked  by  two  or  three  stand- 
ards at  intervals  during  the  run  and  the  indicated  changes  of 
comparison  lamp  current  are  made  when  required  (p.  822). 
After  the  first  run,  cards  for  lamps  of  the  same  voltage,  disk 
opening,    card    position,  etc.  are  grouped  together  to  the  best 


832     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

advantage,  the  extra  information  cards  being  removed  and  filed 
for  future  use.  The  life-test  lot  number,  the  voltage,  and  position 
letter  are  then  printed  or  written  on  each  card,  and  the  lamps  re- 
arranged for  a  second  run  in  the  order  determined  by  the  card 
positions,  thus  facilitating  the  work.  After  the  second  run,  for 
which  the  two  operators  exchange  places,  such  additional  check 
measurements,  as  are  found  necessary  (p.  828),  are  made.  The 
lamps  are  then  ready  for  the  life  test  racks  where  they  are  burned 
at  the  respective  voltages  found. 

After  the  first  period  of  burning  on  the  life  test,  the  lamps  are 
removed,  placed  in  the  proper  order  and  again  run  on  the  photom- 
eter at  the  test  (rack)  voltages.  The  cards  are  now  set  to  the 
black  letter  position  (p.  824)  indicated  on  the  information  cards 
and  on  each  lamp  card,  and  the  stamping-magnet  index  is  placed 
at  the  point  on  the  hour  scale  corresponding  to  the  number  of 
hours  the  lamps  of  the  lot  have  burned. 

The  ampere  scale  is  set  as  in  the  initial  run,  and,  after  the  ob- 
served candlepower  value  is  recorded,  the  photometer  is  set  so 
that  an  index  on  the  movable  part  of  the  w.  p.  c.  computing  device 
is  opposite  the  observed  current  value  and  a  record  of  the  position 
is  stamped.  As  the  voltage  at  every  measurement  of  a  given  lamp 
is  the  same,  this  record  shows  the  variations  in  the  watts  during 
the  life  of  the  lamp.     (These  points  are  surrounded  by  circles  in 

Fig-  4-) 

Measurements  are  made  in  this  manner  after  each  test  life 

period  until  all  lamps  of  the  lot  have  crossed  the  80  per  cent, 
candlepower  line  or  burned  out  above  it. 
THE  LIFE  TEST. 
1.  Design  of  the  Installation. — At  the  time  when  the  design 
of  the  life  test  equipment  was  under  discussion,  the  common 
method  in  use  elsewhere  of  setting  individual  lamps  or  racks  of 
lamps  to  a  desired  test  voltage  was  by  means  of  a  resistance 
in  series  with  each  lamp  or  rack.  The  disadvantages  of  this 
method  were  apparent,  and  search  was  therefore  made  for  an 
arrangement  of  equipment  which  would  be  free  from  these  dis- 
advantages but  which  would  still  conform  to  the  requirements 
to  be  met.  An  arrangement  of  auto-transformers  proposed  by 
Mr.  Brooks  was  adopted  because  of  its  simplicity,  convenience, 
and  general  conformity  to  the  requirements  of  life-test  operation. 


MIDDEEKAUFF,  MULLIGAN,  SK0GLAND :    TESTING  OF  LAMPS      833 


Other  laboratories  have  since  adopted  the  essential  features  of 
this  arrangement  which  are  fully  described  below. 

1.  Wiring  and  Voltage  Adjustment. — Referring  to  the  wiring 
diagram,  Fig.  5,  which  exhibits  the  essential  features  of  the  sys- 
tem, it  is  seen  that  alternating  current  is  supplied  by  the  genera- 
tor to  the  center  of  distribution.     Auto-transformers  T1  to  T4 


■From  Generator 


Fig.  5.  Wiring  diagram  of  the  switchboard  and  life  racks. 

supply  current  to  the  bus-bars  at  the  voltages  indicated.9  These 
bus-bars  are  mounted  on  the  back  of  the  switchboard  panel  to  the 
right  of  the  clock  (Fig.  2).  One  terminal  of  each  rack  (hori- 
zontal row)  is  connected  to  the  common  bus  through  the  second- 
ary of  a  regulating  transformer  B;  the  other  terminal  is  con- 
nected to  a  plug  hole  in  this  same  panel.     Hence,  to  energize  a 

9  No  provision  has  yet  been  made  for  low  voltage  or  series  burning  lamps. 


834    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

given  rack  R  a  connecting  cable  is  plugged  from  the  correspond- 
ing plug  hole  to  the  bus  maintaining  the  voltage  nearest  to  that 
desired.  The  conductors  from  the  switchboard  to  the  racks  are 
of  No.  4  wire  carried  through  ten  lines  of  2-inch  conduit  running 
over  the  tops  of  the  switchboard  and  racks  to  junction  boxes 
from  which  connection  is  made  to  the  terminals  of  the  copper 
rod  conductors  of  the  racks. 

The  special  auto-transformer  ST  maintains  voltages  of  +5, 
+  10,  -+-15  to  +50,  and  corresponding  negative  voltages  on  bus- 
bars located  on  the  front  of  the  middle  panel.  One  primary 
terminal  of  each  of  the  regulating  transformers  B  ends  in  a  cor- 
responding plug  hole  also  on  this  panel.  As  the  ratio  of  trans- 
formation of  the  regulating  transformer  is  5  to  1,  it  follows 
that  -f-  or  —  changes  of  1,2,  3,  to  10  volts  may  be  made  effective 
on  the  rack.  Hence,  by  plugging  from  the  transformer  terminal 
to  the  proper  bus-bar  on  this  panel,  a  second  approximation  to 
the  exact  voltage  desired  on  rack  R  is  obtained. 

The  other  primary  terminal  of  each  of  the  regulating  trans- 
formers ends  in  the  lever  of  a  corresponding  dial  switch  S  located 
on  the  left  panel  of  the  switchboard.  The  buttons  of  each  switch 
are  maintained  one  volt  apart  over  a  range  of  10  volts,  by  leads 
from  adjacent  one-volt  subdivisions  of  transformer  ST,  but  be- 
cause of  the  5  to  1  transformation  in  B  each  volt  at  the  switch 
is  effectively  0.2  volt  on  the  rack.  Hence,  by  properly  setting 
the  switch  the  exact  voltage  desired  is  approximated  to  within 
0.1  volt. 

The  voltage  of  each  rack  is  adjusted  at  the  switchboard  by 
reference  to  a  portable  voltmeter  which  may  be  connected  to  the 
corresponding  pair  of  binding  posts  forming  the  terminals  of  the 
potential  leads  V  from  the  center  of  the  rack.  The  voltage  of 
a  rack  is  thus  adjusted  by  actual  measurement  in  every  case. 
Each  pair  of  binding  posts  appears  on  the  corresponding  dial 
switch.  As  these  switches  are  grouped  on  a  single  panel,  any 
number  of  racks  may  be  quickly  set  without  inconvenience  with 
the  voltmeter  kept  in  a  fixed  position  on  its  stand. 

(b)  Voltage  Regulation. — A  Tirrill  regulator,  which  operates 
by  periodically  short-circuiting  a  resistance  in  series  with  the 
exciter  field,  maintains  the  voltage  at  the  center  of  distribution 


MIDDLEKAUFE,  MULLIGAN,  SK0GLAND  :    TESTING  OE  LAMPS      835 

in  the  life  test  room  constant  to  within  the  limits  of  plus  or  minus 
one  quarter  of  1  per  cent,  as  required  by  the  specifications.  A 
continuous  record  of  this  voltage  is  obtained  on  an  accurate 
recording  voltmeter  located  in  the  dynamo  room. 

(c)  Current  Generator  and  Voltage  Transformers. — The  gene- 
rator which  supplies  current  for  the  life  test  is  a  40  kw.,  125-volt, 
360  r.  p.  m.,  single-phase,  rotating-field  alternator,  directly  con- 
nected to  the  driving  engine,  the  exciter  being  mounted  upon  the 
same  shaft.  Transformers  B  (shown  back  of  the  switchboard 
in  Fig.  2)  are  one-half  kw.,  air-cooled,  shell-type;  while  ST  and 
Tx  to  T4  are  oil-immersed,  auto-transformers  of  the  capacities 
indicated  in  Fig.  5,  the  relative  capacities  of  Tx  to  T4  being 
roughly  in  proportion  to  the  number  of  lamps  usually  run  at  their 
respective  voltages. 

(d)  The  Life  Test  Racks. — The  supporting  frames  of  the  racks 
are  built  up  of  steel  members  consisting  of  vertical  end  posts  of 
channel  section  and  equally  spaced  intermediate  posts  of  I-beam 
section  connected  by  heavy  angles  to  horizontal  top  and  bottom 
pieces  of  channel  section,  the  whole  being  supported  by  cast  iron 
feet  bolted  to  the  composition  (tileine)  floor.  Bolted  to  each  side 
of  the  vertical  members  are  six  equally  spaced  horizontal  strips  of 
asbestos  board  which  support  porcelain  cleat  sockets,  spaced  on 
12  in.  (30.5  cm.)  centers,  with  soldered  electrical  connections  to 
copper  rods  5  mm.  in  diameter.  Midway  between  each  pair  of 
these  sockets,  which  are  arranged  for  burning  the  lamps  in  a 
horizontal  position,  conducting  straps  are  soldered  at  one  end 
to  the  5  mm.  copper  rods  and  at  the  other  end  to  the  terminals 
of  porcelain  cleat  sockets  arranged  for  burning  lamps  in  a  ver- 
tical position.  The  long  racks  (17  ft.  (5.18  m.)  )  have  31  sockets 
on  each  side;  the  short  racks  (13  ft.  (3.96  m.)  ),  23.  On  a  few 
of  the  lower  racks  the  sockets  for  vertical  burning  are  spaced 
on  18-in.  (45.7  cm.)  centers.  The  large  lamps  burned  on  these 
racks  are  thus  kept  well  separated  during  life  test.  The  total 
number  of  vertical  sockets  is  1,200  and  of  horizontal  sockets, 
1,296. 

The  eight  stacks  of  racks  are  spaced  4  ft.  10.5  in.  (1.49  m.) 
apart,  which  gives  a  symmetrical  arrangement  in  the  life  test 


836     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

room  with  sufficient  space  to  permit  safe  and  convenient  handling 
of  lamps. 

(e)  Measurement  of  Life  Test  Periods. — An  important  detail 
in  conducting  a  life  test  is  the  accurate  measurement  of  the  time 
the  lamps  have  burned.  For  this  purpose  an  electric  clock  which 
measures  time  in  hours  from  one  to  one  thousand  is  used.  This 
clock  is  connected  in  the  master  clock  circuit  of  the  Bureau 
and  is  short-circuited  by  a  relay  when  the  power  is  cut  off.  The 
log  of  any  life  test  contains  the  clock  time  to  the  nearest  0.1 
hour,  corresponding  to  the  time  of  placing  the  lamps  on  and 
removing  them  from  the  rack  circuit.  The  time  of  burnouts 
during  the  night  is  either  recorded  by  the  watchman  who  visits 
the  room  every  two  hours,  or  the  lamps  are  considered  as  having 
burned  until  9.00  o'clock  the  following  morning. 

2.  Records  Taken  During  Life  Test. — Summarizing  the  records 
which  are  taken  during  life  test,  as  described  above,  it  will  be 
found  that  the  following  have  been  mentioned : 

(a)  Test  voltage;  initial  candlepower  and  initial  w.  p.  c.  at  test 
voltage. 

(b)  Candlepower  and  watts  at  certain  periods  during  test  life. 
For  carbon  and  metallized  filament  lamps  the  specifications  re- 
quire measurement  after  approximately  50  hours  of  burning  and 
"at  least  every  hundred  hours  thereafter"  throughout  useful  life. 
Five  measurements,  the  first  approximately  one-twentieth  of  the 
test  life  period,  after  the  initial  are  specified  for  tungsten  lamps. 

(c)  Recording  voltmeter  records  of  main  life  test  voltage. 

(d)  Test  log  showing  clock  reading  from  which  test  life 
periods  are  computed. 

In  addition  to  the  above  there  are,  of  course,  required  such 
other  records  as  will  permit  orderly  clerical  procedure.  A  card 
record  system  is  used  throughout,  but  the  details,  which  have 
been  worked  out  to  take  care  of  features  in  some  cases  peculiar 
to  the  Bureau  tests  only,  would  hardly  be  of  general  interest. 

SUMMARIES  OF  LIFE  VALUES. 

After  the  completion  of  a  sufficient  number  of  test  lamps  to 
warrant  quality  comparisons,  life  values  of  lamps  of  the  same 
type,  size,  and  manufacture,  and  of  a  voltage  range  through  which 
a  given  life  value  is  specified,  are  averaged.    A  summary  giving 


MIDDLEKAUFF,  MULLIGAN,  SKOGLAND :    TESTING  OF  LAMPS      837 

the  date,  type,  size,  manufacture,  voltage  range,  number  of 
lamps,  corrected  life  and  percentage  of  required  life  is  prepared 
from  these  data,  so  that  a  manufacturer  may,  at  his  request,  refer 
to  the  summary  for  information  regarding  the  quality  of  his 
lamps  and  those  of  other  manufacturers  supplying  lamps  under 
the  annual  contract.  In  case  lamps  are  rejected  as  the  result  of 
life  test  the  manufacturer  and  purchaser  are  promptly  notified, 
each  being  given  the  life  value  on  which  rejection  is  based. 

Additions  of  other  lamps  are  made  to  this  summary  from  time 
to  time,  so  that  average  quality  values  to  the  corresponding  date 
are  indicated;  except,  that  in  case  of  a  drop  in  quality  of  certain 
items  so  decidedly  below  the  required  life  that  rejection  of  the 
defective  lamps  is  necessary,  the  figures  for  accepted  and  rejected 
lamps  are  kept  separate  until  the  end  of  the  tests,  when  the 
average  life  of  accepted  and  rejected  lamps  combined  is  reported 
as  a  final  value. 


DISCUSSION. 

Mr.  Leonard  J.  Lewinson  :  As  one  "life  tester"  to  another, 
I  want  to  express  my  appreciation  of  this  paper.  The  authors  are 
to  be  congratulated  on  their  able  exposition  of  the  subject,  on  the 
admirable  detail  of  the  equipment  at  their  disposal  and  on  their 
system  of  records. 

There  is  no  mention  in  the  paper  of  measurements  of  mean 
spherical  candlepower.  At  the  laboratories  with  which  I  am  con- 
nected integrating  spheres  are  an  essential  part  of  the  equipment. 
For  filaments  of  different  conformations,  total  flux  measurements 
have  always  been  necessary,  even  in  the  days  of  the  old  carbon 
lamps,  and  now  that  the  gas-filled  lamp  has  come  into  existence, 
the  need  is  strongly  emphasized.  We  make  it  a  practise  to  test 
all  gas-filled  lamps  on  a  mean  spherical  basis,  and  find  very  con- 
siderable changes  in  the  spherical  reduction  factor  throughout 
life.  Even  in  the  vacuum  type,  we  have  detected  such  changes, 
though  of  a  rather  small  order  in  the  lamps  as  constructed  at 
present.  Some  of  our  vacuum  lamp  life  tests  are  now  on  a 
spherical  candlepower  basis,  and  we  expect  to  be  making  all  life 
tests  on  this  basis  in  the  course  of  the  next  year. 

As  the  authors  state,  some  life  testing  organizations  measure 


838     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

lamps  at  an  arbitrary  voltage,  usually  the  labeled  voltage,  and 
calculate  the  rack  voltage,  or  voltage  at  which  they  are  to  be 
burned  on  life  test.  At  the  Bureau  of  Standards,  however,  the 
actual  test  voltage  is  measured.  This  practise  is  to  be  endorsed. 
At  the  Electrical  Testing  Laboratories  we  use  both  methods,  even 
in  forced  tests,  employing  the  calculated  voltage  as  an  approxi- 
mation and  the  actual  measured  voltage  as  the  correct  test  value. 
At  the  Bureau,  the  tests  are  made  on  a  60-cycle  current.  At  the 
Laboratories  the  majority  of  lamps  are  operated  under  similar 
conditions ;  in  addition,  at  least  once  a  year  we  test  a  substantial 
number  of  lamps  on  direct  current.  At  present  we  are  also  en- 
gaged in  testing  several  groups  of  carefully  selected  lamps  at  30, 
40,  60,  90,  and  150-cycles. 

From  the  statement  at  the  foot  of  the  fifteenth  page,  it  appears 
that  tungsten  lamps  are  tested  at  the  Bureau  at  about  1 .0  watt  per 
candle.  Above,  on  the  same  page,  the  relation  of  life  to  watts  per 
candle  is  expressed  as  a  parabolic  curve  with  an  exponent  of 
7.4,  with  a  qualification  to  the  effect  that  the  equation  is  limited 
in  its  use  to  a  certain  range  of  watts  per  candle.  Now  small 
tungsten  lamps,  10  and  15-watts,  are  rated  at  1.35  to  1.15  watts 
per  candle,  so  that  it  would  appear  that  a  test  at  1.0  watt  per 
candle  is  in  effect  a  considerably  forced  test  on  these  small  lamps. 
I  should  like  to  ask  the  authors  what  their  experience  has  been 
in  reference  to  the  applicability  of  the  correction  factor  based  on 
the  7.4  exponent  in  tests  on  such  small  lamps  ? 

Mr.  J.  L.  Minick  :  The  Pennsylvania  Railroad  is  one  of  the 
few  large  corporations  that  makes  a  careful  inspection  and  test 
of  the  incandescent  lamps  purchased  for  its  use.  It  may  be  of  in- 
terest to  some  of  you  to  know  that  their  routine  method  of  inspec- 
tion and  test  follows  closely  that  established  by  the  Bureau  of 
Standards.  Their  laboratory  equipment,  however,  is  not  so 
elaborate  and  probably  not  so  accurate  as  that  used  by  the  Bureau, 
though  check  tests  with  the  Bureau  and  other  laboratories  show 
that  very  accurate  work  is  being  done  at  the  Altoona  laboratory 
of  the  railroad.  The  remodeling  of  the  laboratory  equipment  has 
been  under  consideration  for  some  time,  but  prospective  changes 
in  lamp  design  seem  to  warrant  postponing  definite  action  until  it 
can  be  determined  whether  the  rating  of  lamps   will   be  changed 


TESTING   OF   LAMPS  839 

from  a  "mean  horizontal"  to  a  "mean  spherical"  candlepower 
basis. 

I  am  sorry  that  the  authors  of  this  paper  have  not  touched  upon 
this  phase  of  their  work.  The  introduction  of  the  gas-filled  lamp 
will  undoubtedly  make  it  necessary  to  abandon  "mean  horizontal" 
candlepower  as  the  basis  for  rating  lamps.  This  will  bring  about 
changes  in  routine  methods  of  inspection  and  test  and  will 
probably  require  changes  in  laboratory  equipment  and  it  is  essen- 
tial that  the  Bureau  of  Standards,  which  is  accepted  by  the  manu- 
facturers and  most  of  the  large  purchasers  as  the  arbitrator  in 
case  of  dispute,  be  prepared  to  offer  advice  concerning  the 
changes  indicated  above. 

The  Pennsylvania  Railroad  practise  differs  from  that  of  the 
Bureau  of  Standards  in  that  they  depend  largely  upon  forced  or 
excess  voltage  tests  to  determine  whether  the  life  performance  of 
the  test  samples  is  satisfactory  or  not.  The  excess  voltage  life 
values  used  are  determined  from  the  formula  quoted  by  the 
authors,  that  having  the  exponent  7.4.  The  average  test  life  of  all 
lamps  tested  throughout  a  period  of  some  four  or  five  months 
checks  very  closely  with  the  values  determined  from  the  formula, 
though  many  individual  tests  show  rather  wide  variations. 

Mr.  P.  S.  Millar  :  I  should  like  to  add  a  word  of  commenda- 
tion of  this  paper.  The  authors  have  succeeded  in  presenting 
very  clearly  an  excellent  description  of  the  life  testing  system, 
which  is  very  highly  developed.  They  have  refined  mechanical 
and  electrical  details  in  a  way  which  I  presume  contributes  to  ac- 
curacy and  economy.  I  believe  they  have  an  excellent  system  and 
are  doing  very  good  work. 

Just  a  word  of  a  general  nature  on  this  question  of  lamp  life 
testing.  There  prevails  in  many  quarters  the  notion  that  if  a  few 
lamps  of  a  number  of  different  brands  are  subjected  to  tests, 
the  result  will  be  an  adequate  guide  for  purchasing  purposes. 
That  is  not  so.  You  will  note  that  this  paper  states  that  the  tests 
are  spread  over  a  million  and  a  quarter  lamps.  Mr.  Minick  in 
describing  the  tests  of  the  Pennsylvania  Railroad  states  that  the 
purchases  are  on  the  order  of  a  million  lamps  per  annum.  When 
purchasing  in  such  quantities,  lamp  life  tests  can  be  made  very 
valuable.     In  small  purchases   it  is  impracticable   to  conduct  life 


840     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

tests  which  will  result  in  ultimate  economy.  It  is  important  in 
any  life  testing  of  lamps  to  know  the  real  cost  of  the  work  and  to 
compare  such  cost  with  the  value  derived  from  the  test  in  im- 
provement of  the  quality  of  the  lamp  obtained  for  use. 

There  are  three  questions  which  I  should  like  to  ask  the  authors 
regarding  not  so  much  the  details  of  life  testing  as  the  general 
principles  of  the  conduct  of  such  a  test.  I  ask  them  because  the 
same  problems  have  come  to  me  and  I  have  found  difficulty  in 
meeting  them.  If  two  groups  of,  let  us  say,  6  incandescent  lamps 
of  two  different  brands  are  submitted  to  the  Bureau  of  Stand- 
ards for  life  test,  I  should  like  to  ask  what  action  the  Bureau 
takes.  Do  they  test  the  lamps  ?  Do  they  qualify  the  report  in  any 
way  when  the  report  is  rendered  ?  Second,  if  two  such  groups  of 
lamps  are  presented  for  tests  and  the  lamps  of  one  group  were 
manufactured  to  be  operated  at  one  and  seven  hundredths  watts 
per  candle  and  the  lamps  of  the  other  group  were  manufactured 
to  be  operated  at  one  watt  per  candle,  and  the  groups  are  of  dif- 
ferent brands,  what  action  does  the  Bureau  take  in  regard  to 
tests  and  results?  Are  both  groups  operated  at  one  watt  per 
candle,  or  are  they  operated  at  the  respective  watts  per  candle  for 
which  they  were  intended  ?  Third,  if  two  such  groups  were  pre- 
sented for  tests  and  the  Bureau  does  not  know  at  what  watts  per 
candle  they  were  intended  to  be  operated,  what  action  is  taken  in 
the  running  of  the  test  and  the  preparation  of  the  report?  These 
are  very  important  questions  and  questions  of  a  very  practical  na- 
ture, and  I  am  frank  to  say  that  I  hardly  know  what  is  the  right 
answer. 

Dr.  C.  E.  MeEs:  With  regard  to  Mr.  Millar's  point  as  to 
the  testing  of  lamps  in  small  establishments,  I  will  point  out  that 
there  is  another  side  than  the  question  of  whether  a  saving  could 
be  made  on  the  cost  of  lamps.  In  a  good  many  manufacturing 
establishments  bad  lamps  are  not  replaced  as  adequately  as  they 
should  be  when  their  efficiency  gets  down.  Their  replacement  is 
sometimes  difficult  because  of  the  nature  of  the  work.  It  is 
sometimes  difficult  to  take  out  lamps,  as  in  our  case,  the  Eastman 
Kodak  Company,  and  in  other  cases  the  efficiency  of  the  depart- 
ment replacing  the  lamp  is  not  all  it  should  be;  so  that  bad  lamps 
are  a  source  of  more  cost  than  is  apparent  owing  to  the  insuf- 


TESTING   OF   LAMPS  84I 

ficient  light  leading  to  bad  and  inefficient  work :  in  many  cases  I 
believe  that  a  properly  conducted  life  test  on  all  lamps  purchased 
would  pay,  even  though  the  cost  of  the  test  was  greater  than 
the  actual  saving  made.  We  only  use  a  tenth  as  many  lamps  as 
the  Pennslyvania  Railroad,  but  it  still  pays  us  to  test  lamps  on  the 
life  test. 

Dr.  E.  B.  Rosa  :  We  do  not  make  such  tests  as  Mr.  Millar  de- 
scribes and  therefore  do  not  have  the  difficulty  that  he  has.  Our 
testing  is  almost  entirely  for  the  government ;  it  is  only  occasion- 
ally that  we  make  other  tests  than  for  the  government,  and  those 
are  for  very  special  reasons.  If  we  should  make  such  tests,  we 
should  guard  our  statements  very  carefully  indeed,  and  say  that 
the  results  are  for  the  particular  lamps  submitted  and  that  no 
conclusions  should  be  drawn  for  other  lamps  not  included.  As  a 
rule,  when  we  have  made  tests  for  others  than  the  government, 
it  has  been  on  a  much  larger  number  of  lamps. 

Dr.  G.  W.  Middlfkauff:  In  reference  to  the  question  of  the 
measurement  of  mean  spherical  candlepower,  I  would  say  that, 
up  to  the  present,  measurements  of  this  kind  have  not  been  neces- 
sary in  our  work.  The  reason  for  this  is  that,  in  accordance 
with  standard  specifications,  all  vacuum  tungsten  lamps  are 
tested  on  the  basis  of  mean  horizontal  candlepower;  and,  with 
few  exceptions,  all  carbon  lamps  tested  have  been  of  the  regular 
sizes  the  reduction  factors  for  which  are  well  established.  For 
the  few  special  sizes  of  carbon  lamps  tested,  the  reduction  factors 
are  determined  and  the  proper  corrections  are  made  in  the  rating. 
Furthermore,  there  have  been  so  few  gas-filled  lamps  purchased 
by  the  government  that  the  number  of  samples  selected  during 
inspection  has  been  entirely  too  small  to  justify  the  expense  of 
testing  them.  However,  the  indications  are  that  within  the  very 
neat  future  we  shall  be  testing  gas-filled  lamps  also,  and,  when 
we  do,  it  is  our  intention  to  test  them  on  a  mean  spherical  basis. 

We  have  done  considerable  work  on  the  determination  of  the 
life-efficiency  exponent  for  various  sizes  of  vacuum  tungsten 
lamps,  a  certain  number  of  which  each  year  are  tested  at  or  near 
normal  w.  p.  c,  but  we  do  not  have  at  present  sufficient  data  on 
the  10  and  15  watt  sizes  to  draw  a  definite  conclusion.    However, 


842     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  indications   are  that   the   exponent   which   applies   to   these 
smaller  sizes  is  somewhat  less  than  7.4. 

Although  it  is  not  mentioned  in  the  paper,  our  tests  of  tung- 
sten lamps  have  been  made  at  0.9  to  0.95  w.  p.  c.  and  not  at  1.00 
w.  p.  c.  as  presumed  by  one  of  the  speakers  in  referring  to  the 
last  paragraph  on  page  826.  The  meaning  which  this  paragraph  is 
intended  to  convey  is  that  the  actual  forced  life  values  of  all  sizes 
of  tungsten  lamps  are  corrected  mechanically  to  their  equivalent 
at  1. 00  w.  p.  c,  and  of  all  carbon  lamps  to  their  equivalent  at  3.05 
w.  p.  c,  by  using  the  recording  and  computing  devices  in  the 
manner  described.  For  example,  in  the  record  of  the  40  watt 
tungsten  lamp  shown  in  figure  4,  it  is  seen  that  the  actual  life 
was  505  hours  at  0.947  w.  p.  c,  the  equivalent  of  which  is  757 
hours  at  1.00  w.  p.  c.  This  lamp  was  rated  at  1.05  w.  p.  c.  by  the 
manufacturer  and  the  life  specified  was  1,000  hours.  This  is 
equivalent  to  697  hours  at  1.00  w.  p.  c,  and  hence  the  life  of  the 
lamp  was  108.6  per  cent,  of  the  life  required. 


TRANSACTIONS 

OF  THE 

Illuminating  Engineering  Society 

Vol.  X  DECEMBER  30,  1915  NO.  9 

EFFECT  OF  ATMOSPHERIC  PRESSURE  ON  THE 
CANDLEPOWER  OF  VARIOUS  FLAMES.* 


BY  E.  B.  ROSA,  E,  C  CRITTENDEN  AND  A.   H.  TAYLOR. 


CONTENTS. 

I.  Previous  Investigations  and  Purpose  of  this  Work. 

II.  Apparatus. 

III.  Measurements  on  Pentane  and  Hefner  Lamps. 

IV.  Observations  on  Gas  Flames. 

V.  Computing  and  Combining  Observations  on  Gas. 

VI.  Explanation  of  Effect  of  Pressure  Changes. 

VII.  Effect  of  Water  Vapor. 

VIII.  Effect  of  Vitiation  of  the  Air. 

IX.  Bearing  of  Results  on  Tests  of  Gas. 

X.  Typical  Applications  to  Gas  Measurements. 


I.     PREVIOUS  INVESTIGATIONS  AND   PURPOSE 
OF  THIS  WORK. 

It  has  long  been  known  that  the  candlepower  of  flames  is 
affected  by  atmospheric  pressure.  Quantitative  observations  over 
a  wide  range  of  pressures  were  made  by  Frankland  about  1859.1 

In  more  recent  years  the  matter  has  become  of  practical  im- 
portance through  attempts  to  define  exactly  units  of  luminous 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,   September  20-23,    191 5. 

The   Illuminating   Engineering    Society   is   not   responsible   for   the   statements    or 
opinions  advanced  by  contributors. 
1  Phil.  Trans..  151,  pp.  629-653,  1861. 

Proc.  Royal  Soc,  11,  pp.  366-372,  1860-62. 

Jour.  Ckem.  Soc,  15,  pp.  16S-196,  1862. 

Pogg.  Annalen.,  115,  pp  296-335.  1862. 


844     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

intensity  based  on  flame  standards.  The  development  of  such 
standards  which  were  reliable  enough  to  repeat  values  very  pre- 
cisely, under  given  conditions,  and  the  simultaneous  development 
of  electric  lamps  which  were  independent  of  atmospheric  condi- 
tions, made  possible  fairly  precise  determinations  of  the  effect 
of  pressure. 

In  most  cases  these  determinations  were  made  by  measure- 
ments at  the  prevailing  pressure,  the  variations  obtained  being 
only  those  arising  from  the  natural  changes  in  barometric 
pressure.2 

Bunte3  made  some  attempts  to  control  artificially  the  pressure 
of  the  air  around  a  Hefner  flame,  but  did  not  succeed  in  getting 
satisfactory  results. 


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BAROMETRIC  PRESSURE  CM.  OF  MERCURY 
Fig.  i.— Variation  of  candlepower  of  certain  flames  with  barometric  pressure. 

Butterfield,  Haldane  and  Trotter,4  using  a  steel  cylinder  built 
for  the  study  of  caisson  disease,  carried  out  the  most  extensive 
experiments  of  this  kind  which  had  been  made  up  to  that  time. 
Their  results  on  standard  pentane  and  Hefner  lamps  are  shown 
in  Fig.  I. 

2  I,iebenthal,  E.,  Zs.f.  Instrument.,  15,  p.  163,  1895;/./.  Gas,  u.  IVasser,.  49,  p.  561,  1906. 
Paterson,  C  C,  Electrician  {London),  53,  p.  751,  1904;  /.  Institution  of  Elect.   Engineer, 
ing.,  38,  p.  271,  1906-07;  J.  Gas  Light.,  99,  p.  232,  1907:  N.  P.  L.,  Collected  Researches,  3  p.49, 
1908. 

Rosa  and  Crittenden,  Bureau  of  Standards  Bulletin,  10,  p.  562,  1914. 
*Jour.f.  Gas  u.  IVasser,  p.  310.  1891, 
*J.  Gas  Lighting,  115,  p.  228,  1911. 


ROSA,  CRITTENDEN,  TAYLOR  '.    CANDLEPOWER  OF  FLAMES      845 

In  the  United  States  the  flame  standards  are  not  primary  or 
fundamental,  but  are  calibrated  at  the  Bureau  of  Standards  by 
comparison  with  electric  standards  under  nearly  normal  atmos- 
pheric pressure.  The  correction  for  atmospheric  pressure  is 
therefore  small,  and  although  it  had  never  been  determined  very 
accurately,  the  possible  error  (due  to  this  uncertainty  in  the  cor- 
rection factor)  in  the  normal  value  of  a  flame  standard  was  very 
slight  so  long  as  it  was  used  at  or  near  sea  level.  When,  however, 
such  a  flame  standard  was  employed  at  higher  altitudes,  it  was 
known  that  the  candlepower  was  considerably  less,  but  we 
possessed  no  reliable  data  for  calculating  the  candlepower  at  such 
reduced  pressures.  It  hence  resulted  that  when  flame  lamps  are 
used  as  candlepower  standards,  either  for  testing  the  candlepower 
of  gas  as  given  by  open  flame  burners,  or  the  candlepower  of  gas 
sources  such  as  mantle  burners  or  acetylene  flames,  the  standard 
might  be  10  per  cent,  or  20  per  cent,  over-rated  by  assuming  its 
candlepower  to  be  the  same  as  it  would  be  at  normal  barometric 
pressure,  and  hence  the  same  error  would  be  introduced  into  the 
measurements. 

Nothing  is  more  obvious  than  that  the  candlepower  of  a  light 
source  used  as  a  standard  should  be  known  under  the  conditions 
of  its  use,  and  yet  for  lack  of  means  of  determining  the  effect  of 
varying  atmospheric  pressure,  flame  standards  have  been  used 
very  generally  at  widely  varying  barometric  pressures  with  values 
assigned  under  normal  atmospheric  pressure.  Moreover,  this 
variation  in  candlepower  due  to  variations  in  pressure  was  pre- 
sumably different  for  different  kinds  of  lamps  and  burners,  and 
yet  no  experiments  had  been  made  accurately  enough  to  determine 
correction  coefficients  satisfactory  even  for  commercial  use. 

Values  of  the  pressure  coefficient  for  pentane  lamps  had  been 
computed  from  measurements  made  at  varying  atmospheric 
pressures  at  the  Bureau  of  Standards,  but  the  natural  variations 
in  the  barometer  at  one  place  are  too  small  to  give  reliable  re- 
sults by  this  method  for  pressures  differing  considerably.  It  was 
first  proposed  to  select  two  or  three  test  stations  at  different  alti- 
tudes and  make  a  considerable  series  of  measurements  on  a 
variety  of  flame  sources  at  each,  and  then  compute  the  pressure 
coefficient  from  the  results.     Since  the  trouble  and  expense  of 


846     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

carrying  out  such  a  project  under  conditions  favorable  enough  to 
give  results  of  the  required  accuracy  would  be  very  great,  it  was 
decided  to  attempt  to  build  an  apparatus  that  would  permit  the 
measurements  to  be  made  in  our  own  laboratories  with  variations 
of  pressure  corresponding  to  two  or  three  miles  range  in  altitude 
above  sea  level. 

Our  experience  with  flame  standards  had  shown  that  for  ac- 
curate measurements  it  is  necessary  to  have  an  atmosphere  free 
from  drafts  or  sudden  slight  variations  of  pressure,  and  very 
perfect  ventilation.  At  first  it  appeared  doubtful  whether  we 
could  maintain  the  necessary  circulation  of  fresh  air  in  a  steel 
enclosure  and  keep  the  flame  free  from  the  vibrations  or  move- 
ments due  to  slight  variations  of  pressure  or  drafts  so  as  to  make 
satisfactory  measurements  of  candlepower.  But  the  success  of 
the  apparatus  was  greater  than  we  anticipated,  and  we  found  that 
flames  could  be  burned  enclosed  for  an  indefinite  period  under 
conditions  of  perfect  ventilation,  and  measurements  made  with 
less  error  due  to  variations  in  the  flame  than  when  they  were 
burned  as  usual  in  the  open  room.  The  apparatus  has  also  been 
used  to  re-determine  the  humidity  coefficient,  that  is,  the  effect 
upon  the  candlepower  of  atmospheric  humidity,  usually  expressed 
in  terms  of  liters  of  water  vapor  per  cubic  meter  of  dry  air. 

The  variation  in  the  candlepower  of  a  gas  flame  with  variation 
of  atmospheric  pressure  is  due  to  two  separate  causes ;  first,  the 
quantity  of  gas  burned  is  reduced  when  the  pressure  is  reduced, 
5  cu.  ft.  per  hour  (for  example)  giving  a  mass  of  gas  that  is 
directly  proportional  to  the  pressure.  Second,  the  luminous  effi- 
ciency of  the  flame,  that  is,  the  quantity  of  light  per  unit  mass  of 
gas  burned,  varies  with  the  pressure.  The  experiments  give  the 
combined  effect  of  these  separate  causes,  and  when  the  first  can 
be  calculated  (as  when  the  volume  of  gas  burned  is  measured) 
the  second  can  be  determined  by  itself. 

II.  APPARATUS. 
For  the  purpose  of  controlling  the  pressure  we  designed  and 
built  a  complete  set  of  apparatus  as  shown  in  the  accompanying 
photograph,  and  in  the  sketch,  Fig.  2.  Referring  to  the  sketch, 
tanks  A  and  B  are  each  3  ft.  (0.91  m.)  in  diameter  and  5  ft. 
(1.52  m.)  high.     Tank  A  has  a  wooden  floor  about  1  ft.  from  the 


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Fig.  2a.— Diagram  of  testing  apparatus. 


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Fig.  3-— Variation  of  eandlepower  of  certain  flames  with  barometric  pressure;  i— Hefner 
lamp;  2— Pentane  lamp;  3— No.  7  Bray  slit  union  gas  burner. 


GAS  RATE  AT  BURNER-CU.  FT.  PER  HR. 


Fig.  4. — Variation  of  efficiency  with  consumption  at  various  pressures  of  a  Sugg's  F 

Argand  burner. 


, 


ROSA,  CRITTENDEN,  TAYLOR  :    CANDEEPOWER  OE  FRAMES      847 

bottom.  This  floor  has  a  large  number  of  small  holes,  which 
serve  to  diffuse  the  incoming-  air  and  prevent  drafts.  On  one 
side  is  a  door  15  in.  (38.10  cm.)  by  30  in.  (76.20  cm.)  which  can 
be  made  air-tight,  when  shut,  by  means  of  fourteen  hinged  bolts. 
Above  the  door  a  shaft  enters  the  tank,  and  by  means  of  suitable 
fittings  it  is  used  to  adjust  the  flame  height  of  the  lamp  under 
observation,  there  being  a  glass  window  in  the  door  for  this  pur- 
pose. At  a  point  about  900  from  the  center  of  the  door  is  an- 
other glass  window,  through  which  the  light  from  the  lamp  under 
test  shines  on  the  photometer  screen.  On  the  side  opposite  this 
window  is  arranged  a  cabinet  containing  an  Assman  psychrometer 
for  measurements  of  humidity.  This  cabinet  is  connected  at  top 
and  bottom  to  the  tank,  so  that  air  can  be  drawn  in  at  the  bottom, 
passed  over  the  thermometer  bulbs,  and  back  into  the  tank  at  the 
top  of  the  cabinet.  The  fan  of  this  psychrometer  is  driven  by  an 
electric  motor.  A  mercury  manometer  tube  is  also  connected  to 
this  tank  to  measure  the  atmospheric  pressure  in  the  tank.  About 
15  in.  from  the  top  of  the  tank  is  a  wooden  partition  with  a 
hole  about  16  in.  x  25  in.  (40.64  x  63.50  cm.)  for  preventing  the 
products  of  combustion  from  passing  back  down  around  the 
flame. 

Tank  B  is  used  as  an  equalizing  tank,  to  prevent  sudden 
fluctuations  or  throbs  of  pressure.  It  is  joined  at  top  and  bottom 
with  tank  A  by  3  in.  (7.62  cm.)  pipes.  Near  the  center  it  has  a 
thin  rubber  diaphragm,  to  assist  in  eliminating  pressure  throbs. 
To  the  top  chamber  of  this  tank  is  connected  another  steel  tank, 
14  in.  (10.16  cm.)  in  diameter  and  5  ft.  (1.52  m.)  high,  which 
serves  as  a  further  reservoir  between  the  working  tanks  and  the 
air  pump.  To  the  bottom  chamber  of  tank  B  are  connected  two 
air  meters  in  parallel,  a  calcium  chloride  drying  chamber,  and  a 
tank  containing  water  for  saturating  the  air.  Twelve  valves  are 
so  arranged  that  the  air  may  pass  through  the  tanks  in  any  of  the 
following  ways :  Room  air,  through  or  around  the  meters ;  room 
air  through  the  CaCl,  drying  chamber ;  room  air  through  the  sat- 
urating tank ;  room  air  through  the  pump,  through  the  meters  and 
tanks,  back  out  to  the  room  or  outer  air.  The  last  named  ar- 
rangement is  for  use  in  getting  pressures  above  atmospheric 
pressure.  The  arrows  indicate  the  path  of  the  air  when  the 
pump  is  being  operated  as  a  vacuum  pump,  and  room  air  is  being 


848     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

drawn  through  the  meters.  The  pressure  in  the  tanks  and  the 
rate  of  air  flow  are  controlled  by  valves  6  and  7.  A  Zeiss  re- 
fractometer,  not  shown  in  the  sketch,  was  arranged  to  take 
samples  of  air  from  the  tank  for  tests  of  C02. 

III.  MEASUREMENTS  ON  PENTANE  AND  HEFNER 
LAMPS. 

In  most  of  this  work  photometric  measurements  have  been 
made  against  electrical  standards,  using  the  substitution  method, 
the  electrical  standards  being  burned  in  place  in  the  tank,  the 
voltages  of  the  standard  and  comparison  lamps  being  measured 
by  the  use  of  a  potentiometer. 

When  work  was  begun  on  the  pentane  lamp  it  was  necessary 
to  make  preliminary  tests  to  determine  the  rate  of  flow  of  air 
through  the  tanks  which  would  be  rapid  enough  to  prevent  vitia- 
tion of  the  air,  and  at  the  same  time  not  to  cause  drafts  or  to 
affect  the  candlepower  of  the  lamp  by  cooling  certain  parts  of 
it.  Rates  of  air  flow  at- tank  pressure  from  about  450  to  1,100 
cu.  ft.  (12.74  to  31.14  m.3)  per  hour  were  tried,  and  it  was  found 
that  there  was  no  measurable  effect  on  the  candlepower  due  to 
imperfect  ventilation  until  the  rate  was  reduced  below  550  cu.  ft. 
(15.57  m-3)  Per  hour.  Measurements  of  this  nature  were  made 
at  various  pressures,  results  being  the  same  in  each  case.  The 
rate  finally  adopted  was  from  700  to  800  cu.  ft.  (19.82  to  22.65 
m.3)  per  hour  (at  tank  pressure).  The  refractometer  indicated 
that  there  was  no  increase  of  C02  in  samples  of  air,  taken  from 
near  the  flame,  over  that  in  the  outside  air. 

Each  candlepower  observation  at  any  pressure  was  the  average 
of  about  75  or  more  separate  settings  of  the  photometer.  After 
changing  the  air  pressure  in  the  tanks  and  adjusting  the  rate  of 
air  flow,  no  measurements  were  made  until  the  pressure  had  be- 
come constant.  Candlepower  measurements  on  the  pentane  lamp 
were  made  at  pressures  from  463  to  1,072  mm.  The  results  are 
plotted  in  Fig.  3.  The  average  candlepower  of  the  lamp  under 
normal  conditions,  as  determined  by  previous  measurements  in 
the  open  air,  was  9.78.  The  curve  drawn  to  represent  the  aver- 
age of  observations  at  various  pressures  indicated  a  value  of  9.76 
candles  at  normal  pressure  and  water  vapor.  Hence  it  is  evident 
that  the  unusual  conditions  of  burning  did  not  affect  its  candle- 


ROSA,  CRITTENDEN,  TAYLOR  \    CANDEEPOWER  OF  FLAMES      849 

power  at  normal  pressure.  Also,  the  barometric  pressure  factor 
over  the  range  from  730  to  770  mm.,  the  range  obtainable  under 
natural  conditions  in  this  laboratory,  was  found  to  be  in  close 
agreement  with  that  which  we  had  obtained  when  burning  the 


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4 

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GAS  RATE  AT  BURNER.    CU.  FT.  PER  HOUR. 
Fig-  5-— Variation  of  efficiency  with  consumption  at  various  pressures. 

lamps  in  open  air  in  the  laboratory,  namely,  0.6  per  cent,  change 
in  candlepower  for  1  cm.  change  in  pressure. 

The  method  of  testing  the  Hefner  lamp  under  various  pres- 
sures was  similar  to  the  above,  except  that  it  was  not  necessary 
to  regulate  the  rate  of  air  flow  so  closely.    In  this  case  the  deter- 


85O     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

mining  factor  was  the  maximum  allowable  rate  which  would  not 
disturb  the  steadiness  of  the  flame.  It  is  interesting  to  note  that 
the  Hefner  flame  was  much  steadier  when  burning  in  the  tank 
than  when  burning  in  the  open  air,  and  the  variations  from  the 
mean  value  at  any  pressure  were  very  small,  as  will  be  seen  by 
reference  to  Fig.  3.  This  suggests  the  desirability  of  using  the 
Hefner  in  such  a  ventilated  enclosure  when  the  highest  accuracy 
is  desired. 

For  both  the  pentane  and  the  Hefner  lamps  frequent  measure- 
ments of  water  vapor  content  of  the  air  were  made,  and  observed 
results  were  corrected  to  a  standard  value  of  8  liters  of  water 
vapor  per  cubic  meter  of  dry  air  for  the  pentane  lamp,  and  8.8 
liters  for  the  Hefner. 

IV.    OBSERVATIONS  ON  GAS  FLAMES. 

In  order  to  reduce  measurements  on  gas  flames  to  a  definite 
basis,  it  was  first  necessary  to  determine  the  relative  efficiency  of 
each  burner  at  various  rates  of  gas  flow,  since  it  is  not  always 
possible  to  make  the  rate  exactly  5  cu.  ft.  (0.14  m.3)  per  hour. 
Such  measurements  were  made  at  various  pressures,  and  curves 
plotted  to  show  the  efficiency  at  any  consumption  in  terms  of 
the  efficiency  at  a  rate  of  5  cu.  ft.  per  hour  (see  Figs.  4  and  5), 
and  all  later  observations  were  reduced  to  the  value  which  would 
have  been  obtained  if  the  rate  had  been  made  exactly  5  cu.  ft.  per 
hour  at  the  pressure  and  temperature  prevailing  in  the  tank. 

The  three  burners  tested  were  the  Bray  No.  7  Slit  Union,  the 
Von  Schwarz  No.  8  E.  H.,  and  the  new  Sugg's  F  Argand.  The 
Bray  burner  had  its  maximum  efficiency  near  5  cu.  ft.  per  hour 
at  all  pressures,  but  the  rate  for  maximum  efficiency  for  the  other 
two  burners  increased  as  the  air  pressure  was  lowered.  In  the 
case  of  the  argand  burner,  especially,  the  corrections  made  by 
the  use  of  these  curves  were  very  important.  For  example,  at 
500  mm.  pressure  a  variation  of  1  per  cent,  in  rate  of  flow  of  the 
gas  would  make  2  per  cent,  change  in  the  efficiency,  and  there- 
fore 3  per  cent,  change  in  the  observed  candlepower;  in  other 
words,  the  indirect  effect  in  changing  the  efficiency  was  twice  as 
great  as  the  direct  effect  of  having  more  gas  to  burn. 

As  no  gas  storage  tanks  were  available,  it  was  necessary  to 
make  the  observations  in  such  manner  as  would  eliminate  any 


ROSA,  CRITTENDEN,  TAYLOR:    CANDLEPOWER  OE  FLAMES      85I 

errors  due  to  change  of  quality  of  gas  during  measurement.  The 
method  employed  was  to  make  observations  at  pressures  which 
were  decreased  by  steps  to  the  lowest  value  desired,  then  in- 
creased by  steps  intermediate  between  the  former  pressures 
The  quality  of  gas  usually  was  sufficiently  constant  to  give  very 
good  agreement  between  the  two  series  of  points  thus  obtained. 

All  measurements  to  determine  the  effect  of  barometric  pres- 
sure on  the  candlepower  of  gas  flames  were  made  with  the  gas 
rate  at  the  burner  as  near  5  cu.  ft.  per  hour  as  could  be  obtained 
without  taking  excessive  care,  as  this  is  the  customary  test  con- 
dition. Photometric  and  gas  rate  measurements  were  made  sim- 
ultaneously. The  rate  of  air  flow  through  the  tanks  was  main- 
tained at  approximately  700  to  800  cu.  ft.  per  hour.  Each  point 
plotted  on  the  curves  shown  is  usually  the  mean  of  75  to  150 
separate  settings  of  the  photometer,  the  larger  number  of  read- 
ings being  taken  when  the  candlepower  seemed  to  be  unsteady. 
All  photometer  readings  were  printed  on  a  sheet  by  apparatus  of 
the  kind  regularly  used  at  the  bureau  for  this  purpose,  so  that  a 
great  many  readings  could  be  taken  in  a  short  time,  with  a  mini- 
mum of  prejudice. 

V.    COMPUTING  AND  COMBINING  OBSERVATIONS 
ON  GAS. 

In  each  run  the  observed  value  was  corrected  for  the  variation 
of  efficiency  with  consumption,  if  the  gas  rate  was  not  exactly 
5  cu.  ft.  per  hour.  This  value  was  further  reduced  to  constant 
mass  of  gas,  vis.,  5  cu.  ft.  at  30  in.  (76.20  cm.)  and  6o°  F.  Next 
these  final  corrected  candlepower  values  were  plotted  against 
barometric  pressures,  and  the  curve  which  would  best  represent 
the  points  obtained  in  that  one  run  was  drawn.  As  it  is  not 
possible  to  combine  runs  from  day  to  day  on  a  candlepower  basis, 
because  of  slight  changes  of  quality  of  gas  from  day  to  day,  a 
certain  barometric  pressure,  well  within  the  range  of  pressures 
used,  was  chosen  as  a  combination  point  for  the  various  runs. 
For  one  burner  tested  the  pressure  chosen  was  650  mm.  After 
each  run  had  been  plotted  and  the  curve  drawn,  the  candlepower 
value  at  650  mm.  was  read  off  from  this  curve.  This  candle- 
power  was  then  rated  as  100  per  cent.,  and  all  observed  candle- 
powers  of  this  run  were  reduced  to  percentages  of  this  value. 


852     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Each  run  having  been  worked  up  in  this  manner,  all  were  on  a 
common  basis,  and  could  be  combined  in  a  single  plot.  When 
this  had  been  done,  and  the  most  probable  curve  drawn,  all  ob- 
servations were  then  reduced  to  a  basis  of  100  per  cent,  at  760 
mm.  The  observations,  reduced  as  described  above,  are  plotted 
in  Fig.  6  and  in  order  to  facilitate  comparison  one  of  these  curves 
(No.  3,  that  for  the  Bray  burner)  is  also  plotted  with  the  pentane 
and  Hefner  lamp  data  in  Fig.  3. 

It  is  to  be  noted,  however,  that  the  standard  lamps  are  operated 
at  constant  flame  height,  whereas  the  measurements  on  the  gas 


i.U)  1"  1 

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50  55  60  65  70 

BAROMETRIC     PRESSURE .  CI*-    OF   MERCURY. 

Fig.  6. — Variation  of  candlepower  of  gas  -with  barometric  pressure— constant  mass  of  gas. 
i— Sugg  F  Argand  burner;  2— Von  Schwarz  No.  8  F-  H.  burner;  3 — No.  7  Bray  burner. 


burners  are  reduced  to  the  basis  of  constant  (mass)  consumption. 
These  are  the  conditions  under  which  the  "candlepower"  is  cal- 
culated in  gas  tests,  and  are  therefore  of  most  practical  im- 
portance; but  a  better  comparison  of  the  underlying  phenomena 
is  obtained  by  plotting,  instead  of  the  candlepower  for  constant 
consumption  by  mass,  the  actually  measured  values,  which  are 
for  constant  consumption  by  volume.  This  gives  curve  3a,  show- 
ing a  still  more  rapid  decrease  in  candlepower  with  decrease  in 
pressure.  Of  course  a  part  of  this  decrease  is  due  to  the  re- 
duction in  the  mass  of  gas  burned,  and  for  quantitative  compari- 


ROSA,  CRITTENDEN,  TAYLOR  :    CANDEEPOWER  OF  FLAMES      853 

son  with  the  standard  lamp  curves  we  should  have  either  the 
latter  corrected  to  constant  fuel  consumption  or  the  gas  curves 
corrected  to  constant  flame  size,  which  would  give  a  curve  lying 
between  3  and  3a.  The  point  to  be  noted  is  that  the  open  gas 
flames  fall  off  in  candlepower  much  more  rapidly  than  the  pentane 
lamp,  which  in  turn  decreases  more  rapidly  than  the  Hefner  with 
falling  pressure. 

VI.    EXPLANATION  OF  EFFECT  OF  PRESSURE  CHANGES. 

The  reason  for  the  markedly  different  effects  on  different 
flames  is  easily  found.  The  light  of  the  flame  supposedly  comes 
from  glowing  particles  of  carbon  set  free  in  the  earlier  stages  of 
the  process  of  combustion.  In  the  later  stages  the  carbon  is 
oxidized  and  becomes  non-luminous.  The  amount  of  light  pro- 
duced therefore  depends  on  two  factors ;  first,  the  number  of 
particles  of  glowing  carbon  in  existence  at  one  time,  and  second, 
the  average  temperature  of  these  particles. 

The  number  of  glowing  particles  depends  among  other  things 
upon  the  average  interval  between  the  first  and  the  second  stages 
of  combustion;  in  other  words,  on  the  interval  between  the  time 
when  the  carbon  is  set  free  and  the  time  when  sufficient  oxygen  is 
supplied  to  combine  with  the  carbon.  In  the  case  of  the  Bunsen 
flame,  in  which  the  fuel  and  the  air  are  already  intimately  mixed, 
this  interval  is  practically  non-existent;  the  carbon  is  oxidized 
before  it  becomes  incandescent  and  the  flame  is  therefore  non- 
luminous.  At  the  other  extreme  is  the  smoky  flame  in  which  the 
second  stage  is  never  completed,  so  that  some  of  the  carbon 
escapes  unoxidized.  The  various  types  and  conditions  of 
luminous  flames  come  in  the  intermediate  region. 

Barometric  pressure  affects  the  amount  of  light  produced  be- 
cause it  affects  the  rate  of  diffusion  of  oxygen  through  the  burn- 
ing fuel.  In  general,  as  the  pressure  grows  less,  the  diffusion 
is  more  rapid  and  the  "life"  of  the  glowing  carbon  particles  is 
reduced.  This  reduction  is,  however,  partially  compensated  by 
the  second  factor  mentioned,  that  is,  the  temperature  of  the  par- 
ticles, for  the  more  rapid  access  of  oxygen  results  in  more  vig- 
orous combustion  with  a  resulting  higher  temperature,  which  in 
turn  causes  each  particle  to  emit  more  light  while  it  does  glow. 


854     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

If,  then,  we  start  with  a  smoky  flame  (which  has  an  excess  of 
carbon)  and  reduce  the  pressure,  an  actual  increase  in  light  may- 
result.  This  condition  was,  in  fact,  reached  in  the  case  of  the 
Hefner  lamp  (Fig.  3),  although  the  difficulty  of  setting  the  flame 
height  under  this  condition  is  such  that  not  many  measurements 
were  made  in  this  region. 

As  the  pressure  is  reduced,  however,  a  point  is  soon  reached 
where  the  reduction  in  the  number  of  particles  over-balances  the 
increase  in  the  light  emitted  by  the  individual  particle,  and  from 
this  point  on  the  reduction  in  candlepower  is  more  and  more 
rapid. 

It  may  be  assumed  that  the  curve  as  given  for  the  Hefner  lamp 
is  typical  of  flames  in  general,  but  that  our  limitations  with  regard 
to  pressure  are  such  that  for  the  other  flames  we  get  only  small 
sections  of  the  curve  lying  far  from  the  maximum,  which  is  near 
the  pressure  that  would  give  a  smoky  flame.  In  a  general  way, 
the  whiter  a  flame  is  the  farther  it  is  from  the  smoking  point,  and 
the  more  rapidly  its  candlepower  changes  with  change  of  pressure. 
A  few  measurements  on  an  acetylene  burner,  for  example,  indi- 
cated that  at  a  pressure  of  20  in.  (50.80  cm.)  its  candlepower  was 
about  52  per  cent,  of  normal,  while  the  various  burners  with  il- 
luminating gas  gave  63  to  72  per  cent.,  the  pentane  lamp  73  per 
cent,  and  the  Hefner  lamp  86  per  cent.,  this  being  the  order  of  the 
lamps  with  reference  to  color  also.  Even  the  difference  between 
the  effects  on  the  two  types  of  open  flame  burner  might  have 
been  predicted.  The  Von  Schwarz  burner  showed  a  decidedly 
higher  efficiency  than  the  Bray,  indicating  that  its  flame  was 
nearer  the  smoking  point,  and  as  would  be  expected  from  this  the 
effect  of  pressure  changes  is  less  on  this  burner. 

It  may  appear  that  the  curve  of  the  argand  burner  (Fig.  6)  is 
decidedly  different  in  shape  from  those  of  the  open  flames,  but 
this  burner  has  a  chimney,  which  so  modifies  the  conditions  with 
respect  to  mixing  of  air  and  gas  that  no  comparison  can  be  made 
with  the  other  burners. 

In  this  connection,  however,  the  curves  of  Fig.  4,  showing  the 
variation  of  efficiency  with  consumption  at  various  pressures,  are 
of  interest.     As  the  pressure  is   lowered  the  consumption   for 


ROSA,  CRITTENDEN,  TAYLOR  :    CANDEEPOWER  OF  FLAMES      855 

maximum  efficiency  is  increased,  just  as  it  would  be  by  using  a 
gas  requiring  less  air  for  its  combustion.5 

It  appears,  therefore,  that  in  this  type  of  burner  also  the  effect 
of  decreased  pressure  is  attributable  to  a  more  rapid  mixing  of 
the  air  through  the  gas.  The  chimney,  however,  has  the  effect  of 
making  the  burner  pass  from  the  condition  of  good  aeration  to 
that  of  the  smoking  flame  within  a  relatively  small  range  of 
pressure.  So  we  find  that  at  normal  pressures,  with  the  gas  used 
in  determining  this  curve,  this  burner  has  already  passed  the 
maximum  efficiency  (it  was  in  fact  on  the  verge  of  smoking), 
while  at  the  other  end  of  the  pressure  range  it  is  falling  more 
rapidly  than  the  open  flame.  In  other  words  a  given  range  of 
pressure  gives  a  larger  part  of  the  typical  pressure-candlepower 
curve  for  this  burner  than  it  does  for  the  open  flames. 
VII.    EFFECT  OF  WATER  VAPOR. 

By  means  of  the  apparatus  described  on  page  4,  it  was  possible 
to  vary  the  water  vapor  in  the  air  supplied  to  the  tanks  over  a 
range  of  15  to  20  liters  per  cubic  meter  of  air.  By  making  ob- 
servations on  gas  under  various  weather  conditions,  a  total  range 
of  about  6  to  45  liters  was  obtained.  Similar  measurements  over 
a  smaller  range  were  made  on  an  acetylene  flame  and  an  Elliott 
kerosene  lamp.  All  of  these  measurements  were  made  at  a  baro- 
metric pressure  of  710  mm.  The  observed  points  have  been 
plotted  in  Fig.  7  in  which  the  curve  for  the  pentane  lamp  is  also 
shown  for  comparison.  This  curve  was  determined  by  a  series 
of  measurements  extending  over  several  months,  under  natural 
conditions,  and  was  reported  on  in  previous  papers.6  Its  ac- 
curacy was  further  verified  by  measurements  in  the  tanks.  An 
explanation  of  the  method  by  which  separate  observations  of 
water  vapor  effect  on  gas  were  combined  is  necessary,  since 
the  whole  range  was  not  obtainable  at  any  one  time.  The 
measurements  were  made  in  three  series  of  runs,  with  ranges 
of  24.7  to  45,  12.7  to  38.2,  and  6.4  to  23.1  liters.  The  runs  of 
each  series  were  combined  in  a  manner  similar  to  that  described 
above  for  the  barometric  curves.     The  combination  points  for 

5  Gilpin  F.  H.,  (Proc.  Amer.  Gas  Inst.,  9,  pp.  379-401,  1914.)  gives  a  similar  family  of 
curves  in  which  the  variable  condition  is  the  richness  of  the  gas,  instead  of  barometric 
pressure. 

6  Trans.  III.  Eng.  Soc,  5,  pp.  753-778,  1910;  and  6,  pp.  417-32,  191 1. 
Bureau  of  Standards  Bulletin.,  10,  pp.  391-417,  1913. 

2 


856     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

runs  of  each  series  were  37,  22  and  15  liters  respectively,  the 
values  at  these  points  being  called  100  per  cent,  for  each  series. 
The  curve  representing  each  series  was,  to  all  appearances,  a 
straight  line,  and  the  straight  line  representing  each  series  was 
computed  by  the  method  of  least  squares.  As  the  slopes  of  the 
three  lines  were  not  equal,  and  as  it  was  necessary  to  combine 
these  three  series  on  a  basis  of  100  per  cent,  candlepower  at  8 
liters,  certain  arbitrary  points  of  combination  were  chosen.  The 
three  series  had  been  taken  with  such  ranges  of  water  vapor  that 


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LITERS   OF  WATER   VAPOR  PER  CUBIC    METER  OF  DRY    AIR. 

Fig.  7.— Variation  of  certain  flames  with  atmospheric  moisture— barometric 
pressure,  71  cm. 

two  adjacent  series  would  overlap,  and  the  combination  point  in 
each  case  was  chosen  near  the  middle  of  the  overlapping  section. 
These  points  were  18  and  30  liters.  The  percentages  of  the  three 
series  at  the  various  points  were  as  follows : 

Per  cent.  Per  cent.  Per  cent. 

Series  at  8  i.  at  18  I  at  30  i 

6.4  to  23.1  liters i°3-5  98.4 

12.7  to  38.2  liters —  101.4  96.2 

24.7  to  45  liters —  —  102.8 

Hence  the  percentage  values  of  the  first  series  (basis  of  ioo 

per  cent,  at  15  liters)  were  multiplied  by ,  and  the  other  two 


ROSA,  CRITTENDEN,  TAYLOR  \    CANDLEPOWER  OF  FLAMES      857 
.  IOO  98.4  ,  ,         IOO      w      98.4    w     96.2  .      , 

by  X  — — —  and  by X   — — —  X  — — -,  respectively. 

103.5        101.4  103.5        101.4        102.8 

The  observations  then  being  on  a  common  basis,  they  were  plotted 

and  the  most  probable  curve  drawn.     The  points  included  in 

the  three  groups  are  distinguished  by  dots,  crosses  and  circles, 

respectively. 

The  fact  that  the  three  groups  covering  different  ranges  had 

different  slopes  shows  that  the  decrease  due  to  humidity  is  not 

really  linear.    The  group  of  points  taken  at  the  lowest  humidity 

gave  a  slope  indicating  a  decrease  of  5.0  per  cent,  from  the  normal 

candlepower  for  each  per  cent,  by  volume  of  water  vapor  in  the 

air,  whereas  the  pentane  lamp  decreases  5.7  per  cent.  Gilpin7 

found  6.0  per  cent,  for  an  open  flame  gas  burner. 

VIII.    EFFECT  OF  VITIATION  OF  THE  AIR. 

It  was  expected  that  some  difficulty  would  be  met  in  securing 
satisfactory  ventilation  in  the  tanks,  and  hence  a  few  preliminary 
measurements  on  the  effect  of  vitiation  of  the  air  were  made. 
These  were  not  carried  out  fully,  because  it  developed  that  the 
air  in  the  tank  could  be  kept  as  pure  as  that  in  the  regular  photo- 
meter room,  so  that  no  corrections  on  this  account  were  necessary. 

The  measurements  which  were  made  were  obtained  by  closing 
up  as  tightly  as  possible  a  small  room  in  which  a  pentane  lamp 
and  several  gas  burners  were  kept  burning.  Frequent  measure- 
ments of  the  candlepower  of  the  pentane  lamp  were  made,  while 
air  from  the  neighborhood  of  the  lamp  was  drawn  through  the 
refractometer  mentioned  above  and  readings  of  the  latter  were 
taken  at  short  intervals.  These  readings  (translated  into  per- 
centages of  carbon  dioxide  in  the  air)  and  the  candlepower  of 
the  lamp  were  both  plotted  against  the  time,  smooth  curves  being 
drawn  to  represent  the  march  of  the  two  quantities.  Four  such 
runs  were  made  and  the  combined  results  are  shown  in  Fig.  8. 
The  points  plotted  in  Fig.  8  were  read  from  the  curves  described, 
and  consequently  the  deviations  of  these  points  indicate  the  degree 
of  agreement  between  different  runs,  and  not  the  precision  of 
separate  candlepower  and  carbon  dioxide  measurements. 

The  curve  shows  that  the  degree  of  vitiation  represented  by 
an  increase  of  0.1  per  cent,  in  the  carbon  dioxide  content  of  the 

7  Loco  citato. 


858     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

air  caused  a  reduction  of  3.4  per  cent,  in  the  candlepovver  of  the 
lamp.  As  has  been  pointed  out  in  a  previous  paper  the  percentage 
of  carbon  dioxide  is  not  a  precise  index  of  the  vitiation,  since 
the  important  factor  is  the  reduction  of  the  amount  of  oxygen 
in  the  air,  and  the  relation  between  this  reduction  and  the  increase 
in  carbon  dioxide  depends  on  the  proportions  of  carbon,  hydro- 
gen and  oxygen  in  the  fuel  consumed.  The  present  data  there- 
fore give  only  an  indication  of  the  general  magnitude  of  the  ef- 
fect of  poor  ventilation.  They  are  significant,  however,  in  their 
relation  to  the  use  of  flames  as  primary  or  fundamental  standards, 
which  involves  the  derivation  of  values  for  electric  standards 


100 

(K.  ° 

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95 

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vc 

0 

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0 

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if  0 

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i 

4 

I 

5 

i              .7 

PERCENTAGE   OF  CO,  IN   MR. 
Fig.  8.— Effect  of  vitiation  of  air  on  candlepower  of  pentane  lamps. 

from  the  flames.  Outdoor  air  contains  about  0.03  per  cent,  of 
carbon  dioxide,  while  in  a  well-ventilated  laboratory  this  is  likely 
to  run  up  to  0.06  per  cent.  This  is  a  small  change  for  most  pur- 
poses, but  it  corresponds  to  a  change  of  1  per  cent,  in  candle- 
power.  If  therefore  we  were  to  attempt  to  derive  from  the  flame 
our  fundamental  unit,  which  should  be  certain  to  one  tenth  of  1 
per  cent.,  far  more  elaborate  precautions  than  have  ever  been 
taken  with  respect  to  control  of  the  composition  of  the  air  would 
be  necessary  in  order  to  avoid  uncertainties  due  to  this  cause. 

IX.    BEARING  OF  RESULTS  ON  TESTS  OF  GAS. 
It  is  of  course  realized  that  the  results  of  such  measurements 
as  these  depend  to  a  considerable  extent  on  the  composition  of 


ROSA,  CRITTENDEN,  TAYEOR  :    CANDLEPOWER  OF  FLAMES      859 

the  gas.  The  gas  used  was  a  mixture  of  approximately  30  per 
cent,  of  coal  gas  and  70  per  cent,  of  water  gas,  having  an  open- 
flame  candlepower  under  normal  conditions  of  20  to  23,  and  an 
average  heating  value  in  the  neighborhood  of  630  E.  t.  u.  per 


6--;v:-=  c  ?Pisi.-:-A>ii  cc  j,<=3cu=t 


Fig.'t). — Variation  of  candlepower  of  certain  flames  with  barometric  pressure:  i — Hefner 
lamp:  2 — pentane  lamp;  3 — Sugg  F.  Argand  gas  burner;  4 — Von  Schwarz  No.  8  E.  H. 
gas  burner;  5 — No.  7  Bray  gas  burner. 


BAFOMrmiC   PRC5SURE.INCM5   Of  MERCURY 


Fig.  10. — Variation  of  candlepower  of  gas  with  barometric  pressure, 
Sugg  Argand  burner.    (For  significance  of  curves  see  following  page.) 

cubic  foot.  The  curves  given  are  intended  to  show  the  general 
nature  and  approximate  magnitude  of  the  effects  and  are  not  to 
be  considered  a  basis  for  exact  corrections  to  be  applied  in  other 
cases. 

Nevertheless  the  results  are  sufficiently  significant  so  that  it 


86o    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


has  appeared  worth  while  to  plot  various  combinations  of  the 
data  in  such  a  way  as  to  emphasize  their  bearing  on  tests  of  gas. 
Since  the  data  of  such  tests  are  commonly  expressed  in  English 
units  these  curves  have  been  plotted  with  barometric  pressures 
in  inches. 

In  Fig.  9  are  collected  the  curves  already  given  for  the  two 
flame  standards  and  for  the  three  types  of  test  burners,  the  values 
plotted  for  the  latter  being  as  before  corrected  to  a  rate  of  5 
standard  cu.  ft.  per  hour.  The  significant  point  in  these  curves 
is  the  variation  in  the  ratio  of  gas  flames  to  standard  lamp. 


IOC 

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BAROMETRIC  PRESSURE -INCHES  OF  MERCURY". 


Fig.  11.— Variation  of  candlepower  of  gas  with  barometric  pressure, 
Von  Schwarz  No.  8  E.  H.  burner. 

In  order  to  bring  out  more  clearly  the  effect  of  this  variation 
we  have  plotted  in  Figs.  10,  n,  and  12  four  curves  for  each  type 
of  burner.  In  each  case  curve  No.  1  shows  the  actual  candle- 
power  of  the  gas  flames  (as  measured  by  an  unvarying  standard 
such  as  an  electric  lamp)  burning  a  constant  volume  of  gas  per 
hour,  that  is.  5  cu.  ft.  per  hour  at  6o°  and  prevailing  pressure. 
Curve  No.  2  shows  the  candlepower  corrected  to  a  constant  mass 
per  hour,  that  is,  5  cu.  ft.  at  6o°  and  30  in.  pressure.  Curves 
3  and  4  in  each  case  show  the  apparent  candlepower  which  would 
be  obtained  if  instead  of  an  unvarying  standard  a  Hefner  lamp 


ROSA,  CRITTENDEN,  TAYLOR  \    CANDLEPOWER  OF  FLAMES      86l 

or  a  pentane  lamp  were  used  for  the  measurements  without  mak- 
ing any  correction  for  its  departure  from  normal  value,  the  gas 
rate  being  corrected  in  the  usual  way  to  5  standard  cubic  feet  per 
hour. 


90 

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0 

2    80 

i 

£     70 

z 

0 

©^ 

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_2 

0    "         2 

i 

2               2 

3               2 

- 

2 

5 

Z 

E 

2 

7                2 

a           2 

9               3C 

8AR0METRIC  PRESSURE -INCHES  OF  MERCURY 

Fig.  12. — Variation  of  candlepower  of  gas  with  barometric  pressure,  No.  7  Bray  burner. 


'0 

I 

Q^ 

§ 

^-®_ 

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2           z 

B 

3               2 

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Fig-  13— Effect  of  barometric  pressure  on  "candlepower"  of  gas  as  measured  with'pen- 
tane  lamp.  1 — Sugg  F  (Argand);  2 — Von  Schwarz  No.  8  E.  H.  burner;  3— No.  7  Bray 
burner. 

Since  the  pentane  lamp  is  generally  accepted  in  the  United 
States  as  the  most  suitable  standard  for  gas  tests  the  rated  candle- 
powers  which  would  be  obtained  by  using  it  and  correcting  gas 


862     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

volumes  in  the  customary  way  are  of  special  interest.  Conse- 
quently the  curves  for  the  different  burners  showing  the  results 
which  would  be  obtained  by  tests  made  with  the  pentane  lamp 
as  a  standard  are  collected  in  Fig.  13. 

The  significance  of  these  curves  will  perhaps  be  made  more 
clear  by  considering  a  definite  example.  Suppose  the  candle- 
power  of  a  given  gas,  burning  at  5  cu.  ft.  per  hour  at  sea  level 
(30  in.  barometric  pressure)  in  a  Bray  No.  7  slit  union  burner  is 
20.0.  If  the  same  gas  is  burned  in  the  same  burner  at  5  cu.  ft. 
per  hour  at  25  in.  pressure,  we  might  expect  the  candlepower  to  be 
5/6  as  great,  that  is,  16.7,  since  about  5/(6  as  much  gas  is  contained 
in  the  5  cu.  ft.  But  actually  the  candlepower  is  found  to  be  only 
14.0,  that  is,  70  per  cent,  of  20,  as  shown  in  Fig.  12.  On  the 
other  hand,  a  "10-candle"  pentane  lamp  at  25  in.  pressure  gives 
only  a  little  over  9.0  candles.  Consequently  if  we  call  it  10 
candles,  the  apparent  candlepower  of  the  gas  flame  will  be  15.5, 
and  the  customary  correction  to  allow  for  the  fact  that  only  5/8 
of  5  standard  cu.  ft.  of  gas  are  burned  gives  a  rated  candlepower 
of  18.6.  More  exact  calculations  have  been  plotted  in  the  curves, 
and  from  curve  3  of  Fig.  12  we  see  that  at  25  in.  (63.50  cm.) 
pressure  the  Bray  burner  gave  93.5  per  cent,  of  normal  values, 
or  18.7  candles  when  the  normal  was  20. 

On  the  other  hand  if  one  had  used  the  Sugg  Argand  burner  the 
rated  candlepower  would  have  been  nearly  6  per  cent,  above  the 
normal  value,  while  with  the  Von  Schwarz  burner  it  would  have 
been  3.5  per  cent,  below  the  normal;  the  actual  candlepower, 
however,  being  15.9  and  14.5  respectively,  for  gas  whose  normal 
rating  would  be  20  candles. 

It  should  be  noted  that  by  "normal"  for  each  burner  is  meant 
the  sea-level  value  which  would  be  obtained  with  that  particular 
type  of  burner,  and  similarly  the  100  per  cent,  point  on  all  the 
curves  is  the  sea-level  value  for  the  particular  burner  to  which 
the  curve  applies.  With  the  gas  used  in  these  experiments  the 
Argand  burner  gave  the  highest  candlepower,  the  Von  Schwarz 
and  Bray  burners  being  respectively  2  and  7  per  cent,  lower. 
That  is,  the  same  gas  gave  20  candles  in  the  Von  Schwarz 
burner,  20.4  in  the  argand  and  19.0  in  the  Bray.  Different  burn- 
ers of  the  two  open-flame  types  selected  at  random  were  found 


ROSA,  CRITTENDEN,  TAYLOR  :    CANDLEPOWER  OF  FLAMES      863 

to  give  remarkably  uniform   results,  being  in  this   respect  de- 
cidedly superior  to  argands. 

X.    TYPICAL  APPLICATIONS  TO  GAS  MEASUREMENTS. 

From  reports  of  the  Weather  Bureau,  average  values  of  water 
vapor  and  barometric  pressure  for  five  years,  from  1904  to  1908 
inclusive,  for  eleven  widely  separated  cities  have  been  obtained. 
It  is  customary  to  rate  a  pentane  lamp  at  the  candlepower  it  would 
give  under  normal  conditions  of  8  liters  of  water  vapor  per  cubic 
meter  of  dry  air  and  a  barometric  pressure  of  760  millimeters  of 
mercury.  If  its  candlepower  under  these  conditions  were  10.0, 
the  following  table,  column  3,  would  show  its  average  candle- 
power  for  the  five  years  in  each  of  the  eleven  cities.  Assum- 
ing a  mixed  gas  of  a  composition  like  that  tested  here,  giving  a 
candlepower  of  20  when  burned  in  a  Von  Schwarz  No.  8  E.  H. 
burner  under  normal  conditions  of  8  liters  and  30  in.  pressure, 
the  rate  being  corrected  to  5  cu.  ft.  per  hour  at  30  in.  and  6o°  F., 
its  actual  average  candlepower  in  the  various  cities  is  shown  in 
column  6.  Column  7  shows  the  average  values  which  would  have 
been  obtained  if  measurements  had  been  made  in  terms  of  a 
pentane  lamp  rated  as  explained  above.  Column  5  shows  the 
average  candlepower  which  the  consumer  would  have  obtained 
for  a  meter  rate  of  5  cu.  ft.  per  hour  at  6o°  F. 

TABLE  I.— Calculated  Rating  of  Gas  at  Different  Places. 

Gas  assumed  to  give  20  candles  under  normal  conditions;  all  tests  supposed 

to  be  made  with  pentane  lamp  and  Von  Schwarz  No.  8  E.  H.  Burner. 

Average 

Av.  actual  cp.  of  gas 

Av.  water  cp.  of  gas,  corrected     Av.  cp. 

vapor  at  rate         to  5  cu.        of  gas 

Average        (liters         Av.  cp.      of  5  cu.  ft.  ft.  per  hr.    as  rated 

barometric  per  cubic  of  pentane  per  hour  at  30  in.    with  pen- 
City                             pressure 

Atlanta 28.84 

Boston 29.88 

Cheyenne 24.01 

Chicago 29.15 

Denver 24.73 

El  Paso 26.19 

Helena 25.80 

New  Orleans 30.00 

San  Francisco 29.87 

Sioux  City,  Iowa  ..  28.80 

Washington,  D.  C.  •  29.94 


neter) 

lamp 

at  6o°  F. 

and  6o° 

tane  lamp 

14-3 

9-49 

18.3 

18.8 

19.8 

9-9 

9.88 

19.9 

I9.8 

20.0 

7-3 

8.77 

13-8 

16.9 

19-3 

10.6 

9-75 

18.9 

19-3 

19.8 

7-9 

8-95 

14.4 

17-3 

19-3 

9.2 

9.27 

15.8 

18.0 

19.4 

6.8 

9-3° 

15-6 

18.0 

19-3 

19. 1 

9-37 

19. 1 

18.9 

20.2 

n-3 

9-79 

19.7 

19.6 

20.0 

9.2 

9.78 

18.7 

19-3 

19.7 

12.0 

9-77 

19.7 

19.6 

20.0 

864    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

If  a  different  burner  were  used  the  departure  from  normal 
candlepowers  would  be  different.  For  example,  in  the  case  of 
Denver,  the  Sugg  F  Argand  would  give  for  the  last  three  columns 
15.6,  18.9  and  21.2  (assuming  a  gas  which  under  standard  condi- 
tions would  give  20  candles  in  that  burner). 

From  an  inspection  of  the  last  column  in  the  above  table,  it  is 
readily  seen  that  the  candlepower  obtained  in  tests  by  correcting 
results  in  the  ordinary  way  does  not  necessarily  indicate  the 
quality  of  the  gas  supplied  closely  enough  for  a  comparison  of  gas 
plant  output  in  different  cities.  It  is  still  further  from  an  indi- 
cation of  the  average  service  which  the  customer  is  receiving. 
If  the  latter  is  the  purpose  of  tests  of  gas  candlepower,  it  would 
seem  to  be  a  more  rational  procedure  to  use  a  value  for  the  stand- 
ard lamp  which  represents  its  actual  candlepower  under  the  at- 
mospheric conditions  where  and  when  it  is  in  use.  Also,  instead 
of  correcting  the  volume  of  gas  to  its  volume  at  sea  level,  it  would 
be  better  to  correct  it  to  the  volume  at  average  atmospheric 
pressure  in  the  city  where  tested.  Candlepower  tests  would  then 
indicate  the  service  rendered  much  more  closely  than  at  present. 
The  average  conditions  for  any  city  can  be  determined  quite 
closely  from  the  reports  of  the  Weather  Bureau. 


DISCUSSION. 

Mr.  F.  H.  Gilpin:  I  think  it  is  well  to  emphasize  the  fact 
of  the  type  of  gas  on  which  these  experiments  were  made.  If 
one  takes  a  burner  like  the  Sugg  "F"  Argand  and  burn  it,  first, 
on  a  water  gas  and  then  on  a  coal  gas,  totally  different  results 
will  be  obtained.  That  particular  burner  is  probably  designed 
for  a  little  higher  consumption  than  five  feet.  Atmospheric 
humidity  will  materially  affect  the  efficiency  of  these  burners, 
depending  on  the  kind  of  gas  burned  in  them.  In  burning  a 
coal  gas,  a  higher  percentage  of  error  will  be  obtained  as  the 
humidity  increases,  than  with  the  water  gas.  Another  point  in 
the  measurement  of  the  gas  in  those  tests  is  this;  ordinarily, 
in  measuring  candlepower,  the  gas  is  measured  by  constant 
volume  and  corrected  to  constant  mass.  I  am  interested  to  know 
if  any  different  results  would  have  been  obtained  in  the  curves 


CANDLEPOWER   OF   FLAMES  865 

if  that  had  been  ordinarily  done  in  the  test?     I  notice  in  the 
photograph  that  the  meter  was  located  outside  the  tank. 

Mr.  F.  E.  Cady  :  It  seemed  rather  interesting  to  me  to  notice 
that  this  effect  of  increasing  pressure  on  the  flame  candlepower 
was  in  the  same  direction  as  that  found  by  Lummer  in  his 
measurement  of  the  effect  of  pressure  on  impregnated  carbon 
arc  lamps,  and  I  wondered  whether  the  authors  think  that  the 
explanation  given  of  the  effect  in  this  case  would  be  similar 
and  would  apply  to  the  effect  obtained  on  the  arc  lamp. 

Dr.  E.  B.  Rosa  :  I  might  call  attention  to  one  practical  ef- 
fect of  this  result:  heretofore  the  Bureau  of  Standards  has 
always  certified  pentane  lamps  for  what  we  call  their  normal 
candlepower,  and  that  has  been  used  as  their  actual  candlepower 
in  all  altitudes.  Even  in  places  no  higher  above  the  sea  than 
Chicago,  there  is  an  appreciable  difference  between  the  candle- 
power  and  the  candlpower  at  sea  level,  and  of  course  there  are 
many  cities  of  considerable  size  in  this  country  where  the  al- 
titude is  several  thousand  feet  and  the  barometric  pressure  ef- 
fect is  correspondingly  great.  We  have  never  been  able  to  give 
with  a  certificate  of  the  pentane  lamp,  a  certificate  of  what  its 
candlepower  would  be  at  the  place  where  it  was  destined  to  be 
used,  for  the  lack  of  the  information  now  available.  We  expect 
hereafter  to  give  such  statements,  so  that  the  actual  candle- 
power  will  be  known,  and  that  will  have  a  very  decided  effect 
on  the  value  obtained  by  the  use  of  the  lamp,  if  the  actual  candle- 
power  at  a  given  place  is  used  instead  of  its  candlepower  at 
sea  level  pressure.  We  have  purchased  some  gas  tanks  recently 
and  shall  hereafter  be  able  to  store  the  gas  and  make  tests  on 
different  qualities  of  gas  as  well  as  on  different  types  of  burners. 

Of  course,  the  tests  made  and  reported  here  as  to  the  effect  on 
various  candlepowers  of  gas  burners,  under  different  conditions, 
are  not  intended  as  the  most  important  part  of  this  investigation. 
We  set  out  to  determine  it  first  of  all  for  our  standards,  but 
before  making  the  investigation  complete,  it  will  be  necessary 
to  try  different  kinds  of  gas  to  show  the  variation  with  the 
quality;  that  we  intend  to  do  in  the  future. 

Dr.  E.  P.  Hyde:     There  is  one  question  I  should  like  to  ask 


866     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

the  authors  of  this  paper,  and  that  is  whether  they  have  made 
any  investigation  or  drawn  any  conclusions  from  the  observations 
they  have  made  on  the  relative  effect  of  the  vitiation  of  the  air  on 
the  luminous  value  of  gas  as  burned  in  the  different  types  of 
burners  and  on  the  standard  pentane  and  Hefner  lamps.  In  the 
photometry  of  gas  every  effort  is  made  to  have  the  room  ven- 
tilated, but  some  years  ago  Mr.  Bond  and  myself  made  some 
tests  in  Philadelphia  in  one  of  the  laboratories  of  the  United  Gas 
Improvement  Company  to  endeavor  to  determine  whether  the 
relative  effect  of  vitiation  is  the  same  on  gas  with  the  type  of 
burner  that  was  used  and  on  the  standard  pentane  lamp.  I  think 
that  is  a  point  that  might  be  of  some  practical  importance,  and 
I  should  like  to  ask  the  authors  whether  they  drew  any  conclu- 
sion on  that  point  ? 

If  there  is  no  further  discussion,  I  will  call  on  Mr.  Crittenden 
to  close  the  discussion  of  the  paper. 

Mr.  E.  C.  Crittenden  (In  reply)  :  In  regard  to  Mr.  Gilpin's 
question  as  to  the  method  of  measuring  the  gas — he  remarked 
that  the  meter  was  outside  the  tank,  which  is  true,  but  the  vol- 
ume of  gas  supplied  was  such,  as  to  make  the  volume  constant  at 
the  pressure  in  the  tank.  During  some  of  the  tests  the  meter  was 
put  inside  but  that  caused  other  troubles.  While  the  meters  were 
outside  it  was  easy  to  calculate  the  amount  measured  outside  that 
would  become  5  cubic  feet  inside. 

It  is  recognized,  as  is  stated  in  the  paper,  that  all  of  these  re- 
sults depend  markedly  on  the  nature  of  the  gas,  and  on  its  rich- 
ness. The  data  given  can  be  applied  with  certainty  only  to  the 
particular  type  of  gas  with  which  the  tests  have  been  made.  As 
to  the  effect  of  vitiation,  no  careful  comparison  of  the  effects  on 
the  gas  and  on  pentane  lamps  was  carried  out.  In  a  general  way, 
the  effect  is  very  much  the  same  on  the  two.  I  am  not  prepared 
to  say  that  it  is  exactly  the  same,  but  it  is  approximately  so.  The 
data  which  Dr.  Hyde  has  mentioned  obtaining  in  Philadel- 
phia when  reduced  to  the  same  basis  as  the  curve  of  Fig.  8  indi- 
cate a  change  of  about  3  per  cent,  in  candlepower  for  0.1  per 
cent,  of  C02)  whereas  Fig.  8  shows  3.4  per  cent.  As  stated  in 
the  paper,  however,  the  significant  factor  is  not  really  the  change 
in  C02  but  the  reduction  of  oxygen  in  the  air.     Consequently 


CANDEEPOWER   OF   FLAMES  867 

when  the  variation  is  stated  on  the  basis  of  C02,  the  magnitude 
of  the  effect  depends  on  the  way  in  which  the  CO.  is  produced. 

In  regard  to  Mr.  Cady's  question— the  effects  on  the  arc  were 
much  larger  than  the  effects  here  obtained,  and  are  caused  by  the 
rise  of  temperature  with  pressure.  The  phenomenon  is  quite 
different  in  nature  from  those  involved  in  flames. 


868     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ILLUMINATION  AND  ONE  YEAR'S  ACCIDENTS.* 


BY  R.  E.  SIMPSON. 


Synopsis:  The  paper  presents  the  results  of  a  study  of  one  year's 
industrial  accident  records,  the  purpose  being  to  determine  the  effect  of 
the  lighting  conditions  in  the  causation  of  the  accidents.  Of  the  total 
number  23.8  per  cent,  were  due  either  directly  or  indirectly  to  the  lack 
of  proper  illumination,  and  of  these  51.6  occurred  in  the  four  months 
having  the  fewest  number  of  daylight  hours.  A  few  typical  cases  are 
given  showing  how  the  lighting  conditions  were  responsible  for  injuries 
to  workmen.  The  use  of  proper  reflectors  and  care  in  maintaining  proper 
mounting  heights,  especially  when  high  efficiency  lamps  are  used,  are 
essential  if  accidents  are  to  be  prevented  by  good  illumination. 


There  is  a  widespread  belief  prevalent  to-day  that  there  are 
approximately  500,000  avoidable  accidents  per  year  in  this  coun- 
try, and  that  about  one-quarter  of  this  number  are  caused  directly 
or  indirectly  by  improper  lighting  facilities.  So  far  as  can  be 
learned  these  figures  are  estimates  made  by  persons  who  have 
had  considerable  experience  in  accident-prevention  work.  There 
is  little  evidence  to  show  that  any  systematic  effort  has  been  made 
to  point  out  the  relation  between  light  and  accident  rate.  This 
is  due  to  the  want  of  statistical  data,  owing  to  the  enormous 
labor  and  expense  involved  in  obtaining  such  data.  A  number 
of  men  interested  in  good  lighting  or  in  accident  prevention,  or 
both,  have  pointed  out  the  many  ways  in  which  the  lighting  of  a 
factory  may  influence  the  accident  rate.  In  some  instances  studies 
were  made  of  certain  industries,  notably  by  Mr.  D.  R.  Wilson, 
special  inspector  in  the  Factory  Inspection  Service  in  Great 
Britain,  who  in  191 1  and  1912  investigated  the  lighting  conditions 
in  British  textile  industries  and  in  foundries.  In  neither  one  of 
his  reports  are  there  data  to  enable  one  to  ascertain  the  percentage 
of  accidents  due  to  the  inadequate  lighting  conditions  described. 

At  about  the  same  time,  Mr.  John  Calder  presented  a  paper 
before  the  American  Society  of  Mechanical  Engineers,  showing 
the  increase  in  the  number  of  fatal  accidents  during  that  part  of 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing Society,  Washington,  D.   C,   September  20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


SIMPSON  :    ILLUMINATION  AND  ONE  YEAR'S  ACCIDENTS      869 

the  year  when  the  ordinary  factory  working  hours,  7  a.  m.  to 
6  p.  m.,  extend  beyond  the  daylight  period.  The  curves  presented 
with  his  paper  showed  conclusively  that  the  number  of  accidents 
in  December  and  January  was  40  per  cent,  greater  than  the 
normal  number  that  might  reasonably  have  been  expected  if  there 
were  the  same  number  of  daylight  hours  in  the  winter  as  in  the 
summer. 

The  records  of  workmen's  compensation  and  accident  insur- 
ance companies  offer  a  fruitful  field  for  the  study  of  accidents, 
provided  particular  attention  is  given  to  details  in  the  investiga- 
tions. In  this  respect  a  few  notes  on  the  lighting  arrangement 
will  often  explain  the  cause  of  an  accident.  The  Travelers  Insur- 
ance Company  is  particularly  fortunate  in  having  over  200  men 
who  are  specialists  in  accident-prevention  work.  A  record  is 
kept  of  every  accident  in  and  about  factories,  shops,  and  mills 
carrying  insurance  with  the  Travelers,  and  all  important  ones 
are  investigated  by  the  inspectors,  who  ascertain  the  conditions 
that  prevailed  at  the  time  of  the  accidents.  The  reports  of  these 
men  form  an  authoritative  library  on  causation  and  prevention 
of  industrial  accidents,  and  among  the  causes,  and  the  recom- 
mendations for  the  prevention  of  future  accidents,  the  lighting 
question  plays  an  important  part. 

The  main  object  of  this  paper  is  to  present  the  results  of  a 
study  of  these  reports  covering  a  period  of  one  year  from  Jan- 
uary 1  to  December  31,  1910.  All  accidents  incident  to  the  use 
of  automobiles,  teams,  bicycles,  trolley  cars,  and  slippery  pave- 
ments are  omitted,  as  well  as  all  accidents  occurring  in  and  about 
coal  mines.  While  there  is  absolutely  no  doubt  that  the  darkness 
of  a  coal  mine,  broken  only  by  the  feeble  light  from  the  miner's 
lamp,  is  largely  responsible  for  many  coal  mine  accidents,  there 
are  so  many  other  factors  bearing  on  the  subject  that  reliable 
conclusions  cannot  be  drawn.  It  is  worthy  of  note,  however,  that 
the  introduction  of  electricity  for  haulage  purposes  has  provided 
the  coal  operators  with  a  ready  means  of  lighting  the  more 
important  switching  points  in  the  mines.  The  use  of  steel  and 
concrete  for  roof  support,  and  the  application  of  whitewash  to  the 
roof  and  sides  at  the  turnouts,  switching  points,  and  shaft  bot- 
toms, materially  increases  the  illumination.     Good  lighting  is  es- 


8/0     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

sential  here  in  order  that  the  motorman  may  see  that  the  switches 
are  properly  set,  and  that  no  standing  cars  block  his  way,  thus 
enabling  him  to  avoid  derailments  and  collisions.  The  other 
employees  at  these,  the  busiest  parts  of  the  mine,  can  also  per- 
form their  duties  much  more  efficiently  and  safely  because  of  the 
better  illumination. 

Excluding  these  classes  of  accidents,  there  still  remain  more 
than  91,000  accidents  which  occurred  in  and  about  industrial 
plants;  and  of  this  number  23.8  per  cent,  were  due,  directly  or 
indirectly,  to  the  lack  of  proper  illumination.  This  figure,  23.8 
per  cent.,  corresponds  very  closely  to  the  estimate  of  25  per  cent, 
already  mentioned.  There  is  this  difference,  however,  in  that 
the  estimate  of  25  per  cent,  was  based  on  avoidable  accidents, 
while  the  23.8  per  cent,  obtained  from  the  Travelers  Insurance 
Company's  records  embraces  both  avoidable  and  unavoidable  acci- 
dents. It  is  evident  from  the  records  that  a  large  numVr  of  the 
accidents  were  unavoidable,  particularly  in  those  instances  where 
the  lighting  condition  was  a  contributory  rather  than  a  direct 
cause. 

A  further  analysis  of  the  records  shows  that  10  per  cent,  of 
the  total  industrial  accidents  for  the  year  were  due  primarily  to 
inadequate  illumination,  and  in  the  remaining  13.8  per  cent,  the 
lack  of  proper  lighting  facilities  was  a  contributory  cause.  It  is 
probable  that  another  person  in  going  over  these  records  would 
arrive  at  different  percentages  of  direct  and  indirect  causes  of 
accidents  due  to  the  illumination,  but  this  would  simply  repre- 
sent a  difference  of  opinion  in  those  cases  where  equally  good 
arguments  might  be  put  forth  in  favor  of  one  view  or  the  other. 
The  essential  feature  of  the  analysis  is  the  large  percentage  of 
accidents  in  which  the  illumination  had  an  important  influence. 

Under  the  heading  "direct  cause"  were  included  all  accidents 
on  stairways,  in  passageways,  or  in  the  shop  where  it  was  shown 
that  there  was  no  light  in  the  immediate  vicinity.  It  is  true  that 
many  persons  have  been  injured  by  falling  down  stairways  that 
were  well  lighted,  and,  therefore,  the  illumination  could  have  had 
no  bearing  on  the  accident.  It  is  likewise  true  that  if  none  of 
the  stairways  in  the  country  were  provided  with  light,  the  acci- 
dent rate  from  this  cause  would  be  vastly  increased. 


SIMPSON:    ILLUMINATION  AND  ONE  YEAR'S  ACCIDENTS      87 1 

It  may  be  interesting  to  cite  a  few  typical  cases  where  insuffi- 
cient or  improper  illumination  was  a  cause  of  an  accident.  In  a 
certain  shop  having  widely  spaced  lighting  units  a  supporting 
column  cast  a  shadow  which  hid  a  flat  2-inch  bar  lying  at  an  angle 
across  the  passageway  on  the  floor.  When  one  of  the  front 
wheels  of  a  truck  encountered  the  bar,  the  truck  axle,  swerving 
sharply  to  the  right,  jerked  the  handle  out  of  the  laborer's  hand 
and  struck  the  right  foot  of  a  workman  standing  at  the  side  to 
let  the  truck  pass.  The  blow  broke  one  of  the  small  bones  in  his 
foot.  The  sudden  stopping  of  the  truck  also  caused  one  of  the 
heavy  pipes  on  it  to  roll  off,  and  the  truck  handle,  acting  as  a 
skid,  guided  the  pipe  against  the  workman's  left  leg,  breaking 
both  bones  below  the  knee.  It  is  evident  that  neither  man  saw 
the  bar  of  iron  on  the  floor,  a  fact  which  is  easily  understood 
when  one  considers  that  the  floor  and  the  bar  were  both  dark- 
colored,  and  further  obliterated  by  the  shadow.  It  is  fair  to 
assume  that  had  adequate  light  been  provided,  one  of  the  work- 
men would  have  seen  the  bar,  and  would  have  removed  it  instead 
of  attempting  to  pull  a  heavy  truck  over  it. 

A  paper  mill  employee,  while  feeding  a  conveyor  with  short 
pieces  of  pulp  wood,  noticed  that  the  chute  at  the  other  end  of 
the  conveyor  had  become  clogged.  There  was  no  light  at  the 
chute,  nevertheless  the  man  after  stopping  the  conveyor  attempted 
to  clear  the  way,  and  while  thus  engaged  a  block  of  wood  slipped 
out  and  broke  his  ankle.  There  was  no  occasion  for  any  of  the 
workmen  using  this  part  of  the  mill  unless  the  conveyor  or  the 
material  caused  trouble.  This,  however,  was  just  the  time  light 
was  needed  and  none  was  provided.  The  amount  of  money  re- 
quired to  maintain  a  unit  affording  ample  illumination  at  this 
point  is  negligible  when  compared  with  the  amount  of  the  claim 
paid  the  injured  workmen;  in  fact,  such  a  unit  could  have  been 
kept  burning  all  day,  and  every  day  for  a  hundred  years,  and 
still  the  owner  would  have  realized  a  handsome  profit;  and  one 
employee,  at  least,  would  have  been  saved  from  injury. 

The  following  two  instances  represent  conditions  often  seen 
in  certain  industries.     In  the  first  one,  a  man  fell  into  a  tank 
containing  hot  water  and  acid,  and  was  fatally  burned.    A  num- 
ber of  tanks  were  placed  close  together,  with  narrow  walks  be- 
3 


872     TRANSACTIONS  OF  IEEUMINATING  ENGINEERING  SOCIETY 

tween  them  at  the  top.  There  were  no  guard  rails  along  these 
walks,  and  no  artificial  light  was  provided,  even  though  the  pres- 
ence of  workmen  at  this  point  was  necessary  at  odd  times  of  the 
day.  The  accident  happened  just  before  quitting  time  in  the 
latter  part  of  December.  In  the  other  instance  the  natural  light 
was  not  adequate  and  was  supplemented  by  incandescent  lamps. 
Both  the  lamps  and  the  windows  had  a  thick  coating  of  grease 
and  dirt,  so  that  by  no  stretch  of  the  imagination  could  the  illum- 
ination be  called  other  than  very  bad.  Nor  were  there  any  guard- 
rails along  the  walk  at  the  top  of  the  vats  containing  scalding 
water.  It  is  not  to  be  wondered  at  that  a  workman  made  a  mis- 
step and  was  scalded  to  death. 

In  another  case  lack  of  light  in  the  hold  of  a  vessel  was,  with- 
out doubt,  responsible  for  a  crushed  foot.  A  workman  was  piling 
pig  iron  there,  in  semi-darkness,  the  open  hatch,  far  above,  ad- 
mitting so  little  light  that  he  could  not  see  that  the  pile  was  un- 
even. While  he  was  still  at  work  the  pile  toppled  over  and  in- 
jured him,  as  stated.  Under  exactly  similar  conditions  another 
workman  could  not  see  that  a  hook  was  insecurely  caught  in  a 
bale  of  cotton  that  was  to  be  hoisted  from  the  hold  of  a  steamer, 
and  when  the  hook  slipped  the  falling  bale  struck  the  man  a 
glancing  blow,  breaking  his  collar  bone.  In  this  instance  the  dif- 
ference of  a  few  inches  in  the  man's  position  was  all  the  margin 
there  was  between  injury  and  death.  In  the  punch  press  room 
of  a  certain  factory  an  overhead  skylight  provided  plenty  of  il- 
lumination on  bright  days,  but  in  the  winter  months,  and  es- 
pecially on  gray,  cloudy  days,  the  daylight  illumination  was  so 
much  reduced  as  to  occasion  repeated  requests  for  auxiliary  arti- 
ficial light;  and  an  injured  workman  based  his  claim  for  damages 
on  the  ground  that  the  employer  had  failed  to  provide  sufficient 
illumination. 

Two  steam  fitters,  having  finished  some  work  on  a  temporary 
platform  9  ft.  above  the  floor,  instructed  a  laborer  to  remove  all 
supplies  and  tools.  The  steam  fitters  had  used  an  extension  cord 
drop  light  which  they  took  away  with  them,  thus  compelling  the 
laborer  to  depend  on  the  reflected  light  from  the  units  below 
him.  He  failed  to  see  a  short  piece  of  steam  pipe,  which  soon 
afterward  fell  on  a  workman  below,  fracturing  his  skull.     This 


SIMPSON  :    ILLUMINATION  AND  ONE  YEAR'S  ACCIDENTS      873 

is  the  type  of  accident  generally  classed  under  the  item  of 
"struck  by  falling  material."  It  is  probable  that  if  sufficient  illum- 
ination had  been  provided,  the  laborer  would  have  seeri  the  pipe 
and  taken  it  away  with  the  other  material,  thereby  preventing  the 
accident ;  and  under  the  circumstances  it  is  certainly  fair  to  state 
that  the  lack  of  illumination  was  a  contributory  cause. 

Two  trucks  being  pushed  in  opposite  directions  collided  on  an 
overhead  bridge,  and  both  truckmen  were  injured  by  material 
falling  from  the  trucks.  The  noise  in  adjoining  shops,  in  addi- 
tion to  that  caused  by  the  trucks  themselves,  prevented  each  truck- 
man from  hearing  the  approach  of  the  other.  The  covered 
bridge  had  side  windows,  but  no  other  means  of  providing  light, 
and  as  the  accident  occurred  late  in  the  afternoon  in  January,  the 
lack  of  light  plus  the  noise  were  responsible. 

A  machine  with  four  saws  on  one  shaft  was  well  guarded,  but 
the  drop  light  had  been  so  arranged  by  the  operator  that  one  of 
the  guards  cast  a  deceiving  shadow.  The  man  thought  he  was 
placing  his  hand  on  the  guard,  but  instead  he  placed  it  on  the 
shadow  and  was  badly  injured.  This  was  purely  a  case  of  im- 
proper lighting,  and  it  points  out  the  hazard  in  the  practise  of 
permitting  a  workman  to  adjust  the  lighting  units  to  suit  his  own 
convenience,  instead  of  having  them  placed  by  a  lighting  expert 
who  has  studied  the  safety  problem  carefully. 

A  workman  using  an  extension  cord  light  found  it  necessary 
to  use  both  hands,  and  he,  therefore,  made  a  loop  of  the  cord 
and  hung  it  about  his  neck.  The  worn  out  insulation  of  the 
lamp  cord  allowed  sufficient  arcing  to  set  fire  to  the  man's  celluloid 
collar,  causing  extremely  painful  burns  about  the  neck  and  head. 
In  this,  as  in  most  other  accidents,  a  great  many  "ifs"  might  be 
thought  of;  but  none  of  them  can  hide  the  fact  that  there  were 
no  permanent  means  of  lighting  the  section  of  the  shop  in  which 
this  particular  accident  occurred. 

Finally,  there  may  be  mentioned  the  correlation  between  a 
workman's  broken  wrist  and  the  rather  prosaic  escape  of  two 
hogs  from  a  pen.  No  doubt  all  would  have  gone  well  had  not  one 
of  the  hogs  elected  to  sleep  on  the  path  between  two  buildings  in  a 
plant.  True  to  his  name  and  nature,  the  hog  obstructed  the 
whole  width  of  the  path,  causing  the  workman  to  stumble  over 


874     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

him.  There  was  no  means  provided  to  light  this  pathway,  even 
though  it  was  the  direct  route  between  the  buildings,  and  as  such 
was  in  constant  use. 

There  were  several  cases  where  inadequate  illumination  had  im- 
paired workmen's  vision,  so  that  these  men  were  subsequently  in- 
jured while  working  under  lighting  conditions  that  were  ex- 
cellent for  normal  vision.  Their  claim  that  their  injuries  were 
due  to  insufficient  lighting  was  hardly  justifiable  when  applied 
to  the  last  working  place,  but  it  is  certain  that  the  impairment  of 
their  eyesight  due  to  the  poor  lighting  at  their  previous  work- 
place had  an  important  bearing  on  the  case. 

At  the  beginning  of  this  investigation  an  attempt  was  made  to 
classify  the  accidents  due  to  the  lighting  conditions  in  greater 
detail  than  "direct"  and  "indirect,"  but  this  soon  proved  to  be 
impracticable.  If  the  same  proportion  had  prevailed  throughout 
the  records  as  was  evidenced  in  the  first  5,000  cases  investigated, 
the  lighting  accidents  on  stairways,  passageways,  and  other 
seldom-used  parts  of  shops  would  have  had  by  far  the  highest 
rank.  It  is  very  generally  recognized  by  illuminating  engineers 
that  these  are  just  the  places  that  are  likely  to  be  slighted  in  the 
original  installation,  or  the  maintenance,  of  factories  equipped 
and  operated  by  the  rule-of -thumb  method.  If  one  compares 
the  number  of  accidents  that  occur  at  these  points,  bearing  in 
mind  the  relatively  short  time  that  they  are  used  by  a  few  men, 
with  the  number  of  accidents  occurring  in  the  better  lighted  shops, 
again  having  in  mind  the  large  number  of  men  and  the  greater 
length  of  time  they  are  subject  to  the  hazards,  it  is  found  that 
the  accident  rate  in  the  first-mentioned  places  is  abnormally  high. 
It  is  impossible  to  draw  any  other  conclusion  than  that  the  lack 
of  illumination  is  largely  responsible. 

Fig.  1  shows  in  a  diagrammatic  form  the  monthly  distribution 
of  all  the  industrial  accidents  reported  for  the  year,  and  Fig.  2 
shows  a  similar  distribution  of  all  the  accidents  caused  by  inade- 
quate illumination.  There  is  a  striking  similarity  between  these 
curves  and  those  published  by  Mr.  Calder  and  other  investigators. 
From  Fig.  2  the  fact  may  be  deduced  that  51.6  per  cent,  of 
the  accidents  due  to  poor  illumination  occurred  in  the  months 
of  November,  December,  January,  and  February,  while  48.4  per 


SIMPSON  :    ILLUMINATION  AND  ONE  YEAR'S  ACCIDENTS      875 

cent,  occurred  in  the  remaining  eight  months.  This  indicates  that 
the  likelihood  of  an  accident  being  caused  by  poor  lighting  is 
more  than  twice  as  great  in  any  one  of  these  four  months  as  in 
any  one  of  the  remaining  eight  months. 


JULY 

AUG 

5EPT 

OCT 

NOV 

DEc|jAN 

FEB 

MAR 

APR 

MAY  JUNE 

11000 

r    \_ 

10000 

\ 

3000 

7000 

60O0 

5000 

-^5= 

4OO0 

3OO0 

Fig.  1.— Showing  the  seasonal  distribution  of  all  industrial  accidents  for  the  year. 


JULY 

AUG  |  SEPT 

OCT 

NOV 

DEC  |  JAN 

FEB 

MAR 

APR 

MAY 

JUNE 

1 

2000 

/ 

1500 

1000 

500 

^*^ 

O 

Fig.  2.— Showing  the  seasonal  distribution  of  all  industrial  accidents  caused  by 
inadequate  illumination. 

Fig.  3  shows  the  seasonal  distribution  of  accidents  exclusive 
of  those  in  which  the  lighting  conditions  had  an  influence.  It  will 
be  noted  that  the  increase  in  the  accident  rate  in  the  months  of 
November,  December,  January,  and  February  is  not  so  pronounced 
as  in  Figs.  I  and  2.    If  the  lighting  condition  was  the  only  factor 


8/6    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

contributing  to  the  increase  in  accidents  in  the  winter  months, 
the  curve  in  Fig.  3  would  be  practically  straight.  The  similarity 
of  the  three  curves  raises  the  question  as  to  whether  or  not  a 
greater  number  of  accidents  than  those  shown  were  due  to  the 
lighting  conditions.  It  is  probable  that  the  lack  of  information 
in  some  of  the  reports  is  responsible  for  a  certain  number  of 
accidents  attributed  to  the  lighting  conditions  being  overlooked, 
but  just  what  this  number  would  be  is  purely  conjectural. 

There  is  another  factor  which  will  help  to  explain  the  increase 
in  the  accident  rate  in  winter  months,  and  in  this  the  lighting 
conditions  play  an  important  part,  though  it  is  impossible  to 
obtain  any  reliable  figures.    It  is  partly  psychological  and  partly 


JULY 

AUG 

SEPT 

OCT 

NOV 

DEC 

JAN 

FEB 

MAR 

APR 

MAV 

JUNE 

sooo 

TOOO 

6000 

5000 

4000 

3000 

3000 



Fig-  3.— Showing  the  seasonal  distribution  of  all  industrial  accidents  exclusive  of  those 
due  to  inadequate  illumination. 


physiological,  but  may  be  better  understood  by  referring  to  it  as 
the  depressing  effect  of  cold  and  dreary  weather  on  mankind. 
It  is  a  well  known  fact  that  the  members  of  an  exploration  party 
to  the  Arctic  region  are  carefully  selected  not  only  for  their  scien- 
tific attainments,  but  also  for  their  physical  and  temperamental 
fitness  to  withstand  the  rigors  of  the  weather  and  the  strain  of 
the  long  hours  of  darkness.  Notwithstanding  this  careful  selec- 
tion, the  history  of  almost  every  Arctic  expedition  records  the 
failure  of  some  of  the  men  under  conditions  which  would  have 
been  easily  surmounted  if  they  had  prevailed  at  the  beginning  of 
the  expedition.  The  intense  cold  and  the  cheerless  outlook  brought 
about  by  the  lack  of  comforts  craved  by  the  human  body,  coupled 


SIMPSON  :    ILLUMINATION  AND  ONE  YEAR'S  ACCIDENTS      8/7 

with  the  long  stretches  of  darkness,  render  the  men  unfit  for 
their  work. 

We  do  not  have  such  extremes  of  coldness  and  darkness,  nor 
such  lack  of  associations  or  bodily  comfort,  in  our  industries. 
On  the  other  hand,  our  workmen  are  not  selected  to  bear  up 
under  such  conditions.  Everyone  is  aware  of  the  depressing 
effect  of  a  week  of  overcast  skies  with  a  more  or  less  steady  rain- 
fall. Substituting  cold  weather  and  snow  for  rain,  one  can  pic- 
ture the  conditions  that  prevail  in  the  winter  months.  Colds  and 
other  ailments  are  more  prevalent  in  winter,  and  the  afflicted 
workmen  are  less  able  to  guard  against  injury.  Then  again  there 
are  many  buildings  where  the  window  area  and  arrangement 
affords  inadequate  illumination  on  cloudy  days,  even  when  it  is 
satisfactory  on  bright  days.  This  is  a  condition  that  is  likely  to 
be  overlooked  by  the  inspector  if  he  makes  an  inspection  on  a 
bright  day.  It  is  quite  evident  that  a  large  number  of  accidents 
might  occur  under  these  conditions,  and  little,  if  any,  thought  be 
given  to  the  underlying  cause. 

It  is  hoped  at  a  later  date  to  make  a  study  of  the  accidents  for 
the  year  1915,  in  order  to  ascertain  what  influence,  if  any,  the 
educational  campaign  of  the  Illuminating  Engineering  Society,  the 
lamp  manufacturers,  the  insurance  companies  that  have  studied 
this  matter,  and  others  interested  in  good  lighting,  has  had  on 
the  reduction  of  accidents.  An  examination  of  a  few  of  this 
year's  reports  indicates  the  trend  of  the  times  in  that  five  years 
ago  general  expressions  such  as  "no  light"  or  "insufficient  light" 
were  commonly  used  in  describing  the  cause  of  an  accident, 
whereas  at  the  present  time  we  meet  with  much  more  definite 
statements,  such  as  "improperly  placed  lighting  units"  or  "low- 
hanging,  unshaded  lamps."  From  this  one  may  gather  the  cheer- 
ing information  that  the  workmen  are  gradually  appreciating  the 
vast  difference  between  light  and  illumination.  It  might  be 
expected  that  fanciful  claims  will  be  made,  such  as  that  put  forth 
by  an  injured  workman  to  the  effect  that  the  actinic  rays  of  the 
lighting  unit  impaired  his  vision.  The  lighting  unit  in  question 
was  a  16-candlepower  carbon  lamp  equipped  with  a  bowl-shaped 
aluminum-finished  reflector. 

A  statement  has  been  made  to  the  effect  that  the  introduction 


878    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

of  the  high-efficiency  lighting  units  was  the  largest  single  factor 
for  the  increase  of  accidents  in  our  industries  during  the  period 
of  artificial  lighting.  This  statement  is  not  to  be  taken  as  a  con- 
demnation of  these  lighting  units,  but  rather  as  a  protest  against 
the  common  method  of  using  them.  There  are  hundreds  of  small 
manufacturing  establishments  in  this  country,  each  one  occupy- 
ing a  single  floor  or  part  of  one  floor  in  a  building.  The  owners 
have  had  the  floor  wired  and  connected  for  central-station  service 
or  piped  for  gas  service.  They  have  procured  incandescent  lamps, 
gas  tips,  or  mantles,  as  the  case  might  be,  and  used  them  without 
proper  accessories.  Of  diffusing  glass,  reflector  equipment, 
mounting  height,  and  other  fundamentals  of  good  lighting  they 
either  know  nothing  or  care  nothing.  The  workmen  adjust  the 
units  so  that  they  can  "see,"  the  adjustment  generally  consisting 
in  placing  the  lighting  unit  close  to  the  work,  very  often  between 
the  man  and  the  work,  and  almost  always  in  the  direct  line  of 
vision.  The  carbon  lamp  or  the  open-flame  gas  light  contributed 
a  distinct  hazard  under  these  conditions,  and  the  hazard  was 
greatly  increased  when  the  high-efficiency  incandescent  gas  man- 
tle and  electric  lamp  were  substituted  without  any  other  change 
being  made  at  the  same  time. 

In  some  cases  the  meterman  is  the  only  public  utility  repre- 
sentative to  visit  these  small  manufacturing  concerns,  and  very 
little  advice  on  the  lighting  conditions  is  given  by  these  men. 
The  consulting  engineer  or  lighting  expert  is  seldom,  if  ever, 
called  in  to  give  advice  on  installations  where  the  total  connected 
lighting  load  is  in  the  neighborhood  of  one  kilowatt.  In  the 
larger  manufacturing  plants  the  lighting  bill  will  bear  about  the 
same  proportional  relation  to  overhead  expense  as  it  does  in  the 
small  shop,  although  the  bill  itself  will  be  many  times  larger. 
Economy  has  generally  influenced  the  management  in  securing 
expert  advice  on  the  lighting  question  with  a  noticeable  improve- 
ment in  the  illumination.  This  in  a  measure  accounts  for  the 
modern  lighting  equipment  in  the  large  plants  and  also  shows 
why  they  compare  so  favorably  with  the  small  establishments. 
A  workman  may  be  just  as  seriously  injured  in  a  small  shop  as 
in  a  large  one ;  in  fact,  the  accident  rate  due  to  the  lighting  con- 
ditions is  likely  to  be  higher  in  the  small  shop  than  in  the  large 


SIMPSON  :    ILLUMINATION  AND  ONE  YEAR'S  ACCIDENTS      879 

shop  doing  the  same  class  of  work.  The  accident  insurance 
companies  are  assuming  risks  in  the  small  shops  as  well  as  the 
large  ones,  and  once  a  policy  is  written  the  premises  must  be  in- 
spected periodically.  It  is  the  duty  of  the  inspector  to  prevent 
accidents  by  recommending  changes  in  conditions  which  tend  to 
cause  injuries  to  workmen.  Since  inadequate  and  improper  illum- 
ination is  recognized  as  a  cause  of  accidents  the  insurance  com- 
pany inspector  tries  to  improve  the  lighting  conditions,  and  in 
this  capacity  he  is  probably  the  most  potent  factor  for  improving 
the  illumination  in  the  small  shops. 

In  the  past  year  the  gas-filled  tungsten  lamp  has  become  an  es- 
tablished commercial  product  in  a  constantly  increasing  range 
of  sizes  for  multiple  circuits.  The  concentrated  filament  of  this 
lamp,  more  nearly  approaching  a  point  source,  coupled  with  its 
higher  intrinsic  brilliancy  as  compared  with  other  tungsten  lamps, 
makes  the  use  of  reflectors  absolutely  essential.  The  manu- 
facturers are  earnestly  insistent  that  users  equip  these  lamps  with 
proper  reflectors,  but  unfortunately  this  advice  is  not  always  fol- 
lowed. In  some  instances  shallow  dome-type  reflectors  were 
used  with  the  vacuum-type  tungsten  lamp,  but  when  the  gas- 
filled  lamps  were  substituted  no  change  was  made  with  respect  to 
the  reflector  equipment  or  mounting  height,  even  though  the 
light  sources  were  within  the  range  of  vision.  Excellent  results 
in  the  way  of  diffusion  and  distribution  can  be  and  have  been  ob- 
tained by  the  use  of  the  dome-type  reflector  with  the  gas-filled 
tungsten  lamp,  but  when  viewed  from  the  safety  standpoint  they 
should  never  be  used  together,  unless  the  mounting  height  is 
such  as  to  preclude  any  possibility  of  the  lighting  source  being 
within  the  range  of  vision.  Unless  this  principle  is  followed  it 
is  inevitable  that  the  eyesight  of  the  workmen  will  be  impaired, 
and  with  impairment  of  a  workman's  eyesight  comes  a  greater 
likelihood  of  injury. 

DISCUSSION. 

Mr.  G.  S.  Barrows:  There  are  a  number  of  inspection  or- 
ganizations who  make  a  practise  of  visiting  their  clients  and  ad- 
vising them  regarding  the  various  hazards  and  the  best  methods 
of  overcoming  them.     I  think  from  what  I  have  seen  of  them, 


88o     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

however,  that  on  the  subject  of  proper  illumination  they  are 
not  as  well  grounded  as  they  might  be  and  I  believe  it  is 
a  very  desirable  thing  for  central  station  companies  to  get 
in  as  close  touch  with  such  inspection  bureaus  as  possible, 
in  order  to  advise  them  as  to  the  proper  steps  they  should  take 
to  provide  adequate  illumination.  On  the  eleventh  page  of  this 
paper  there  is  a  suggestion  which  I  think  is  a  very  fruitful  one ; 
Mr.  Simpson  says,  "In  some  cases  the  meter  man  is  the  only 
public  utility  representative  to  visit  these  small  manufacturing 
concerns,  and  very  little  advice  on  the  lighting  conditions  is  given 
by  these  men."  Now  what  I  am  going  to  say  applies  rather  more 
to  the  gas  than  the  electric  central  station;  nearly  all  gas  com- 
panies have  a  maintenance  department  for  taking  care  of  in- 
candescent gas  lamps ;  there  is  no  reason  at  all  why  the  main- 
tenance men  should  not  be  given  a  very  thorough  training  in  the 
proper  placing  of  lamps.  They  cannot,  of  course,  become  illu- 
minating experts  but  they  can  be  so  instructed  that  they  will  be 
able  to  recognize  hazards ;  and  while  they  may  not  be  able  to 
give  the  best  suggestions  for  overcoming  the  hazard,  they  could 
nil  in  reports  regarding  the  placing  of  lamps,  etc.,  which 
would  enable  a  representative  of  the  illumination  department  to 
inspect  the  various  plants  and  make  suggestions  for  improving 
the  lighting  conditions.  I  don't  know  that  that  is  being  done  by 
any  company  in  this  country,  but  I  believe  it  is  something  that 
the  companies  ought  to  begin  to  do,  and  I  can  say  that  at  least 
one  company  is  going  to  take  this  matter  up  immediately. 

Mr.  G.  Bertram  Regar  :  The  Philadelphia  Electric  Company 
has  recently  organized  a  department  known  as  the  lighting  service 
department,  practically  along  the  lines  as  suggested  by  Mr.  Bar- 
rows. The  headquarters  of  the  department  are  at  the  central 
office.  Here  the  lighting  experts  are  stationed,  and  a  complete 
system  of  data,  instruments,  and  records  of  cases  investigated 
are  kept.  A  representative  of  the  department  is  stationed  at  each 
of  the  district  offices,  whose  duty  it  is  to  constantly  make  in- 
spections, by  day  and  night,  of  consumers'  installations  and  advise 
the  consumers  having  inefficient  installations  as  to  changes  to 
remedy  the  defects.  The  lamp  boys  are  being  educated  to  a 
better  understanding  of  illumination  and  it  is  their  duty  when 


ILLUMINATION   AND   ONE   YEAR'S   ACCIDENTS  88l 

making  lamp  renewals  to  report  poor  installations.  The  instal- 
lation men  and  meter  men  also  have  a  blank  form  to  notify  the 
lighting  service  department.  In  cases  of  complaints  on  bills, 
after  the  meters  have  been  tested  and  the  results  explained  to  the 
consumer,  the  lighting  service  department  is  notified,  in  order  that 
they  may  make  a  thorough  inspection  for  the  purpose  of  possibly 
offering  suggestions  for  a  more  efficient  installation.  The  whole 
policy,  as  can  be  seen,  is  to  ever  improve  the  service  to  the 
consumer. 

Mr.  J.  L,.  Minick  :  In  reading  this  paper  it  has  been  my  im- 
pression, probably  an  erroneous  one,  that  Mr.  Simpson  believes 
that  the  high  percentage  of  accidents  during  the  winter  months 
can  be  attributed  largely  to  lighting  conditions.  This  does  not 
seem  to  me  to  be  the  impression  that  should  be  given;  not  be- 
cause we  do  not  wish  to  prevent  accidents  so  far  as  it  is  possible, 
but  because  a  study  of  the  curves  shown  in  the  paper  indicates 
that  there  will  be  a  greater  number  of  accidents  during  the  winter 
months  regardless  of  lighting  or  any  other  condition. 

Mr.  R.  E.  Simpson  (In  reply)  :  The  two  concrete  cases  cited 
by  Mr.  Barrows  emphasize  the  importance  of  not  depending  too 
much  on  the  ideas  of  the  workmen  on  the  lighting  question,  and 
in  particular  on  the  location  of  local  lamps.  In  almost  every 
shop  may  be  found  some  workmen  who  can  tell  just  where  they 
want  a  lighting  unit  to  be  placed,  and  it  will  be  found  that  their 
ideas  conform  to  illuminating  engineering  principles.  We  must 
not  lose  sight  of  the  fact  that  this  class  of  workmen  is  in  the 
minority.  There  were  thousands  of  cases  noted  in  the  investi- 
gation where  men  were  employed  on  drilling  machines  and  simi- 
lar operations,  where  drop  lamps,  usually  unshaded,  were  de- 
pended on  for  illumination.  The  lamps  are  usually  placed  close 
to  the  work  while  the  controlling  mechanism  is  above  the  head. 
While  watching  the  work  or  even  when  looking  up  the  men  often 
place  a  hand  in  the  gears  instead  of  on  the  controlling  wheel. 
A  crushed  hand  or  finger  is  very  probable  under  these  conditions. 
I  am  sure  that  all  who  are  interested  in  good  lighting  and  accident 
prevention  work  will  be  glad  to  cooperate  in  the  plan  advocated 
by  Mr.  Barrows. 

It  is  to  be  regretted  that  definite  information  on  the  cost  of 


882     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

industrial  accidents  is  not  available.  There  are  so  many  varying 
factors  such  as  the  face  or  amount  of  the  policy,  the  seriousness 
of  the  accident,  attorney  fees,  etc.,  that  it  is  hard  to  arrive  at  an 
average.  The  15-watt  lamp  burning  100  years  would  cost  only 
one  half  as  much  as  was  paid  to  the  injured  paper  mill  employee. 
Another  man  receiving  the  same  kind  of  injury  might  receive 
twice  as  much,  or  only  one  half  as  much,  depending  on  the  factors 
already  mentioned. 

There  was  no  intention  of  ascribing  the  high  accident  rate  in 
winter  months  to  poor  illumination  solely.  The  curves  clearly 
indicate  this,  in  that  their  general  outline  is  the  same.  These 
curves  tend  to  prove  that  the  "number  of  accidents  caused  by 
poor  lighting  are  twice  as  high  in  the  winter  months  as  in  the 
summer  months.  It  is  in  the  winter  months  that  artificial  light 
must  be  depended  on  to  a  greater  extent  than  in  the  summer 
months.  In  the  latter  part  of  the  paper  other  factors  influencing 
the  accident  rate  in  winter  are  discussed.  Mr.  Minick's  discus- 
sion really  opens  up  the  whole  subject  of  accident  prevention  and 
is  too  broad  to  be  thoroughly  treated  here. 


EVANS:     INDUSTRIAL   LIGHTING  883 

INDUSTRIAL  LIGHTING  WITH  MERCURY- VAPOR 

LAMPS.* 

BY  WILLIAM  A.  D.  EVANS. 

Synopsis:  In  the  following  paper,  the  mercury-vapor  lamp  is  treated 
as  strictly  an  industrial  illuminant  and  it  is  intended  to  give  an  idea  of 
its  various  industrial  uses  and  the  practise  now  in  vogue.  Considerable 
data  from  actual  installations  are  given  which  should  enable  those  con- 
templating installing  lamps  to  follow  out  the  lines  already  established. 
The  variety  of  industries  in  which  these  lamps  are  used  embraces  prac- 
tically every  operation  in  machine  shops,  foundries,  textiles,  printing,  glass 
manufacturing,  motion  picture  studio  lighting,  etc.  In  each  of  the  depart- 
ments in  which  mercury-vapor  lamps  are  used,  the  lamps  have  a  certain 
peculiar  adaptation  for  that  class  of  work ;  for  instance,  metal  working 
plants,  in  the  making  of  moulds;  the  grinding  and  polishing  departments, 
and  in  the  body  finishing  and  varnishing  departments  of  wood-working 
plants,  where  slight  flaws,  scratches,  blemishes,  etc.,  are  easily  detected.  In 
machine  work  there  is  very  little  reflection  from  bright  and  shiny  parts ; 
in  the  testing  department  for  engines  and  in  foundries,  the  light  pene- 
trates the  atmosphere;  in  textile  manufacturing  and  in  the  inspection  of 
all  kinds  of  finished  products,  the  magnifying  quality  of  the  light  makes 
details  easily  perceived ;  and  in  motion  picture  studio  work,  the  softness 
of  the  light,  its  high  actinic  value  and  diffusion  and  ease  on  the  eye  are 
especially  desirable.  Numerous  photographs  are  shown  and  a  bibliography 
of  articles  on  lighting  with  mercury-vapor  lamps  is  given. 

INTRODUCTION. 

Artificial  lighting  in  interiors  may  roughly  be  divided  into  two 
classes,  esthetic  and  industrial;  esthetic  embracing  the  lighting 
installations  where  the  idea  prevails  of  harmonizing  the  illumina- 
tion with  surroundings;  and  industrial  covering  the  lighting  of 
manufacturing  plants  where  the  prime  consideration  is  to  enable 
the  eye  to  do  its  work  with  the  greatest  rapidity  and  least  fatigue. 

Mercury-vapor  lamps  on  account  of  the  peculiar  bluish-green 
color  of  the  light  and  the  tubular  form  of  the  light  source  may 
be  classified  as  strictly  an  industrial  illuminant. 

Among  the  advantages  derived  from  these  characteristics, 
which  makes  the  light  particularly  desirable  for  industrial  lighting, 
are  visual  acuity,  low  intrinsic  brilliancy  and  natural  differences. 

The  first  mercury-vapor  lamps  for  industrial  lighting  purposes 
were  installed  in  the  composing  room  of  the  old  building  of  the 
New  York  Evening  Post  during  the  summer  of  1903.  Two  200- 
watt  lamps  were  placed  over  the  make-up  tables.  From  this 
small  installation  in  a  printing  plant  has  developed  the  use  of 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing Society,  Washington,  D.   C,   September  20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


884     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

mercury-vapor  lamps  for  industrial  lighting  in  all  of  its  different 
branches,  and  at  the  present  time  one  metal  working  plant  alone 
is  using  a  total  of  about  2,500  tube  lamps. 

Classification  of  Industries  Where  Mercury-Vapor  Lamps  are 
in  Use. — The  industries  in  which  mercury-vapor  lamps  have  been 
successfully  used  are  many  and  varied,  and  while  it  has  not  been 
possible  to  collect  data  regarding  every  operation  which  is  carried 
on  under  the  lamps,  an  attempt  has  been  made  to  gather  sufficient 
material  which  will  enable  anyone  contemplating  installing  lamps 
to  follow  the  practise  which  has  been  carried  out  for  similar 
classes  of  work.  To  attempt  to  classify  the  entire  industrial  field 
would  be  far  beyond  the  scope  of  this  paper,  and  it  is  only  possi- 
ble to  give  a  broad  classification.  The  general  divisions  will  be 
given  below  and  the  lighting  of  each  operation  treated  separately. 

Table  I — General    classification    of    industries    in    which 
mercury-vapor  lamps  are  used  for  illum- 
ination. 
Metal  working  plants. 

Foundries. 

Forge  and  blacksmith  shops. 

Machine  shops. 

Erecting  and  heavy  machine  shops. 
Woodworking  plants. 
Varnish  and  finishing  plants. 
Textile  plants. 

Silk  mills. 

Cotton  mills. 

Woolen  and  worsted  mills. 

Knitting  mills. 

Embroidery  plants. 
Newspaper  and  printing  plants. 
Paper  manufacturing. 
Clothing  manufacturing. 
Power  houses. 
Glass  manufacturing. 
Shipping  and  storage. 
Motion  picture  film  manufacturing. 
Miscellaneous. 


EVANS:     INDUSTRIAL   LIGHTING  885 

In  the  installations  referred  to,  the  lamps  used  consist  of  four 
different  types,  the  20-in.  (50.8  cm.)  type  for  direct  current  des- 
ignated as  the  200-watt  lamp  (nominally  192.5  watts)  and  the 
50-in.  (1.27  m.)  lamp  for  direct  current  and  alternating  current, 
both  designated  as  400-watt  almps  (nominally  385  watts)  and 
the  quartz  or  high  pressure  lamp  for  direct  current  designated  as 
a  725-watt  lamp. 

METAL  WORKING  PLANTS. 

The  illumination  of  metal  working  plants  probably  offers  the 
largest  field  for  the  use  of  mercury- vapor  lamps,  not  only  on  ac- 
count of  the  size  of  the  industry,  but  due  to  the  manner  in  which 
marks  and  imperfections  on  metal  stand  out  under  the  light.  The 
use  of  mercury-vapor  light  is  found  throughout  the  entire  field 
from  the  making  of  moulds,  where  slight  blemishes  in  the  sand 
are  perceived,  through  the  different  manufacturing  processes  up 
to  the  final  inspection  of  the  finished  product. 

Foundries. — The  lighting  of  a  foundry  may  roughly  be  divided 
into  three  different  parts;  moulding,  embracing  core  making; 
casting  floor  and  the  finishing  operations,  embracing  tumbling, 
chipping  and  cleaning.  For  none  of  these  is  there  a  particular 
large  amount  of  light  necessary.  Most  foundries  are  dark  holes 
at  night,  and  even  in  the  daytime,  during  the  period  of  pouring 
off,  it  is  extremely  difficult  to  see  down  the  floor  on  account  of  the 
vapor  in  the  atmosphere.  It  should  be  borne  in  mind,  however, 
that  accidents  are  a  very  frequent  occurrence  and  too  much  light 
cannot  be  provided  to  guard  against  the  dangers  of  workmen 
falling  over  moulds,  kettles  and  castings,  which  may  happen  to 
be  in  the  way.  Lamps  should  be  placed  out  of  the  field  of  vision 
as  far  as  possible. 

The  following  table  shows  a  number  of  different  foundries 
varying  in  size,  which  are  lighted  by  mercury-vapor  lamps  with 
data  relative  to  the  energy  consumption. 

Moulding  Departments. 

Total  sq.  ft. 

I  6,680 

2    14,170 

3    22,225 

4   4,920 

5   83,500 


Watts 
per  lamp 

Watts 
per  sq.  ft. 

Height  above 
floor,  Feet 

725 

0.33 

22 

400 

0.27 

15-27 

400 

O.56 

12 

400 

0.31 

15 

200-400 

0.21 

18 

886     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


Casting  Floor. 

Watts  Watts      Height  above 

Total  sq.  ft.         per  lamp         per  sq.  ft.      floor,  Feet 

1  ■ 15,200  725  O.52  22 

2    12,400  725  0.23  27 

3    24,000  725  0.24  45 

4    28,180  725  O.34  22 

5   5>ooo  725  0.29  42 

6  44,000  400  0.20  27 

7  44.500  400  0.55  12 

8  16,300  400  0.30  20 

9  30,800  400  0.31  23-35 

10   6,900  400  0.31  15 

11    13,400  400  0.28  16 

12   90,500  400  0.34  18 

13   12,000  400  0.26  18 

14   28,350  200-400  0.29  18 

Tumbling,  Chipping  and  Cleaning. 

1   25,500  400  0.29  21 

2  16,300  400  0.33  13 

3   4,400  200  0.32  10 

Forge  and  Smith  Shops. — For  this  class  of  work  where  there 

is  apt  to  be  moving  machinery  and  high  machines,  the  quantity 
of  illumination  should  be  somewhat  greater  than  in  the  foundries. 
Welding,  case-hardening  and  tempering  are  included  under  this 
designation.  Data  on  typical  installations  for  this  class  of  work 
are  given  below. 

Watts  Watts  Height 

Total  sq.  ft.  per  lamp         per  sq.  ft.  Feet 

i.  Forge  shop   24,430  725  0.60  33 

2.  Forge  shop   14,000  725  0.31  27 

3.  Forge  shop   26,000  400  0.29  23 

4.  Forge  shop   3,780  400  0.71  15 

5.  Forge  shop   3,000  400  0.77  10 

6.  Forge  shop   13,820  200  0.17  14 

7.  Flange  shop    16,900  725  0.21  30 

8.  Smith  shop    16,800  725  0.35  27 

9.  Smith  shop   61,380  725-400  0.37  24-34 

10.  Welding   11,700  400  0.39  14 

11.  Welding   3,424  400  0.24  20 

12.  Case  hardening   2,770  200  0.82  12 

13.  Tempering  1,200  400  1.28  9 

Machine  Shops. — Machine  shops  may  be  roughly  denned  as 
all  shops  where  metal  is  worked  with  the  purpose  of  reducing 
or  altering  the  shape  by  means  of  cutting  away  a  certain  portion 


EVANS:     INDUSTRIAL   LIGHTING 


887 


of  the  material.  This  will  embrace  the  use  of  lathes,  shapers, 
millers,  planers,  drill  presses,  automatic  machines,  punch  presses 
and  so  forth.  Closely  allied  to  this  class  of  work  is  the  as- 
sembling or  erecting  of  the  finished  pieces,  and  the  inspection  of 
the  parts  and  final  product.  There  are  other  operations  which 
are  so  closely  related  to  machine  shop  work  that  they  are  in- 
cluded under  this  heading. 

The  machine  shops  listed  below  are  all  lighted  entirely  by  the 
use  of  mercury-vapor  lamps  without  any  individual  lamps  of  the 
machines,  except  in  very  few  cases  where  it  is  necessary  to  bore 
inside  of  castings  or  some  such  similar  work,  which  would  necessi- 
tate the  use  of  individual  lamps  even  with  the  best  daylight.  Due 
to  the  low  intrinsic  brilliancy  and  the  absence  of  bright  spots  with 
the  tube  lamps,  the  reflection  from  bright  metal  parts  is  kept  at  a 
minimum. 


Machine  Work  With  Small  Tools. 

Total 
Class  of  work                       sq.  ft. 

Watts 

per 

lamp 

Watts 

per 
sq.  ft. 

Height 
Feet 

I 

Miscel.  small  tools  •  •   22,800 

400 

O.66 

II 

Gear  cutting 

2 

<  t 

•         ii 

•  25,240 

400 

O.62 

14 

Auto  parts 

3 

(i 

1         11 

•  11,400 

400 

1. 12 

30 

Gen.  mach.  wk. 

4 

" 

1         1 1 

.     4,800 

400 

O.92 

12 

11 

5 

<  i 

1         11 

•     2,190 

400 

0.95 

12 

" 

6 

" 

«         11 

•     5.840 

400 

0.73 

12 

Ball  bearings 

7 

*    •< 

•         ii 

•  54,650 

400 

O.52 

13 

Auto  engines 

S 

" 

'      .   " 

•  30.950 

400 

O.92 

13 

Auto  parts 

6 

11 

•         11 

.   14,880 

400 

O.63 

22-28 

Breech  mechanism 

10 

" 

ii 

.    12,180 

400 

0.95 

IO 

Revolver  parts 

11 

" 

1         11 

•  38,980 

200-400 

O.60 

14 

Air  brake  parts 

12 

11 

1         1 1 

.    10,800 

400-200 

0.50 

12 

Auto  parts 

13 

11 

•         ii 

•  8,736 

200 

O.88 

9 

Gun  parts 

14 

■1 

1         ii 

.  20,520 

200 

O.68 

9 

1 1 

15 

11 

•         11 

•     7.760 

200 

O.89 

9 

11 

16 

" 

1         1 1 

•    5.750 

200 

O.80 

9 

1 1 

17 

" 

•         11 

•    5.175 

200 

0  75 

9 

*' 

iS 

" 

•         11 

.   14,700 

200 

0.55 

10 

Auto  parts 

19 

" 

1         ii 

■•    5,400 

20O 

0.57 

10 

" 

20 

" 

«         ii 

.     7,800 

200 

1. 18 

14 

Torpedo  mfg. 

21 

Tool 

room 

•   11,760 

200 

O.92 

11-14 

22 

1  ( 

"                             2,500 

400 

O.80 

12 

23 

•  1 

6,75o 

400 

O.80 

14 

24 

II 

3.240 

400-200 

O.7I 

12 

25 

Drill 
4 

pre* 

•    1,790 

200 

O.65 

12 

Auto  parts 

TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


Machine  Work  With  Small  Tools.— {Continued.) 

Watts 

per 

lamp 

400 

400 

400 

400 

400 

20O 

200 

400 

400 


Total 
Class  of  work  sq.  ft. 

26.  Milling  machines  .  . .   12,220 

27.  "  "        small  12,220 

28.  Lathes 12,220 

29. 
30. 
3i- 
32. 
33. 


Watts 
per 

sq.  ft. 

i-i5 
1.18 
0.79 
1. 12 
1.22 
0.81 

c-75 
1. 00 
1.28 


Height 
Feet 

IO 

IO 

IO 

IO 

IO 

8 

8 
12 
10 


Reamers 12,220 

Model  making 12,220 

Screw  machines 12,390 

5,188 
"  "  11,200 

34.  Saw  finishing 900 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  1. 

The  above  machine  shops  are  all  those  where  only  small  tools 
are  employed.  Where  large  engine  lathes,  boring  machines  and 
similar  tools  are  used  for  working  on  heavy  castings  or  material 
which  generally  necessitates  the  use  of  an  overhead  travelling 
crane,  the  lamps  are  usually  placed  above  the  cranes  or  under  the 
crane  rails.  These  shops  are  designated  as  heavy  machine  shops 
and  the  following  data  relates  to  them. 

Heavy  Machine  Work. 

Watts 

per        Height 
sq.  ft.       Feet 

0.18        40      Structural  steel 

0-65         5°      Shrapnel  mfg. 

0.52 

0.62 


Watts 
per 
lamp 


5 

6 

7 

S 

9 

10 
11 
12 
13 
14 
'5 
16 


725 
725 
725 
725 


Total 
Class  of  work  sq.  ft. 

Heavy  machine  work  300,000 
23.35o 
28,000 
69,600 

14,900  725  0.39 

14,500  725  0.40 

8,250  725  0.35 

6,980  725  0.52 

Large  lathes 14,335  725  0.71 

29,400  400  0.59 

19,700  400  0.64 

11,250  400  0.57 

45,780  400  0.48 

22,800  400  0.44 

17,860  200  0.63 

11,400  200  0.44 


Heavy  machine  work 


40 
50 

45 
30-48 
18 
18 
18 
25 
35 
12 
12 

24 
20-50 

25 
23 
14 


Torpedo  mfg. 

Eng.  mfg. 

Shrapnel  mfg. 
11 

Car  Wheels 
Large  gun  mfg. 
Loco  bldg 


Punch  Presses.— Punch  press  lighting  requires  lighting  some- 
what different  from  the  ordinary  machine  shop  as  it  is  necessary 
for  the  light  to  shine  in  and  around  the  dies  and  to  a  certain  extent 
the  light  will  be  blocked  off  by  the  frame  of  the  press.  Moreover, 
extreme  care  must  be  taken  not  to  have  dazzling  light  sources  in 


EVANS:     INDUSTRIAL   LIGHTING  889 

the  field  of  vision,  for  if  the  eye  happens  to  be  momentarily 
blinded,  it  may  mean  the  loss  of  a  finger  for  the  operator.  While 
the  following  table  gives  data  for  typical  lighting  of  punch  press 
rooms,  however,  each  installation  should  be  treated  separately 
and  the  lamp  located  with  reference  to  the  machines. 

Watts  Watts  Heigbt 

Class  of  work  Total  sq.  ft.  per  lamp  per  sq.  ft.  Feet 

1.  Pressroom    8,750  400  0.78  12 

2-  "  n,750  400  0.55  12 

3-  "  18,400  400  0.76  36 

Grinding  and  Polishing. — Another  operation  which  is  somewhat 
distinctive  from  regular  machining  is  that  of  grinding,  polishing 
or  buffing.  Extremely  good  illumination  is  necessary  for  these, 
as  slight  flaws  and  scratches  must  be  detected  easily  and  rapidly 
by  the  men  while  working. 

Watts      Watts 
Total  per  per        Height 

Class  of  work  sq.  ft.  lamp       sq.  ft.       Feet 

i.  Grinding 49,980        200        0.26        14      Rim  grinding 

2.  "  1,230        200        0.63         12      Auto  parts 

3.  Polishing 1,510        400        0.80        12       Plated  silver 

4.  "  8,310        400        0.72         14      Revolver  parts 

5.  "  2,090        200        0.74  9      Gun  parts 

6.  "  1,280        200         1.20        12       Engine  valves 

Boiler,  Tank  and  Plate  Shops. — Another  class  of  large  shops  is 
embraced  under  the  classification  of  boiler,  tank  and  plate  shops 
where  large  pieces  of  sheet  metal  are  worked  up  for  use.  This 
class  of  shops  as  a  rule  requires  very  little  general  lighting  as  a 
good  part  of  the  work  is  carried  on  inside  of  the  boilers  and 
tanks,  and  local  lighting  is  necessary. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.  per  lamp         per  sq.  ft.  Feet 

1.  Boiler  shop  30,624  725  0.24  45 

2.  Boiler  shop   26,400  725  0.41  36 

3.  Boiler  shop  12,220  400  0.50  20 

4.  Tank  shop  18,000  725  0.28  35 

5.  Tank  shop  18,000  400  0.34  18 

6.  Tank  shop  6,000  400  0.33  24 

7.  Tank  shop  12,000  400  0.40  20 

8.  Plate  shop  46,900  400  0.15  28 

Assembling  and  Erecting. — The  final  operations  in  most  metal 

working  plants  is  the  assembling  or  erecting  of  the  finished  parts. 
Here  the  lighting  is  apt  to  vary  between  wide  limits  depending 
upon  the  nature  of  the  product.     The  following  data  give  in- 


89O     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

formation  relative  to  assembling  of  parts  in  different  industries. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.  per  lamp         per  sq.  ft.  Feet 

1.  Asmblg.    revolver   parts  12,220               400  0.75  12 

2.  Asmblg.  auto  parts 6,192  200-400  0.81  12 

3.  Asmblg.  automobiles...  11,566  200-400  0.59  12 

4.  Asmblg.  locks 3,264               200  0.94  10 

5.  Asmblg.  gun  parts 6,180               200  0.88  9 

6.  Erectg.   locomotives* . . .  30,625               725  0.28  45 

7.  Erectg.   locomotives 30,400               725  0.29  51 

8.  Erectg.    cars 117,000                400  0.30  20-29 

9.  Erectg.    cars 24,000               400  0.40  25-37 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  2. 

Testing  Departments. — With  certain  machinery  it  is  absolutely 
essential  that  it  be  thoroughly  tested  under  service  conditions  and 
in  numerous  cases  24  hours  or  longer  tests  are  run,  necessitating 
as  good  lighting  at  night  as  during  the  day.  In  testing  auto- 
mobile engines,  particularly  this  condition  occurs  and  due  to  the 
large  amount  of  fumes  and  smoke  in  the  atmosphere,  the  mercury 
vapor  lamps  have  proven  particularly  desirable  on  account  of  the 
penetrating  power  of  the  green  light.  Good  illumination  is  very 
important  as  it  is  often  necessary  to  adjust  the  carburetors, 
magnetos,  etc. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.         per  lamp         per  sq.  ft.  Feet 

1.  Testing  large  machines  7,840  725  0.65  25 

2.  Auto  engine  test* 12,750  400  0.41  14 

3.  Auto  engine  test 19,200  400  0.75  12 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  3. 

Inspection  Departments. — Inspecting  might  be  termed  the  most 
important  operation  in  the  entire  shop  as  every  part  that  passes  an 
inspection  and  proves  defective  in  the  hands  of  a  customer,  gives 
the  manufacturer  a  bad  reputation.  The  value  of  good  illumin- 
ation in  this  department  cannot  be  too  strongly  dwelt  upon. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.         per  lamp         per  sq.  ft.  Feet 

1.  Inspectg.  revolver  parts  6,110  400  0.75  12 

2.  Silverware  inspection. . .  3,400  400  0.82  12 

3.  Inspectg.  auto  parts 1,230  200  0.63  10 

4.  Inspectg.   browning 6,550  200  0.94  10 

5.  Inspectg.  gun  parts 12,390  200  0.88  9 

WOODWORKING  PLANTS. 
The   lighting  of   woodworking  plants   is   similar   to   that   of 
machine  shops,  inasmuch  as  the  machines  must  be  adequately 


EVANS:     INDUSTRIAL,   LIGHTING 


891 


illuminated  to  prevent  accidents, 
marks  on  the  material.     In  most 
stands  out  particularly  clear  under 
vapor  lamp. 


and  it  is  necessary  to  see  the 

cases  the  grain  of  the  wood 

the  green  color  of  the  mercury- 


Total 

Class  of  work  sq.  ft. 

i.  Planning  mill 30,000 

2.  "  7.000 

3.  Carpenter  shop  •  •  •  3,640 

4.  Woodworking  shop  3,000 

5.  Carpenter  shop  •  •  •  9,000 

6.  "  12,390 

7.  Woodworking 6,795 

8.  "  4,807 

9.  Carpenter  shop  •  •  •  5,600 

10.  "  5,400 

11.  Woodworking 6,550 

12.  "  7,775 


Watts 
per 
lamp 

400 

400 

400 
400-200 
400-200 
400-200 

200 

200 

200 

200 

200 

200 


Watts 

per 
sq.  ft. 

0.28 

0.35 
O.69 
I.28 

0.39 
O.56 
0.9I 
0.96 
O.83 
O.71 
O.94 
O.50 


Height 
Feet 

20 

17 
12 

8 
15 
15 
10 
10 
10 

9 
10 
10 


Car  parts 

Genl.  carpenter  wk. 

Carriage  bodies 

Rough  carptr.  work 

Genl.  carpenter  wk. 

Gun  stocks 

"  finishing 

Box  making 
<t 

Stock  inspection 
Auto  bodies 


VARNISHING  AND  BODY  FINISHING  SHOPS. 
Closely  akin  to  woodworking  shops  are  the  varnish  shops  where 
the  finish  is  placed  on  a  great  many  articles.  Under  the  same 
heading  is  included  "Body  Finishing"  which  embraces  the  painting 
and  finishing  of  automobile  bodies.  This  latter  is  an  extremely 
important  item  in  the  automobile  business,  as  the  finish  on  the  car 
is  the  first  point  to  strike  the  average  purchaser.  This  work  is 
generally  done  in  a  long  narrow  room  with  windows  on  one  side, 
and  the  dark  rooms  on  the  other.  The  room  is  kept  closed 
throughout  the  process  in  order  to  keep  out  insects  and  the 
temperature  is  maintained  at  a  constant  point.  When  working 
in  daylight  it  is  necessary  to  turn  the  bodies,  after  rubbing  down, 
to  obtain  light  on  the  opposite  side.  This,  however,  has  been 
obviated  by  the  use  of  two  rows  of  mercury-vapor  lamps  with 
angle  reflectors,  throwing  light  on  both  sides  of  the  body  and 
permitting  the  work  to  be  done  in  a  great  deal  less  time. 


I. 

Class  of  work 

Total 
sq.  ft. 

••    3,756 

Watts 
per 
lamp 

200 

Watts 
per 
sq.  ft. 

O.82 

Height 
Feet 

10      Gun  stocks 

2. 

ii 

3.IOO 

200 

0.75 

10               " 

3- 
4- 

11 

..    4,400 
2,800 

400 
400 

2.28 
2.86 

%yz       Auto 

8K 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  4. 


892     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


TEXTILE  MANUFACTURING. 

The  lighting  of  textile  plants  varies  somewhat  from  that  of 
machine  shop  lighting.  In  almost  all  cases  the  machines  are  en- 
tirely automatic  and  the  necessity  for  seeing  generally  occurs 
when  a  thread  breaks  which  automatically  stops  the  machine. 
Until  this  thread  is  repaired  that  portion  of  the  work  is  at  a 
standstill  and  every  second  saved  in  quick  repairs  means  just  so 
much  more  output.  As  the  threads  in  silk  work  are  as  fine  as  one 
two-thousandth  of  an  inch,  not  only  is  a  large  amount  of  light 
necessary,  but  also  a  light  with  high  visual  acuity. 

Silk  Mills. — The  first  operation  in  silk  is  what  is  known  as 
"throwing,"  which  is  simply  twisting  and  doubling  the  threads 
over  and  over  again  to  work  them  up  to  the  required  thickness. 
Winding  and  spinning  are  also  a  similar  operation,  and  the  fol- 
lowing data  will  cover  all  of  these  operations. 

Preliminary  Operations. 

Total  Watts  Watts  Height 

Class  of  work  sq.  ft.  per  lamp         per  sq.  ft.  Feet 

1.  Reeling  2,091  400  0.95  9 

2.  Reeling  4,400  400  1.40  10 

3.  Spinning    4,185  400  1.00  12 

4.  Winding    16,200  400  0.50  12 

5.  Spinning    7,040  400  0.80  12 

6.  Spinning    10,032  400  1.47  10 

7.  Spinning    3,000  400  1.02  12 

8.  Spinning   28,020  400  0.73  10 

9.  Winding  6,790  400  0.69  12 

10.  Winding  3,000  400  0.77  12 

11.  Doubling  4,680  400  0.82  10 

12.  Winding  20,448  400  0.57  10 

13.  Reeling  2,150  200  0.54  8 

14.  Reeling  840  200  0.69  10 

15.  Spinning    6,465  200  0.48  9 

16.  Winding  6,220  200  0.69  9 

17.  Twisting   8,515  200  0.59  9 

18.  Winding  1,680  200  0.69  10 

19.  Spinning    3,400  200  1.02  10 

20.  Winding  2,520  200  0.69  10 

Warping  and  Quill  Winding. — After  the  silk  has  been  worked 
up  to  the  proper  thickness  and  twisted,  a  portion  of  it  is  sent  to 
the  warping  department  and  the  balance  to  the  quilling  depart- 
ment. 


EVANS:     INDUSTRIAL   LIGHTING  §93 

In  the  warping  operation,  the  silk  is  unwound  from  small 
spools  onto  a  large  drum  or  beam,  from  which  it  is  rewound  on 
the  warp  and  placed  in  the  loom.  The  balance  of  the  silk  is 
wound  up  into  small  bobbins  which  are  placed  in  the  shuttles  of 
the  loom. 

Good  illumination  is  even  more  necessary  for  these  processes 
than  for  the  throwing  operations. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.         per  lamp  per  sq.  ft.  Feet 

1.  Warping    10,780  400  I.H  12 

2.  Warping    10,906  400  1.16  12 

3.  Warping    2,940  200  0.53  10 

4.  Warping 7,ioo  400  1.08  10 

5.  Quill  winding 2,020  400  l£l  10 

Entering. — When  the  warp  is  finished,  it  is  necessary  to  thread 

it  through  reeds  of  the  harness  before  the  warp  can  be  placed  on 
the  loom.  Automatic  machines  are  in  use  for  this  work,  but  a 
great  deal  of  it  is  done  by  hand  and  requires  a  high  degree  of 
illumination. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.        per  lamp  per  sq.  ft.  Feet 

I.  Entering 2,800  400  1.65  12 

Weaving. — The  main  operation  in  silk  is  weaving,  as  this  pro- 
duces the  goods  in  the  final  form.  Broad  silk  looms  are  generally 
lighted  by  using  one  400  or  200-watt  mercury-vapor  lamp  to 
every  four  looms,  while  for  ribbon  looms  one  or  two  200-watt 
lamps  are  used  per  loom. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.        per  lamp         per  sq.  ft.  Feet 

1.  Broad  silk  11,800  400  1.00  14 

2.  Broad  silk  7.620  400  1-47  12 

3.  Broad  silk  11,508  400  1.27  11 

4.  Broad  silk*  10,780  400  1.21  n 

5.  Broad  silk  10,906  400  1.27  « 

6.  Broad  silk  10,045  400  1.30  II 

7.  Broad  silk  8,890  400  1.37  10 

8.  Broad  silk  29,295  400-200  1.18  14 

9.  Broad  silk   6,000  400-200  1.15  8 

10.  Broad  silk  11,508  400-200  1.6  n 

11.  Broad  silk   7,285  400-200  0.73  10 

12.  Broad  silk   6,340                200  0.55  10 

13.  Ribbon  looms  750               200  1.54  9 

14.  Ribbon  looms  4,800  200-400  0.84  12 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  5- 


894     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


Picking  and  Inspecting. — After  the  silk  comes  from  the  loom, 
it  is  carefully  gone  over  and  picked,  which  consists  of  removing 
the  knots  and  loose  ends  and  the  detection  of  other  flaws  which 
may  have  occurred  through  the  carelessness  of  the  weaver. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.        per  lamp  per  sq.  ft.  Feet 

i.  Picking 2,800  400  1.65  12 

2.  Picking 340  200  1.39  10 

Cotton. — The  lighting  of  cotton  mills  in  the  arrangement  of 
lamps  is  somewhat  similar  to  that  of  silk,  with  the  exception  that 
due  to  the  greater  thickness  of  the  threads,  less  light  is  needed. 

Preliminary  Operations. — The  preliminary  operations  consist- 
ing of  lapping,  carding,  drawing,  spooling  and  spinning  are  some- 
what along  the  line  of  the  throwing  operation  in  silk  manufactur- 
ing, the  purpose  being  to  prepare  the  cotton  for  the  loom. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.       per  lamp         per  sq.  ft.  Feet 

i.  Carding   600               200  0.23  10 

2.  Ring  spinning 3,330                200  0.47  10 

3.  Ring  spinning 12,000  200-400  0.68  12 

4.  Twisting    15,170  200-400  0.68  12 

5.  Winding  3,660  200-400  0.58  10 

6.  Warping*    1,500                200  0.64  12 

7.  Beaming    1,760               200  0.44  12 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  6. 

Weaving. — In  cotton  weaving  the  looms  are  generaly  lighted 
by  one  400-watt  mercury-vapor  lamp  to  approximately  every  14 
looms  or  one  200-watt  lamp  to  about  every  eight  looms,  depending 
somewhat  on  the  arrangement  and  size  of  the  looms. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.  per  lamp         per  sq.  ft.  Feet 

1.  Weaving  (coarse  goods)  25,200  200-400  0.52  15 

2.  Weaving  (coarse  goods)  26,000               200  0.37  12 

3.  Weaving  (coarse  goods)  21,573               200  0.45  10 

4.  Weaving 36,570               400  0.74  12 

5.  Weaving 4,580               200  0.78  gy2 

6.  Weaving 21,000               400  0.66  14 

Finishing. — The  finishing  operation  in  cotton  consists  practi- 
cally of  cleaning  the  goods,  and  is  the  final  preparation  for  the 
market. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.         per  lamp         per  sq.  ft.  Feet 

i.  Finishing 6,080  400  0.64  12 


"frq  H 


Fig.  i. -A  machine  shop  illuminated  by  mercury-vapor  lamps. 


Fig.  2.-I<ocomotive  shop  illuminated  by  mercury-vapor  lamps. 


Fig.  3.- Automobile  test  shop  illuminated  by  mereury-vapor  lamps. 


Fig.  4.— Automobile  body  finishing  department  illuminated  by  mercury-vapor  lamps 


n 


Fig.  5._Silk  looms  illuminated  by  mercury-vapor  lamps. 


Fig.  6.— Cotton  warp 


department  illuminated  by  mercury-vapor  lamps. 


Fig.  y.-A  roving  department  illuminated  by  mercury-vapor  lamps 


Fig.  S.-Paper  machine  room  illuminated  by  mercury-vapor  lamps. 


eqt 


Fig.  9  _A  power  plant  illuminated  by  mercury-vapor  lamps. 


Fig.  io 


.-A  plate  glass  inspection  department  illuminated  by  mercury-vapor  lamps. 


Fig.  ii.— Craneway  illuminated  by  mercury-vapor  lamps. 


Fig.  12.— Interior  of  a  moving  picture  studio. 


EVANS:     INDUSTRIAL   UGHTING 


895 


Woolen  and  Worsted. — The  preliminary  operations  in  woolens 
and  worsted  consist  in  scouring  the  wool  to  remove  the  grease, 
then  carding,  combing,  spinning  and  so  forth  in  preparation  for 
the  looms,  simlar  to  other  textile  operations. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.  per  lamp         per  sq.  ft.  Feet 

1.  Carding  and  roving*...  26,000  400  0.30  14 

2.  Carding   6,000  200  0.23  10 

3.  Mule   spinning 5,400  400  0.57  10 

4.  Winding  2,000  200  0.58  10 

5.  Spinning    6,600  200  0.30  10 

6.  Spinning    13,728           200-400  0.53  12 

7.  Winding  6,500  400  0.94  10 

8.  Spinning   26,000  400  0.30  14 

9.  Winding  26,000  400  0.30  14 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  7. 

Weaving. — In  woolen  and  worsted  weaving,  the  amount  of 
light  necessary  and  the  arrangement  is  very  similar  to  that  in 
cotton  mills. 

Total  Watts  Watts         Height 

Class  of  work  sq.  ft.  per  lamp     per  sq.  ft.        Feet 

1.  Weaving 3,75°  4°o  1.13  10      Special  goods 

2.  "  60,000  200  0.64  12 

3.  "  58,880  200  0.78  9 

4.  *'  58,880  200  0.71  9 

Finishing. — The  finishing  operation  is  similar  to  cotton,,  though 
somewhat  more  exacting. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.         per  lamp  per  sq.  ft.  Feet 

1.  Finishing 2,670  200  0.43  10 

2.  "  2,375  200  0.57  10 

3.  "  6,600  200  0.35  10 

Knitting  Mills. — In  knitting,  the  preliminary  operations  are 
similar  to  those  in  woolen  manufacturing  and  the  data  given 
above  will  cover  these.  After  the  wool  is  wound  on  the  bobbins, 
it  is  placed  in  the  knitting  machines,  and  worked  up  into  the  de- 
sired form. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft  per  lamp         per  sq.  ft.  Feet 

1.  Knitting  machines 6,500  400  0.94  10 

2.  *'  4,600  200  0.67  10 

3.  "  15,000  200  0.56  11 


Watts 

Watts 

Height 

per  lamp 

per  sq.  ft. 

Feet 

400 

1-33 

IO 

400 

0.94 

IO 

200 

0.43 

12 

896     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

Stitching  Department. — After  the  goods  are  taken  off  the  ma- 
chines, it  is  necessary  to  inspect  carefully  and  sew  up  the  defects. 
This  is  done  in  the  stitching  departments. 


Class  of  work  Total  sq.  ft. 

i.  Stitching  machine    5,200 

2.  Stitching  machine    6,500 

3.  Cutting  room 4,5°o 

Embroidery  Plants. — Embroidery  machines  can  be  satisfac- 
torily lighted  by  providing  sufficient  general  illumination  to  ade- 
quately light  all  parts.  The  machines  are  about  30  to  40  feet 
(9.14  to  12.19  m.)  long  and  lamps  are  generally  placed  directly 
over  them. 

The  working  out  of  the  patterns  is  accomplished  by  means  of 
a  pantagraph.  On  most  machines  this  is  guided  by  hand,  though 
in  some  large  plants  it  is  operated  automatically. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.  per  lamp         per  sq.  ft.  Feet 

1.  Automatic  machine   19,200  400  0.95  14 

2.  Hand  machines 2,400  200  2.00  10 

3.  Hand  machines 2,750  200  0.98  9 

NEWSPAPER  AND  PRINTING  PLANTS. 

The  illumination  of  newspaper  and  printing  plants  covers  the 
lighting  of  composing  room,  stereotype,  press  and  mailing  rooms, 
all  of  which  will  be  treated  separately. 

Composing  Rooms. — In  a  number  of  composing  rooms,  the 
make-up  tables  are  equipped  with  inverted  V-shaped  racks  placed 
over  the  tables,  and  200-watt  mercury-vapor  lamps  are  placed  in 
under  these  racks. 

For  other  tables  and  banks,  lamps  are  hung  directly  from  the 
ceiling,  and  provide  general  illumination  throughout  the  room. 
Linotype  machines  are  lighted  by  overhead  lamps  to  cover  the  re- 
pairs to  the  mechanism,  but  small  individual  lamps  must  be  placed 
on  each  machine  to  light  the  slugs. 


EVANS:     INDUSTRIAL   UGHTING 


897 


Class  of  work 
Newspaper  composing 


Printing  plant 


1. 
2. 

3- 

4- 

5- 

6. 

7.  Newspaper  composing 

8. 

9- 

10.  Printing  plant 

11.  Newspaper  composing 
12. 

13. 

14.  Linotype  machines  •  • . 


Total 
sq.  ft. 

2,515 
6,075 
9,400 
3,120 
12,400 
6,085 
6,300 
480 

3.430 
I,2l8 

1,200 
1,480 

3,500 
2,205 


Watts 

Watts 

per 

per 

Height 

lamp 

sq.  ft. 

Feet 

400 

2-3 

12 

.400 

I-5I 

12 

200-400 

0.72 

14 

Incl.  linotypes 

200-400 

I.84 

IO 

200-400 

I.92 

9 

200-400 

i-45 

10 

200 

1.47 

8 

200 

3-2 

6 

Rack  lighting 

20O 

2.4 

8-12 

200 

1.58 

9 

200 

i-55 

11 

200 

1.70 

10 

200 

1.70 

10 

400 

0.70 

12 

Supplemented    by 
individual  lamps 
on  machines. 

Stereotype  Room. — After  the  forms  are  made  up  in  the  com- 
posing room,  impressions  are  made  of  them  on  the  matrix,  and 
this  is  taken  to  the  stereotype  room  where  the  cylinders  are  cast 
from  them  to  go  on  the  presses.  This  lighting  is  somewhat 
similar  to  that  of  machine  shop  lighting,  as  the  plates  also  have 
to  be  trimmed  and  cut  to  size. 


Class  of  work 

Total  sq.  ft. 

Watts 
per  lamp 

Watts 
per  sq.  ft. 

Heigh 
Feet 

I. 

400 

I.03 

12 

2. 

(i 

I,000 

400 

O.77 

IO 

3- 

4- 

11 
11 

2,4IO 
880 

200 
200 

O.48 
O.44 

IO 
16 

Press  Rooms. — Press  rooms  have  been  lighted  either  by  general 
illumination  or  by  placing  lamps  directly  on  the  presses  in  news- 
paper work,  or  by  a  combination  of  the  two  methods. 


Class  of  work 
i.  Newspaper  presses 
2. 

3- 

4- 

5- 


Magazine  presses . . 
Newspaper  presses 


6. 

7- 

8.  Job  presses 

9.  Newspaper  presses  • 

10.  Small  power  presses. 

11.  Hand  presses 12,100 

12.  Paper  handling  mach 


Total 
sq.  ft. 

Watts 
per 
lamp 

Watts 

per 

sq.  ft. 

Height 
Feet 

6,000 

400 

O.83 

14 

I,000 

400 

i-54 

15 

9,800 

400 

o.55 

15 

7,980 

400 

0.48 

IO 

4,000 

200 

1.05 

8-15 

Some  lamps 
presses 

7,320 

200 

0.84 

8-14 

«( 

2,875 

200 

0.94 

IO 

650 

400 

1. 19 

12 

5,150 

200-400 

0.82 

27 

7,728 

400 

1.82 

IO 

Engraving  pr 

I2,IOO 

400 

i-95 

IO 

" 

7,250 

200 

o.53 

9 

898     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Mailing  Room. — The  work  in  the  mailing  room  consists  of 
wrapping  and  addressing  papers  or  magazines  and  requires  a 
fairly  good  general  illumination. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.         per  lamp  per  sq.  ft.  Feet 

i.  Mailing  department  ••••         4,485  400  0.52  12 

2.  Mailing  department 4,180  200  0.46  10 

PAPER  MANUFACTURING. 
Paper  manufacturing  consists  essentially  of  four  operations: 
the  grinding  room  where  the  wood  is  ground  up,  the  beater  room 
where  the  pulp  is  mixed,  the  machine  room,  and  for  high  grade 
paper  manufacturing,  the  calendar  room,  which  is  equipped  with 
machines  for  putting  on  the  finish.  Not  a  great  deal  of  light  is 
necessary  to  see  these  different  operations  as  not  many  of  them 
are  particularly  fine  work,  but  sufficient  illumination  must  be  pro- 
vided to  obviate  any  possibility  of  accidents. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.         per  lamp         per  sq.  ft.  Feet 

1.  Grinding  room  2,400  400  0.50  20 

2.  Beater  room  9,000  200  0.13  10 

3.  Machine  room*   8,000  200  0.38  10 

4.  Machine  room   4,000  725  0.35  30 

5.  Machine  room   3,040  200  0.63  12 

6.  Calendar  room  5,615  400  0.50  10 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  8. 

CLOTHING  MANUFACTURING. 
In  clothing  manufacturing  certain  processes  have  been  satis- 
factorily lighted  by  mercury-vapor  lamps.  A  large  quantity  of 
light,  however,  is  necessary  to  properly  see  the  texture  of  the 
goods,  especially  in  the  pressing  where  one  400-watt  lamps  is 
generally  placed  over  each  pressing  table. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.         per  lamp         per  sq.  ft.  Feet 

i.  Cutters   . ..- 448  400  1.72  10 

2.  Hand  sewing   5,400  400  0.74  10 

3.  Pressing  4,500  400  1.60  10 

4.  Pressing  1,650  400  0.95  10 

5.  Pressing  880  400  2.19  10 

6.  Pressing  2,445  400  1.64  IX 

POWER  HOUSE  LIGHTING. 
Power  house  lighting  covers  the  illumination  of  the  boiler 
rooms  and  engine  and  generator  rooms.    In  the  boiler  rooms  gen- 


EVANS:     INDUSTRIAL,   UGHTING 


899 


eral  illumination  is  provided  for  the  aisles  with  small  individual 
lamps  placed  at  the  gauge  glasses.  While  in  the  engine  and  gen- 
erator rooms,  individual  lamps  in  some  cases  are  used  in  and 
under  the  engines.  The  amount  of  illumination  is  generally  not 
very  high. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.  per  lamp  per  sq.  ft.  Feet 

1.  Boiler  room  12,985  200  0.60  18 

2.  Boiler  room  8,945  200  0.64  18 

3.  Boiler  room  12,670  200  0.58  16 

4.  Boiler  room  18,000  400  0.17  40 

5.  Boiler  room  7,065  400  0.27  20 

Engine  and  Generator  Rooms. 

1.  Turbine  room 20,000               725  0.25               46 

2.  Turbine  room 27,000               725  0.24              85 

3.  Turbine  room 10,500               725  0.2 1               81 

4.  Sub-station  4,200               400  0.64               25 

5.  Turbine  room 13,980               400  0.33               40 

6.  Turbine  room* 27,000               400  0.17               18 

7.  Engine  room   10,470               400  0.22              32 

8.  Turbine  room 25,345  200-400  0.49  18-45 

9.  Engine  room    8,100               200  0.24               14 

10.  Engine  room    13,200               400  0.58  30-75 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  9. 

GLASS  MANUFACTURING. 
The  operations  in  glass  manufacturing  which  have  been  suc- 
cessfully lighted  by  mercury-vapor  lamps  are  all  grades  of  in- 
spection, the  grinding  and  polishing  and  similar  operations  of  plate 
glass,  machine  cutting  and  engraving  of  cut  glass.  The  latter  and 
inspection  requires  extremely  good  illumination. 

Watts  Watts  Height 

Class  of  work  Total  sq.  ft.  per  lamp        per  sq.  ft.  Feet 

1.  Lehr  inspection 384  400  2.00  12 

2.  Polishing   and   grinding  11,890  400  0.71  22 

3.  Polishing  and   grinding  42,000  725  0.38  36 

4.  Stripping    11,890  400  0.71  15 

5.  Laying  7,680  400  1.10  15 

6.  Final  inspection* 3,000  400  1.28  10 

7.  Machine  cutting 10,300  400  0.85  12 

8.  Engraving   600  400  5.00  12 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  10. 

SHIPPING  AND  STORAGE. 
Practically  all  manufacturing  plants  have  shipping  and  storage 
departments,  and  while  in  a  great  many  cases  where  there  are  high 


900     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

bins  mercury-vapor  lamps  on  account  of  the  size  may  not  be  avail- 
able, still  in  numerous  cases  they  have  been  successfully  used  for 
storage  and  for  shipping  and  similar  departments. 

Class  of  work  Total  sq.  ft.  peTtp        pJSfft  *&£' 

i.  Warehouse  i4)6oo  200  0.24  10 

2.  Shipping  platform 1,000  200  0.96  8 

3.  Freight  house 76,000  200  0.20  8-10 

4.  Freight  house 14,400  200  0.32  8-10 

5.  Freight  house 9,600  200  0.24  10-12 

6.  Shipping  dept 7,800  400  0.49  12 

7.  Craneway*    33j6oo  725  0.25  80 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  n. 

MOTION  PICTURE  STUDIOS. 

Whether  motion  picture  studios  may  be  termed  industrial  plants 
is  somewhat  open  to  discussion,  but  it  is  in  the  studio  that  the 
first  operation  in  the  manufacture  of  the  film  is  performed, 
and  as  mercury-vapor  lamps  are  extensively  used  for  this  class 
of  work,  data  regarding  them  may  be  of  interest. 

As  far  as  is  known,  there  are  in  the  United  States  about  50 
studios  using  artificial  light  for  the  taking  of  motion  pictures. 
Of  these  43  are  using  mercury-vapor  lamps  either  entirely  or  in 
combination  with  other  systems.  Nearly  all  of  them  use  at  least 
one  or  two  large  arc  lamps  to  obtain  special  lighting  effects.  The 
data  furnished  below  do  not  take  into  account  the  energy  con- 
sumed by  these  arcs. 

Watts  per 
,  sq.  ft.  of  floor 

IS  umber  stages       Watts  per  lamp  area  illuminated         Height,  Feet 


I 
2 

3 
4 

5 

6 

7 
8 

9 

10 


4                             400  100.0  8-16 

1  725-400  65.0  8-10 

1  725-400  47.0  8-15 

2  4oo  128.0  8-14 
2  400  100.0  8-15 
1  4oo  83.0  8-12 
1  400  99.0  8-13 
1  400  104.0  8-13 
1           400  89.0  8-12 

i-I2 


1  400  85.0 

*  A  night  photograph  of  this  installation  is  shown  in  Fig.  12. 


EVANS:     INDUSTRIAL   LIGHTING  901 

MISCELLANEOUS  INDUSTRIES. 
In  addition  to  the  data  given  in  the  previous  tables,  there  have 
been  obtained  information  relative  to  the  lighting  of  certain  oper- 
ations in  other  industries  which  are  all  grouped  under  the  head- 
ing of  miscellaneous  industries. 

Illum'd.       Watts      Watts  per     Height 
Plant  Operation  sq.  ft.      per  lamp        sq.  ft.  Feet 

1.  Rubber  Rubberizing  cloth  •  •  4,550  200-400  0.46  16 

2.  Steel  Rolling  mill 24,000        400  0.20  15 

3.  Metal  fur.  Finishing 9,405        4°o  0.49  12 

4.  Metal  boats                  "  16,900        400  0.36  14 

5.  Hatmfg.  Sizing  room 7,240        400  0.64  12 

6.  Shoemfg.  Cutting 870  200-400  3.12  10 

7.  Copper  refg.  Electrolytic  room ••  •  86,400        725  0.18  29 

8.  Metal  plant  Electroplating 8,340        200  1.00  11 

9.  Copper  refg.  Grind'g  and  crush'g  4,500        200  0.13  40 

10.            "  Concentrating 8,000        200  0.14  12-16 

TI-            "  Jigs 10,000        200  0.15  18-28 

12.  Powder  mfg.     Pressroom 1,200        400  1.00  9^ 

13.  Sugar  plants    Inspection  dept. 200  One  for  ea  insp.  8 

14.  Ivory  plants      Sorting  dept 200        "  sorter  8 

CONCLUSIONS. 

The  data  furnished  in  this  paper  have  been  the  result  of 
practically  twelve  years  use  of  mercury-vapor  lamps  in  the  in- 
dustrial field.  While  the  figures  vary  somewhat  for  the  same 
class  of  work,  it  might  be  said  that  this  condition  depends  to  a 
certain  extent  on  the  state  of  mind  of  the  different  plant  man- 
agers. Some  appreciate  the  fact  that  up  to  a  certain  limit  they 
cannot  have  too  much  light  to  produce  the  best  results  and  look 
upon  good  lighting  as  an  asset;  whereas  others  feel  that  they 
wish  to  get  along  with  as  little  light  as  possible,  and  feel  that  light 
is  merely  a  necessary  evil  which  must  be  used. 

By  using  the  figures  given  there  is  no  doubt  but  what  the  plant 
engineer  of  any  concern  desirous  of  using  mercury-vapor  lamps 
will  be  able  to  estimate  fairly  accurately  the  amount  of  light  that 
may  be  needed  for  different  operations. 

In  designing  a  good  industrial  lighting  system,  the  following 
points  should  be  borne  in  mind.  Provide  an  illumination  that  will 
not  dazzle  the  eyes  of  the  operatives,  one  with  a  low  intrinsic 
brilliancy  and  with  as  little  glare  as  possible  that  will  be  easy  on 
the  eyes  of  the  operatives  and  thoroughly  diffused,  all  of  which 


902     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

will  tend  to  prevent  accidents  and  safeguard  the  health  of  those 
working  under  it. 

The  system  of  lighting  should  be  installed  with  the  idea  of  pro- 
ducing the  greatest  quantity  of  goods  of  the  best  quality,  in  other 
words,  design  the  lighting  not  with  the  idea  of  the  "proximate" 
efficiency  of  the  lighting  unit,  but  with  the  "ultimate"  efficiency  of 
the  plant. 

BIBLIOGRAPHY  ON  ARTICLES  DEALING  WITH  MERCURY- 
VAPOR  LAMPS  FOR  INDUSTRIAL  LIGHTING. 

Allen,  F.  B. 

Important  Considerations  in  Factory  Lighting. 
Electric.  Review,  Aug.  2,  191 1. 

Bell,  Louis. 

Chromatic  Aberration  and  Visual  Acuity. 
Electrical  World,  May  11,  191 1. 

Clover,  G.  R. 

Lighting  a  Stock  Room. 
111.  Eng.,  vol.  6,  No.  12. 

Evans,  W.  A.  D. 

Illumination  of  a  Large  Foundry. 

111.  Eng.,  vol.  5,  No.  11 
Lighting  Problems  in  the  Automobile  Industry. 

111.  Eng.,  vol.  6,  No.  10. 
Lighting  a  Large  Power  House. 

111.  Eng.,  vol.  6,  No.  1. 
Illuminating  a  Newspaper  Printing  Office. 

111.  Eng.,  vol.  5,  No.  12. 
Illumination  of  a  Glass  Factory. 

Elect.  Review,  July  10,  1915. 
Light  as  a  Factor  of  Efficiency. 

Textile  World  Record,  Nov.  and  Dec,  19 14. 
The  Mercury-vapor  Quartz  Lamp. 

Paper  presented  before  I.  E.  S.,  Sept.  22,  1913. 
Artificial  Lighting  of  Motion  Picture  Studios. 

111.  Eng.,  London,  June,  1915. 

Fortune,  F.  R. 

Foundry  Lighting. 

Haviland,  F.  M. 

The  Light  for  the  Printer. 
Inland  Printer,  Jan.,  1914. 


EVANS:     INDUSTRIAL   LIGHTING  903 

Hubbard,  A.  S. 

Lighting  an  Embroidery  Shop. 

111.  Eng.,  May,  191 1. 
Mercury -vapor  Lamps  in  the  Textile  Industry. 

111.  Eng.,  vol.  3,  No.  9. 
Illumination  of  a  Cotton  Mill. 

111.  Eng.,  vol.  5,  No.  7. 
Cooper  Hewitt  Lamps  in  a  Silk  Mill. 

American  Silk  Journal,  May,  1908. 
Lighting  the  Stehli  Plant  at  Lancaster. 
American  Silk  Journal,  Sept.,  1908. 
Hubbard,  W.  C. 

Three  Interesting  Problems  in  Industrial  Illumination. 
111.  Eng.,  vol.  6,  No.  2. 
Keech,  G.  C. 

Carefully  Planned  Factory  Lighting. 

Mfrs.  News,  Nov.  5,  1914. 
Quartz  Tube  Lamp  in  Railroad  Service. 

Before  Electric  Club  of  Chicago,  Nov.  14,  1912. 
Knapp,  S.  H. 

Lighting  of  Erecting  and  Heavy  Machinery  Shop. 

R.  R.  Age  Gazette. 
Modern  Artificial  Lighting. 

Knit  Goods,  Jan.  and  April,  191 1. 
Morrison,  D.  P. 

Railway  Classification  Yard  Lighting. 

Proceedings  of  Eng.  Society  of  Western  Pa.,  Oct.,  1914. 
Wade,  F.  K. 

Lighting  Problems. 
Silk,  March,  191 1. 
Walker,  G.  W. 

Artificial  Illumination  of  a  Modern  Machine  Tool  Plant. 
111.  Eng.,  vol.  6,  No.  11. 


904    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

DISCUSSION. 

Mr.  R.  B.  Ely:  Several  questions  have  occurred  to  me  in 
reference  to  the  use  of  mercury-vapor  lamp,  particularly  where 
it  is  used  around  iron  and  steel  works.  There  are  a  great  many 
markings  on  the  iron  which  indicate  the  relative  positions  for 
placing  the  various  pieces  together,  etc.,  and  I  was  wondering 
whether  the  red  chalk  or  red  paint  marks  would  show  dis- 
tinctly under  the  light  from  this  lamp.  I  know  there  has  been 
some  trouble  experienced  in  determining  red  markings,  the  red 
pencil  marks  on  packing  cases  calling  attention  to  special  ship- 
ments, for  instance.  The  red  might  appear  black  under  a  mer- 
cury-vapor light.  Now  on  an  iron  surface  would  the  red  chalk 
marks  show  up  at  all,  or  would  they  appear  of  a  different  color? 

Mr.  W.  A.  D.  Evans  (In  reply)  :  The  red  chalk  marks  would 
not  appear  a  bright  red  under  the  mercury-vapor  lamp,  but  will 
appear  a  dark  brown.  With  a  little  practise,  however,  one  could 
very  easily  differentiate.  We  use  the  mercury-vapor  lamps  in 
our  office  and,  of  course,  in  our  ledgers  both  red  and  black  ink 
are  used  to  indicate  different  accounts,  and  the  clerks  do  not 
have  any  difficulty  in  distinguishing  one  from  the  other,  and  I 
know  the  same  condition  occurs  in  other  cases. 


benford:   the  parabolic  mirror  905 

THE  PARABOLIC  MIRROR.* 


BY  FRANK  A.  BENFORD,  JR. 


Synopsis:  The  following  discussion  of  the  parabolic  mirror  is  divided 
into  two  main  sections,  one  devoted  to  such  mirrors  with  a  spherical  light 
source  and  the  other  devoted  to  mirrors  reflecting  light  from  a  disk  source. 
These  two  types  of  sources  are  ideal  cases  of  incandescent  and  arc  lamps, 
respectively.  Preceding  the  two  main  sections  a  short  discussion  of  a 
parabolic  mirror  with  a  point  source  is  given.  In  ordinary  photometry 
the  fiction  of  a  "point  source"  is  highly  useful  and  may  usually  be  used 
without  question  as  to  its  accuracy.  However,  all  present  known  light 
sources  fall  far  short  of  performing  as  a  "point  source"  when  placed  at 
the  focal  point  of  a  parabolic  reflector. 


A  searchlight,  or  headlight,  consists  of  a  source  of  light,  usually 
of  small  area  and  high  brilliancy,  placed  at  the  focal  point  of  a 
parabolic  mirror,  or  some  nearly  equivalent  form  of  reflector. 
There  is  an  extremely  large  number  of  uses  that  may  be  found 
for  an  intense  beam  of  light  of  small  angular  width.  In  military 
and  naval  service,  in  all  types  of  navigation,  and  in  nearly  every 
type  of  land  transportation,  the  searchlight  and  headlight  play  a 
highly  important  part.  There  is  also  a  large  field  for  the  search- 
light in  flood  lighting  and  spectacular  work.  In  all  of  these 
various  types  of  service  the  principles  of  design  are  the  same, 
and  the  difference  between  one  searchlight  and  another  is  a  differ- 
ence in  degree,  not  in  principle. 

SYMBOLS. 
F — focal  length  of  mirror,  in  inches. 
D — diameter  of  mirror,  in  inches. 
R — radius  of  mirror,  in  inches, 
r — radius  of  light  source,  in  inches, 
m — coefficient  of  reflection  of  mirror, 
s — area  of  light  source,  in  square  inches. 
Ia — intensity  of  light  source  at  angle  a  from  axis  of  mirror,  in  international 

candles. 
Ib — intensity  of  beam,  in  international  candles. 
B — brilliancy  of  light  source,  in  candles  per  square  inch. 
L — distance  from  focal  point  to  point  in  beam,  in  feet. 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,   Washington,   D.   C,    September  20-23,    1915. 

The   Illuminating   Engineering    Society   is   not   responsible   for   the   statements    or 
opinions  advanced  by  contributors. 


906     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

A — area  illuminated,  in  square  feet. 

E— illumination  on  a  plane  normal  to  beam,  in  foot-candles. 
Q — light  flux,  in  lumens. 

a — angles  measured  about  the  focal  point  of  mirror,  in  degrees, 
b — beam  angles  measured  from  the  axis  of  mirror,  in  degrees, 
e — angle  subtended  by  the  radius  of  the  source  at  any  point  on  the  mirror 
in  degrees. 

PARABOLIC  MIRROR  AND  POINT  SOURCE. 
In  all  that  is  to  follow,  the  mirror  is  assumed  to  be  ideal  in 
form.    The  variations  that  occur  in  practice  represent  manufac- 
turing problems  and  difficulties  and  need  not  be  considered  here. 


\  1 

a 
i 

t 
C 

I 

\ 

/ 

\ 

Figs,  i  and  2. — Parabolic  mirror  ;  equation  of  generating  curve. 

The  parabolic  curve  from  which  the  parabolic  mirror  is  gene- 
rated by  rotating  the  curve  about  its  axis  has  for  its  equation 
either 

y  =  4** (o 

the  rectangular  form,  see  Fig.  i,  or 

2F 


(2) 


1  +  cos  a 
the  polar  form,  see  Fig.  2. 

Using  the  rectangular  form  of  equation,  we  have 

y  =  4F* 

and  the  slope  of  the  line  drawn  tangent  to  the  parabola  at  point 
P,  Fig,  3,  is 

dy  _      2F 

dx  y 


=  tan  c, 


(3) 


benpord:   the  parabolic  mirror 


907 


(6) 
(7) 


The  slope  of  the  normal  to  the  curve  at  this  point  is 

J?L  =  -  -*-  =  tan  e (4) 

~~    dy  2F 

From  the  figure,  light  emitted  from  the  focus  follows  the  line 
OP,  and 

y  co 

tan  a  =  ^^j^ 

a  _j_  c  +  d  =  180 

tan  (a  +  c)=  tan  (180  -  d)  =  tan  d 

and  from  (3),  (5)  and  (7),  we  obtain 

tan^-f    (») 

From  the  law  of  reflection  of  light,  we  have 

d'  =  d, 
and,  therefore,  as  tan  c  and  tan  d  are  numerically  equal, 

d'  =c 

and  the  reflected  ray  PC  is  parallel  to  the  axis. 


(9) 


Figs.  3  and  4.— Parabolic  mirror  and  point  source. 


A  beam  of  light  made  up  of  rays  such  as  PC  would  form  a 
true  cylinder  of  unvarying  diameter.  Each  ray  would  pursue  an 
independent  path  parallel  to  all  the  other  rays,  and  hence,  the 
intensities  of  flux  found  in  any  cross  section  of  the  beam  would 
be  identical  with  the  intensities  in  all  other  cross  sections.    It  is 


908    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

obvious  that  in  this  case  we  may  find  the  flux  density  or  illumina- 
tion at  any  point  of  the  beam,  but  we  may  not  assign  any  candle 
intensity  to  it.  The  beam  has  some  of  the  properties  of  a  beam 
coming  from  an  intense  source  at  an  infinite  distance.  These 
conditions  are  as  physically  impossible  as  the  "point  source"  that 
was  assumed  in  the  beginning. 

It  may  be  shown  that  the  flux  intensity  in  any  section  of  the 
beam  db,  Fig.  4,  is  equal  to  the  flux  intensity  at  a  distance  p  from 
the  source  before  reflection  takes  place. 

Let  a  small  area  dA  on  the  surface  of  the  mirror  be  illuminated 
from  a  point  source  at  the  focal  point.  The  cone  of  light  striking 
this  area  has  an  angle  of  incidence  ix,  as  shown  in  Fig.  4.  The 
spherical  area  of  this  cone  at  the  radius  p  is 

ds  —  dA  cos  ix  square  inches    (10) 

The  right  section  of  the  reflected  beam  has  an  area 

db  =  dA  cos  i2  square  inches (11) 

and  as  r,  =  z2  degrees (12) 

db  =  ds  square  inches (13) 

The  areas  db  and  ds  contain  the  same  quantity  of  light,  AQ, 
and,  therefore,  the  density  is  the  same. 

The  intensity  of  radiation  at  radius  p  is 

E  =  —  foot-candles (14) 

p'  =y  +  (F  —  x)\  from  Fig.  1. 
=  4F*  +  F2  —  2F*  +  x2 
=  F2  +  2F*  +  x*  =  (F  +  x)2  inches2 (15) 

E  =  (F  +  xy  foot-candles (16) 

and  with  a  mirror  having  a  coefficient  of  reflection  m  the  beam 
intensity  is 

E  =  (p^  xy  foot-candles ( i7) 

In  Fig.  5  the  beam  intensities  are  plotted  for  a  source  having 
a  uniform  intensity  of  one  candle  in  three  typical  18-inch  (45.7 
cm.)  mirrors.  The  angular  openings  of  the  mirrors  are,  measur- 
ing from  the  axis,  6o°,  900  and  1200. 


benford:    the  parabolic  mirror 


909 


PARABOLIC  MIRROR  AND  SPHERICAL  SOURCE. 
In  solving  for  the  beam  characteristics  of  a  spherical  source  in 
a  parabolic  mirror,  it  is  necessary  to  make  the  assumption  that 
the  distance  across  the  mirror  is  very  small  in  comparison  to  the 
distance  out  along  the  axis  of  the  beam  where  the  intensities  are 
to  be  calculated.  The  effect  of  distance  on  the  apparent  intensity 
of  the  beam  will  be  taken  up  later. 


K\ 

!\\   ! 

1  \!\l 

\      vs 

1 

\ 

V* 

y 

9 

■^^ 

i 

1 

1 

1 4 

1 

, 

0 

l/f] 

VI 

r~~  CJ^SV^X-^S  . 


Fig.  5.— Parabolic  mirror  and  point  source  beam  characteristics. 


Fig.  6.— Parabolic  mirror  and  spherical  source. 

In  Fig.  6,  two  small  sections  of  the  mirror,  Px  and  P2,  reflect 
two  rays  which  at  a  considerable  distance  from  the  mirror  will 
overlap.  If  the  distance  is  great  enough  the  areas  A1  and  A2 
become  very  large  and  the  distance  2y  between  their  centers  may 
be  neglected. 


9IO     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Assume  the  plane  area  of  a  great  section  of  the  spherical  source 
to  be  j  square  inches,  then  the  areas  Ax  and  A2  are  found  by  the 
proportion 

or  A  =sf — J    square  feet (18) 

The  shaded  section  of  mirror,  Fig.  6,  may  be  considered  as  a 
ring  of  small  elements  Plf  P2,  etc.,  all  at  the  same  distance  P  from 
the  focus. 

The  quantity  of  light  reflected  from  the  ring  is 

AQ  =  2TrmI  sin  a  Aa  lumens (19) 

I  is  the  intensity  of  the  source,  assumed  to  be  equal  in  all  direc- 
tions, and  m  is  the  coefficient  of  reflection  of  the  mirror. 

The  illumination  from  the  ring  is 

A 

2irml  sin  a  Aa  . 

foot-candles (20) 


<¥)' 


From  equation  (2) 


2F 

P  = 


1  -f  cos  a 


and 

877-wIF2  sin  a  Aa 


AE  = 


sV(i  +  cos  a)' 


-  __  87rwIF'l        sin  a  da 


sV        \      (l+COStf)2 

_4ttwIF2        2     . 
—  ~7l7 — tan    H«n  foot-candles (21) 

This  is  one  form  of  the  equation  for  the  central  density  of  a 
beam  from  a  spherical  source  and  a  parabolic  mirror.  With  a 
fixed  focal  length,  the  intensity  varies  as  the  square  of  the  tangent 
of  half  the  angle  alt  or  given  a  fixed  angular  opening,  the  inten- 
sity varies  as  the  square  of  the  focal  length. 


benford:    the  parabolic  mirror 


911 


We  may  write 


—  =  B 
s 


(22) 


the  brilliancy  in  candles  per  square  inch,  then  (21)  becomes 

4irwBF2 


V 


tan2  y2a1  foot-candles. ...  (23) 


This  equation  is  particularly  valuable  as  it  shows  that  the  inten- 
sity at  the  center  of  the  beam  depends  upon  the  brilliancy  of  the 
light  source  and  is  independent  of  the  size  of  the  luminous  sphere. 
This  has  an  important  bearing  on  the  design  of  incandescent  fila- 
ments for  searchlights,  etc. 

The  above  equation  may  be  written 
twiBR2 


E  = 


L2 


foot-candles  (24) 


g 

£ 

-p 

t 

? 

\s> 

C*7f*£*£-  £-^ 


Fig.  7. — Parabolic  mirror  and  spherical  source  beam  characteristics. 


The  focal  length  does  not  enter  into  equation  (24),  and  this 
brings  out  the  highly  interesting  fact  that  all  parabolic  mirrors 
having  the  same  diameter  should  give  the  same  illumination  at 
points  on  the  axis.  The  difference  in  action  between  a  shallow 
and  deep  reflector  is  shown  in  Fig.  7,  where  the  beam  intensities 
of  three  18  in.  (45.7  cm.)  mirrors  of  different  focal  lengths  are 
plotted.  The  same  source,  having  a  uniform  brilliancy  of  1,000 
candles  per  square  inch  and  a  diameter  of  0.5  in.  (1.27  cm.),  is 
used  in  all  three  mirrors. 


912     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  two  latter  equations,  by  a  simple  transformation,  may  be 
used  to  calculate  the  candle  intensities  on  the  axis. 

Ib  =  4twBF2  tan2  y^  ax  candles (25) 

and  Ib  =  7rR2Bw     candles (26) 

The  last  equation  states  that  the  intensity  of  a  searchlight  beam 
is  equal  to  the  product  of  the  brilliancy  of  the  source,  the  plane 
area  of  the  mirror  and  the  coefficient  of  reflection. 


3^' 

i ::  :~:~t\  :::: :: :: :: :__ 

I     U-^ 

t_  \>^ 

3      \  _^ __ 

N            \ 

:" :::::::::  ::v: :: ::  :vi:~ 

A.          A                  A 

Fig.  8. — Parabolic  mirror  and  spherical  source.    Angular  width  of  beam  from 
different  radii  on  mirror. 

The  intensities  at  points  not  on  the  axis  of  the  beam  may  be 
found  by  the  use  of  (26)  and  the  following  relations: 

The  apparent  angular  radius  of  the  source  viewed  from  the 
central  point  on  the  mirror  is 


e0  =  tan" 


Po 


tan" 


_I  -=%■  degrees 

V 


(27) 


At  other  points  on  the  mirror  we  have  as  a  good  approximation 


Po     , 

e  =  e0  —  degrees 
P 


(28) 


The  light  incident  upon  the  center  of  the  mirror  has  the  greatest 
spread  and  is  distributed  throughout  the  entire  beam.  The  light 
from  the  edges  of  the  mirror  is  concentrated  within  a  smaller 
angle  and  this  light  forms  the  center  of  the  beam.  By  noticing 
the  angle  of  spread  at  different  parts  of  the  mirror,  the  area 
covered  by  any  section  may  be  readily  obtained. 

Values  of  (28)  for  the  three  mirrors  of  Fig.  7  are  given  in 
Fig.  8.  The  angle  of  spread  of  the  beam,  b,  is  equal  to  the  angle 
subtended  by  the  source,  e. 


benford:    the  parabolic  mirror  913 

The  curves  in  Fig.  8  may  be  interpretated  as  follows :  Suppose 
an  observer  to  stand  at  a  considerable  distance  from  mirror  C 
and  slowly  approach  the  axis  of  the  beam.  When  he  reaches  a 
point  5. 50  from  the  axis  the  center  of  the  mirror  will  become 
visible.  At  a  point  50  from  the  axis  the  luminous  spot  will  be 
1.7  in.  in  radius.  The  luminous  area  will  continue  to  grow  until 
the  observer  reaches  a  point  1.380  from  the  axis  when  the  entire 
mirror  will  be  covered.  From  this  point  to  a  similar  point  1.380 
on  the  opposite  side  of  the  axis,  the  area  and  the  total  apparent 
beam  intensity  will  remain  constant,  and  from  this  point  the 
luminous  area  will  appear  to  decrease  until  the  observer  steps 
out  of  the  beam  at  5. 50. 

It  is  rather  difficult  to  actually  observe  the  action  of  the  lumi- 
nous spot  on  the  mirror  as  outlined  above  on  account  of  the 
great  distance  at  which  the  observer  must  stand.  At  an  insuffi- 
cient distance  the  mirror  will  first  appear  luminous  at  the  center 
and  the  edge  nearest  the  observer.  These  two  spots  will  merge 
and  form  an  oval  area  that  gradually  approaches  the  size  of  the 
mirror  as  the  observer  comes  up  to  the  axis  of  the  beam. 

Under  ideal  conditions  the  area  of  the  mirror  that  is  active  is 
found  from  (28),  and  this  area  substituted  in  (26)  gives  the 
beam  intensity  at  the  beam  angle  b. 

The  illumination  curves  in  Fig.  5  seem  to  differ  in  practically 
every  respect  from  the  beam  intensity  curves  in  Fig.  7.  If  foot- 
candle  readings  are  taken  very  close  to  the  surface  of  the  mirror 
of  Fig.  7  the  illumination  curves  will  be  found  to  approach  the 
point  source  curves  in  form.  The  two  sets  of  curves  represent 
the  conditions  at  opposite  ends  of  the  beam.  Between  these  two 
extremes  of  distance,  zero  and  infinity,  the  beam  undergoes  a 
gradual  transformation,  and  it  is  in  this  region  of  transformation 
that  our  practical  interest  is  centered. 

When  tests  are  made  to  determine  the  beam  characteristics  of 
a  searchlight  one  of  the  first  questions  that  comes  up  is  the 
question  of  the  proper  testing  radius.  It  is  well  known  that  the 
apparent  intensity  and  angular  spread  of  the  beam  may  vary  at 
different  distances,  and  that  tests  made  at  relatively  short  dis- 
tances are  unreliable. 

One  of  the  most  desirable  conditions  of  a  searchlight  test  is 


914     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


that  the  data  may  be  used  to  calculate  illumination  at  various 
distances  by  making  use  of  the  inverse  square  law. 

The  intensity  of  the  beam  has  been  shown  to  be  proportional 
to  the  area  of  the  mirror,  that  is,  with  a  given  source,  all  para- 
bolic mirrors  have  the  same  brilliancy.  Equation  (26)  may  be 
rewritten 


— —  =  mB  candles  per  square  inch 

7rK. 


(29) 


The  beam  candles  divided  by  the  area  of  the  mirror  gives 
mirror  brilliancy 

Bm  =  mB  candles  per  square  inch (30) 

and  it  is  at  once  evident  that  the  beam  has  a  maximum  and  con- 
stant candle  intensity  at  all  points  receiving  light  from  the  entire 
mirror. 


co    /g  /w-s>/rcw 


Fig.  9. — Parabolic  mirror  and  spherical  source.    I,aw  of  inverse  squares. 

Once  the  intensity  reaches  a  constant  value  the  inverse  square 
law  may  be  used  to  calculate  illumination  at  other  distances,  within 
what  is  called  the  inverse  square  region  in  Fig.  9.  The  boun- 
daries of  this  region  are  formed  by  the  rays  from  the  extreme 
edge  of  the  mirror. 

The  angle  which  the  boundaries  make  with  the  axis  may  be 
found  from  equation  (28)  or  calculated  directly. 


tan" 


1  —  degrees 
Pi 


(30 


where  px  is  the  distance  from  the  focus  to  the  edge  of  the  mirror, 
and  the  distance  at  which  these  boundaries  cross  the  axis  is 

ho  —  —  cot  b.  feet (32) 

12 


benford:    the  parabolic  mirror 


915 


The  following  form,  which  is  often  more  convenient,  may  be 
used : 


ho 


»{''+*) 


I2r 


feet 


(33) 


The  way  in  which  the  centers  of  the  beams  from  the  three 
18  in.  mirrors  approach  the  maximum  intensity  is  shown  in 
Fig.  10.  These  curves  were  determined  by  giving  R  various 
values,  and  solving  (33)  for  the  distance  L0  at  which  the  maxi- 
mum beam  candles  would  be  obtained,  and  with  the  same  value 
of  R  solving  (26)  for  the  intensity.  If,  in  place  of  18  in.  mirrors, 
we  had  larger  mirrors  of  the  same  focal  lengths,  the  points  at 


*. 

«>■ 

j 

' 

rr  ff' 

3m 

eao  00c 

■s 

^ 

f 

>, 

b 

\ 

{ 

\  s&o  000 

y 

& 

I  uuu 

'J 

/ 

J 

y 

/ 

/ 

< 

y 

2 

s 

t 

'  V 

* 

,r 

* 

JJ 

A 

/ 

yn 

A 

0 

eo  £5 


Fig.  10. — Parabolic  mirror  and  spherical  source.    Apparent  candles  at  points 
on  axis  of  beam. 

which  the  beams  come  to  full  intensity  could  be  found  by  extend- 
ing the  curves  of  Fig.  10.  An  increase  in  diameter  will  not  affect 
the  axis  intensity  at  points  less  than  L0  because  the  added  zone 
of  mirror  will  reflect  a  beam  from  points  farther  removed  from 
the  axis  and  having  a  smaller  angle  of  divergence,  and  hence,  this 
added  part  of  the  beam  will  reach  the  axis  at  points  beyond  L0 
for  the  18  in.  mirrors. 

It  can  be  shown  that  there  is  considerable  freedom  of  move- 
ment allowed  the  light  source  without  changing  the  central  beam 
intensity.  This  intensity  has  been  shown  to  depend  directly  upon 
the  brilliancy  of  the  source,  and  from  this  we  could  infer  without 
further  proof  that  the  size  and  shape  of  the  source  affects  only 


gib    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

the  width  and  side  intensities  of  the  beam.  The  light  on  the  axis 
comes  from  those  rays  of  the  source  that  pass  through  the  focal 
point.  It  follows  that  the  source  may  have  any  size,  shape  or 
position  whatever,  without  changing  the  central  beam  intensity, 
providing  only  that  every  line  from  the  mirror  through  the  focus 
will  touch  the  light  source. 


"    Fig.  ii. — Parabolic  mirror  and  spherical  source.    Freedom  of  movement  of  source. 

In  Fig.  ii  the  sphere,  which  is  the  source  of  light,  is  shown  in 
two  positions,  Ox  and  02.  An  inspection  of  this  figure  will  show 
that  a  line  from  any  part  of  mirror  A  through  F  will  touch  the 
source  in  either  position,  and  in  all  intermediate  positions.  The 
allowable  movement  either  way  from  the  focus  is  then 

n  =  r  sec  a1  inches    (34) 

As  the  source  is  moved  from  Ox  to  02  the  width  and  shape  of 
the  intensity  curve  will  change,  but  the  intensity  on  the  axis  will 
not  change.  The  point  at  which  the  inverse  square  region  begins 
will  also  shift  as  the  source  moves,  being  closest  when  the  source 
is  at  the  greatest  distance  from  the  mirror. 

With  the  source  in  positions  Ox  or  02,  there  will  be  a  zone  of 
mirror  B  between  Y*1  and  P2  that  will  not  be  active  in  reflecting 
light  to  the  axis.  With  this  mirror,  and  the  deeper  mirror  C,  the 
source  can  be  moved  only  through  its  own  radius, 

or  n  =  r  inches (35) 

PARABOLIC  MIRROR  AND  DISK  SOURCE. 
A  disk,  placed  so  that  its  luminous  side  is  at  the  focal  point 
and  facing  the  mirror,  is  the  ideal  case  of  the  carbon  arc.    The 
intensity  on  the  axis  of  the  beam  is 

IB  =  7rR2Bw  candles    (36) 


bexford:    the  parabolic  mirror 


917 


The  proof  of  this  is  almost  identical  with  that  given  for  a 
spherical  source  and  will  not  be  repeated.  For  points  not  on  the 
axis  the  line  of  reasoning  is  not  so  simple,  however,  because  the 
beam  from  any  small  section  of  the  mirror  is  elliptical  in  section 
and  the  summation  of  these  elliptical  elements  leads  to  compli- 
cated mathematical  forms.  This  is  not  a  serious  matter,  however, 
as  the  chief  interest  of  an  arc  searchlight  attaches  principally  to 
the  central  beam  intensity. 


K 

• 

: 

f. 

1 

bv 

K 

4^ 

1 : 

is 

"  ' 

< 

' 

1 

-r 

LLP* 

\j 

\ 

s^ 

« 

-z 

Fig.  12.— Parabolic  mirror  and  desk  source.    Beam  characteristics.     (Slopes 
approximated) . 

The  width  of  the  crest  of  the  intensity  curve  is  determined  by 
the  angle  subtended  by  the  source  from  a  point  on  the  edge  of 
the  mirror.  From  the  point  P1?  Fig.  12,  the  disk  appears  to  be 
an  ellipse  having  a  major  axis  r,  and  a  minor  axis  r  cos  ax.  The 
cross  section  of  the  beam  from  this  element  is  an  ellipse  having 
the  same  proportions. 

The  angular  half- width  of  the  flat  crest  of  the  curve  is 

b,  ==  tan-  x  -      — -1  degrees (37) 


or 


t>,  =  tan- 


Pi 
r  cos  a1 


degrees 


(38) 


It  has  been  assumed  that  the  disk  is  luminous  on  one  side  only. 
The  part  of  mirror  C  between  900  and  1200  is  not  active.  The 
radius  R  in  equations  (36)  and  (38)  must  in  this  case  be 

2F 

R  = s  =  2F  inches   (39) 

1  —  cos  90 


918     TRANSACTIONS  OF  IEEUMINATING  ENGINEERING  SOCIETY 

The  width  of  the  crest  for  mirrors  B  and  C  is  zero.  This  is 
evident  both  from  the  above  expressions  for  e  and  from  the  fact 
that  the  source  appears  to  be  a  line  when  viewed  from  an  angle 
of  900.  The  overlapping  line  beams  will  give  full  intensity  only 
at  the  common  crossing  point. 

The  maximum  width  of  the  beam  is 


or 


b0  =  tan-1  —  degrees 

Po 


b0  =  tan-1  -=:  degrees 


(40) 


(41) 


The  brightness  of  the  mirror  is  as  before 

Bm  =  wB  candles  per  square  inch (42) 


Fig.  13.— Parabolic  mirror  and  desk  source.    Freedom  of  movement  of  source. 

The  boundaries  of  the  inverse  square  region  make  an  angle 

b,  =  tan-1 degrees (43) 

Pi 
or 

r  cos  a.  ,  , 

bx  =  tan-1 =i  degrees (44) 

with  the  axis. 

The  distance  at  which  these  boundaries  meet  is 

ho  =  —  cot  b1  feet (45) 

or 

R(F  +  a) 

L„  = ^—  feet (46) 

12  r  cos  a. 


benford:    the  parabolic  mirror  919 

Mirrors  having  an  angle  of  900  or  over  do  not  have  an  inverse 
square  region  for  the  rays  from  the  edge  of  the  mirror  are  parallel 
and  do  not  meet. 

The  degree  of  freedom  allowed  a  disk  source  is 

n  =  r  cos  a1  inches (47) 

either  way  from  the  focus.     See  Fig.  13.     The  movement  for  a 
900  mirror  is  zero. 

The  beam  characteristic  at  the  surface  of  the  mirror  does  not 
follow  the  point  source  characteristic  developed  in  the  first  sec- 
tion.   The  intensity  of  radiation  at  angle  a  is 

la  =  Io  cos  a  candles (48) 

and  the  foot-candle  curve  close  to  the  mirror  may  be  found  from 
the  equation 

E  =  (V+*)*  foot-candles  (49) 

DISCUSSION. 

Mr.  J.  L.  Minick  :  Searchlights,  and  in  fact  all  forms  of  light 
units  giving  approximately  parallel  rays  of  light,  are  receiving 
considerable  attention  at  the  present  time  and  this  paper  will 
undoubtedly  be  of  great  value  in  solving  many  of  the  problems 
incidental  to  this  class  of  lighting. 

During  the  past  few  years  about  two  thirds  of  the  states  and 
territories  have  passed  laws  requiring  the  use  of  locomotive  head- 
lights of  much  higher  beam  candlepowers  than  are  in  common 
use  to-day.  The  requirements  of  these  laws  are  usually  very 
indefinite  due  in  some  degree  at  least  to  the  fact  that  they  have 
been  prepared  by  persons  having  little  or  no  technical  knowledge 
along  lighting  lines.  In  some  instances  the  candlepower  or  wat- 
tage of  the  lamp  without  reflector  is  the  principal  requirement; 
in  others  the  diameter  of  the  reflector  only  is  given ;  in  still  others 
the  distance  at  which  an  object  can  be  seen  is  specified,  while 
the  speed  of  the  train,  weather  conditions,  color  of  background, 
etc.,  are  not  even  referred  to. 

The  railroads  have  been  faithfully  trying  to  solve  this  prob- 
lem and  papers  of  this  kind  will  be  of  material  assistance  in  this 
connection.  The  principal  objections  to  the  lawrs  now  existing 
are,  as  stated  above,  their  requirements  are  very  vague  and  in- 
6 


920    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

definite  and  the  requirements  of  adjoining  states  usually  differ 
from  each  other,  so  that  one  kind  of  headlight  is  required  in 
one  state  and  another  kind  in  another  state. 

I  am  not  prepared  to  discuss  the  technical  features  of  Mr. 
Benford's  paper  to  any  great  extent  as  my  work  has  generally 
been  along  slightly  different  lines.  I  have  done  some  work, 
however,  that  checks  closely  with  Mr.  Benford's  work. 

Mr.  Benford  states  that  in  the  application  of  the  law  of  inverse 
squares,  the  distance  is  measured  from  the  reflector.  I  presume 
the  focal  center  is  the  point  from  which  it  is  intended  that  this 
measurement  is  to  be  made.  I  have  discussed  this  question  with 
several  authorities  on  parabolic  reflectors  and  semaphore  lenses 
and  I  am  told  that  in  the  case  of  the  parabolic  reflector  the 
measurement  should  be  made  from  the  center  of  gravity  of  the 
longitudinal  section  of  the  reflector  which  will  be  found  on  the 
axis  of  the  reflector  at  a  distance  from  the  front  of  the  reflector 
equal  to  one  third  the  total  depth  of  the  reflector.  In  the  case 
of  semaphore  and  inverted  semaphore  type  lenses  the  distance 
should  be  measured  from  the  flat  surface  of  the  lens. 

I  should  like  to  see  some  investigation  of  lenses  of  the  above 
described  types  for  headlight  service.  They  can  be  readily 
cleaned,  they  require  no  polishing  and  on  the  whole  are  much 
more  desirable  for  this  class  of  service  than  are  metal  reflectors. 
The  polishing  of  metal  reflectors  very  quickly  destroys  their  re- 
flecting surfaces,  making  it  necessary  to  continually  replate 
them. 

Dr.  C.  E.  K.  Mees:  The  beam  brightness  with  the  parabolic 
mirror  is  the  brightness  of  the  source  multiplied  by  the  reflecting 
power  or  transmission  coefficient  of  the  lens  or  mirror  involved. 
That  being  so,  since  the  road  brightness  is  as  the  candlepower  of 
the  source,  it  is  obvious  that  what  is  required  is  to  produce  as 
large  a  source  as  possible.  The  remedy  in  fact,  for  glare  in  head- 
lights is  fairly  simple,  in  that  if  one  produces  a  large  source — it 
must  be  remembered  that  in  an  automobile  headlight  a  very  long 
beam  is  not  required — on  ccan  produce  a  large  road  brightness 
with  a  comparatively  small  glare.  Unfortunately  the  tendency  in 
automobile  headlights  is  toward  the  development  of  extremely 
bright,    concentrated    sources    as    shown   by   the   production    of 


THE  PARABOLIC    MIRROR  921 

6-volt  lamps  of  as  much  as  72  candlepower,  all  concentrated  into 
an  extremely  small  spherical  filament.  When  you  start  to  apply 
the  remedy  to  your  own  headlight,  the  practical  difficulty  is,  how 
to  do  it  ?  No  ground  glass  at  present  made  and  no  opal  glass  has 
a  sufficiently  high  diffusing  coefficient  to  diffuse  the  modern 
tungsten  lamp.  What  is  needed  is  a  globe  for  a  lamp,  since  the 
automobile  headlight  has  no  medium  to  carry  a  diffusing  screen, 
a  globe  which  shall  be  sufficiently  diffusing  to  produce  an  evenly 
diffusing  surface  for  the  high  power  lamps  used.  One  can  get  a 
wide  beam  with  as  little  as  a  hundredth  or  perhaps  a  thousandth 
of  the  glare  now  existing,  and  still  get  the  total  illumination,  be- 
cause a  driver  wants  to  clearly  see  the  sides  of  the  road;  so  it 
seems  to  me  that  we  must  look  to  the  lamp  makers  to  produce 
such  a  diffusing  globe  for  their  high  candlepower  automobile 
lamps,  and  then  we  can  bring  pressure  to  bear  on  municipal 
authorities  to  compel  the  adoption  of  diffusing  globes  on  auto- 
mobile headlights. 

Mr.  J.  R.  Cravath  :  There  seems  to  be  considerable  miscon- 
ception about  the  real  problem  to  be  met  in  the  case  of  automo- 
bile headlights,  in  reducing  the  blinding  effect.  Replacing  the 
clear  glass  of  the  headlight  by  a  diffusing  glass,  reduces  the 
maximum  effective  candlepower  of  the  beam  many  hundreds  of 
times ;  in  other  words,  it  spreads  out  the  beam  very  nice  for  illum- 
inating the  weeds  alongside  the  roadway,  but  most  drivers  object 
to  it  for  country  road  driving  as  not  throwing  enough  light  far 
ahead.  I  presume  we  have  all  thought  of  directing  the  light  so 
that  it  will  be  confined  to  the  surface  of  the  roadway  and  not  into 
the  eyes  of  approaching  drivers.  But  the  practical  difficulty  is 
that  road  inequalities  will  raise  the  beam  in  many  cases,  and 
furthermore,  it  is  very  difficult  to  design  reflectors  and  place 
lamps  accurately  enough  in  practise  so  that  there  will  not  be  suf- 
ficient spread  in  the  beam  to  catch  the  opposing  vehicle  driver  in 
the  eye.  The  practical  way  out  of  it  seems  to  be  to  require  all  the 
powerful  headlights  to  be  turned  off  when  on  lighted  city  streets 
and  go  only  with  marking  lights,  which  is  entirely  practicable,  and 
is  required  in  some  cities.  Most  of  the  city  ordinances  on  this 
point  are  very  indefinite.  The  city  of  Chicago  prohibits  a  blind- 
ing, dazzling  or  confusing  light  but  does  not  define  what  such  a 


922     TRANSACTIONS  Of  ILLUMINATING  ENGINEERING  SOCIETY 

light  is.  I  found  upon  inquiry  at  the  municipal  bureau  that  is 
established  for  that  purpose,  that  it  is  a  light  that  a  certain  com- 
mittee of  three  looks  at  and  decides  to  be  such.  (Laughter.) 

Dr.  E.  P.  Hyde:  I  recall  some  years  ago  that  a  committee 
of  the  National  Electric  Light  Association  presented  a  report 
on  street  lighting,  and  I  think  the  aspect  of  the  report  that 
impressed  most  of  us  most  strongly  was  the  apparent  indecision 
regarding  the  desiderata  of  street  lighting.  It  is  rather  dif- 
ficult to  formulate  specifications  for  street  lighting  when  there 
is  no  agreement  on  the  requirements  that  are  to  be  met  by  the 
specified  installation,  and  it  has  seemed  to  me  for  sometime  that 
the  same  condition  exists  regarding  automobile  lighting  and  the 
question  of  glare, — the  desiderata  which  are  to  be  met  in  de- 
signing a  proper  automobile  lighting  scheme  are  not  definitely 
agreed  upon.  We  are  impressed  more  with  the  case  when  we 
hear,  as  we  have  heard  this  morning,  more  or  less  divergent 
views  regarding  the  matter.  I  think  that  on  the  one  hand  lamp 
makers  and  the  makers  of  the  automobile  headlights  them- 
selves have  been  endeavoring  to  get  as  nearly  as  possible  the 
full  value  of  a  parabolic  reflector  by  having  a  point  source  and 
keeping  the  light  cone  narrow.  On  the  other  hand,  Dr.  Mees 
suggests  that  the  great  difficulty  with  it  is  the  fact  that  there 
is  a  narrow  light  cone.  Now  those  two  views  are  diametrically 
opposite  and  the  question  arises  as  to  just  what  we  do  want 
in  the  way  of  illumination  by  automobile  headlights.  I  think 
that  this  Society  should  take  some  action  in  the  matter.  The 
question  of  automobile  headlights  is  one  of  the  livest  questions 
of  the  day,  and  I  do  not  know  any  body  in  the  country  to  whom 
the  problem  should  be  presented  for  consideration  and  action, 
other  than  the  Illuminating  Engineering  Society.  I  should  like 
to  recommend — I  don't  want  to  put  it  in  the  form  of  a  motion — 
but  I  should  like  to  recommend  that  this  Society  take  some 
action  whereby  a  consideration  of  this  question  is  definitely 
undertaken  either  by  some  of  the  existing  committees  or  by 
some  committee  formed  for  the  purpose  in  order  that  the  Soci- 
ety may,  if  possible,  arrive  at  some  conclusions  which  can  be 
suggested  to  those  who  desire  to  know  them  and  may,  in  a  way, 
serve  as  a  basis  for  specifications  for  automobile  headlights,  with 


THE   PARABOLIC    MIRROR  923 

the  hope  that  in  time  the  municipalities  and  counties  may  adopt 
these   specifications   in   order  that  there  may   be   a   uniformity 
throughout  the  country  and  in  any  one  city  the  specifications 
may  be  such  that  an  automobile  driver  may  be  able  to  know  with 
certain  positiveness  that  his  headlight  conforms  to  the  require- 
ments and  not  be  subject  to  the  vagaries  of  committees  of  three 
or  any  one  of  the  committee  of  three  who  may  happen  to  be 
the  victim  in  the  case.     With  regard  to  the  problem  itself,  I 
think  that  we  still  are  far  from  knowing  the  most  important 
elements  that  enter  into  producing  what  we  term  a  glare.     I 
know  that  it   is   frequently   considered  that   brightness   of   the 
source   itself   is   the   principal    element,   and   possibly    it    is.      I 
would  gather  from     Mr.  Cravath's  remarks  that  he  thinks  that 
the  size  of  the  searchlight  in  some  way  affects  the  brightness. 
As  I  see  it,  if  the  mirror  is  a  true  parabola  and  if  the  light 
source   a   point   source   or   approximately   a   point    source,   the 
brightness  is  not  affected  by  the  size  of  the  parabolic  mirror;  it 
is  the  same  whether  you  have  a  large  or  a  small  parabolic  mirror, 
so  long  as  you  have  a  parabolic  mirror.    I  think  there  is  another 
element,  however,  besides  brightness  which  determines  glare,  and 
I  believe  that  each  of  you  could  convince  himself  of  it  if  you  per- 
form a  rather  simple  experiment.    I  think  you  will  find  that  the 
glaring  effect,   considering  the  contrast  between  the   source  at 
which  you  are  looking  and  the  surroundings  to  be  the  same  in 
each  case — because  of  course  contrast  is  a  very  important  ele- 
ment— is  determined  not  only  by  the  brightness  of  the  source 
but  by  the  total  flux  of  light.     I  remember  some  years  ago  we 
performed  in  our  laboratory  a  very  simple  experiment;  we  set 
up  a  Nernst  glower  and  a  condensing  lens  in  such  a  way  that  the 
image  of  the  glower  was  formed  on  the  cornea.     The  lens  was 
seen  to  be  filled  with  light.    You  did  not  change  the  brightness  of 
the  source  by  changing  the  aperture  of  the  lens,  but  you  could 
change  tremendously  the  glaring  effect  by  changing  the  effective 
size  of  the  lens  which  changed  the  amount  of  light  coming  into 
the  eye.    I  think  you  will  find  that  the  two  elements  enter ;  there 
may  be  other  elements  which  enter,  but  it  seems  to  me  we  should 
undertake  to  determine  in  this  Society,  in  some  rather  definite 
way,  ( 1 )  what  the  elements  are  that  produce  the  glare  and  how 
to  avoid  them,  and  (2)  what  the  desiderata  in  automobile  head- 


924     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

lights  are,  and  endeavor  to  draw  up  some  specifications  by  which 
these  desiderata  may  be  met. 

Mr.  L.  C.  Porter:  Taking  up  the  question  of  the  spread  of 
the  beam,  it  is  obvious  that  for  headlight  work,  for  example,  a 
very  narrow  pencil  of  light  is  not  satisfactory.  That  brings  in  the 
question  of  how  you  are  going  to  determine  the  spread  of  the 
beam;  in  other  words,  where  is  the  edge  of  the  beam?  What 
figure  can  you  take?  If  you  had  a  theoretical  point  source,  you 
could  have  a  sharp  edge  beam,  but  with  the  sources  which  are 
practical — the  arc  crater  and  especially  the  incandescent  lamp 
filament — the  beam  does  not  have  a  sharp  edge. 

In  specifying  a  headlight  there  must  be  some  method  used  to 
take  into  account  not  only  the  maximum  candlepower  of  the 
headlight,  but  also  the  spread,  and  I  should  like  to  ask  Mr.  Ben- 
ford  if  he  has  any  suggestions  as  to  how  he  would  determine  the 
edge  of  the  beam.  For  practical  manufacturing  we  must  have  a 
method  of  rating  headlights  which  takes  into  consideration  the 
spread,  the  average  intensity  across  this  spread,  as  well  as  the 
pick-up  distance.  I  should  like  to  see  the  valuable  theory  in  this 
paper  supplemented  by  some  of  the  practical  problems  which 
must  enter  in  the  manufacture,  testing  and  use  of  searchlights. 

The  incandescent  lamp  is  having  a  very  widely  increased  ap- 
plication to  headlight  service.  It  is  possible  now,  with  six-volt 
lamps  of  about  150  candlepower  (a  standard  lamp)  to  get  over 
900,000  beam  candlepower  from  a  20-inch  parabolic  mirror,  and 
many  such  headlights  are  now  in  service.  With  a  little  more 
powerful  lamp  one  is  able  to  obtain  considerably  over  a  million 
in  beam  candlepower.  Such  beams  are  applicable  to  navigation 
service,  and  many  other  classes  of  work  which  do  not  require 
extremely  high  candlepower  beams. 

On  the  eleventh  page,  Mr.  Benford  gives  a  formula  which 
shows  the  distance  at  which  one  can  begin  to  measure  beam 
candlepower.  In  practise  you  can  generally  obtain  more  accurate 
results  by  using  considerably  greater  distances  than  the  minimum 
which  the  formula  shows.  At  this  distance,  the  intensity  is  so 
high  that  it  is  difficult  to  measure  it  with  a  photometer,  but  if 
you  go  off  several  hundred  feet  you  can  get  photometric  readings 
fairly  accurate. 


THE   PARABOLIC    MIRROR  925 

In  regard  to  the  question  of  automobile  headlights,  in  New 
Jersey  there  is  a  rule  forbidding  the  use  of  headlights  which 
produce  glare,  and  a  commissioner  passes  upon  devices  which 
eliminate  glare.  It  may  be  of  interest  to  you  to  know  of  some 
of  these  devices  which  have  been  approved.  One  of  the  first 
schemes  was  to  dip  the  upper  two  thirds  of  the  front  glass  of  the 
headlight  in  either  an  opal  or  an  amber  dip,  amber  being  recom- 
mended. As  has  been  pointed  out,  that  has  the  disadvantage  of 
largely  reducing  the  illumination  on  the  road.  Another  method 
is  to  put  a  dip  on  the  lamp  itself,  this  dip  generally  being  opal 
and  taking  a  form  which  will  cover  the  lower  half  of  the  bulb 
and  the  direct  rays  from  the  filament  itself.  Another  method 
which  has  been  approved  is  to  paint  or  paste  paper  on  the  lower 
half  of  the  parabolic  reflector,  i.  e.,  dull  it  by  some  method.  Still 
another  one  is  the  use  of  a  Venetian  blind  effect  across  the  front 
of  the  headlight,  the  idea  of  this  being  that  it  will  protect  the 
pedestrian's  eyes  but  will  let  the  light  go  down  on  the  road. 
Another  method  in  common  use  is  a  small  candlepower  lamp  in 
the  top  of  the  reflector.  Still  another  one  is  the  use  of  resis- 
tance to  simply  cut  down  the  candlepower  of  the  light  for  city 
driving.  In  New  Jersey  such  a  device  is  not  acceptable ;  the  rule 
states  that  no  device  will  be  acceptable  which  is  within  the  control 
of  the  driver.  That  seems  to  be  a  little  unreasonable.  For  city 
use,  a  powerful  beam  is  not  required  because  the  cars  move 
slowly  and  the  driver  has  the  street  lamps  to  help  out,  and  either 
the  method  of  reducing  the  candlepower  of  the  lamp  by  resis- 
tance or  turning  on  a  small  lamp  and  extinguishing  the  main 
lamp  gives  perfectly  satisfactory  illumination.  In  the  country 
one  should  naturally  be  able  to  use  a  more  powerful  beam,  be- 
cause there,  one  drives  faster.  As  Mr.  Cravath  has  pointed  out, 
it  is  not  a  very  simple  matter  to  direct  the  beam  down  on  the 
road  because  the  distance  at  which  a  driver  wants  to  see  the  road 
varies  with  the  speed  of  the  car,  and  at  the  same  time  the  driver 
must  be  able  to  see  down  on  the  immediate  foreground.  It  is 
very  difficult  to  drive  with  a  bright  spot  of  light  several  hundred 
feet  ahead  and  darkness  in  the  immediate  foreground  of  your  car. 
Another  method  which  has  been  used  to  some  extent  is  the  use 
of  lenses  to  more  or  less  accomplish  this,  and  I  believe  that  Dr. 
Gage  is  going  to  say  something  on  that  subject. 


926     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

I  thoroughly  agree  with  Dr.  Hyde  that  there  should  be  further 
research  on  this  question  and  that  the  Illuminating  Engineering 
Society  should  cooperate  with  those  having  to  do  with  the 
automobile  industry  in  this  work.  I  do  not  feel  that  the  glare 
reducing  device  should  be  a  part  of  the  incandescent  lamp  itself. 
The  lamp  should  be  as  simple  as  possible  and  applicable  to  any 
kind  or  type  of  headlight.  The  sockets  in  many  headlight  equip- 
ments are  not  adjustable ;  therefore,  a  glare  reducing  device  if 
put  on  the  lamp  itself  might  be  satisfactory  for  one  car  and  not 
for  another. 

One  method  which  can  be  easily  applied  to  the  lamp,  though, 
and  which  has  been  applied  to  some  of  the  high  candlepower 
tungsten  lamps  is  to  all-frost  the  bulb  having  a  concentrated  fila- 
ment. With  the  all-frosted  bulb  there  is  enough  of  the  main 
beam  left  to  show  light  at  a  distance,  and  yet  the  all-frosted  bulb 
gives  considerable  light  in  the  foreground  and  reduces  the  glare 
somewhat. 

I  have  felt  that  good  results  might  be  accomplished  by  the  use 
of  polarized  light  either  having  two  sets  of  tourmaline  crystals 
for  the  front  glass  of  the  headlight,  or  one  set  on  the  headlight 
and  the  other  set  used  by  the  driver  for  goggles. 

Dr.  H.  P.  Gage  :  I  should  like  to  add  something  to  Mr.  Ben- 
ford's  paper  on  the  theoretical  calculation  of  the  intensity  of 
the  beam  as  obtained  by  the  use  of  semaphore  lenses.  The  re- 
sults come  out  very  similar  to  those  of  the  parabolic  reflector. 
We  start  out  with  a  certain  intrinsic  brilliancy  of  the  source, 
which  we  can  call  I  or  S.  The  lens  or  mirror  re-directs  the  light 
from  this  source  into  a  practically  parallel  beam.  All  actual 
sources  which  it  is  necessary  to  consider  are  not  point  sources, 
but  extended  sources ;  consequently,  looking  at  this  lens  from  in 
front,  at  any  reasonable  distance  for  which  the  lens  is  to  be  used, 
the  apparent  size  of  the  source  is  magnified  so  that  it  covers  the 
entire  front  surface  of  the  lens.  The  simple  method  of  calcu- 
lating the  candlepower  in  this  case  is  to  multiply  the  intrinsic 
brilliancy  of  the  source  by  the  area  of  the  lens,  and  by  some 
factor  which  in  my  experiments  I  call  area  efficiency,  and  which 
Mr.  Benford  calls  reflective  efficiency.  As  the  lens  is  seen  from 
the  front,  one  gets  an  appearance  of  a  solid  disk  of  light  inter- 


THE  PARABOLIC    MIRROR  927 

rupted  by  dark  rings.  The  average  intrinsic  brilliancy  of  the 
lens  is  reduced  by  those  dark  rings  as  well  as  by  the  reflection 
losses  and  absorption  losses  of  the  lens  itself. 

Regarding  the  comment  as  to  where,  when  a  lens  is  set  up,  the 
distance  from  the  lens  should  be  measured — the  distance  is 
measured  from  the  edge  of  the  lens,  because  the  lens  appear  as 
a  luminous  disk  of  light.  At  the  Corning  Glass  Works  we 
specify  the  projected  beam  as  follows:  First,  the  apparent 
candlepower  of  the  center  of  the  beam,  calling  that  the  beam 
intensity.  For  the  spread  of  the  beam,  we  take  the  angle  between 
the  two  directions  where  the  intensity  has  fallen  off  to  50  per  cent, 
of  the  axial  intensity  and  call  it  the  spread  of  50  per  cent,  in- 
tensity. For  signal  purposes,  the  angle  between  the  directions 
where  the  beam  shows  about  1  candlepower  is  called  the  ex- 
treme spread.  The  spread  of  50  per  cent,  intensity  would,  I 
think,  be  a  good  measure  to  take  for  the  spread  of  beam  with  the 
different  headlight  reflectors. 

I  should  like  to  make  a  few  comments  on  the  parabolic  re- 
flector as  used  as  an  automobile  headlight  and  some  of  the  de- 
vices for  reducing  glare.  Frosting  the  upper  two  thirds  of  the 
reflector  has  been  suggested.  Placing  a  small  source  at  the  exact 
focus  of  the  parabola,  results  in  a  perfectly  parallel  beam  of  light. 
Any  light  source  available  is  an  extended  source  and  generally 
approximately  spherical.  The  angle  subtended  at  the  center  of 
the  reflector  extended  forward  gives  the  spread  from  the  apex 
of  the  parabola,  making  the  small  spot  in  the  center  referred  to 
by  Mr.  Benford.  At  the  extreme  edge  of  the  parabola,  the 
angle  subtended  by  the  source  is  very  small;  consequently  there 
is  a  very  small  spread ;  that  is,  each  zone  of  the  reflector  has  a 
different  spread  from  every  other  zone,  the  outside  being  the 
smallest.  If  the  person  setting  up  an  automobile  headlight 
focuses  the  source  inside  the  focus,  the  beam  from  the  lower 
clear  part  of  the  parabola  is  directed  downward  toward  the  road 
exactly  the  same  as  though  the  whole  headlight  were  directed 
down.  If,  on  the  other  hand,  the  lamp  is  set  in  front  of  the 
focus  the  beam  from  the  lower  part  of  the  parabola  is  directed 
upward  right  into  the  eyes  of  an  approaching  automobile  driver 
and  no  illumination  of  the  road  in  front  of  the  lamp  results.     If 


928     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  Illuminating  Engineering  Society  decides  on  specifications, 
this  device  should  be  considered  practically  worthless.  I  have 
had  some  slight  experience  driving  an  automobile  against  glaring 
headlights,  and  perhaps  what  I  can  say  will  appeal  to  a  number 
of  others  as  the  result  of  actual  experience.  In  meeting  an  ap- 
proaching automobile,  the  glare  seems  to  me  proportional  to 
the  intensity  of  the  light;  that  is,  the  candlepower  of  the  ap- 
proaching light,  and,  as  Dr.  Hyde  mentioned,  the  glare  depends 
on  the  square  root  of  the  candlepower  rather  than  on  whether 
the  headlight  is  of  large  or  small  diameter ;  i.  e.,  it  is  the  question 
of  candlepower  rather  than  of  intrinsic  brilliancy.  The  im- 
portant criterion  of  glare  is  not  the  discomfort  to  the  eyes  of  the 
driver,  but  it  is  the  question  whether  the  driver  can  see  beyond 
the  light.  Some  devices  will  reduce  the  discomfort  of  the  op- 
posing light,  but  do  not  increase  the  visibility  beyond  that  light. 
That  question  is  coming  up,  and  my  suggestion  of  the  solution 
would  be  something  as  follows :  Set  up  a  large  white  screen, 
perhaps  larger  than  this  blackboard,  with  a  hole  in  the  center 
through  which  can  be  seen  the  headlight  to  be  tested ;  around  the 
opening  paste  or  write  on  test  letters  such  as  are  used  by  occu- 
lists,  twice  the  size  usually  employed  for  the  given  distance. 
If  the  headlight  is  to  be  observed  at  50  ft.  (15.24  m.),  use  the  size 
for  100  ft.  The  test  is  made  by  illuminating  moderately  the  test 
letters  and  observing  the  conditions  under  which  these  letters  can 
be  read  and  how  close  to  the  axis  of  the  headlight  they  can 
be  read. 

Norman  Macbeth  :  My  experience  has  been  that  the  glare 
effect  of  headlights  depends  more  largely  upon  the  extent  of  the 
retina  covered  by  an  after  image  and  the  period  of  recovery 
which  is,  of  course,  largely  dependent  upon  the  extent  and  nature 
of  the  retinal  burn.  The  solution  of  this  problem  lies  in  the 
control  of  the  light  as  against  the  more  generally  practised 
methods  of  absorbing  the  uncontrolled  and  misdirected  light.  I 
have  driven  many  hundred  miles  making  observations  with  head- 
lights, particularly  those  where  the  beams  are  confined  within  a 
very  narrow  angle — where  a  very  narrow  beam  was  directed 
forward  and  downward  along  the  road.  The  parabolic  reflector, 
the  kind  we  experimented  with,  was  shallow  and  intercepted  only 


THE  PARABOLIC    MIRROR  929 

a  third  of  the  light  flux  generated  by  the  lamp,  and  there  was 
considerable  direct  light  from  the  lamp  around  the  front  of  the 
machine.  I  have  driven  in  machines  equipped  with  headlights 
having  proper  reflectors  and  there  is  absolutely  no  light  within  a 
safe  distance  of  the  eyes  of  approaching  drivers. 

Three  or  four  years  ago,  when  the  amber  glasses  came  out,  the 
manufacturers  said,  "The  solution  of  the  headlight  glare  is  to 
wear  a  pair  of  amber  glasses."  My  personal  opinion  after  road 
tests,  was  that  the  amber  glasses  resulted  in  about  the  same  effect 
as  if  you  closed  your  eyes  when  you  were  approaching  a  headlight 
and  opened  them  immediately  after  it  had  passed,  thus  eliminating 
a  burning  of  the  retina  and  enabling  you  immediately  to  see  the 
road  again. 

There  has  been  a  great  deal  of  foolishness  attached  to  this 
headlight  proposition.  One  manufacturer,  for  instance,  uses  a 
hemispherical  globe  on  the  front  of  the  lamp,  etching  all  but  a 
small  clear  spot  below  the  center  and  makes  the  claim  that  "this 
headlight  is  without  glare  because  of  the  illuminated  background 
surrounding  the  high  intensity  spot."  The  illuminated  back- 
ground being  10  in.  (25.4  mm.)  in  diameter,  subtends  but  a 
slightly  wider  angle  and  in  area  is  far  from  being  a  background. 
The  real  trouble  is  that  headlights  are  part  of  a  car  equipment. 
Manufacturers  of  automobiles  to-day  are  putting  out  their  cars  by 
the  thousands  and  tens  of  thousands  and  I  know  manufacturers 
who  have  supplied  devices  for  automobiles  one  year  and  lost  that 
business  the  following  year  because  their  devices  cost  5  cents  per 
car  more  than  some  other  available  device,  and  on  fifty  thousand 
cars  the  saving  was  reckoned.  The  reflector  for  automobile 
headlights,  as  used  to-day,  cost  60  to  80  cents.  There  was  none 
of  this  difficulty  in  the  old  type  of  lamps  using  acetylene, 
not  because  they  were  gas  lamps  but  because  they  used  mangin 
mirrors. 

I  made  a  test  a  short  time  ago  with  properly  designed,  well 
made  metal  reflectors.  I  had  two  of  these  reflectors  freshly 
plated,  polished  and  put  in  good  condition;  then  I  took  one  of 
them  and  with  a  piece  of  fine  emery  cloth,  carefully  scratched  the 
surface  of  the  reflector.  This  was  just  the  cleaning  process  ex- 
aggerated and  that  reflector  had  a  light  distribution  as  wide  as 


930     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

one  would  secure  with  a  China  dinner  plate.  The  other  reflector 
confined  the  beam  within  30  in  a  similar  manner  to  a  good  ground 
and  polished  mirrored  glass  reflector.  Many  hours  of  observation 
with  headlights  having  reflectors  good  and  bad  have  convinced 
me  that  a  well  made  properly  ground  to  shape,  mirrored  glass 
reflector  with  a  beam  within  20  or  30  will  meet  all  the  just  re- 
quirements— that  light  should  not  be  directed  higher  than  4  or  5 
feet  above  the  ground  in  order  to  protect  both  the  driver  and  those 
approaching  a  car  so  equipped.  From  one  pair  of  such  reflectors 
I  obtained  a  beam  of  68,000  candlepower  with  24-candlepower 
lamps.  The  reflectors  were  shallow  and  intercepted  less  than  half 
the  light  generated. 

A  very  simple  and  effective  method  was  adopted  for  city  driv- 
ing. The  lamp  sockets  were  attached  to  a  sleeve  with  a  hinge 
controlled  by  magnets  in  such  a  manner  that  by  pressing  a  con- 
venient button  the  lamp  was  moved  up  about  an  inch  and  out 
of  focus  with  the  result  that  a  large  pear-shaped  image  of  the 
lamp  filament  was  projected  onto  the  pavement  just  in  front  of 
the  machine  and  forward  for  about  40  feet.  My  conclusion  has 
been  that  the  solution  of  the  headlight  glare  proposition  is  sim- 
ply a  matter  of  the  control  of  light,  which  is  not  difficult  unless 
one  is  required  to  do  it  for  an  amount  not  exceeding  one  dollar 
per  lamp. 

Mr.  W.  R.  Mott  :  The  headlights  on  automobiles  are,  most 
of  them,  stationary,  and  it  is  perfectly  possible  now,  with  the 
development  of  headlight  turning  apparatus,  to  turn  the  head- 
light with  the  wheels.  I  have  ridden  in  automobiles  thus  equipped 
and  noticed  a  great  improvement  in  the  lighting. 

Dr.  P.  G.  Nutting:  I  do  not  wish  to  take  the  time  of  the 
Society  with  any  further  discussion,  but  I  wish  to  make  the  an- 
nouncement that  this  whole  subject  is  adequately  treated,  I  think, 
in  the  report  on  automobile  headlights  of  the  Committee  on 
Glare.*  In  this  report  we  have  discussed  the  subject  from  ele- 
mentary optics  to  model  ordinances.  A  great  deal  of  discussion 
would  have  been  saved  if  this  report  had  been  presented  here. 
Nearly  all  the  questions  raised  this  morning  are  answered  in  that 
report. 

*  This  report  is  to  appear  in  the  next  issue  of  the  Transactions. 


THE   PARABOLIC    MIRROR  931 

Mr.  F.  A.  Benford  (In  reply)  :  Mr.  Minick  brought  up  the 
question  of  measuring  the  zero  point  along  the  beam.  I  have 
taken  the  zero  point  at  the  source.  Actually  the  zero  point  should 
be  in  the  edge  of  the  plane  of  the  opening  of  the  mirror.  This 
applies  both  to  a  lens  and  to  any  type  of  reflector.  The  difference 
between  the  edge  of  the  plane  of  the  opening  and  the  source  is 
ordinarily  very  small  and  may  be  neglected. 

Dr.  Mees'  suggestion  as  to  frosting  the  bulb  was  answered  by 
Mr.  Cravath's  saying  that  the  intensity  of  the  beam  would  be 
reduced  in  the  same  proportion  as  the  intensity  of  the  parent 
source. 

Dr.  Mees  :  I  suggested  the  frosting  of  the  bulb  and  Mr.  Cra- 
vath  was  talking  about  the  frosting  of  the  lens. 

Mr.  Beneord:     It  works  out  somewhat  the  same,  though. 

Dr.  Mees  :     Not  at  all. 

Mr.  Benford  :  In  reducing  the  candlepower  in  the  center, 
I  mean. 

Dr.  Mees  :     Not  in  distribution. 

Mr.  Benford  :  Mr.  Porter  brought  up  the  question  of  the 
edge  of  the  beam  with  a  view  of  establishing  some  percentage 
of  intensity  which  may  be  called  the  edge.  That  may  be  done 
for  certain  classes  of  work  and  yet  would  not  be  a  good  thing  as 
a  rule.  Take  the  automobile  headlight,  as  an  example,  the  in- 
tensity of  one  candlepower  at  an  angle  of  45  °  downward  from 
the  lens  will  produce  more  illumination,  on  the  average,  than 
10,000  candlepower  in  the  center  of  the  beam,  because  of  the 
great  distance  at  which  the  center  will  strike  the  road  and  the 
high  angle  of  incidence ;  so  if  one  puts  an  arbitrary  edge  to  the 
beam  at  10  per  cent,  of  the  center  intensity,  one  will  be  losing 
much  of  the  effective  light. 


932     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

ULTRA-VIOLET  RADIATION  AND  THE  EYE  * 


BY   W.   E.   BURGE. 


Synopsis:  Transparent,  free-swimming,  unicellular  organisms,  para- 
mecia  were  exposed  to  the  radiation  from  a  quartz  mercury  burner  and 
observed  under  the  microscope  during  the  exposure.  The  organisms 
became  more  and  more  opaque  during  the  exposure  and  were  dead  after 
30  minutes.  The  conclusion  is  drawn  that  ultra-violet  radiation  kills 
living  cells  by  coagulating  the  protein  of  the  cells,  as  is  the  case  when 
they  are  heated  to  ioo°  C. 

A  square  of  glass  was  covered  with  a  thin  film  of  egg  white  and  per- 
mitted to  dry.  A  piece  of  cardboard  with  a  circular  area  cut  from  the 
center  was  fitted  over  the  transparent  film.  This  preparation  was  placed 
10  cm.  from  a  quartz  mercury  burner  and  allowed  to  remain  for  30  hours. 
Thus  the  circular  area  of  egg  white  was  exposed  to  the  radiation  while 
that  under  the  cardboard  was  not.  At  the  end  of  the  30  hours  the  card- 
board was  removed.  No  difference  could  be  seen  between  the  exposed 
and  unexposed  parts  of  the  film  of  egg  white.  The  preparation  was 
immersed  in  0.1  per  cent,  calcium  chloride  for  10  minutes.  The  exposed 
circular  area  became  an  opaque  coagulum  while  the  unexposed  part 
remained  transparent.  The  conclusion  is  drawn  that  ultra-violet  radia- 
tion coagulates  protein  by  changing  it  in  such  a  way  that  certain  salts 
such  as  those  of  calcium  can  combine  with  it  to  form  a  coagulum. 

The  eyes  of  one  batch  of  frogs  living  partially  immersed  in  0.1  per 
cent,  sodium  silicate  were  exposed  to  the  radiation  from  a  quartz  mer- 
cury burner.  The  eyes  of  another  batch  living  partially  immersed  in  tap 
water  were  also  exposed.  Those  living  in  the  silicate  developed  very 
severe  anterior  eye  trouble,  while  those  living  in  tap  water  developed  it 
very  slightly.  The  eyes  of  fish  living  in  0.1  per  cent,  sodium  silicate  were 
exposed  to  the  radiation  from  a  quartz  mercury  burner  for  the  same 
length  of  time  as  those  living  in  tap  water.  Those  in  the  silicate  solution 
developed  cataract,  while  those  in  tap  water  did  not.  The  unmoistened 
human  skin  was  exposed  to  the  sunlight  as  well  as  skin  moistened  with 
water  rich  in  calcium  salts.  The  skin  that  was  moistened  sunburned 
much  more  quickly  and  severely  than  that  which  was  not  moistened.  The 
conclusion  is  drawn  that  ultra-violet  in  the  radiation  from  the  quartz 
mercury  burner  and  from  the  sun  produced  these  injuries  by  modifying 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,   September   20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


BURGE  :    ULTRA-VIOLET  RADIATION  AND  THE  EYE  933 

the  protein  of  the  cells  of  the  crystalline  lens  and  of  the  skin  in  such  a 
manner  that  the  salts  present  can  combine  with  it  to  form  a  coagulum. 

Cataract  is  prevalent  among  people  living  in  India  and  among  glass 
blowers.  Analyses  of  human  cataractous  lenses  from  the  United  States 
show  a  great  increase  in  the  salts  of  calcium  and  magnesium  and  those 
from  India  in  addition  an  appreciable  amount  of  sodium  silicate.  Tropical 
light  is  comparatively  rich  in  ultra-violet  radiation.  Silicious  earths  form 
part  of  the  diet  of  certain  classes  in  India.  To  explain  the  prevalence  of 
cataract  among  people  living  in  the  tropics  and  among  glass  blowers  the 
assumption  is  made  that  ultra-violet  radiation  modifies  the  protein  of  the 
lens  so  that  the  salts  of  calcium  and  of  magnesium  and  sodium  silicate 
when  present  in  abnormal  amounts  can  combine  with  the  modified  pro- 
tein of  the  lens  to  form  a  coagulum  and  hence  an  opacity  or  cataract. 

The  wave-lengths  in  the  ultra-violet  region  of  the  spectrum  effective 
in  changing  the  protein  so  that  certain  salts  can  combine  with  it  to  form 
a  coagulum  lie  between  254MM  and  302M1"  inclusive. 


It  has  been  recognized  for  some  time  that,  unless  protected 
by  a  glass  globe,  the  radiation  from  a  quartz  mercury  arc  or 
from  an  iron  arc  or  from  any  light  source  emitting  large  quan- 
tities of  ultra-violet  rays  is  harmful  to  the  eye.  In  a  general  way 
it  has  been  assumed  that  all  radiation  of  shorter  wave-lengths 
than  350/n/n  is  injurious  to  living  tissues.  So  far  as  I  know  little 
or  no  attention  has  been  paid  to  the  mode  of  action  of  this  radia- 
tion in  producing  the  injury.  The  object  of  this  investigation, 
among  other  things,  was  to  determine  which  wave-lengths  in  the 
ultra-violet  region  of  the  spectrum  are  injurious  to  living  tissues 
and  the  mode  of  action  of  these  wave-lengths  in  producing  the 
injury. 

An  organ,  e.  g.,  the  eye,  is  composed  of  tissues,  connective 
tissue,  nervous  tissue,  etc.  The  tissues  are  composed  of  cells. 
The  most  important  constituent  of  the  cell  is  the  protein.  Pro- 
tein is  a  nitrogenous,  semi-fluid  organic  compound,  colloidal  in 
nature.  Egg  white  is  a  good  example  of  a  protein.  This,  how- 
ever, consists  of  several  proteins.  Dreyer  and  Hanssen1  showed 
that  egg  white  is  converted  into  an  opaque  coagulum  by  exposure 
to  ultra-violet  radiation  just  as  it  is  when  it  is  heated  to  ioo°  C. 

I  exposed  free-swimming  organisms,  paramecia,  to  the  radia- 

1  Dreyer  and  Hanssen  ;  Comptes  Rendus,  1907,  vol.  CXI<V,  p.  234. 


934     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

tion  from  a  quartz  mercury  burner  and  observed  them  under  the 
microscope  during  the  exposure.  These  organisms  are  fairly 
transparent  and  are  just  visible  to  the  unaided  eye.  During  the 
exposure  they  moved  more  and  more  slowly  and  gradually 
became  more  granular  and  opaque.  After  twenty  or  thirty  min- 
utes the  organisms  were  dead.  Fig.  I  ( I )  represents  the  normal 
transparent  animal,  (2)  represents  an  organism  that  was  killed 
by  ultra-violet  radiation  and  (3)  one  killed  by  heating  to  45 °  C. 
It  may  be  seen  that  whereas  the  normal  animal  ( 1 )  is  transparent, 
(2)  and  (3)  are  both  granular  and  opaque.  As  exposure  of 
egg  white  to  ultra-violet  radiation  caused  it  to  lose  its  trans- 
parency and  to  become  an  opaque  mass,  so  the  exposure  caused 
the  living  material  or  protoplasm  of  these  organisms  to  coagulate 
and  to  become  an  opaque  mass.  The  conclusion  may  be  drawn 
that  ultra-violet  radiation  injures  or  kills  living  cells  by  coagu- 
lating or  rendering  insoluble  the  protoplasm  or  living  material 
of  the  cells. 

Experiments  were  carried  out  in  an  attempt  to  determine  the 
mode  of  action  of  ultra-violet  radiation  in  coagulating  or  render- 
ing insoluble  the  protein  of  cells  and  to  determine  the  specific 
wave-lengths  in  the  quartz  mercury  arc  active  in  this  respect. 
A  normal  excised  crystalline  lens  was  placed  between  two  quartz 
plates  and  pressed  into  a  thin  layer  by  squeezing  the  plates 
together.  By  means  of  a  quartz  spectrograph  the  spectrum  from 
a  quartz  mercury  burner  operating  at  70  volts  and  800  candle- 
power  was  focused  on  the  layer  of  lens  material.  This  layer  of 
material  was  almost  perfectly  transparent.  The  exposure  was 
made  for  one  hundred  hours.  At  the  end  of  this  time  there  was 
no  visible  change  in  the  material.  It  was  as  transparent  as  at 
the  beginning  of  the  experiment.  However,  when  the  preparation 
was  immersed  in  a  0.1  per  cent,  calcium  chloride  solution  four 
bands  of  coagulated  lens  protein  appeared  where  the  bands  of 
the  spectrum  had  been  focused.  Fig.  2  (3)  is  a  photograph  of 
the  preparation  after  it  had  been  immersed  in  the  calcium  chloride 
solution ;  ( 1 )  is  a  photograph  of  the  spectrum  that  was  focused 
on  the  material.  It  may  be  noticed  that  the  lens  material  (3) 
was  precipitated  in  the  extreme  ultra-violet  region  of  the  spectrum 
where  the  photographic  plate  (1)  was  not  affected. 


burge:    ultra-violet  radiation  and  the  Eye         935 

A  similar  preparation  was  made  except  that  the  lens  was 
soaked  in  a  o.i  per  cent,  solution  of  calcium  chloride  for  several 
hours  previous  to  being  pressed  between  the  quartz  plates.  The 
spectrum  was  focused  on  this  layer  of  lens  material  just  as  it 
had  been  focused  on  the  layer  of  normal  lens  material.  After 
fifteen  hours  of  exposure  nine  bands  of  coagulated  lens  material 
could  be  seen  where  the  corresponding  bands  of  the  spectrum  had 
been  focused.  Fig.  2  (2)  is  a  photograph  of  the  lens  material 
on  which  the  spectrum  had  been  focused  for  fifteen  hours.  The 
line  of  coagulated  lens  protein  in  (2)  where  the  spectral  line  of 
wave-length  254/i/i  was  focused  appeared  after  sixty  minutes 
exposure;  that  where  the  spectral  line  of  wave-length  265^/1,  was 
focused  after  seventy-five  minutes  of  exposure.  The  other  lines 
of  coagulated  lens  protein  where  the  lines  of  the  spectrum  was 
focused  appeared  after  two  hundred  minutes  of  exposure. 

Egg  white  was  introduced  into  a  quartz  cell.  The  spectrum 
from  the  quartz  mercury  burner  was  focused  on  this  material 
for  fifteen  hours.  At  the  end  of  this  time  nine  bands  of  coagu- 
lated egg  white  could  be  seen  where  the  bands  of  the  spectrum 
had  been  focused.  These  bands  of  coagulated  egg  white  occurred 
where  the  bands  of  coagulated  lens  protein  had  occurred  and 
the  time  of  appearance  of  the  different  bands  was  about  the  same 
as  those  of  the  lens  protein,  (2)  Fig.  2. 

Egg  white  was  poured  on  a  glass  plate  and  spread  out  in  a  thin 
layer.  After  the  egg  white  was  dry  the  spectrum  from  the  quartz 
mercury  burner  was  focused  on  it  for  fifteen  hours.  At  the  end 
of  this  time  no  visible  change  had  been  produced  on  the  egg 
white  by  the  spectrum.  The  glass  plate  with  the  layer  of  egg 
white  on  it  was  immersed  in  a  0.1  per  cent,  calcium  chloride  solu- 
tion. In  a  few  minutes  nine  lines  of  coagulated  egg  white 
appeared  in  the  region  of  the  spectrum  where  the  lines  of  coagu- 
lated lens  protein  had  appeared. 

From  these  experiments  it  would  seem  that  calcium  salts  in 
some  way  make  it  possible  for  ultra-violet  radiation  to  precipitate 
protein.  It  would  seem  that  ultra-violet  radiation  acts  on  the 
protein  in  such  a  way  that  calcium  salt  can  combine  with  it  and 
form  a  precipitate  or  coagulum.  Magnesium  salts  and  silicates 
have  the  same  effect  as  the  calcium  salts. 
7 


936     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Cataract  is  an  opacity  of  the  crystalline  lens.  Analyses  of 
human  cataractous  lenses  from  America  show  a  great  increase 
in  the  salts  of  calcium  and  magnesium  and  those  from  India  show 
in  addition  to  these  salts  silicates.  I  am  told  that  silicious  earth 
forms  a  part  of  the  diet  of  certain  classes  in  India.  This  may 
account  for  the  silicates  in  the  cataractous  lenses  from  there. 
Cataract  is  of  very  common  occurrence  in  India.  Tropical  light 
is  comparatively  rich  in  ultra-violet  radiation.  To  explain  the 
prevalence  of  cataract  in  India,  the  assumption  is  made  that  the 
relatively  great  amount  of  ultra-violet  radiation  in  tropical  day- 
light acts  on  the  lens  protein  in  such  a  way  that  the  silicates  in 
the  eye  media  can  precipitate  it  and  produce  an  opacity.  To 
explain  the  prevalence  of  cataract  among  glass  blowers,  the 
assumption  is  made  that  the  eyes  of  glass  blowers  are  subjected 
to  more  of  the  short  wave-lengths  than  the  eyes  of  people  gen- 
erally and  for  this  reason  the  protein  of  the  lens  is  modified  and 
if  such  substances  as  salts  of  calcium,  magnesium  or  silicates  are 
present  in  sufficient  concentration  the  protein  will  be  precipitated 
and  the  lens  rendered  opaque  or  cataractous.  The  glass  blowers 
who  develop  cataract  form  a  relatively  small  percentage  of  those 
engaged  in  that  occupation.  Since  the  eyes  of  those  who  do  and 
those  who  do  not  develop  cataract  are  exposed  to  the  same  quality 
and  quantity  of  radiation  from  the  furnaces,  it  is  assumed  that 
those  who  do  develop  it  have  a  disturbed  condition  of  nutrition 
expressing  itself  in  an  increase  of  those  substances  which  can 
precipitate  the  protein  of  the  lens  acted  on  by  ultra-violet 
radiation. 

PRODUCTION  OF  AN  OPACITY  IN  THE  LENS  OR 
CATARACT  IN  LIVING  ANIMALS. 

Experiments  were  carried  out  in  an  attempt  to  increase  in  the 
fluids  of  the  body  of  living  animals  and  hence  in  the  eye  media, 
those  substances  found  to  be  greatly  increased  in  cataractous 
lenses  with  the  hope  that  on  exposure  of  the  eyes  of  the  animals 
to  ultra-violet  radiation  cataract  would  develop.  Many  observers 
have  demonstrated  that  it  is  impossible  to  produce  an  opacity  of 
the  lens  or  cataract  in  a  normal  living  animal  by  exposure  of  its 
eye  to  ultra-violet  radiation.     Burge2  showed  that  it  was  im- 

2  Burge  ;  Amer.Jour.  o/Phys.,  vol.  XXXVI,  1914. 


Fig.  i. 


-Paramecia.     (i)  the  normal  transparent  animal.     (2)  Paramecium  killed  by  ultra 
violet  radiation.     (3)  Paramecium  killed  by  heating  to  450  C. 


1        Sl       3         1 


400^ 


436, 
4  04. 
36&. 


31.T 

302  

297 

289 

1  *0' 

2  80 

276  

2  70 

265 

120' 

.ao.o' 
..2o.p-  ... 

.I.6.V.... 

2S4 

_..5.0'.  . 

249 

.2.  P.  P.'... 

Fig.  2.— Photograph  of  spectrum  of  quartz  mercury  arc.  (1)  Made  on  a  photographic 
plate.  (2)  Made  on  lens  protein  extracted  by  0.1  per  cent,  calcium  chloride.  (3)  Made 
on  a  thin  layer  of  lens,  immersed  in  0.1  per  cent,  calcium  chloride  after  the  exposure. 


Fig.  3—  Fish  (1)  living  in  tap  water  and  exposed  to  ultra-violet  radiation  for  12  hours. 
Fish  (2)  living  in  0.1  per  cent,  sodium  silicate  and  exposed  to  ultra-violet  radiation 
for  12  hours.  Fish  (3)  living  in  0.1  sodium  silicate  and  exposed  to  ultra-violet  radia- 
tion for  24  hours. 


Fig.  4- — Frog  (i)  living  in  tap  water  and  exposed  to  ultra-violet  radiation  for  5  hours. 
Frog  (2)  living  in  0.2  per  cent,  sodium  silicate  and  exposed  to  ultra-violet  radiation 
for  5  hours. 


burge:   ultra-violet  radiation  and  the  eye         937 

possible  to  produce  an  opacity  of  the  excised  lens  exposed  directly 
to  ultra-violet  radiation  for  very  long  periods.  Fish  were  chosen 
for  the  experiments  because  they  could  be  kept  alive  in  the  solu- 
tions of  the  salts  desired.  One  batch  of  gold  fish  was  kept  in 
0.8  per  cent,  calcium  chloride,  another  in  0.8  per  cent,  calcium 
lactate,  another  in  1.0  per  cent,  dextrose,  another  in  0.1  per 
cent,  sodium  silicate  for  ten  days.  At  the  end  of  this  time  each 
fish  in  its  turn  was  introduced  into  a  small  box  with  a  quartz 
window  in  one  side.  In  practise  four  of  these  boxes  were  used 
so  that  four  fish  were  exposed  at  one  time.  Clear  tap  water  was 
kept  flowing  through  these  boxes  during  the  exposure.  The 
boxes  containing  the  fish  were  adjusted  so  that  the  quartz  win- 
dows were  15  cm.  from  a  quartz  mercury- vapor  burner  operating 
at  140  volts,  3.3  amperes  and  2,400  cp.  In  this  manner  one  eye 
of  each  fish  was  exposed  to  the  radiation.  Each  exposure  was 
of  six  hours'  duration.  After  the  exposures  the  batches  of  fish 
were  replaced  in  the  solutions  from  which  they  were  taken.  For 
comparison  the  eyes  of  fish  living  in  tap  water  were  exposed  in 
the  same  manner  and  for  a  similar  length  of  time  as  those  living 
in  the  salt  solutions.  As  a  rule  a  slight  opacity  in  the  cornea  of 
the  eye  exposed  appeared  about  fifteen  hours  after  the  first  ex- 
posure. 

Ten  days  after  the  first  exposure  the  eyes  of  the  fish  that  had 
been  exposed  were  exposed  again  for  another  six-hour  period. 
At  the  time  of  this  second  exposure  as  a  rule  an  opacity  of  the 
cornea  and  lens  of  the  fish  living  in  the  salt  solutions  had  increased 
while  the  opacity  of  the  cornea  of  the  fish  living  in  tap  water  had 
cleared  up.  Several  hours  after  the  second  exposure  as  a  rule 
the  opacity  of  the  lens  and  cornea  of  the  fish  living  in  the  salt 
solutions  became  more  marked.  An  opacity  of  the  cornea  of  the 
fish  living  in  tap  water  also  developed,  but  it  was  slight  and 
cleared  up  in  a  few  days,  while  that  of  the  fish  living  in  the  salt 
solutions  increased. 

After  the  second  exposure  no  prescribed  rule  as  to  time  for 
the  third  exposure  can  be  laid  down.  In  order  to  clear  up  the 
opacity  of  the  cornea  of  the  fish  in  the  different  salt  solutions, 
it  is  necessary  to  transfer  them  to  tap  water.  As  a  rule  the 
opacity  of  the  cornea  will  clear  up  in  a  few  days,  while  the  lens 


938     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

remains  opaque.  By  nursing,  by  exposing  to  ultra-violet  radia- 
tion, by  transferring  back  and  forth  from  salt  solutions  to  tap 
water,  I  have  been  able  to  obtain  fish  in  the  condition  indicated 
in  Fig.  3.  Fish  1  had  been  living  in  tap  water  in  the  laboratory 
for  thirty  days  and  had  been  exposed  to  ultra-violet  radiation  for 
two  six-hour  periods  or  twelve  hours.  Fish  2  had  been  living 
in  0.1  per  cent,  sodium  silicate  for  twenty-eight  days  and  had  been 
exposed  to  ultra-violet  radiation  for  two  six-hour  periods  or 
twelve  hours.  Fish  3  had  been  living  in  0.1  per  cent,  sodium 
silicate  for  forty-two  days  and  had  been  exposed  to  ultra-violet 
radiation  for  four  six-hour  periods  or  twenty-four  hours. 

It  may  be  seen  that  the  lens  of  fish  3  living  in  the  silicate  solu- 
tion and  exposed  to  ultra-violet  radiation  for  twenty-four  hours 
had  become  perfectly  opaque,  that  of  fish  2  living  in  the  same 
solution  but  exposed  to  ultra-violet  radiation  for  twelve  hours 
had  become  partially  opaque,  while  the  lens  of  fish  1  living  in 
tap  water  and  exposed  to  ultra-violet  radiation  for  twelve  hours 
was  practically  clear.  The  results  of  these  experiments  would 
seem  to  support  the  assumptions  made  in  explaining  the  preva- 
lence of  cataract  among  people  living  in  the  tropics  and  among 
glass  blowers. 

THE  PRODUCTION  OF  ANTERIOR  EYE  TROUBLE 
BY  MEANS  OF  ULTRA-VIOLET  RADIATION. 

One  batch  of  frogs  was  kept  partially  immersed  in  0.2  per  cent, 
sodium  silicate,  another  in  0.8  per  cent,  calcium  chloride,  another 
in  1  per  cent,  dextrose  for  fifteen  days.  The  eyes  of  these  frogs 
were  exposed  to  the  radiation  from  a  quartz  mercury  burner  at 
a  distance  of  20  cm.  one  hour  each  day  for  five  successive  days. 
Photographs  of  the  frogs  were  made  fifteen  days  after  the 
exposures.  Fig.  4,  frog  2  had  been  living  partially  immersed 
in  0.2  per  cent,  solution  of  sodium  silicate  previous  to  the 
exposure.  Frog  1  had  been  living  partially  immersed  in  tap 
water  for  the  same  length  of  time.  It  may  be  seen  that  the  skin 
covering  the  anterior  part  of  the  eye  of  the  frog  living  in  the 
salt  solution  had  been  coagulated  and  converted  into  an  opaque 
mass,  while  that  of  the  frog  living  in  tap  water  was  very  little 
injured.  The  solution  of  calcium  chloride  and  of  dextrose  had 
the  same  effect  as  the  solution  of  silicate.    The  conclusion  may 


BURGE:     ULTRA-VIOLET   RADIATION   AND  THE   EYE  939 

be  drawn  that  salts  such  as  are  found  to  be  greatly  increased  in 
human  cataractous  lenses  not  only  increase  the  effectiveness  of 
ultra-violet  radiation  in  producing  an  opacity  of  the  lens  or  cata- 
ract, but  they  also  increase  the  effectiveness  of  ultra-violet  radia- 
tion in  producing  anterior  eye  trouble. 

The  skin  is  more  easily  sunburned  when  it  is  wet  than  when 
it  is  dry.  Sunburn  is  a  precipitation  of  the  protein  of  the  cells 
of  the  skin  by  the  ultra-violet  radiation  in  sunlight.  Ultra-violet 
radiation  acts  on  the  protein  of  the  cells  of  the  skin  in  such  a  way 
that  certain  salts  in  the  lymph  bathing  the  cells  can  combine  with 
it  and  precipitate  it.  If  the  skin  is  wet,  the  salts  in  the  water 
facilitate  this  process. 

CONCLUSIONS. 

i.  Ultra-violet  radiation  kills  living  cells  and  tissues  by  chang- 
ing the  protoplasm  of  the  cells  in  such  a  way  that  certain  salts 
can  combine  with  the  protoplasm  to  form  an  insoluble  com- 
pound or  coagulum.  The  effective  region  of  the  spectrum  in 
coagulating  the  living  material  of  the  cell  or  protoplasm  is 
between  249/x/i  and  302^.  The  most  effective  region  is  around 
254/1/u,  in  case  of  the  mercury  arc  used. 

2.  An  opacity  of  the  lens  or  cataract  can  be  produced  in  fish 
living  in  solutions  of  those  salts  found  to  be  greatly  increased 
in  human  cataractous  lenses  by  exposing  the  eye  of  the  fish  to 
ultra-violet  radiation.  This  cannot  be  done  with  fish  living  in 
tap  water. 

Nela  Research  Laboratory, 

National  Lamp  Works  of  General  Electric  Co., 
Nela  Park,  Cleveland,  Ohio. 
August  25,  1915. 

DISCUSSION. 
Mr.  W.  R.  Mott:  Referring  to  glass  1  millimeter  thick  not 
absorbing  ultra-violet  light  at  300/z/a,  I  think  it  makes  an  enor- 
mous difference  what  kind  of  glass  is  used.  The  ordinary  win- 
dow glass  really  cuts  off  ultra-violet  quite  well ;  therefore  a  state- 
ment of  the  kind  of  glass1  referred  to  might  be  of  advantage.    I 

1  Note  on  Non-transmission  of  ultra-violet  (300/u.fi)  through  glass  ;  p.  94,  E.  C  C  Baly's 
book  on  Spectroscopy ;  p.  3,  Plotnikow,  Photochemische  Versuchs-technik  Lepzig,  1912, 
Akademische  Verslagsgesellschaft ;  pp.  301  and  335,  Eder's  Handbuch  ber  Photographic, 
1912;  p.  608,  Light  Energy  by  Dr.  M.  Cleaves. 


940     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

have  made  a  few  little  experiments  on  the  coagulation  of  albu- 
men with  different  kinds  of  flame  arcs.  With  the  white  flame 
arc  there  is  very  little  coagulation  if  cooled  by  air  or  water  when 
very  near  the  arc.  With  an  iron  arc  there  is  very  marked  coagu- 
lation. 

Relative  to  the  point  that  some  people  who  are  afflicted  with 
cataract  have  diabetes,  I  call  attention  to  the  fact  that  uranium 
has  been  used  as  a  homeopathic  remedy  for  diabetes,  and  in 
large  doses,  undoubtedly  produces  conditions  of  chronic  nephri- 
ties.  Uranium  has  another  interesting  characteristic :  it  responds 
to  the  action  of  light  in  the  presence  of  organic  material,  causing 
very  severe  decomposition  of  almost  any  organic  acid.  The  com- 
bined action  of  the  chemical  and  of  light  produces  entirely  dif- 
ferent results  from  the  action  of  either  alone.  The  same  is  true 
to  a  limited  extent  of  iron,  and  this  again  raises  the  question : 
What  is  the  chemical  reaction  in  some  of  these  cases?  In  that 
connection,  I  have  been  doing  some  experiments  on  dye  fading,2 
and  in  looking  up  the  literature,  I  find  that  dyes  ordinarily  are  not 
faded  if  they  are  placed  in  a  vacuum  where  the  oxygen  cannot  get 
at  them ;  and  I  saw  a  reference  to  the  statement  that  bacteria  are 
not  killed  by  ultra-violet  light  in  a  vacuum.3  I  don't  know  how 
true  it  is,  but  it  is  an  interesting  statement. 

Another  valuable  article  is  that  by  N.  P.  Peckoff  on  "Quantita- 
tive Light  Filters  for  the  Ultra- Violet  Part  of  the  Spectrum," 
which  has  appeared  in  the  Journal  of  the  Russian  Society  of 
Physical  Chemistry,  vol.  47,  pp.  918-942,  191 5. 

A  simple  and  easy  test  for  determining  the  presence  of  the 
ultra-violet  light  is  much  desired.  I  have  worked  on  about  nine 
different  tests.  A  well  known  test  is  to  use  paraphenylendiamine, 
which  is  white,  on  weighted  blotting  paper  with  nitric  acid  and 
quickly  dry.  This  turns  blue  or  green  blue  in  the  presence  of 
ultra-violet  light  (radiations  beyond  about  380/x/u),  and  is  a  very 
satisfactory  test  because  it  is  unaffected  by  ordinary  light.  The 
amount  of  ultra-violet  light  in  sunlight,  by  the  way,  with  that 
test  is  a  little  greater  than  it  is  with  the  white  flame  arc.    As  an- 

2  Mott  W.  R.,  A  paper  read  at  the  Sept.  1915,  meeting  of  the  American  Electrochemical 
Society.    Use  of  the  Flame  Arc  in  Paint  and  Dye  Testing. 

3  Hirshberg  L.  K.,  Scientific  American,  vol.  112,  p.  313,  April  3,  1915.  Review  of  French 
work  of  Prof.  Roux. 


ULTRA-VIOLET   RADIATION   AND   THE   EYE  941 

other  test,  lithopone,  under  the  action  of  ultra-violet  light,  darkens 
very  readily  and  is  a  very  good  test  though  somewhat  slow. 

Dr.  J.  W.  Schereschewsky  :  I  think  that  Prof.  Burge's 
statements  are  extremely  interesting  and  offer  some  very  valuable 
suggestions  for  further  investigation  in  this  interesting  field.  I 
should  like  to  ask  Prof.  Burge  a  few  questions  in  regard  to  his 
work.  While  it  is  quite  possible  that  the  ultra-violet  content  of 
light,  in  the  light  of  Prof.  Burge's  experiments  and  of  the  spec- 
ulations of  other  people,  might  have  something  to  do  with  the 
production  of  cataract,  it  is  rather  hard  to  see  how  glass  blower's 
cataract  can  be  produced  by  the  ultra-violet  component  of  light. 
According  to  Prof.  Burge's  researches,  it  is  evident  that  the  active 
region,  so  far  as  ultra-violet  light  is  concerned,  is  rather  closely 
restricted  to  wave-lengths  which  are  shorter  than  302  millimi- 
crons. It  is  hard  to  see  how  the  light  from  molten  glass,  at  the 
temperature  at  which  the  furnaces  are  held,  can  produce  such 
ultra-violet  light.  At  this  temperature  it  seems  to  me  extremely 
unlikely  that  there  would  be  any  ultra-violet  radiation  from 
glass  furnaces  of  a  wave-length  shorter  than  360  millimicrons. 
I  should  like  to  ask  Prof.  Burge  what,  if  any,  effect  was  ob- 
served in  the  eyes  of  fish  placed  in  the  solution  of  mineral  salts 
while  they  were  becoming  adapted  to  the  solution?  Of  course,  if 
one  goes  into  an  aquarium  there  will  be  seen  a  number  of  fishes 
which  though  apparently  exposed  only  to  the  water,  tap  water  or 
artificial  sea  water  as  the  case  may  be,  which  suffer  from  corneal 
opacities  of  various  kinds  and  often  from  cataracts.  Now,  of 
course,  we  ought  to  presume,  from  Prof.  Burge's  paper,  that  fish 
living  in  these  mineral  solutions  were  unaffected  by  those  solu- 
tions until  they  were  exposed  to  the  ultra-violet  light ;  but  I  should 
like  a  definite  statement  in  regard  to  any  effects  which  might  have 
been  observed  in  the  eye  apparatus  of  fish  due  to  the  solutions 
alone.  I  suppose,  too,  that  the  boxes  in  which  the  fish  were 
placed  were  so  narrow  that  it  was  impossible  for  more  than  one 
eye  of  the  fish  to  be  exposed  to  the  light.  I  notice  that  while  the 
photograph  on  the  fifth  page  shows  the  spectral  regions  which  are 
most  effective  in  producing  coagulation  and  that  undoubtedly 
certain  portions  of  the  spectrum  which  are  apparently  effective  in 
producing  coagulation  of  protein  material,  may  penetrate  the 


942     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

cornea,  we  have  to  remember  that  the  cornea  may  be  somewhat 
variable  in  its  transmission.  Most  figures  for  the  transmission 
of  the  cornea  show  that  absorption  is  complete  of  wave-lengths 
shorter  than  300,  but  there  seems  to  be  room  for  considerable  in- 
dividual variation  in  this  respect,  in  that  the  tissues  of  young 
animals  are  more  permeable  to  ultra-violet  rays  than  those  of 
older  animals.  Inasmuch  as  cataract  is  usually  a  development  in 
the  aged,  I  do  not  know  that  we  can  always  infer  that  the  ab- 
sorption of  the  cornea  is  within  the  limits  of  300  in  such  cases.  I 
mean  that  in  older  persons  it  is  quite  conceivable  that  the  cornea 
may  have  become  more  opaque,  so  that  the  absorption,  instead 
of  stopping  at  300,  may  possibly  extend  to  305.  In  this  way  the 
spectral  regions  shown  by  Mr.  Burge  to  be  especially  active  would 
be  prevented  by  corneal  absorption  from  acting  on  the  lens. 

Mr.  I.  G.  Priest:  It  is  stated  commonly  that  the  tanning  of 
the  human  skin  is  due  to  ultra-violet  light.  I  should  like  to  know 
whether  there  is  a  definite  source  for  that  statement  and  also,  is 
there  any  work  which  shows  the  cause  of  the  difference  in  the 
action  of  the  light  upon  different  individual  skins?  It  is  well 
known  to  people  who  are  out  in  the  summer  time  that  some  people 
tan  and  get  a  nice,  leathery  tan,  while  others  repeatedly  burn  and 
never  get  a  tan.  Has  any  scientific  work  been  done  on  that  sub- 
ject? 

I  am  interested  in  the  question  Mr.  Mott  raised  as  to  whether 
it  is  true  that  bacteria  are  not  killed  by  ultra-violet  light  in  the 
absence  of  oxygen  ?  I  can  answer  Mr.  Mott's  question  by  experi- 
ments I  have  recently  made  myself  on  cotton  seed  oil.  The  color 
is  very  permanent  when  exposed  to  direct  sunlight,  that  is,  sun- 
light that  comes  through  a  thin  layer  of  glass,  if  sealed  in  a 
vacuum,  while  a  sample  of  the  same  oil  exposed  to  the  same  sun- 
light, with  a  thicker  layer  of  glass  but  in  contact  with  the  atmos- 
phere, will  fade  in  a  very  few  hours  from  amber  to  nearly  water 
white.  The  same  sample,  exposed  in  a  vacuum,  in  three  weeks' 
exposure  to  all  the  sun  that  would  shine,  showed  no  change  in 
color  as  followed  colorimetrically  on  the  Arons  chromoscope. 

On  the  seventh  page  very  specific  data  are  given  in  regard  to 
dimensions  distances  of  lamps,  etc,,  but  not  as  to  the  dimensions 
of  the  box  in  which  the  fish  was  contained,  nor  as  to  the  thickness 


ULTRA-VIOLET   RADIATION   AND  THE   EYE  943 

of  water  between  the  quartz  window  and  the  eye  of  the  fish.  I 
should  think  it  would  be  well,  in  revising  the  paper  for  the 
Transactions,  to  add  these  data.  And  it  seems  to  me  rather 
vague  to  specify  water,  where  one  is  interested  in  the  mineral 
content  of  the  water,  merely  as  "tap  water."  I  presume  that  it 
was  Cleveland  tap  water,  which  would  be  different  from  Wash- 
ington tap  water,  St.  Louis  tap  water  or  other  tap  waters. 
Wouldn't  it  be  well  to  supplement  the  statement  with  an  analysis 
of  the  tap  water,  or  perhaps  better  to  have  made  the  experiments 
in  distilled  water? 

Dr.  E.  P.  Hyde:  It  has  been  my  privilege  and  pleasure  to 
follow  the  experiments  of  Dr.  Burge  throughout  most  of  their 
course.  There  is  one  point  he  did  not  mention,  and  I  presume 
that  he  did  not,  consistent  with  the  idea  which  he  presented  that 
he  does  not  care  to  insist  upon  the  explanation  of  various 
phenomena  which  one  encounters,  on  the  basis  of  these  experi- 
ments, but  prefers  rather  to  let  the  experiments  stand  for  them- 
selves. There  is  one  point,  however,  which  I  think  of  interest, 
and  inasmuch  as  it  has  been  raised  by  one  of  the  other  speakers 
before  myself,  I  should  like  to  refer  to  it,  namely,  the  produc- 
tion cataract  in  the  eyes  of  glass  workers.  I  had  the  pleasure, 
some  years  ago,  of  talking  with  Dr.  Parsons,  at  the  time  when 
the  Governmental  Commission  was  being  formed  in  England, 
to  consider  this  question.  The  results  of  the  investigation  in 
England,  as  published  by  Professor  Crooks,  indicated — if  I 
may  use  the  word  indicated,  because  I  scarcely  think  that  the 
data  which  were  presented  by  Crooks  would  justify  such  a  con- 
clusion— indicated  to  him  at  least,  or  suggested  to  him,  the  sig- 
nificance of  infra-red  rather  than  ultra-violet  radiation  as  the 
cause  of  the  malady.  One  of  the  first  experiments  Dr.  Burge 
performed  was  to  expose  the  excised  eyes  of  pigs  and  cattle  to 
radiation  of  different  wave-lengths.  He  exposed  the  eyes  to 
ultra-violet  radiation,  and  under  conditions  of  modified  nutri- 
tion, obtained  cataractous  lenses.  He  exposed  the  eyes  to  in- 
tense radiation  in  the  visible  region  and  secured  no  evidence 
of  cataract.  He  placed  the  opening  of  an  electric  furnace  at 
about  i,ooo°  or  1,200°,  very,  very  rich  in  infra-red  radia- 
tion, as  close  to  an  eye  as  he  could  without  actually  burning 


944    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  eye  by  the  heat,  and  in  all  cases  in  which  he  was  able  to 
keep  the  lens  at  a  reasonable  temperature,  he  obtained  no  in- 
dication whatever  of  any  modification  which,  in  the  presence 
of  the  saline  solutions,  would  produce  cataract.  That  may  be 
taken  for  what  it  is  worth.  I  do  not  say  that  this  proves  that 
infra-red  radiation  may  not  play  a  part.  I  do  not  think  it 
proves  that  ultra-violet  radiation  is  the  actual  cause  of  cataract 
in  the  eyes  of  glass  workers,  but  the  fact  itself  is  significant  and 
anyone  may  draw  whatever  conclusion  he  wants  to  draw  from  it. 
From  what  I  have  heard  from  Dr  Burge,  he  is  not  willing  to 
draw  positive  conclusions,  but  I  think  it  is  significant  that  infra- 
red radiation  in  such  quantity  and  intensity  as  he  has  obtained 
did  not  produce  cataract  or  modify  the  lens  in  any  such  way 
that  cataract  was  ultimately  produced  with  the  saline  solutions, 
and  that  ultra-violet  radiation  did  modify  the  lens  in  such 
a  way  that  cataract  was  formed.  The  paper,  as  a  whole,  marks 
a  distinct  advance  in  our  knowledge  of  the  effect  of  radiation. 

Dr.  H.  P.  Gage:  Since  the  investigation  of  Crooks,  every- 
body interested  in  the  manufacture  of  spectacles  has  taken  a 
sudden  and  deep  interest  in  getting  a  glass  which,  in  a  thin 
layer  of  one  or  two  millimeters,  would  cut  out  ultra-violet  rays, 
and  we  are  certainly  very  glad  to  know  what  radiations  are 
of  the  greatest  danger;  one  might  say  fatal  radiations.  The 
question  whether  radiations  nearer  the  visible  are  harmful  could 
only  be  determined  by  very  long  experiment.  We  are  also  glad 
to  learn  something  of  the  effect  of  the  infra-red.  Apparently 
the  eye  needs  no  protection  from  the  infra-red  when  working 
with  any  source  except  where  the  intensity  of  the  light  or  the 
infra-red  is  so  great  that  there  is  danger  of  actually  cooking  the 
tissues  of  the  eye  by  the  thermal  effect  of  the  infra-red,  and  then 
it  simply  becomes  a  question  of  getting  a  glass  which  will  cut 
down  the  infra-red  enough  for  comfort  when  working. 

Mr.  I.  G.  Priest:  In  regard  to  the  suggestion  just  made  by 
Mr.  Gage,  I  know  the  opinion  seems  to  be  current  that  there  is  a 
cooking  of  the  tissues.  Now  I  do  not  pretend  to  know  any- 
thing about  biology,  but  Dr.  Schereschewsky  is  here  and  can  per- 
haps answer.  Isn't  that  idea  absurd  upon  the  face  of  it?  Any 
amount  of  energy  that  could  go  into  the  eye  could  not  possibly 


ULTRA-VIOLET   RADIATION    AND  THE   EYE  945 

raise  the  temperature  of  the  lens,  (as  long  as  the  subject  is 
living),  enough  to  cook  it.  That  is,  would  it  ever  get  above  a 
fever  temperature  ? 

Dr.  ScherESCHewsky  :  No,  I  hardly  think  that  is  possible 
at  all.  Any  injurious  temperature  like  that  would  certainly  burn 
the  skin  long  before  it  could  possibly  affect  the  tissues  of  the 
eye  itself.  As  a  matter  of  fact,  the  conjunctiva,  which  is  very 
effective  in  absorbing  infra-red  radiation,  will  probably  not  trans- 
mit more  than  10  per  cent,  of  all  the  infra-red  radiation  falling 
on  the  eye. 

There  was  one  other  question  Mr.  Priest  brought  up  which 
I  would  like  to  mention  in  regard  to  tanning  and  sunburn.  I 
notice  that  Dr.  Burge,  in  his  paper,  states  sunburn  is  a  form 
of  coagulation.  I  do  not  know  whether  that  is  so  or  not;  but  it 
has  been  noticed,  especially  in  the  last  few  years,  when  exposure 
to  the  sun  has  become  a  rather  favorite  method  for  improv- 
ing the  condition  of  persons  suffering  from  tuberculosis,  that 
if,  in  the  process  of  acquiring  a  good  tan,  excessive  sunburn  is 
permitted,  this  retards  very  much  the  development  of  pigment 
in  the  skin  which  is  the  result  of  tanning.  The  object  of  this 
treatment  by  tanning  is  to  improve  the  metabolism;  that  is  all  it 
does.  The  aim  is  to  cover  the  entire  body  with  as  deep  a  coat 
of  tan  as  can  be  secured.  Certain  precautions  are  adopted,  the 
exposure  must  be  very  gradual  and  must  be  only  a  few  minutes 
to  start  with.  The  entire  body  cannot  be  exposed,  but  only 
certain  portions,  first  the  extremities  and  then  the  thorax.  If 
the  exposure  goes  as  far  as  severe  sunburn,  the  deposition  of 
pigment  is  interfered  with.  Dark  persons  tan  deeply ;  very  blonde 
persons  are  almost  incapable  of  tanning  under  usual  circum- 
stances, but  by  careful  exposure  one  finds  that  even  very  blonde 
persons,  with  a  correspondingly  small  amount  of  pigment  in 
the  skin,  are  capable  of  taking  a  fair  amount  of  tan.  If  severe 
sunburn  is  allowed,  it  so  alters  the  protective  functions  of  the 
skin  that  tanning  does  not  develop  so  well  as  when  sunburn  is 
avoided.  The  protection  afforded  by  a  good  coat  of  tan  is  very 
marked.  There  are  marked  individual  differences;  some  per- 
sons have  such  good  pigment  production  that  they  can  stand  any 
amount  of  sunshine  and  it  will  merely  intensify  the  deposit  of 


946     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

pigment  in  the  skin.  On  the  other  hand  sunshine,  in  others, 
produces  an  amount  of  reaction  which  prevents  good  pigmenta- 
tion. 

Mr.  I.  G.  Priest:  Chemically,  what  is  the  difference  between 
sunburn  and  tan? 

Dr.  ScherEschewsky:  Sunburn  is  a  reaction  of  the  skin  to 
ultra-violet  rays  and  is  quite  comparable  to  a  slight  burn,  where- 
as tanning  is  a  protective  which  consists  in  the  deposition  in 
the  skin  of  absorbing  pigment. 

Dr.  W.  R.  Burge  (In  reply)  :  Only  one  eye  was  exposed  and 
the  other  was  not  exposed.  The  unexposed  eye  was  the  control. 
So  far  as  the  objections  to  the  carrying  out  of  our  experiments  on 
living  animals  in  tap  water  is  concerned,  and  the  suggestion  that 
we  should  have  used  distilled  water,  it  is  known  that  living  pro- 
toplasm is  killed  by  distilled  water.  I  think  that  Dreyer  and 
Hansen  exposed  many  substances  to  the  radiation  from  a  quartz 
mercury-vapor  burner.  In  Parke-Davis'  laboratory  the  work 
has  taken  up  during  the  last  year  or  two  and  many  more  addi- 
tional substances  have  been  exposed  to  the  radiation  from  a 
quartz  mercury  burner.  So  far  as  glass  blower's  cataract  is  con- 
cerned, I  do  not  wish  to  say  anything  about  the  application  of 
this  work  or  whether  it  may  be  applied  or  not.  I  think  such 
discussion  would  be  futile,  and  all  that  can  be  done  is  to  take  the 
experiments  for  what  they  are  worth.  If  the  experiments  have 
any  practical  value  it  is  to  be  hoped  that  such  application  may 
be  made  in  due  time.  So  far  as  the  experiments  on  the  tanning 
of  the  skin  are  concerned,  these  were  incidental.  Anyone  can 
perform  the  experiment  for  himself,  if,  before  going  out  to  row, 
he  wets  one  side  and  leaves  the  other  dry.  It  will  be  found  that 
the  wet  side  always  sunburns  much  more  quickly  than  the  dry 
side.  The  salt  in  solution  on  evaporation  of  the  water  on  the 
skin,  becomes  more  concentrated,  and  acts  as  the  salt  in  these 
experiments.    I  don't  know  of  any  data  on  the  subject. 

Mr.  Priest:  Was  your  experiment  made  with  salt  water  or 
fresh  water. 

Dr.  Burge:     Fresh  water  from  Lake  Erie. 


MEES:     ARTIFICIAL  IELUMINANTS  947 

ARTIFICIAL  ILLUMINANTS  FOR  USE  IN 
PRACTICAL  PHOTOGRAPHY.* 


BY  C.  E.  KENNETH  MEES. 


Synopsis:  Artificial  illuminants  can  be  used  in  negative  making  for 
portraiture,  cinematograph  work  and  photo-engraving.  For  portraiture 
diffused  sources  are  necessary,  and  either  a  large  source  must  be  used  or 
the  light  must  be  reflected  from  a  large  area.  In  cinematograph  work 
about  a  quarter  kilowatt  per  square  foot  of  stage  is  used,  the  usual 
arrangement  including  the  use  of  mercury-vapor  lamps  overhead  and  at 
one  side  of  the  stage,  and  arcs  in  front.  For  photo-engraving  an  arc  lamp 
is  hung  on  each  side  of  the  copy  board,  most  engravers  using  flame  carbon 
arcs. 

For  printing  papers  the  enclosed  arc  is  used  for  silver  papers  while 
for  platinum  the  mercury-vapor  lamp  is  satisfactory.  In  printing  fish  glue 
on  metal  it  is  important  that  a  small  source  of  light  should  be  used  in 
order  to  get  sharp  definition  of  the  dots,  and  the  printing  should  be  as 
far  away  as  possible.  The  photographic  efficiency  of  artificial  illuminants 
depends  upon  their  quality  and  upon  their  visual  efficiency,  but  must  be 
considered  from  the  point  of  view  of  the  materials  used,  which  materials 
are  of  three  chief  kinds:  (1)  panchromatic  materials  sensitive  to  the 
whole  spectrum  and  used  with  filters  to  give  a  rendering  similar  to  that 
seen  by  the  eye,  or  for  color  photography;  (2)  ordinary  materials  having 
their  maximum  sensitiveness  in  the  blue  violet;  (3)  materials  sensitive 
only  to  the  ultra-violet.  For  panchromatic  materials  the  efficiency  of  the 
illuminant  will  depend  almost  entirely  upon  its  visual  efficiency,  while  for 
ordinary  materials  the  chief  point  of  importance  is  the  efficiency  in  the 
blue  violet,  but  since  the  latitude  and  freedom  from  halation  increase 
with  shorter  wave-lengths  it  is  better  to  use  light  sources  having  their 
maximum  near  400/"/"'  rather  than  near  470MM.  It  is  pointed  out  that  nearly 
all  artificial  illuminants  have  application  in  some  branch  of  photography 
or  other. 


While  in  the  early  days  of  photography  almost  the  only  source 
of  light  was  the  sun,  the  application  of  artificial  illuminants  to 
the  art  is  continually  increasing.  The  illuminants  which  are 
available  are  of  many  kinds,  and,  indeed,  include  all  the  more 
powerful  sources  of  light.  The  advantages  of  artificial  illum- 
inants which  have  caused  their  introduction  are  chiefly  their 
constancy  and  their  ready  availability ;  the  variation  of  the  inten- 
sity of  natural  light  makes  the  judging  of  the  time  for  which  the 
sensitive  material  is  exposed  a  difficult  task,  so  that  the  photog- 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,   September  20-23,    '91 5- 

The   Illuminating   Engineering   Society   is   not   responsible    for   the   statements    or 
opinions  advanced  by  contributors. 

Communication  No.  31  from  the  Research  laboratory  of  the  Eastman  Kodak  Com- 
pany. 


948     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

rapher  has  to  acquire  considerable  skill  and  experience  in  order  to 
avoid  obtaining  results  showing  the  effect  of  incorrect  exposure, 
while  with  most  artificial  illuminants  the  matter  of  exposing  can 
be  reduced  to  a  simple  calculation  of  time,  thus  eliminating  one 
chance  of  insuccess.  The  possibility  of  working  at  any  time 
under  evenly  uniform  conditions  is  certainly  an  advantage  in  such 
divisions  of  photography  as  photo-engraving,  trade  enlarging  and, 
indeed,  all  commercial  work ;  while  it  is  a  further  advantage  that 
the  artificial  sources  of  light  are  available  whenever  they  are  re- 
quired and  that  the  worker  is  not  confined  to  a  small  portion  of 
the  day  or  to  an  intensity  dependent  on  meteorological  conditions. 
One  may  summarize  the  purpose  for  which  artificial  illumi- 
nants are  used  and  the  properties  required  in  the  illuminant  when 
it  is  applied  to  a  particular  purpose  somewhat  as  follows : 

Negative  Making:  Portraiture. — For  portraiture  a  large  dif- 
fused light  source  is  a  necessity  in  most  work  and  only  occasion- 
ally can  a  concentrated  source  be  used.  Consequently,  either  a 
very  extended  source  such  as  that  given  by  the  mercury-vapor 
lamp  must  be  employed,  or  else  a  completely  diffusing  system  is 
arranged;  thus,  for  an  arc  it  is  convenient  to  place  the  reflector 
behind  the  arc  so  that  the  light  is  directed  away  from  the  sitter  on 
to  a  large  secondary  reflector,  which  may  be  a  wall,  though  it  is 
usually  more  convenient  to  have  a  movable  arrangement.  What- 
ever system  is  used  for  obtaining  a  large  source  of  diffused  light 
curtains  and  screens  are  necessary  so  that  the  operator  can  adjust 
the  area  and  direction  of  the  light  at  will.  An  arrangement  which 
has  given  satisfaction  consists  of  a  battery  of  12  or  16  nitrogen 
tungsten  lamps  placed  in  a  frame  behind  a  diffusing  medium  and 
covering  an  area  of  30  or  40  sq.  ft.,  the  area  to  be  utilized  being 
modified  by  applying  independent  control  to  the  separate  lamps. 

Cinematograph  Work. — In  moving  picture  studios  a  consider- 
able amount  of  light  is  necessary  owing  to  the  speed  at  which  the 
pictures  are  taken,  the  exposure  being  only  1/40  of  a  second  with 
an  aperture  of  about  F/8.  The  average  stage,  including  an  area 
of  perhaps  240  sq.  ft.,  requires  about  60  kilowatts  for  illumination, 
and  a  typical  arrangement  of  the  lights  will  consist  of  40  to  50 
kilowatts  expended  in  mercury-vapor  lamps  or  quartz  arcs  ar- 
ranged about  12  to  15  ft.  above,  as  a  roof  to  the  stage  and  down 


MEES:     ARTIFICIAL   ILLUMINANTS  949 

one  side  to  a  distance  of  about  3  ft.  from  the  floor,  and  about 
12  kilowatts  used  in  some  form  of  arc,  conveniently  a  flame  arc, 
about  10  ft.  in  front  of  the  stage  and  the  same  distance  from  the 
floor ;  such  an  arrangement  is  typical  of  many  of  the  stages  used 
by  the  large  producers  of  moving  pictures  in  this  country  and  the 
importance  of  artificial  illumination  in  this  work  can  be  realized 
when  it  is  understood  that  many  producers  will  have  six  such 
stages  working  at  a  time. 

Photo-Engraving.  In  photo-engraving  the  copy-board  is  gen- 
erally lighted  by  an  arc  lamp  hung  on  each  side.  In  the  earlier 
days  these  were  usually  open  arcs  and  later,  especially  in  Europe, 
the  enclosed  long  flame  carbon  arc  came  into  use,  and  is  still  very 
convenient  for  work  with  wet  collodion,  but  it  is  unsuitable  for 
color  work  owing  to  the  deficiency  of  red  and  especially  of  green 
light.  In  this  country  many  photo-engravers  use  open  arcs  with 
white  flame  carbons,  which  appear  to  be  quite  satisfactory.  The 
quartz  lamp  would  be  suitable  for  black  and  white  work  if  it  came 
up  to  efficiency  in  less  time,  but  a  great  lag  in  reaching  efficiency  is 
against  it.  Neither  the  quartz  lamp  nor  the  mercury-vapor  lamp 
seems  to  be  as  efficient  as  the  flame  or  enclosed  arcs;  for  color 
work  the  nitrogen  tungsten  lamp  might  perhaps  be  applied  to  ad- 
vantage. 

For  color  photography,  such  for  example  as  color  portraiture, 
the  most  important  thing  about  a  lighting  system  is  the  constancy 
of  the  quality  of  the  light ;  but  high  intensity  is  required  and  the 
conditions  as  to  size  of  source  already  explained  under  portraiture 
fully  apply:  we  have  adopted  the  battery  of  nitrogen  tungsten 
lamps  already  spoken  of  as  being  very  suitable  for  color  por- 
traiture. 

In  ordinary  photographic  printing  the  Aristotype  and  solio 
papers  which  used  to  be  very  popular  are  often  printed  by  means 
of  a  large  enclosed  arc  instead  of  daylight,  and  this  seems  to  be 
very  suitable  for  the  printing  of  such  silver  papers.  For  platinum 
printing,  however,  it  is  advisable  to  use  a  source  of  light  which  is 
not  so  hot,  as  the  heat  is  very  liable  to  give  mealy  prints.  One 
large  company  do  their  trade  printing  by  means  of  mercury- vapor 
lamps  which  are  held  constant  by  a  resistance  and  ammeter,  the 
current  being  watched  and  the  printing  being  done  entirely  by  time. 


950    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Bromide  and  chloride  papers  are,  of  course,  printed  by  artificial 
light  exclusively,  the  usual  printing  cabinet  containing  tungsten 
lamps,  though  for  quick  trade  work  an  arc  lamp  or  mercury-vapor 
lamp  is  frequently  used,  thus  enabling  very  short  exposures  to  be 
given. 

For  enlarging  it  has  been  customary  to  use  an  open  arc,  but  if 
a  condenser  is  used,  it  would  seem  to  be  better  to  employ  a  con- 
densed filament  tungsten  lamp  because  of  its  great  constancy,  the 
changes  in  the  intensity  of  an  arc  making  accurate  exposure  diffi- 
cult unless  the  arc  is  one  which  permits  of  very  good  regulation. 
Much  enlarging  in  trade  houses  is  done  without  a  condenser,  the 
negative  being  lighted  by  a  diffusing  screen  behind  which  the 
source  is  placed,  such  a  suitable  diffusing  screen  being  a  sheet  of 
opal  glass.  For  such  work  suitable  illuminants  are  the  enclosed 
flame  or  open  white  flame  arcs,  but  if  mercury-vapor  lamps  are 
used,  a  powerful  diffuser  is  not  needed,  a  sheet  of  ground  glass 
being  sufficient  if  the  tubes  of  the  lamp  are  arranged  so  that  there 
are  a  number  parallel  to  each  other  a  short  distance  apart. 

For  the  printing  of  fish  glue  or  a  similar  resist  on  metal  in 
photo-engraving  it  is  important  to  have  a  small  source  of  light  in 
order  to  get  sharp  dots,  as  otherwise  a  very  high  pressure  is  re- 
quired to  ensure  sufficiently  good  contact ;  and  it  is,  indeed,  almost 
impossible  to  print  dry  plates  made  on  ordinary  sheet  glass  by 
means  of  large  sources  of  light.  The  arc  must  necessarily  be 
powerful,  but  the  flame  should  be  as  small  as  possible  and  the 
distance  as  great  as  can  be  used  in  order  to  prevent  the  exposure 
being  too  long.  It  would  appear  that  for  metal  printing  there  is 
an  opening  for  the  development  of  some  form  of  lamp  in  which 
approximately  parallel  light  of  high  intensity  is  obtained. 

For  some  photographic  purposes  constancy  and  lack  of  flicker 
are  essential,  average  constancy  being  important  in  almost  all  pho- 
tographic operations.  Flickering  is  a  less  serious  disadvantage 
in  many  operations  than  lack  of  average  constancy,  but  where  the 
exposure  is  short,  as  in  developing  out  printing,  enlarging  or 
photo-engraving,  flickering  of  the  light  source  is  very  much  to  be 
deprecated,  and  this  is  a  great  disadvantage  of  enclosed  and  open 
arcs.  The  table  on  the  fifth  page  summarizes  the  advantages  and 
disadvantages  of  various  illuminants  for  different  classes  of  work, 


MEES:     ARTIFICIAL   ILLUMINANTS 


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952     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  efficiency,  which  is  considered  in  the  next  section,  being  also 
taken  into  account. 

In  addition  to  the  suitability  of  a  light  source  as  to  size,  con- 
stancy, intensity,  etc.,  the  efficiency  and  quality  of  the  light  must 
be  considered.  The  visual  efficiency  and  the  quality  taken  to- 
gether will  represent  the  photographic  efficiency,  since  this  can 
be  calculated  if  one  knows  the  spectral  energy  curve,  which  is  the 
quality,  and  the  height  of  one  portion  of  it  which  is  given  by  the 
visual  efficiency.  This  relation  between  the  visual  and  photo- 
graphic efficiency  for  a  number  of  light  sources  and  for  three 
different  classes  of  photographic  materials  has  been  dealt  with  by 
Messrs.  Jones,  Hodgson  and  Huse  in  their  paper*  presented  to 
this  meeting. 

When  we  consider  the  quality  and  efficiency  of  an  artificial 
illuminant  for  use  in  photography  we  are  confronted  with  a 
problem  of  rather  different  type  from  that  with  which  we  meet 
when  the  illuminant  is  for  visual  use.  The  color  sensitiveness  of 
the  human  eye  in  different  individuals  is  so  nearly  alike  that  we 
need  consider  only  the  visibility  curve  of  the  average  human  eye, 
which  can  be  determined  with  sufficient  accuracy  by  taking  the 
mean  of  the  curves  obtained  by  a  number  of  observers,  after- 
wards rejecting  any  results  where  the  sensibility  is  not  approx- 
imately the  same  as  that  of  the  average  as  being  abnormal  or 
pathological  cases  which  can  be  ignored  in  the  general  choice  of 
an  illuminant ;  but  there  is  no  such  average  sensitiveness  in  photo- 
graphic materials.  In  dealing  with  the  choice  of  an  illuminant 
for  photographic  purposes  we  must  consider  the  use  to  which  it 
is  to  be  put  and  the  materials  which  are  likely  to  be  exposed  by 
means  of  it. 

There  are  three  main  groups  of  photographic  materials  as  re- 
gards their  spectral  sensitiveness :  ( i )  materials  which  have  been 
sensitized  by  means  of  dyes  to  the  longer  wave  lengths  of  the 
spectrum  and  which  are  intended  for  use  with  color  filters  either 
to  obtain  a  rendering  approximating  to  that  perceived  by  the 
human  eye  or  for  use  in  color  photography  where  exposures  are 
made  for  two  or  more  defined  areas  of  the  spectrum.  These 
materials  are  usually  known  as  "panchromatic."  Panchromatic 
plates  are  sensitive  to  the  whole  visible  spectrum,  their  sensitive- 

*  Published  in  this  number  of  the  Transactions. 


MEES:     ARTIFICIAL   ILLUMINANTS  953 

ness  between  Asoo^/x  and  A6oo/i/i  being  about  one  eighth,  and  be- 
tween A6oo/x  and  A800/A  about  one-tenth  of  their  total  sensitive- 
ness to  daylight.  (2)  Positive  or  negative  materials  sensitive  only 
to  the  blue  violet  and  ultra-violet  regions  of  the  spectrum,  and 
with  their  maximum  sensibility  in  the  blue-violet  region,  these 
including  all  ordinary  plates  or  films  used  for  landscape  or  por- 
traiture, dry  plates  used  in  photo-engraving,  and  all  the  printing 
materials  which  are  developed,  such  as  bromide  or  gas  light 
papers.  These  materials  have  a  sensitiveness  extending  from  the 
ultra-violet  to  about  A500/1M,  the  sensitiveness  diminishing  rap- 
idly with  longer  wave  length  after  about  M6ow*-  (3)  Materials 
which  are  sensitive  almost  exclusively  to  the  ultra-violet,  such  as 
printing  out  papers  or  the  wet  collodion  plates  used  in  photo- 
engraving. 

These  classes  of  materials  do  not  coincide  with  those  discussed 
by  Messrs.  Jones,  Hodgson  and  Huse;  their  "ordinary"  materials 
are  my  second  class  materials  sensitive  only  to  the  blue  and  ultra- 
violet regions,  and  their  panchromatic  or  orthochromatic  materials 
are  considered,  as  they  explain,  as  being  used  without  filters  and 
therefore  do  not  coincide  with  my  first  class,  where  the  materials 
are  considered  as  being  used  only  with  filters,  because  in  practise 
color  sensitive  materials  are  almost  always  used  with  filters  which 
correct  the  light  affecting  the  plate  so  that  the  plate  sensibility 
and  the  spectral  energy  curve  of  the  light  and  the  filter  together 
produce  a  rendering  comparable  with  that  observed  by  the  eye  by 
daylight.  A  light  source  is  therefore  more  efficient  with  these 
materials  if  it  enables  us  to  make  use  of  a  weaker  filter  to  attain 
the  same  result. 

For  panchromatic  materials  the  efficiency  of  an  illuminant  de- 
pends chiefly  on  its  visual  efficiency,  since  it  is  used  under  such 
conditions  that  the  light  affecting  the  materials  is  nearly  the 
same  as  that  to  which  the  eye  is  sensitive.  Any  ultra-violet  light 
is  of  no  use  whatever,  since  it  must  be  cut  out  by  the  filters,  but 
inasmuch  as  the  most  color-sensitive  materials  which  can  be  made 
are  still  deficient  in  their  red  sensitiveness  compared  with  their 
sensitiveness  to  the  green  or  blue,  it  is  advisable  that  the  maxi- 
mum energy  of  the  light  source  should  be  shifted  towards  the  red 
end  of  the  spectrum  as  compared  with  daylight;  in  fact,  the  high- 


954     TRANSACTIONS  OF  IEEUMINATING  ENGINEERING  SOCIETY 

est  efficiency  will  be  realized  with  a  quality  of  light  where  the 
energy  maximum  is  about  A6oo/*/ji,  and  any  source  approximating 
this,  provided  its  spectrum  is  continuous  or  nearly  continuous, 
will  be  of  suitable  quality,  the  decision  as  to  which  illuminant 
is  to  be  used  resting  chiefly  on  the  question  of  its  visual  efficiency 
and  its  suitability  in  other  respects,  such  as  area  and  steadiness. 

The  "ordinary"  materials,  which  comprise  by  far  the  greater 
quantity  of  all  photographic  materials  used,  require  a  source  of 
light  of  which  the  maximum  is  in  the  blue  violet  and,  indeed,  the 
energy  maximum  of  these  materials  is  between  \380n1x  and  \460n11, 
varying  somewhat  from  one  material  to  another  but  having 
X440fi/j.  as  a  fair  average  for  the  maximum  of  the  negative  mater- 
ials of  this  group.  The  photographic  efficiency,  therefore,  of  a 
light  for  use  in  ordinary  negative  making  depends  upon  its  in- 
tensity around  A440/UJU. 

Another  question  than  efficiency,  however,  enters  into  the  choice 
of  a  light  for  negative  making;  the  latitude  of  the  photographic 
emulsion  varies  very  rapidly  with  its  absorption,  and  the  scale, 
gradation,  and  latitude  of  photographic  materials  depend  upon 
the  wave-length  of  the  light  to  which  they  are  exposed,  since  the 
absorption  varies  greatly  with  the  wave-length,  the  scale  being 
greater  the  shorter  the  wave-length.  Other  things  being  equal, 
a  negative  taken  by  light  of  A48o/u,/u,  will  have  a  shorter  and  steeper 
scale  and  less  perfect  gradation  than  if  it  were  taken  by  light  of 
A400/X/*. 

Halation  is  caused  by  the  penetration  of  light  through  the 
emulsion  and  its  reflection  from  the  back  of  the  support,  there 
being  more  halation  the  longer  the  mean  wave-length  of  the  il- 
luminant employed,  since  the  emulsion  is  more  transparent  the 
lower  the  frequency  of  the  light.  Where  halation  is  a  difficulty, 
therefore,  as,  for  instance,  in  portraiture  or  cinematographic 
work,  it  is  desirable  to  use  an  illuminant  where  the  photographic 
effect  is  largely  in  the  ultra-violet  rather  than  one  which  depends 
upon  the  longer  wave-length  end  of  the  blue  violet  for  its  effect. 

It  is  an  advantage,  therefore,  both  for  the  attaining  of  the  best 
gradation  and  for  the  reduction  of  halation  to  a  minimum  to  use 
for  these  ordinary  materials  light  of  an  average  wave-length  as 
near  as  possible  to  A400/i|u.  rather  than  light  having  its  maximum 
near  X^yofifi. 


MEES:     ARTIFICIAL   IU.UMINANTS 


955 


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956     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  third  class  of  materials,  sensitive  only  to  the  ultra-violet, 
naturally  require  illuminants  producing  as  much  ultra-violet  as 
possible,  and  the  efficiency  of  the  illuminant  depends  largely  upon 
the  intensity  of  the  ultra-violet  light  which  can  get  through 
glass,  because  it  must  be  remembered  that  the  ultra-violet  light 
which  cannot  penetrate  glass  is  of  no  use  in  photography,  where 
the  lenses  or  negative  supports  will  cut  out  all  rays  below  A330JU/A. 
It  may  be  mentioned  that  carbon  tissue,  photogravure  tissue, 
bichromated  fish  glue  and,  in  fact,  all  the  materials  which  depend 
on  the  sensitiveness  of  bichromate  are  more  sensitive  in  the  blue- 
violet  than  in  the  ultra-violet,  the  maximum  sensitiveness  of 
these  materials  being  near  A460/X/X. 

The  table  on  the  ninth  page  summarizes  the  various  qualities  of 
the  chief  artificial  illuminants.  The  figures  for  visual  and  photo- 
graphic efficiency  are  from  the  paper  by  Messrs.  Jones,  Hodgson 
and  Huse,  100  being  taken  as  the  efficiency  of  sunlight. 

It  will  be  seen  that  almost  all  sources  of  artificial  illumination 
have  application  in  some  branch  or  other  to  photography.  Each 
source  has  its  own  particular  sphere  of  application,  and  no  one 
source  is  suitable  for  all  purposes.  Claims  are  often  made  on 
behalf  of  one  or  other  method  of  producing  light  as  being  the 
ideal  source  for  all  purposes,  but  such  exaggerated  claims  only 
do  harm  to  the  cause  which  they  are  intended  to  advance,  and  it 
is  better  to  recognize  that  photography  is  a  wide  field,  having 
many  sub-divisions,  and  that  nearly  all  sources  of  light  can  be 
applied  with  special  advantage  in  some  one  or  other  of  those 
divisions. 

DISCUSSION. 

Mr.  M.  Luckiesh  :  My  side  of  this  subject  involving  the  de- 
velopment of  a  photographic  tungsten  lamp  and  the  general  appli- 
cation of  the  tungsten  lamp  to  photography  was  presented  before 
this  Society  in  January  (Trans.  I.  E.  S.,  vol.  X,  No.  2,  p.  149, 
1915),  and  I  believe  Dr.  Mees  is  in  general  agreement  with  the 
conclusions  presented  in  that  paper.  It  is  very  difficult  and  I 
believe  inadvisable  to  attempt  to  draw  sweeping  conclusions  in 
dealing  with  such  a  subject  as  photographic  illuminants,  and  I 
am  glad  to  hear  Dr.  Mees  qualify  some  of  his  conclusions  while 
presenting  his  paper. 


ARTIFICIAL   IU/UMINANTS  957 

With  the  recent  increase  in  the  efficiency  of  tungsten  lamps, 
there  appeared  the  first  important  opportunity  for  the  tungsten 
lamp  to  enter  the  photographic  field,  therefore  we  made  an  exten- 
sive study  of  the  subject  in  relation  to  the  tungsten  lamp.  This 
brought  us  into  the  practical  application  of  our  developments  and 
we  have  long  ago  realized  that  in  portraiture  (the  chief  field  at 
which  we  aimed)  the  personal  opinions  of  photographers  dif- 
fered so  that  no  general  decisions  as  Dr.  Mees  attempts  to  give 
in  his  tables  are  worth  much.  If  the  author  of  this  paper  repre- 
sented the  composite  portrait  photographer  his  conclusion  would 
be  of  considerable  interest  but  very  likely  such  is  not  the  case 
because  opinions  are  so  varied. 

The  tungsten  lamp  at  present  can  not  be  introduced  into  all 
photographic  fields.  It  is  operating  at  present  with  considerable 
success  in  portraiture,  color  photography,  printing,  enlarging, 
copying,  and  to  some  extent  in  moving-picture  production.  The 
principal  development  has  been  in  the  blue-bulb  photographic 
tungsten  lamp  which  emits  a  light  that  approximately  matches 
daylight  in  color  and  by  absorbing  some  of  the  rays  that  do  not 
affect  ordinary  plates  a  light  of  high  actinic  value  per  lumen  is 
obtained.  The  actinic  value  per  lumen  is  roughly  the  same  as 
daylight  with  the  result  that  short  exposures  without  glare  can 
be  obtained  in  portraiture.  The  actinic  value  and  color  of  the 
light  approaching  closely  to  that  of  daylight,  makes  it  possible  to 
use  this  illuminant  in  combination  with  daylight.  This  has  been 
a  desirable  feature  in  many  cases.  The  success  of  the  unit  has 
been  demonstrated  by  thousands  of  practical  installations  and 
demonstrators  of  a  large  photographic  supply  house  are  com- 
pletely equipped  with  them.  Opinions  of  noted  portrait  photo- 
graphers are  much  more  valuable  than  such  a  summary  as  is 
given  in  this  paper  by  one  who  in  presenting  the  paper  stated 
that  he  could  not  qualify  as  portrait  photographer  or  as  an  expert 
in  most  of  the  fields  considered.  Such  a  unit  as  the  photographic 
tungsten  lamp  has  an  additional  feature  of  merit  namely  the  ease 
of  control  by  rheostats  or  reactances.  As  I  have  stated  on  several 
occasions  the  lamps  operate  satisfactorily  at  normal  voltage  but 
inasmuch  as  photographic  conditions  are  so  different  from  or- 
dinary lighting  conditions,  it  is  justifiable  to  operate  these  lamps 
considerably  above  normal  voltage  thereby  taking  advantage  of  a 


958     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

tremendous  gain  in  actinic  value.  Dr.  Mees'  data  and  conclusions 
are  no  doubt  based  upon  normal  operating  voltage.  They  would 
have  been  still  more  favorable  to  the  tungsten  lamp  if  based  on 
a  voltage  above  normal  which  is  justifiable. 

Dr.  Mees  stated  that  in  the  moving-picture  studio  the  aperture 
at  which  pictures  are  taken  is  F8.  Several  producers  have  stated 
to  me  that  F5.6  is  the  maximum  aperture  necessary  for  indoor 
work  and  that  on  many  sets  F4.5  is  used  indoors. 

The  clear  tungsten  lamp  has  been  found  successful  in  color 
photography  but  Dr.  Mees  fails  to  give  the  blue-bulb  photographic 
tungsten  lamp  any  mark  in  this  column.  Apparently  he  believes 
it  has  no  continuous  spectrum  because  any  illuminant  having  a 
continuous  spectrum  is  at  least  "very  poor"  for  color  photo- 
graphy. Color  photography  is  at  present  a  very  crude  process 
yielding  far  from  perfect  results.  I  have  found  that  the  blue- 
bulb  lamp  yields  practically  the  same  results  as  daylight  even 
when  the  same  filters  are  used.  Of  course  it  is  wasteful  to 
throw  away  light  that  is  photographically  active  and  we  would 
not  recommend  the  blue-bulb  lamp  for  general  adoption  in  color 
photography.  However,  these  are  studios  in  which  some  work  is 
done  along  this  line.  If  these  studios  are  equipped  with  blue-bulb 
photographic  lamps  for  portraiture  I  wish  to  assure  the  operators 
that  they  can  use  these  lamps  very  successfully  for  color-photo- 
graphy. Quite  the  same  argument  holds  for  enlarging.  Dr. 
Mees  fails  to  give  a  mark  to  the  blue-bulb  photographic  lamp  in 
this  column  which  is  again  misleading. 

One  great  advantage  of  a  portable  unit  such  as  the  tungsten 
photographic  lamp  is  that  it  can  be  placed  in  any  position.  This  is 
a  dominating  feature  in  portraiture  after  actinic  value  has  passed 
the  test.  Dr.  Mees  does  not  lay  any  stress  upon  this  point,  but 
an  acquaintance  with  a  few  hundred  studios  equipped  with  such 
a  unit  would  convince  him  that  there  are  many  features  to  be 
considered  in  making  out  tables  such  as  he  has  attempted. 

Inasmuch  as  I  have  gone  into  detail  on  this  subject  on  several 
occasions,  I  will  not  discuss  it  further  but  will  conclude  by  stating 
that  Dr.  Mees  has  presented  a  personal  opinion  in  this  paper 
which  loses  weight  inasmuch  as  he  stated  in  introducing  his 
paper  that  he  could  not  qualify  as  an  expert  in  many  of  the  fields 


ARTIFICIAL   ILLUMINANTS  959 

which  he  discussed.  After  all  the  conclusions  of  those  who  use 
illuminants  daily  in  various  photographic  fields  will  determine  the 
future  of  photographic  illuminants. 

Mr.  W.  R.  Mott:  Dr.  Mees'  paper  represents  a  very  broad 
subject  and  one  that  deals  with  an  enormous  variety  of  processes. 
I  admire  very  much  his  sound  and  careful  treatment  of  the  whole 
subject  and  I  agree  with  him  in  nearly  all  respects.  While  ad- 
mitting the  superior  efficiency  of  the  flame  arc,  he  has  suggested 
some  of  the  objections  to  the  flame  arc,  namely,  that  of  fumes, 
odor  and  the  question  of  its  being  a  concentrated  source  of  light. 
With  regard  to  fumes  and  odor,  these  can  be  taken  care  of  by 
placing  a  little  ammonium  carbonate  in  a  cabinet  with  a  diffusing 
screen.  Such  a  cabinet  was  exhibited  two  years  ago  before  two 
hundred  photographers  and  no  one  complained  in  the  least  of 
odor,  although  it  was  running  (nearly  continuously)  during  the 
four  days.  The  construction  of  such  a  cabinet  may  be  described 
as  about  5  feet  across,  7  feet  high  and  3  feet  deep.  It  is  arranged 
with  the  curtain  at  a  45  °  inclination  both  vertically  and  on  the 
side  so  that  a  perpendicular  from  the  center  of  the  curtain  enters 
the  field  where  maximum  illumination  is  desired.  Such  a  cabinet 
(with  white  flame  arc)  has  been  in  satisfactory  commercial  oper- 
ation in  a  portrait  studio  for  over  five  years  in  Cleveland.  Since 
then  others  have  been  using  the  flame  arc  on  quite  an  extensive 
scale. 

Since,  other  things  being  equal,  the  test  comes  on  the  question 
of  efficiency,  I  wish  to  call  attention  to  the  fact  that  the  flame 
arc  is  ahead  of  all  the  other  sources  of  light  for  efficiency  in 
the  high  amperage  arcs.    This  is  shown  in  the  following  tables. 

Line  volts  Arc  volts  Amperes 

White  flame  arc  (open) 115  63          28.0 

Nitrogen  lamp,  clear  globe  ... .      117  117            6.7 

Nitrogen  lamp,  blue  globe 115  115            8.5 

The  gas-filled  incandescent  lamp  with  a  blue  bulb  taking  8.5 
amperes  gave  485  mean  spherical  candlepower.  The  candlepower 
for  the  28  ampere  flame  arc  was  5130.  (For  equal  line  wattage 
the  flame  arc  gave  over  three  times  the  candlepower.)  The  candle- 
power  efficiency  is  not  only  much  in  favor  of  the  white  flame 
arc,  but  also  there  is  the  quality  of  the  light  which  is  an  almost 


Mean 
candle- 

Spherical 
photo. 

power 

power 

5.I30 

IOO 

866 

4 

485 

5 

960     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

exact  duplicate  of  sunlight  plus  blue  sky.  This  means  that  the 
light  is  bluer  than  that  of  the  lamp  with  a  blue  glass  bulb  (and 
because  of  the  higher  content  of  blue,  violet  and  ultra-violet), 
and  the  light  is  photographically  more  efficient. 

Dr.  MEES :    What  was  the  material  ? 

Mr.  Mott:     Solio  paper. 

Dr.  Mees  :  That  is  the  most  disadvantageous  paper  one  could 
select;  it  is  only  sensitive  to  ultra-violet  light. 

Mr.  Mott  :  I  tested  it  through  glass  and  found  that  the  ultra- 
violet light  of  the  white  flame  arc  was  nearly  the  same  in  amount 
and  quality  as  in  sunlight  plus  blue  sky. 

A  Member:  Might  I  add  that  these  tests  were  made  for  wet 
plates. 

Mr.  Mott:  In  regard  to  other  photo-chemical  reactions,  as 
in  dye  fading,  I  have  found  that  the  time  required  with  a  750- 
watt  clear  glass  gas-filled  incandescent  lamp  was  17  to  100  times 
longer  at  equal  distances  than  with  the  white  flame  arc  at  28 
amperes  on  115  line  voltage. 

I  write  these  figures  here  in  the  tabe  for  comparison.  Then, 
in  addition  to  these  factors  (candlepower,  quality  of  light, 
and  dye  fading  tests)  we  must  remember  that  the  flame 
arc  is  capable  of  enormous  improvement,  and  I  would  say  that 
it  is  possible  with  known  processes,  by  combining  them  all  to- 
gether to  increase  the  efficiency  not  100  per  cent,  but  300  per  cent. 
In  further  examination  of  these  efficiencies,  I  might  say  that  a 
test  was  made  by  Lux,  in  which  he  showed  that  a  gas-filled 
tungsten  lamp  using  495  volts  had  an  effect  photographically  of 
8850;  while  that  of  a  220  volt  enclosed  arc  lamp  of  9.3  amperes 
had  a  value  of  243,000.  The  quartz  mercury  arc  had  a  rather 
considerable  change  in  photographic  value  with  change  in  cur- 
rent, and  after  a  certain  amperage  decreased  in  photographic  in- 
tensity. 

A  paper,  "The  Commercial  Light  Sources  in  Photography,"  by 
Dr.  H.  Lux,  Blectrotechnische  Zeitschrift,  pages  203,  204,  April 
29,  191 5,  and  Sheppard's  book  on  Photochemistry,  page  102,  give 
some  interesting  data  on  the  photographic  power  of  various  light 
sources. 


ARTIFICIAL   ILLUMINANTS  961 

The  enclosed  arc  lamp  on  no  volts  at  28  amperes  is  not  as 
efficient  for  action  on  solio  paper  or  blue  print  paper  as  the  flame 
arc  at  the  same  amperage.  My  tests  on  blue  printing  and  on 
solio  papers  show  two  and  a  half  to  three  times  greater  speeds 
for  like  line  power.  (On  220  volts,  two  to  four  high  amperage 
flame  arcs  are  used  in  series.)  The  important  consideration  is 
that  the  white  flame  arc  on  no  volts  is  much  more  efficient  than 
the  efficient  enclosed  arc  of  high  amperage.  (Many  photographic 
operators  use  flame  carbons  even  under  semi-enclosed  arc  con- 
ditions.) 

Dr.  C.  E.  K.  Mees  (In  reply)  :  I  would  like  the  opportunity 
of  just  replying  to  the  criticism  with  regard  to  the  lens  aperture 
in  the  cinematograph  studios.  I  am  sorry  Mr.  Luckiesh  was 
misled,  and  only  wish  you  could  see  an  aperture  of  4.5  in  the 
studios;  I  shouldn't  have  any  trouble  whatever  with  sensitive 
materials.  There  is  not  enough  depth  on  the  stage  in  the  focal 
plane  to  use  such  an  aperture  as  4.5.  You  can  use  it  when  you 
are  working  with  your  actors  sitting  down  at  a  table,  but  when 
they  chase  each  other  over  the  stage  and  fall  down  stairs,  it 
doesn't  work.  With  regard  to  windows  in  studios,  and  the  sug- 
gestion that  they  be  made  smaller  and  put  nearer — that  is  satis- 
factory where  one  sitter  is  to  be  photographed;  but  studios  are 
usually  designed  to  take  groups  of  not  less  than  six  people ;  so  I 
think  you  must  be  prepared  to  make,  for  good  workers  and  large 
studios,  quite  considerable  windows.  The  artist  himself  will  cut 
that  window  down  ruthlessly  with  blinds,  but  you  cannot  help  that. 

With  regard  to  Mr.  Mott's  point — I  only  referred  to  the  fumes 
and  odor  of  the  flame  arc  when  used  for  color  photography. 
When  a  single  lamp  is  used,  there  is  no  difficulty,  but  in  color 
work  you  have  to  use  an  enormous  number  of  lamps  and  it 
is  quite  a  difficult  problem  to  handle  the  fumes  from  the  flame 
arc.  I  would  like  to  make  a  suggestion  to  Mr.  Mott,  and  I  know 
he  will  take  it  as  being  from  a  neutral.  He  has  published  these 
figures  before,  and  they  created  on  me  a  very  unfavorable  im- 
pression. If  an  illuminating  engineer  wants  to  give  figures,  I 
think  he  ought  to  give  them  in  watts  per  spherical  candle. 

As  to  comparisons  on  solio  paper,  that  would  be  satisfactory  if 


962     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

it  were  stated  that  it  was  for  the  purpose  of  wet  plates  but  not 
for  ordinary  photographic  work.  It  is  most  important,  when 
you  have  a  perfectly  good  case,  as  Mr.  Mott  has  on  photographic 
efficiency,  that  you  should  make  the  most  of  the  other  fellow's 
case. 


JONES,  HODGSON,  HUSE :    EFFICIENCIES  OE  ILLUMINANTS    963 

RELATIVE  PHOTOGRAPHIC  AND  VISUAL  EFFICIEN- 
CIES OF  ILLUMINANTS.* 


BY  L.   A.  JONES,   M.  B.   HODGSON   AND  KENNETH   HUSE. 


CONTENTS. 

PAGE 

I.  Introduction  •  964 

II.  Method 965 

III.  Apparatus • 9^7 

a.  Sensitometer. 

b.  Photometer. 

c.  Densitometer. 

IV.  Photographic  Materials 969 

a.  Ordinary. 

b.  Orthochromatic. 

c.  Panchromatic. 

V.  Sources •••  97° 

a.  Sun 97o 

b.  Sky 97o 

c.  Acetylene 971 

d.  Screened  acetylene   971 

e.  Pentane 971 

f.  Mercury  arc,  quartz  tube 971 

g.  Carbon  arc,  open 971 

h.  Carbon  arc,  white  flame  carbons 971 

i.  Carbon  arc,  enclosed,  short  arc 972 

/.  Aristo  arc,  enclosed,  long  arc 972 

k.  Magnetite  arc • 972 

/.  Carbon  incandescent 972 

m.  Tungsten,  vacuum 972 

n.  Tungsten,  gas-filled 972 

0.  Tungsten,  gas-filled,  blue  bulb    972 

p.  Mercury-vapor    972 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing Society,  Washington,  D.  C,   September  20-23,   1915. 

The   Illuminating   Engineering   Society  is  not   responsible   for   the  statements    or 
opinions  advanced  by  contributors. 

Communication  No.  30  from  the  Reasearch  laboratory  of  the  Eastman  Kodak  Co. 


964     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


PAGE 

VI.  Experimental  details  and  errors 972 

VII.  Results 974 

Typical  curves  and  data ...   970b,  975 

Efficiency  curves 97ob,  975 

a.  Carbon  incandescent 970b 

b.  Tungsten,  evacuated  975 

c.  Tungsten,  gas-filled 975 

d.  Tungsten,  gas-filled,  blue  bulb 975 

Efficiency  tables 977 


INTRODUCTION. 

It  is  well  known  that,  of  two  light  sources  which  measured 
visually  are  of  equal  intensity,  one  may  produce  a  much  greater 
effect  on  a  photographic  plate  than  the  other.  This  is  due  to  the 
fact  that  the  spectral  sensibility  curve  of  the  photographic  plate 
differs  greatly  in  shape  and  position  from  that  of  the  retina.  The 
maximum  of  the  visibility  curve  lies  at  555/t/*,  while  the  maxi- 
mum of  the  spectral  sensibility  curve  of  an  ordinary  plate  lies  in 
the  blue-violet  region  at  approximately  460^/x.  Hence,  if  we  have 
two  sources  of  equal  visual  intensity,  one  being  bluish  and  the 
other  yellowish  in  color,  the  blue  source  will  produce  the  greater 
effect  on  the  photographic  plate.  For  these  reasons  it  is  not 
possible  by  a  measurement  of  visual  efficiency  to  decide  upon  the 
effectiveness  of  a  source  for  photographic  work;  that  is  to  say, 
the  photographic  efficiency  is  not  proportional  to  the  visual 
efficiency. 

A  further  complication  arises  from  the  fact  that  different  types 
of  photographic  materials  have  very  different  spectral  sensibili- 
ties, ordinary  plates  being  sensitive  only  to  blue,  while  ortho- 
chromatic  plates  are  sensitive  to  blue  and  yellow-green,  and  pan- 
chromatic to  blue,  green  and  red.  The  problem  presented,  there- 
fore, is  the  determination  of  the  relation  existing  between  the 
visual  and  photographic  efficiencies  of  various  illuminants  when 
used  in  connection  with  photographic  materials  having  certain 
typical  spectral  sensibilities.  In  this  paper  the  work  is  confined 
to  high  speed  materials  used  for  negative  making,  no  attempt 
being  made  to  cover  the  entire  field  of  photographic  sensitive 
materials. 


JONES,  HODGSON,  HUSE :    EFFICIENCIES  OF  ILLUMINANTS    965 

METHOD. 

The  method  adopted  for  obtaining  the  desired  ratios  is  essen- 
tially that  used  in  the  determination  of  plate  speeds,  and  is  briefly 
outlined  in  the  following  paragraphs. 

If  a  strip  of  the  plate  to  be  tested  be  exposed  in  such  a  way 
that  successive  areas  receive  exposures  increasing  by  consecutive 
powers  of  2,  it  will  be  found  upon  development  that  a  series  of 
spots  of  increasing  opacity  are  obtained.  By  measuring  the 
density  of  each  of  these  spots  and  plotting  the  value  obtained 
against  the  logarithms  of  the  exposures  given,  a  curve  is  obtained 
which  is  known  as  the  characteristic  curve  of  the  plate.  Such  a 
curve  is  shown  in  Fig.  I. 

The  term  "density"  as  used  in  this  work  is  defined  as  follows : 
Let     T  =  Transmission 

Then  7p  =  Opacity,  O 

and  log  O  =  Density,  D.         D  =  —  log  T. 

It  will  be  noted  by  reference  to  Fig.  1  that  the  portion  of  the 
characteristic  curve  between  A  and  B  is  a  straight  line.  This 
line  extended  cuts  the  log  exposure  axis  at  O,  and  the  value  of 
the  exposure  at  the  point  O  is  termed  the  "inertia"  of  the  plate. 
This  "inertia"  value  is  proportional  to  the  insensitiveness  of  the 
plate,  and  the  reciprocal  of  the  inertia  is  proportional  to  the  sen- 
sitiveness or  speed  of  the  plate.  Speed  numbers  for  a  plate  are 
obtained  by  multiplying  the  reciprocal  of  the  inertia  by  some 
arbitrarily  chosen  constant.  The  inertia  value  obtained  does  not 
in  general  depend  upon  the  time  of  development  or  upon  the  con- 
stitution, concentration,  or  temperature  of  the  developer  used. 
In  Fig.  1,  curve  a  was  plotted  from  a  strip  developed  three  min- 
utes, and  curve  b  from  one  developed  six  minutes.  It  will  be 
noted  that  the  straight  line  portion  of  each  curve  cuts  the  log  E 
axis  at  the  same  point,  showing  that  the  inertia  value  is  inde- 
pendent of  the  time  of  development. 

The  value  of  the  inertia,  however,  does  depend  upon  the  quality 
of  the  light  to  which  the  plate  is  exposed.  Thus,  if  the  plate  is 
sensitive  to  blue  light  only,  a  lower  inertia  (higher  speed  number) 
will  be  obtained  when  a  bluish  light  is  used  than  when  one  of 
yellowish  color  is  employed.     Hence,  for  a  standard  source  for 


966    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

use  in  sensitometry  it  is  necessary  to  specify  not  only  the  intensity 
but  also  the  quality  of  the  light  emitted.  The  fact  that  the  inertia 
value  obtained  depends  upon  the  quality  of  the  light  to  which  the 
plate  is  exposed  offers  a  very  convenient  means  of  measuring 
the  relative  photographic  efficiencies  of  different  illuminants. 

In  testing  plates  for  speed  the  light  source  is  kept  constant  in 
quality  and  intensity,  and  the  reciprocal  of  the  inertia  value 
obtained  is  proportional  to  the  speed  of  the  plate.  Now,  if  the 
plate  speed  be  kept  constant  and  the  quality  of  the  light  changed 
by  using  different  sources,  the  reciprocals  of  the  resulting  inertia 
values  may  be  taken  as  directly  proportional  to  the  relative 
photographic  efficiencies  of  the  various  sources. 


/ 

/^ 

/ 

4 

/ 

^ 

jr 

/ 

^ 

y 

w 

/ 

s 

0 

/ 

b 

S 

% 

"a 

/f> 

5 

A 

0 

LOG  EXPOSURE 

Fig.  1. 

Suppose  that  using  source  A  an  inertia  value  of  ix  is  obtained, 
and  with  another  source  B  the  inertia  is  i2.     Then  the  photo- 

graphic  efficiency  of  B  relative  to  that  of  A  will  be  —  X  100. 

h 

Obviously,  in  making  such  a  comparison  it  is  necessary  to  choose 

some  source  to  be  used  as  a  standard.    Since  in  practical  work  a 

great  majority  of  the  plates  used  are  exposed  to  light  from  the 

sun,  it  seems  most  logical  to  adopt  that  as  the  standard  of  quality 

by  which  to  judge  all  artificial  illuminants.     Some  may  contend 

that   daylight   or   north   skylight   would   be   more   suitable  and 


JONES,  HODGSON,  HUSE :    EFFICIENCIES  OF  ILLUMINANTS    967 

nearer  to  actual  practise  as  a  standard  of  quality.  Daylight  is  a 
mixture  of  sunlight  and  skylight  in  some  indefinite  and  variable 
proportion,  and  skylight  is  likewise  indefinite  in  quality  and  not 
reproducible.  Sunlight,  on  the  other  hand,  if  taken  between 
9  a.  m.  and  3  p.  m.  on  a  clear  day,  is  of  a  very  definite  quality. 
For  these  reasons  sunlight  has  been  chosen  as  a  standard  of 
quality,  and  its  photographic  efficiency  on  any  plate  is  taken  to 
be  100  per  cent. 

APPARATUS. 
The  sensitometer  used  in  this  work  is  of  the  "falling  plate"  type. 
An  aluminum  plate  in  which  a  series  of  openings  of  varying 
lengths  are  cut  moves  up  and  down  between  a  pair  of  ways.    This 
plate  is  driven  at  a  very  uniform  rate  by  a  constant-speed  gov- 
erned motor.     The  openings  in  the  plate  increase  in  length  by 
powers  of  \/l  so  that  a  sensitive  plate  placed  behind  it  in  a  suit- 
able dark  slide  will  receive  a  series  of  exposures  increasing  by 
consecutive  powers  of  T/T;  thus,   twice  as  many  points  are  ob- 
tained as  in  the  usual  type  of  sensitometer,  allowing  the  charac- 
teristic curve  to  be  more  precisely  located  and,  hence,  the  inertia 
value  more  definitely  determined.    The  rate  at  which  the  falling 
plate  moves  is  very  constant  and  is  so  precisely  known  that  the 
time  of  exposure  can  be  determined  to  within  ±0.2  per  cent. 
In  order  to  measure  the  illumination  on  the  photographic  plate 
a  means  is  provided  by  which  a  modified  Lummer-Brodhun  pho- 
tometer head  may  be  inserted  in  place  of  the  dark  slide,  the  pho- 
tometer screen  occupying  the  same  plane  as  the  photographic 
plate  when  in  position  for  exposure.    One  side  of  the  photometer 
screen  is  illuminated  by  a  small  electric  glow  lamp  carefully 
seasoned  and  controlled  to  constant  current  by  potentiometer 
method.    This  lamp  is  mounted  on  a  small  carriage  moving  on  a 
pair  of  rails,  with  scale  and  index.    The  scale  was  calibrated  by 
means  of  a  standard  glow  lamp  set  at  varying  distances  from 
the  other  side  of  the  photometer  screen.    Thus  it  is  possible  to 
measure  very  accurately  the  illumination  incident  on  the  photo- 
graphic plate. 

The  sensitometer  is  mounted  on  a  pair  of  rails  running  along 
the  top  of  a  table  extending  down  the  side  of  the  photometer 
room.    At  one  end  of  this  table  is  the  photometer  bench  on  which 
9 


968     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

is  mounted  a  three  meter  photometer  of  the  National  Physical 
Laboratory  type.  The  rails  carrying  the  sensitometer  are  lined 
up  in  such  a  way  that  as  the  instrument  is  moved  along  the  ways, 
the  plate  holder  containing  the  plate  to  be  exposed  remains 
always  on  the  photometric  axis  of  the  bench  photometer.  The 
light  source  to  be  tested  is  mounted  on  the  photometer  and  by 
moving  the  sensitometer  along  the  rails  the  distance  between  the 
plate  and  source  can  be  adjusted,  as  desired,  to  any  value  up  to 
twelve  meters. 

The  sensitometer  is  provided  with  a  set  of  gears  so  that  the 
falling  plate  can  be  driven  at  various  velocities.  The  highest 
velocity  of  movement  gives  an  exposure  of  two  and  one-half  min- 
utes to  that  portion  of  the  plate  behind  the  longest  slot.  It  was 
found  that  for  medium  speed  plates  and  with  the  machine  run- 
ning at  its  highest  velocity  that  an  illumination  of  0.1  meter 
candle  on  the  plate  gave  the  proper  exposure  for  the  production 
of  a  complete  characteristic  curve.  Hence,  an  illumination  of  0.1 
meter  candle  was  adopted  as  standard. 

The  distance  available  (12  meters)  is  only  sufficient  to  make 
possible  the  use  of  sources  running  up  to  an  intensity  of  14.4 
candlepower ;  therefore,  in  order  to  test  high  candlepower  sources 
such  as  the  1,000- watt  gas-filled  lamps,  it  was  necessary  to  devise 
some  means  of  reducing  their  intensity  without  altering  the 
quality  of  the  light.  A  rotating  sector  cannot  be  used  on  account 
of  the  danger  of  introducing  errors  due  to  the  intermittency  of 
the  exposure  given  to  the  photographic  plate.  Various  absorb- 
ing and  diffusing  screens  were  tried  but  none  were  found  suffi- 
ciently non-selective  to  permit  of  their  being  used  in  work  of 
this  kind.  Finally,  a  lens  system  was  tried  and  found  to  be  very 
satisfactory  for  the  purpose. 

Two  lenses  of  short  focal  length  are  mounted  so  as  to  move 
along  the  photometric  axis.  The  one  nearest  to  the  source  is  so 
placed  that  an  image  of  the  source  is  formed  at  the  principle 
point  of  the  other  lens — the  one  nearest  to  the  sensitometer. 
This  arrangement  gives  a  very  uniformly  illuminated  field,  readily 
adjustable  to  any  intensity  by  varying  either  the  focal  lengths  of 
the  lenses  used  or  the  distance  from  the  source  to  the  first  lens. 

The  lenses  used  for  this  purpose  are  made  either  of  a  clear 


a 


ORDINAE-Y 


mil-1 j  •  iiiiiiiiiiiiii1111111111""11'111 

ORTHO  -CHROMATIC 


PANCHROMATIC 


Fig.  2.— Spectral  sensibilities  of  photographic  materials. 


r 

a       l 

UMENS 

=  2  3£ 

WATT 

b- 

c- 

; 

=  &.S5 
=  150 

i 

-b 

% 

f// 

/y>/ 
/  /  // 

4f. 

4f/ 

LOG  EXPOSURE 
Fig-  3- 


Fig.  4. 


JONES,  HODGSON,  HUSE  :    EFFICIENCIES  OF  IELUMINANTS    969 

white  crown  glass  or  of  quartz.  All  reduction  of  intensity,  then, 
is  made  either  by  increasing  the  distance  or  by  use  of  lenses,  and 
thus  any  change  in  the  quality  of  the  light  is  avoided.  Since 
the  sensitometer  is  of  the  falling  plate  type  the  exposures  are 
always  continuous,  and  all  danger  of  intermittency  errors  is 
avoided. 

The  photometric  measurements  were  made  on  the  bench  pho- 
tometer. The  head  is  of  the  ordinary  Lummer-Brodhun  type  and 
the  standards  used  are  certified  by  the  Bureau  of  Standards  and 
by  the  National  Physical  Laboratory.  These  standards  were 
operated  on  a  storage  battery  and  controlled  by  the  potentiometer 
method.  The  electric  sources  used  were  operated,  when  possible, 
from  the  storage  cells  and  controlled  by  potentiometer  or  by 
reliable  Weston  volt  and  ammeters.  Measurements  involving  a 
difference  in  color  were  made  directly  without  the  aid  of 
compensating  filters  or  a  flicker  photometer.  Readings  were 
made  by  two  experienced  observers,  and  errors  occurring  due  to 
a  lack  of  color  match  are  undoubtedly  much  less  than  those  due 
to  other  factors  involved  in  the  sensitometric  measurements. 

The  measurements  of  density  were  made  by  means  of  a  Mar- 
tens polarization  photometer,  the  plates  being  placed  with  the 
emulsion  side  in  contact  with  an  opal  glass  diffusing  screen  so 
that  the  values  obtained  were  for  the  diffuse  density  of  the 
deposit. 

PHOTOGRAPHIC  MATERIALS. 

Photographic  materials  used  for  negative  making,  classified 
with  respect  to  the  spectral  sensibility,  fall  into  three  distinct 
groups ;  ordinary,  orthochromatic  and  panchromatic. 

The  first  of  these,  the  ordinary,  is  sensitive  only  to  violet,  blue 
and  blue-green,  the  maximum  occurring  at  about  460/uft.  This 
is  shown  by  the  photograph  reproduced  in  Fig.  2,  which  is  a 
spectrum  photograph  made  on  an  ordinary  plate  (Seed  23)  by 
exposure  to  an  acetylene  flame.  The  photograph  was  made  in 
a  grating  spectrograph  in  front  of  the  slit  of  which  was  placed  a 
neutral  gray  wedge,  thus  causing  the  intensity  to  decrease 
logarithmically  from  one  end  of  the  slit  to  the  other.  The  curve 
outlined  by  the  dark  portion  is,  therefore,  the  resultant  of  the 


970     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

spectral  sensibility  curve  of  the  plate  and  the  spectral  energy 
curve  of  the  source — in  this  case  an  acetylene  flame. 

Materials  of  the  second  class,  orthochromatic,  are  sensitive  to 
blue  and  yellow-green,  as  is  shown  in  Fig.  2,  this  being  a  spectrum 
photograph  made  on  an  orthochromatic  plate.  In  this  case  a 
second  maximum  occurs  in  the  yellow-green  at  about  560^. 

The  third  class  of  materials,  panchromatic,  is  sensitive  to  prac- 
tically the  entire  visible  spectrum;  Fig.  2  shows  a  photograph 
made  on  a  Wratten  panchromatic.  The  panchromatic  plates  were 
used  in  this  work  without  the  interposition  of  a  colored  screen 
between  the  source  and  the  plate.  In  practise,  these  plates  are, 
as  a  rule,  used  with  a  filter  of  such  nature  that  the  resultant 
spectral  sensibility  of  the  plate  is  very  nearly  the  same  as  the 
visibility  curve  of  the  eye,  thus  giving  correct  rendering  to  the 
different  colors  in  the  subject  being  photographed.  Under  such 
conditions,  with  the  filter  adjusted  to  the  plate  and  source,  the 
relative  photographic  efficiency,  Er  ,  of  any  source  is  approxi- 
mately 100. 

One  plate  typical  of  each  class  was  chosen  for  use  in  this  work ; 
each  is  of  medium  speed  and  is  a  good  average  representative  of 
its  group.    Those  used  are  : 

a.  Ordinary — Seed  23. 

b.  Orthochromatic — Special  experimental  plate. 

c.  Panchromatic — Wratten  panchromatic. 

SOURCES. 

1.  Sunlight. — A  heliostat  was  placed  outside  a  window  at  the 
end  of  the  photometer  bench  and  a  beam  of  sunlight  reflected 
inward  along  the  axis  of  the  photometer.  The  heliostat  mirror 
is  of  clear  white  optical  glass,  silvered  on  the  back  surface.  The 
illumination  incident  on  the  photographic  plate  was  reduced  to 
0.1  meter  candle  by  crown  glass  lenses.  The  exposures  were 
made  between  1.30  and  2.30  p.  m.  on  a  clear  day. 

2.  Skylight. — The  heliostat  mirror  was  set  in  such  a  position 
that  by  looking  down  the  photometric  axis  a  portion  of  the  sky 
near  the  zenith  could  be  seen.  The  window  was  then  closed  by  a 
diaphragm  which  allowed  no  light  except  that  reflected  from  the 
mirror  to  enter  the  room.  Glass  lenses  were  used  to  reduce  the 
intensity.  Exposures  were  made  between  2.30  and  3.00  p.  m.  on 
a  clear  day. 


JONES,  HODGSON,  HUSK:    EFFICIENCIES  OF  ILLUMINANTS    971 

3.  Acetylene. — A  standard  acetylene  burner  of  the  type  pre- 
viously described  was  used.  The  flame  is  of  the  cylindrical  type 
and  is  screened  down  to  give  approximately  1.3  candlepower. 

4.  Screened  Acetylene. — The  above  source  was  screened  with  a 
blue  filter  of  such  quality  that  the  transmitted  light  matches  very 
closely  the  color  of  average  daylight. 

5.  Pentane. — A  standard  Harcourt  pentane  lamp  was  used,  be- 
ing adjusted  in  accord  with  standard  specifications. 

6.  Mercury  Arc. — A  200-250  volt  quartz  mercury  arc  running 
at  220  volts  and  3.4  amperes  was  used.  A  reflector  consisting  of 
a  highly  polished  plate  of  black  glass  2  cm.  thick  was  employed  in 
this  case.  All  the  light  utilized  was  reflected  from  the  first 
surface  (air-glass),  such  reflection  being  considered  to  be  very 
non-selective.  The  intensity  was  reduced  by  a  pair  of  quartz 
lenses. 

7.  Mercury  Arc. — The  above  source  was  screened  with  a  piece 
of  heavy  lead  glass  4  mm.  thick,  sold  under  the  trade  name  of 
"Nultra"  and  recommended  for  use  in  the  absorption  of  the  ultra- 
violet rays.  This  glass  is  quite  colorless  and  transparent,  the 
sample  used  having  a  transmission  (measured  visually)  of  about 
90  per  cent. 

8.  Mercury  Arc. — The  conditions  were  the  same  as  described 
under  No.  6,  the  one  exception  being  that  a  clear  white  crown 
glass  lens  was  substituted  for  one  of  the  quartz  lenses  used  prev- 
iously. 

9.  Carbon  Arc,  Open. — An  automatic  feed  arc,  with  carbons  at 
right  angles,  was  used  for  this  test.  The  positive  carbon  was 
coincident  with  the  photometric  axis,  the  crater  facing  the  sensi- 
tometer.  The  arc  was  operated  on  1 10  volts,  d.  c,  and  a  current 
of  6  amperes  was  used.  The  drop  across  the  arc  was  about  60 
volts.  The  positive  carbon  was  about  6  mm.  in  diameter  and  was 
cored.    Intensity  was  reduced  by  glass  lenses. 

10.  Carbon  Arc,  White  Flame  Carbons. — A  115  volt  d.  c.  arc 
with  a  10  mm.  white  flame  carbon  below  and  a  13  mm.  cored  car- 
bon above.  The  arc  was  connected  so  as  to  make  the  lower  car- 
bon -f  and  was  mounted  in  such  a  way  that  the  flame,  which  was 
about  2.5  to  3  cm.  long,  occupied  a  position  on  the  photometric 
axis.    The  intensity  was  reduced  by  means  of  one  quartz  and  one 


9/2     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

crown  glass  lens.    The  voltage  across  the  arc  was  about  85  volts 
and  the  current  24  to  26  amperes. 

11.  Enclosed  Arc. — In  this  case  the  arc  was  enclosed  in  a  glass 
cylinder  provided  with  close  fitting  metal  ends.  The  carbons  were 
of  the  ordinary  cored  type,  placed  at  right  angles  to  each  other, 
the  positive  crater  being  on  the  photometric  axis  and  facing  the 
sensitometer.  It  was  run  on  no  volts,  d.  c,  and  consumed  8 
amperes,  the  drop  across  the  arc  being  65  volts. 

12.  Aristo  Arc. — This  was  an  enclosed  arc  with  carbons  verti- 
cal, positive  above.  It  was  operated  on  220  volts,  d.  c,  and  con- 
sumed 16  amperes.    The  length  of  arc  was  approximately  2.5  cm. 

13.  Magnetite  Arc. — This  was  of  the  ordinary  commercial  type 
running  on  no  volts,  d.  c,  and  using  a  current  of  4  amperes.  In- 
tensity was  reduced  by  glass  lenses. 

14.  Carbon  Glow  Lamp. — For  these  tests  a  50-volt  lamp  with 
hairpin  type  filament,  giving  16  cp.  at  normal  voltage  was  used. 
Tests  were  made  at  several  points,  beginning  at  1  cp.  and  running 
up  to  21  cp.  The  m.  h.  cp.  was  determined  by  the  point  to  point 
method  and  a  reduction  factor  of  0.79  was  assumed  for  obtaining 
the  mean  spherical  candlepower. 

15.  Vacuum  Tungsten. — A  120  volt,  10  watt  lamp  or  the  or- 
dinary commercial  type  was  used.    Reduction  factor  =  0.78. 

16.  Nitrogen-filled  Tungsten. — A  120  volt,  400  watt  lamp  was 
employed,  tests  being  made  at  various  points  between  59  and  130 
volts.    Reduction  factor  =  0.86. 

17.  Photolite  Tungsten,  Blue  Glass  Bulb. — A  120  volt,  1,000 
watt  G.  E.  photolite  was  used,  being  operated  at  various  voltages 
from  55  up  to  134.    Reduction  factor  =  0.88. 

18.  A  mercury-vapor  arc  in  a  glass  tube  45  x  2.8  cm.  was 
used.  The  tube  was  operated  on  115  volts  d.  c,  the  drop  across 
the  tube  being  33  volts  with  a  current  of  3.5  amperes.  The 
tube  was  mounted  so  as  to  intersect  the  photometric  axis  at  an 
angle  of  900  and  a  diaphragm  being  so  placed  that  a  section  of  the 
tube  2  cm.  long  midway  between  the  ends  of  the  tube  and  on  the 
photometric  axis  was  used  in  exposing  the  plates. 

EXPERIMENTAL  DETAILS  AND  ERRORS. 
In  exposing  the  plates  the  source  to  be  tested  was  placed  on 
the  photometer  and  conditions  so  adjusted  that  the  illumination 


JONES,  HODGSON,  HUSE:    EFFICIENCIES  OF  ILLUMINANTS    973 

on  the  plane  of  the  photographic  plate  was  o.i  meter-candle.  For 
sources  under  14.4  cp.  this  was  done  by  computing  from  the 
known  candlepower  the  distance  required  and  setting  the  position 
of  the  sensitometer  accordingly.  For  sources  of  greater  intensity 
the  reducing  lenses  were  placed  in  position  and  the  sensitometer 
adjusted  to  such  a  position  that  the  required  illumination  was  ob- 
tained. This  was  determined  by  readings  taken  on  the  illumin- 
ometer  attached  to  the  sensitometer,  the  probable  error  of  the  value 
thus  determined  being  approximately  ±2  per  cent.  A  light  tight 
partition  separated  the  source  and  photometric  apparatus  from 
the  portion  of  the  room  containing  the  sensitometer,  an  opening 
on  the  photomertic  axis  admitting  light  from  the  source  to  the 
photographic  plate.  Screening  diaphragms  placed  at  proper  in- 
tervals prevented  any  stray  light  from  reaching  the  plate,  while 
being  exposed.  All  walls  and  ceilings  were  painted  dead  black 
to  prevent  reflections. 

The  photographic  plates  were  backed  in  order  to  prevent  hala- 
tion and  development  was  done  with  a  standard  pyro-soda  devel- 
oper used  at  a  fixed  temperature,  70  °  F.  The  plates  were  devel- 
oped in  a  tray  which  was  rocked  continually  by  hand  during  de- 
velopment. This  method  has  been  found  to  give  the  most  satis- 
factory results  where  uniformity  of  development  is  desired. 

Three  to  six  plates  were  exposed  under  each  condition  and  the 
average  of  the  inertia  values  obtained  was  used  in  calculating  the 
photographic  efficiency. 

The  experimental  error  liable  to  occur  in  work  involving  the 
sensitometry  of  photographic  materials  are  numerous  and  rather 
large.  By  using  a  "falling  plate"  sensitometer  all  possibility  of 
errors  due  to  an  intermittent  exposure  was  eliminated.  Errors 
arising  from  a  failure  of  the  reciprocity  law  were  eliminated  by 
keeping  constant  the  exposure  time  and  the  illumination  on  the 
plate.  The  exposure  times  were  determined  to  within  ±0.2  per 
cent,  and  the  illumination  on  the  plate  to  within  ±2.0  per  cent. 
Variations  due  to  lack  of  uniformity  of  coating  and  to  inequalities 
in  sensitiveness  may  in  some  cases  amount  to  as  much  as  20  per 
cent,  from  plate  to  plate.  However,  by  making  several  exposures 
and  averaging  the  results  the  uncertainty  can  be  reduced  to  a 
probable  error  of  about  ±5  per  cent.     The  total  probable  error 


974    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

in  values  given  in  this  paper  is  estimated  at  approximately  ±7 

per  cent. 

RESULTS. 
In  Fig.  3  are  shown  three  curves  obtained  from  three  groups 
of  plates  (Seed  23)  exposed  to  a  nitrogen  filled  tungsten  lamp 
operated  at  three  efficiencies.  The  exposure  was  the  same  in  all 
cases  and  the  shift  in  the  inertia  value  indicates  the  increase  in 
photographic  efficiency  corresponding  to  the  increase  in  visual  ef- 
ficiency at  which  the  lamp  was  operated.  In  Table  I  are  given 
the  data  obtained  from  the  individual  plates  of  the  group  from 
which  curve  A,  Fig.  3,  was  plotted.  This  table  of  data  is  pre- 
sented merely  to  show  the  order  of  agreement  that  can  be  ex- 
pected in  work  of  this  nature. 

TABLE  I. 

Density 


Step 

Exposure 
M.  C.  S. 

No.  108 

No.  109 

No.  no 

No.  in 

Mean 

I 

0.06 

O.O 

O.O 

O.O 

O.O 

O.O 

2 

0.08 

O.OI 

0.0 

0.02 

O.03 

0.02 

3 

O.I2 

O.05 

O.03 

0.09 

O.08 

O.08 

4 

O.17 

O.16 

O.I2 

O.17 

O.16 

O.15 

5 

0.24 

O.3O 

O.27 

O.27 

0.26 

O.27 

6 

0.34 

O.46 

0.43 

O.42 

O.41 

0.43 

7 

O.47 

O.68 

0.63 

O.63 

O.58 

0.61 

8 

O.67 

O.92 

0.87 

0.86 

O.83 

0.87 

9 

0.94 

I.20 

1. 14 

I. IO 

I.09 

1.13 

10 

i-33 

1-43 

I.32 

1-43 

I.29 

i-37 

11 

1.88 

i-73 

I.60 

I.60 

i-57 

1.62 

12 

2.66 

1.97 

I.83 

I.87 

1.82 

1.87 

13 

3-75 

2.29 

2.13 

2.IO 

2.10 

2.16 

*4 

5-31 

2.72 

2.38 

2.45 

2.48 

2.51 

15 

7-5o 

2.96 

2.91 

2.9I 

3-i6 

2.98 

16 

10.60 

— 

— 

— 

— 

— 

17 

15.00 

— 

— 

— 

— 

— 

Log? 

o.33 

O.32 

o-35 

o.33 

o-332 

i 

0.214 

0.209 

0.229 

0.214 

0.216 

S 

4.67 

4-79 

4-37 

4.67 

4.62 

The  results  obtained  from  the  exposures  made  to  sunlight  are 
as  follows : 

On  Seed  23  (ordinary  blue  sensitive) 

log  i  =  2.86 
i  =  0.0725 

Sensitiveness  =  —7-  =  1^.8. 
i 

On  Experimental  Ortho.     (orthochromatic) 

log  **=  2.71 
i  =  0.0513 

Sensitiveness  =  — r  =  19.5. 


JONES,  HODGSON,  HUSE  :    EFFICIENCIES  OF  ILEUMINANTS    975 


On  Wratten  panchromatic  (panchromatic) 

log  i  =  2.796 
*  =  0.0625 

Sensitiveness  = 


16.0. 


Fig.  5- 


60 

NITRO 

SEN  F 

LLED 

TUNG 

>TEN 

a- 
b- 
c- 

ORDir 
ORTI- 
PANC 

ARY  P 
OCHRC 
HROM 

LATE 
MATIC 
\T1C 

0 

u70 
0 

s*o 

^0 

e 

''o 

0 
C 

fceo 

u 

> 

"6 

c 

'b 

0 

•"& 

'5 

iLl 

0=50 

S* 

0 ** 

xt£ 

^ 

0  ^ 

*/- 

LUME 

« 

WAT 

r 

10          12  14          16  15         20        22        24        23 


Fig.  6. 


Since  sunlight  is  used  as  a  standard  of  comparison  in  this  work, 
its  efficiency  on  each  plate  is  assumed  to  be  ioo  per  cent,  and  the 
relative  photographic  efficiency  of  any  illuminant  is  obtained  by 


976    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


taking  the  ratio  (xioo)  of  the  sensitiveness  value  -r-  obtained 

with  that  source  on  a  given  plate,  to  that  obtained  with  sunlight 
on  the  same  plate.  This  ratio  is  termed  the  relative  photographic 
efficiency  and  is  designated  by  the  symbol,  Er  .  Therefore,  if  the 
relative  efficiency  ~Er  of  a  source  is  50  per  cent. ,  in  order  to  obtain 
a  given  effect  on  a  photographic  plate  twice  as  great  an  exposure 
(measured  in  meter  candle  seconds)  must  be  given  when  using 
that  source  as  would  be  required  in  case  sunlight  were  used. 

In  Table  II  is  given  a  complete  set  of  data  obtained  by  using  a 
nitrogen  filled  tungsten  lamp  at  various  efficiencies  on  an  ordi- 
nary blue  sensitive  (Seed  23)  plate.  Four  plates  were  exposed 
at  each  efficiency  and  the  individual  log  i  values  are  given  in  the 
table,  the  Er  values  being  computed  from  the  mean  of  each  group. 
The  agreement  between  the  log  i  values  in  this  set  is  somewhat 
better  than  the  average  with  the  exception  of  the  third  group.  In 
this  group  (at  9.67  lumens  per  watt)  the  maximum  deviation 
from  the  mean  of  the  inertia  values  is  -f-22  per  cent.  This  is 
much  greater  than  the  average  deviation  existing  and  can  only 


Fig.  7- 


be  ascribed  to  inequalities  of  coating  or  sensitiveness,  since  all 
other  errors  are  known  to  be  less  than  ±5  per  cent. 


JONES,  HODGSON,  H USE  I    EFFICIENCIES  OF  ILLUMINANTS    977 


59 


78 


TABLE  II. 

Source — Nitrogen-filled  tungsten. 

Watts,  400. 

Volts,    120. 

Reduction  factor,  0.88. 
Plate— Seed  23  (Ordinary,  blue  sensitive). 
Exposure — Meter-candle  seconds  =  15.0. 

Illumination  on  plate  =  0.10  m.c. 

Time  =  150  sec. 

Sensitometric  data 


Photometric  data 


Volts       Amps.    M.h.cp. 


2.42 


2.8l 


30.8 


Rumens 
Watt 


2.38 


5.61 


hog  1 

o-33 
0.32 

o.35 
o.33 

M  0.33 

0.26 
0.26 
0.26 
0.27 

M  0.26 


0.214 


-7-  Er 


4.67 


0.182  5.50 


34 


40 


95.6     3.12       274.0 


8.55 


0.29 
0.15 
0.20 
0.18 


0.20 


0.160 


6.25 


45 


3-34      5M.o 


15.4 


0.10 
0.13 
0.12 
0.12 

0.12 

0.06 
0.07 
0.06 
0.08 


0.132 


7.58 


55 


120        3.52      760.0 


19.9 


0.07 

0.06 
0.05 
0.05 
0.05 


0.1 17 


8-55 


62 


125        3.61      920.0 


22.6 


0.05 

0.03 
0.03 
0.03 
0.05 


0.1 12        8.93        65 


13°        3-66    1080.0 


25.0 


0.03 


0.107 


9-35 


68 


978     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


In  Tables  III  to  VI,  inclusive,  are  given  the  summarized  results 
on  glow  lamps,  as  follows : 

Table  III — Carbon  from  0.5  to  3.8  lumens/watt. 
Table  IV — Tungsten  from  3.23  to  10.9  lumens/watt. 
Table     V — Nitrogen  tungsten  from  2.48  to  23.8  lumens/- 

watt. 
Table  VI — Nitrogen  filled  blue  bulb  Photolite,  1.00  to  12.8 
lumens/watt. 
The  data  on  these  sources  are  given  as  curves  in  Figs.  4,  5,  6 
and  7.     The  curves  obtained  are  all  straight  lines  within  the 
limits  of  experimental  errors  and  over  the  ranges  of  efficiencies 
used. 

tXble  in. 

Source — Carbon  glow  lamp. 

Volts,    45. 

Watts,  40. 

Reduction  factor,  79. 
Exposure — 15.0  meter-candle  seconds. 

Illumination  ==  0.10  m.c. 

Time  =  150  sec. 

Photographic  material 


Visual  eff. 
lumen 
watt 

2-33 
6.09 
9.00 
IO.9 


Visual  eff. 
lumen 
watt 

Ordinary 

Orthochromatic 

Panchromatic 

S 

nr 

S 

Ur 

S 

Kr 

0.51 

1-7 

12 

4.2 

22 

5-1 

32 

I.09 

2.2 

17 

4.8 

25 

5-6 

35 

I.79 

2.6 

19 

5-9 

30 

6.2 

39 

2.25 

2.8 

21 

5-9 

30 

6.6 

4i 

2.70 

3-i 

23 

6.2 

32 

6.9 

43 

3-14 

3-4 

25 

7.0 

36 

7-5 

47 

3-4i 

3-7 

27 

7-4 

38 

7-5 

47 

3-9° 

4.1 

3° 

7.2 

37 

7-7 

48 

TABLE  IV. 
Source — Tungsten  glow  lamp. 

Watts,    10. 

Volts,  120. 

Reduction  factor,  78. 
Exposure — 15  meter-candle  seconds. 

Illumination  =  0.10  m.c. 

Time  --  150  sec. 

Photographic  material 


S 
3-1 

4-3 
4.8 

5-2 


Ordinary 

23 
31 

35 
38 


Orthochromatic 


S 
6.05 
7.2 
8.4 
8.9 


31 
37 
43 
46 


JONES,  HODGSON,  HUSE:    EFFICIENCIES  OF  ILLUMINANTS     979 


TABLE  V. 

Source — Nitrogen-filled  tungsten. 

Watts,  400. 

Volts,    120. 

Reduction  factor  88. 
Exposure — 15  meter-candle  seconds. 

Illumination,  =  0.10  m.c. 

Time  =  150  sec. 

Photographic  material 


Visual  eff . 
lumens 

Ordinary 

Orthochromatic 

Panchromatic 

watt 

S 

Er 

S 

Er 

S 

Er 

238.0 

4.8 

35 

8.6 

44 

8-3 

52 

5.6l 

5.o 

40 

8.8 

45 

9-1 

57 

8-55 

6-3 

46 

IO.  I 

52 

9-4 

59 

15-4 

7-5 

55 

II.7 

60 

10.7 

67 

19.9 

8.6 

62 

13.0 

67 

12.0 

75 

22.6 

8.8 

64 

13-6 

70 

12.0 

75 

25.0 

9.2 

67 

14.O 
TABLE  VI. 

72 

12.5 

78 

Source- 

-Nitrogen-filled,  blue 

glass  bult 

1. 

Watts,  1,000. 

Volts,      120. 

Reduction  factor,  86. 

Exposure—  15 

meter-candle  seconds. 

Illumination  = 

=  0.10  m.c. 

Time  =  150  sec. 

Photographic 

material 

Visual  eff. 

Ordi 

nary 

Orthochromatic 

Panchromatic 

watt 

s 

Er 

S 

B, 

S 

nr 

0.9 

6.8 

49 

8.4 

43 

9.0 

56 

3.22 

8.7 

63 

IO.9 

56 

I0.6 

66 

5-8i 

10.6 

77 

14. 1 

72 

12.8 

80 

8.48 

12.4 

90 

l6.2 

83 

14.6 

9i 

10.6 

15-3 

in 

19-5 

100 

16.6 

104 

12.8 

16.3 

118 

20.5 

105 

18.1 

113 

The  results  obtained  with  other  illuminants  are  summarized  in 
Table  VII.  The  visual  efficiencies  of  some  were  not  measured 
in  this  laboratory.  In  such  cases  the  available  data  on  the  sub- 
ject were  consulted  and  from  them  an  estimate  of  the  efficiency 
existing  under  the  conditions  of  operation  employed  in  this  work 
was  made,  such  values  being  indicated  by  stars. 


980     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

TABLE  VII. 

Photographic  materials 

Visual  Ortho-                   Pan- 
efficiency  Ordinary  chromatic  chromatic 

lumens       , • ,     , « ,  , < , 

Source                                 watt  S           Er  S           Er            S          ~Br 

1.  Sun *i5o.o  13.8  100  19.5  100  16.0  100 

2.  Sky   —  25.0  181  30.0  155  2I.O  130 

3.  Acetylene    *o.7  4.1  30  8.6  44  8.3  52 

4.  Acetylene  screened *o.c>7  11. 2  81  16.5  85  14.2  89 

5.  Pentane *o.45  2.5  18  5.5  28  6.7  42 

6.  Mercury  arc — quartz..-.  *4o.o  83.0  600  98.0  500  59.0  367 

7.  Mercuryarc — nultraglass  *35.o  30.0  218  38.0  195  26.4  165 

8.  Mercuryarc — crown  glass  *37.o  44.7  324  53.7  275  39.8  249 

9.  Carbon  arc — ordinary.  ••  *i2.o  17.4  126  22.0  112  17.0  104 

10.  Carbon  arc — white  flame  *29.o  35.5  257  46.5  234  34.4  215 

11.  Carbon  arc — enclosed  ••  •  *9.o  24.2  175  34.5  177  26.4  165 

12.  Carbon  arc — "Aristo"...  *i2.o  110.0  796  209.0  1,070  119.0  744 

13.  Magnetite  arc *i8.o  14.6  106  22.4  115  13. 1  82 

14.  Carbon  glow  lamp 2.44  3.2  23  6.2  32  6.7  42 

Carbon  glow  lamp 3.16  3.4  25  6.8  35  7.2  45 

15.  Tungsten  evacuated 8.0  4.6  33  8.0  41  8.0  50 

Tungsten  evacuated 9.9  5.1  37  8.8  45  8.5  53 

16.  Tungsten  nitrogen-filled  16.6  7.7  56  12. 1  62  11. 2  70 
Tungsten   nitrogen-filled  21.6  8.8  64  13.3  68  12.2  76 

17.  Tungsten  blue  bulb 8.9  13. 1  95  17.0  87  15.2  95 

Tungsten  blue  bulb 11.0  15.0  108  19.3  99  17.0  106 

18.  Mercury-vapor *23.o  42.7  316  69.0  354  43.7  273 

As  previously  stated  the  values  of  Er  given  in  Table  VII  are 
relative  values  and  do  not  express  the  photographic  efficiencies 
of  the  various  sources  in  terms  of  the  energy  consumption  of 
that  source.  As  the  efficiency  in  terms  of  energy  consumption 
is  of  considerable  interest  the  values  obtained  have  been  reduced 
to  that  basis  and  are  given  in  Table  VIII. 

The  inertia  values  (i)  obtained  from  the  characteristic  plate 
curves  are  expressed  in  exposure  units,  that  is,  meter-candle 
seconds.  The  luminous  flux  incident  upon  unit  area  (1  square 
cm.)  at  a  meter  distant  from  a  source  of  1  mean  spherical  candle- 
power  is  -*—. ;  =  t,  lumens.   This  is  the  value  of  the  luminous 

r  47rr  100 

flux  incident  upon  a  unit  area  of  a  surface  at  which  the  illumina- 
tion is  1.0  meter-candle.     Then 

i  (in  m.  c.  s.)   .  . 

ie  — 1 is  the  inertia  value 

100 

-  .      lumens  seconds 

expressed  in  5 . 

cm. 


JONES,  HODGSON,  HUSE :    EFFICIENCIES  OF  ILLUMINANTS    981 


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982     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Now,  if  the  efficiency  of  the  source  used  is  E  ( in )  the  value 

V        watt   / 

,  .   .    lumen  seconds     1    .     , 

remains  the  same  when  expressed  in — .  ■=-  is  the 

watt  second      E 

„  .  .       watt  seconds  , 

efficiency  in  : =-.  and 

lumen  seconds 

.     _  i  (in  m.  c.  s. )  1      _  watts  seconds 

1002  E  cm. 

. i  (in  m.  c.  s.)        107  _      ergs 

100  E  cm. 

ie  is,  therefore,  the  inertia  value  expressed  in  ergs  consumed  at 
the  source  per  cm.*  at  the  plate.  This  value  is  inversely  pro- 
portional to  the  photographic  efficiency  of  the  source  when  used 
on  that  particular  plate.  The  photographic  efficiency  may  be 
obtained,  therefore,  by  taking  the  reciprocal  of  ie. 

In  order  to  make  the  results  obtained  on  different  plates  com- 
parable with  each  other  it  is  necessary  to  use  some  source  as  a 
standard.  Sunlight  is  used  as  before,  its  efficiency  being  taken 
as  100  on  each  plate. 

The  values  of  visual  efficiency  for  many  sources  were  not  meas- 
ured directly,  but  were  estimated  from  the  last  available  data 
found  in  the  literature  on  the  subject.  The  values  tabulated  in 
Table  VIII  are: 

*  (m.  c.  s. )  103  _      ergs 


E,= 


E  cm.1 

1,000  ie  (for  sun) 


(for  particular  source) 
It  will  be  noted  by  reference  to  the  curves  in  Figs.  4,  5  and  6 
that  the  curves  of  relative  efficiency  are  straight  lines  slightly 
convergent  toward  the  higher  efficiencies.  The  curve  for  the 
orthochromatic  material  lies  about  midway  between  the  other  two 
in  each  case.  In  the  case  of  the  gas-filled  lamp  with  blue  bulb 
the  curves  for  the  ordinary  and  the  panchromatic  materials  con- 
verge and  cross  at  Er  =  95  per  cent.,  while  the  ortho  curve  is 
entirely  below  them.  This  is  due  to  the  fact  that  the  glass  of 
which  the  bulb  is  made  has  an  absorption  band  in  the  green,  the 
region  of  extreme  sensitiveness  for  orthochromatic  materials. 
The  light  emitted  is,  therefore,  relatively  weak  in  the  green  and 


JONES,  HODGSON,  HUSE  '.    EFFICIENCIES  OE  IEEUMINANTS     983 

as  a  consequence  gives  low  efficiencies  on  orthochromatic 
materials. 

The  values  of  ~Er  given  in  Table  VII  enable  us  to  pick  from 
any  group  of  sources  the  one  giving  the  greatest  photographic 
efficiency  when  used  in  connection  with  either  of  the  three  typical 
classes  of  photographic  materials,  for  a  fixed  value  of  the  illumi- 
nation. The  values  in  Table  VIII,  on  the  other  hand,  enable  us 
to  choose  for  either  class  of  materials,  the  source  that  is  most 
efficient  photographically,  from  the  standpoint  of  energy  con- 
sumption. 

The  choice  of  a  source  for  any  particular  purpose  frequently 
depends  on  factors  other  than  efficiency,  but  no  attempt  is  made 
in  this  paper  to  deal  with  such  cases. 

Other  photographic  materials  such  as  wet  plates,  printing 
papers  and  processes  depending  upon  the  sensitiveness  of  bichro- 
mate involving  different  spectral  sensibilities  have  not  been  dealt 
with  in  this  paper.  The  authors  hope  at  some  future  time  to 
extend  the  measurements  to  cover  such  cases  and  also  some  other 
illuminants  not  dealt  with  at  this  time. 

The  authors  wish  to  acknowledge  their  indebtedness  and  to 
express  their  thanks  to  Mr.  R.  B.  Wilsey  for  his  able  assistance 
rendered  in  connection  with  the  experimental  work  involved  in 
this  research. 


DISCUSSION. 

Mr.  M.  LuckiESH  :  I  want  to  compliment  the  authors  for  this 
excellent  summary  and  also  to  point  out  the  fact  that  there  are 
other  important  viewpoints  from  which  to  consider  an  illuminant 
for  photographic  purposes.  We,  as  lighting  people,  are  inclined 
to  apply  ordinary  lighting  criteria  and  ideals  to  the  photographic 
field,  but  it  is  easy  to  show  this  is  not  justifiable.  I  also  want 
to  call  attention  to  the  fact  that  the  so-called  efficiencies  of  il- 
luminants for  photographic  processes  must  be  considered  a  good 
deal  as  we  should  consider  efficiencies  in  lighting;  that  is,  the 
element  of  satisfactoriness  must  enter  which  is  determined  by 
many  factors  besides  the  photographic  efficiency  given  here.  This 
discussion  is  not  presented  to  detract  from  the  value  of  this 
excellent  work  but  to  emphasize  the  other  viewpoints  so  that 
10 


984     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  illuminating  engineers  will  not  overlook  these  facts  and  as- 
sume that  the  illuminants  from  a  practical  standpoint  lie  in  the 
order  given  here  because  they  do  not.  I  am  glad  the  authors 
include  Tables  VII  and  VIII  because  in  much  of  the  photo- 
graphic field,  energy  consumption  (or  photographic  efficiency 
given  in  Table  VIII)  is  of  minor  importance  provided  it  is 
within  reasonable  bounds.  Of  more  importance  is  Table  VII 
because  it  is  necessary  to  have  a  light  of  high  actinic  value  per 
lumen  in  order  to  obtain  portraits  with  short  exposures  and 
without  glare.  In  the  portrait  studios  it  takes  only  a  few  min- 
utes to  do  the  posing  and  make  the  exposure  so  it  is  seen  that 
other  factors  may  easily  over-shadow  photographic  efficiency 
(actinic  value  per  watt).  Even  in  the  moving  picture  studios 
where  excessive  wattages  are  used,  it  has  been  found  that  energy 
consumption  is  far  from  being  the  most  important  factor.  Actinic 
value  per  lumen,  cost,  portability,  simplicity,  color,  etc.,  are 
factors  of  great  importance  to  those  who  use  photographic  il- 
luminants especially  in  portraiture  and  moving  picture  produc- 
tion. 

I  am  pleased  to  note  that  the  authors  have  checked  my 
measurements  given  for  the  gas-filled  tungsten  lamps.  Through- 
out my  work  in  converting  the  gas-filled  tungsten  lamp  (Trans. 
I.  E.  S.,  Vol.  X,  No.  2,  p.  149)  into  an  acceptable  unit  for  the 
portrait  photographers,  the  kind  of  plate  used  was  of  great 
importance.  The  ordinary  plate  which  is  used  very  predomin- 
antly in  portraiture  was  the  determining  factor  in  the  develop- 
ment of  this  photographic  tungsten  lamp.  Of  course  it  is  the 
photochemists'  dream  that  some  day  the  panchromatic  plate  will 
be  in  general  use  and  that  this  plate  will  be  cheap,  efficient,  and 
capable  of  recording  brightnesses  in  the  same  relative  value  as 
the  eye  sees  them.  That  may  be  the  ideal  but  it  is  far  from 
realization,  so  that  the  ordinary  plate  must  be  recognized  as  the 
determining  factor  in  dealing  with  the  practise  of  photography 
in  general.  This  was  done  in  the  development  of  the  blue  bulb 
for  the  photographic  tungsten  lamp  and  therefore  it  is  most 
efficient  for  these  plates.  In  Table  VII,  the  light  from  this  unit 
is  seen  to  be  comparable  with  daylight  in  actinic  value.  Another 
point  of  importance  is  the  color  of  this  light.  It  is  a  close  match 
to  daylight  when  considered  integrally.     It  does  not  match  day- 


EFFICIENCIES  OF  IEEUMINANTS  985 

light  spectrally,  but  this  is  of  no  importance  for  ordinary  plates. 
The  fact  that  this  light  is  approximately  of  the  color  and  actinic 
value  of  daylight  has  proved  to  be  highly  in  its  favor  because 
of  the  possibility  of  using  it  combined  with  daylight.  Incidental- 
ly, this  illuminant  is  satisfactory  for  orthochromatic  or  panchro- 
matic plates  and  for  color-photography  for  orthochromatic  or 
panchromatic  plates  and  for  color-photography  because  all  rays 
are  present  in  its  spectrum  although  it  is  less  efficient  for  these 
processes. 

I  want  to  emphasize  that  it  is  necessary  to  distinguish  be- 
tween the  photographic  process  and  the  visual  process,  as  the 
authors  have  done,  and  that  in  dealing  with  photography  we 
are  dealing  with  a  lot  of  'eyes'  that  differ  from  each  other  a  great 
deal  more  than  normal  eyes  differ  from  each  other,  and  that 
these  photographic  'eyes'  are  in  general  tremendously  different 
in  sensibility  from  the  human  eye.  That  means  that  we  must 
alter  our  criteria  for  judging  illuminants  for  photographic  pur- 
poses. For  instance,  the  life  which  may  be  considered  the  most 
economical  for  an  electric  incandescent  lamp  for  ordinary  light- 
ing service  will  not  be  the  most  economical  for  a  photographic 
unit.  The  authors  have  taken,  no  doubt,  the  incandescent  lamps 
operated  at  their  normal  efficiencies  which  are  determined  by 
ordinary  lighting  service  and  the  human  eye.  When  we  use 
photographic  units  a  few  minutes  now  and  a  few  in  the  next 
hour,  we  can  boost  the  efficiency  up  and  the  life  down  very 
considerably,  and  approach  a  more  economical  operating  point 
for  an  incandescent  lamp.  As  I  have  shown  in  my  papers  on 
the  subject,  a  slight  increase  in  voltage  causes  a  much  greater 
increase  in  the  actinic  value  of  the  light  from  the  tungsten  lamp 
for  ordinary  plates,  with  an  accompanying  reduction  in  life ; 
however,  by  increasing  the  voltage,  we  have  approached  the  most 
economical  point  at  which  to  operate  these  lamps  for  photogra- 
phic purposes. 

In  order  to  avoid  confusion  I  wish  to  distinguish  between  two 
units,  namely,  actinic  value  per  lumen  and  actinic  value  per  watt. 
The  relation  between  these  two  units  is  fairly  definite  (if  the 
photographic  process  is  specified)  for  a  given  illuminant  but 
the  relation  differs  with  each  illuminant.  Therefore,  in  general 
there  is  no  relation  between  the  two  units. 


986     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Mr.  h.  A.  Jones:  In  regard  to  Mr.  Luckiesh's  point  con- 
cerning other  considerations  coming  in  for  photographic  work, 
I  think  the  point  is  very  well  taken.  As  stated  in  the  paper,  we 
do  not  attempt  to  cover  all  the  points  of  advantage  and  disad- 
vantage in  the  various  sources;  but  only  treat  the  subject  from 
the  standpoint  of  illumination  and  energy;  also,  I  might  add, 
there  are  a  great  many  other  photographic  materials  having  dif- 
ferent spectral-sensibilities  which  we  have  not  treated  here,  such 
as  wet  plates,  bichromated  gelatine,  etc.  In  regard  to  the  question 
as  to  the  Aristo  arc  and  white  flame — I  believe  that  has  been 
answered  very  satisfactorily.  The  Aristo  lamp  was  an  enclosed 
arc  burning  hard  carbons  and  the  white  flame  was  an  arc  equipped 
with  the  ordinary  white  flame  photographic  carbons  burning  open. 
In  regard  to  the  quartz  lamp,  No.  6,  the  intensity  in  that  case 
was  reduced  by  means  of  quartz  lenses,  as  I  believe  is  stated 
in  the  paper.  No.  7  was  shielded  by  means  of  a  piece  of  lead 
glass  designed  and  sold  as  an  absorber  of  the  ultra-violet,  while 
in  the  case  of  No.  8,  thre  same  arc  was  used  with  the  exception 
that  a  piece  of  crown  glass,  such  as  is  used  in  making  photo- 
graphic lenses,  was  substituted,  in  place  of  the  lead  glass.  Of 
course,  the  efficiency  given  in  No.  6  could  never  be  realized  in 
case  a  glass  lens  is  used  in  the  camera,  while  the  efficiency  of 
No.  8  is  the  efficiency  that  would  be  realized  in  case  a  camera 
with  a  crown  glass  lens  were  used.  No.  18  is  the  Cooper-Hewitt 
glass  tube  mercury-vapor  arc.  In  regard  to  the  term  "falling 
plate"  as  descriptive  of  the  sensitometer  used,  I  probably  failed 
to  clearly  define  its  meaning.  The  term  is  used  among  workers 
in  photographic  sensitometry  to  differentiate  between  the  class 
of  sensitometer  in  which  the  exposure  is  continuous,  and  those 
in  which  the  exposure  is  intermittent,  as  is  the  case  when  a 
rotating  sector  is  used.  As  a  previous  speaker  has  pointed  out 
it  is  not  the  photographic  plate  which  moves,  but  a  metal  plate 
in  which  apertures  of  varying  lengths  are  cut.  This  plate  travels 
at  a  uniform  rate  between  the  photographic  plate  and  the  light 
source. 


GENERAL   REPORT  ON    GLARE  987 

GENERAL  REPORT  ON  GLARE.* 


Synopsis:  The  work  of  the  committee  the  past  year  is  summarized. 
Tentative  definitions  are  offered  of  different  classes  of  glare  and  the 
phenomenon  of  glare  is  analyzed  and  defined  with  as  much  precision  as 
seems  possible  at  the  present  time.  Limits  of  tolerance  of  the  eye  to 
brightness  conditions  above  which  limits  glare  may  be  said  to  exist  are 
stated  as  definitely  as  possible.  The  twelve  reports  supplementary  to  this 
general  report  of  the  committee  are  briefly  outlined. 


INTRODUCTION. 
The  word  glare  has  been  commonly  used  since  the  beginning 
of  illuminating  engineering  and  its  general  meaning  is  fairly  well 
understood.  However,  both  our  definitions  and  our  common 
conceptions  of  what  constitutes  glare  have  not  been  definite  or 
well  defined.  The  work  of  this  committee  the  past  year  has, 
therefore,  been  confined  mainly  to  the  analysis  of  glare  into  its 
fundamental  causes  and  the  formulation  of  precise  definitions 
and  data  relating  to  glare.  In  addition  to  this  general  report  on 
the  subject  of  glare  the  committee  has  prepared  supplementary 
reports  which  have  been  issued  from  time  to  time  during  the  past 
year  as  follows : 

1.  General  report  on  glare  (classification  and  definitions). 

2.  Diffusing  media  I  (classes  and  definitions  of  diffusion). 

3.  Diffusing  media  II  (measurement  and  theory  of  diffusion). 

4.  Papers  and  inks. 

5.  Photographic  papers. 

6.  Window  envelopes. 

7.  Interior  furnishings. 

8.  Projection  and  focusing  screens. 

9.  Diffusing  glassware. 

10.  Effect  of  glare  on  vision. 

11.  Automobile  headlights. 

12.  Interior  illumination. 

13.  Street  illumination. 

Reports  i  to  9  were  drawn  up  by  the  chairman  of  the  com- 
mittee, No.  10  by  Richtmyer,  No.  11  by  the  chairman,  No.  12 
by  Cravath,  and  No.  13  by  Vaughn. 

*  Report  No.  I.  of  the  I.  E.  S.  Committee  on  Glare. 


988     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

CLASSIFICATION. 

Conditions  for  Comfortable  Vision. — The  brightness  of  white 
diffusing  paper  in  the  open  on  a  clear  day  at  noon  is  about  three 
candles  per  square  centimeter  or  ten  lamberts  in  full  sun  and 
skylight,  or  about  three  lamberts  if  illuminated  by  sky  alone. 
This  is  about  the  upper  limit  of  comfortable,  accommodated 
vision.  The  lower  limit  is  about  a  millionth  part  of  this  or 
3  x  io-6  lambert,  about  the  brightness  of  white  paper  illuminated 
by  full  moonlight.  The  absolute  limit  of  vision  (white  threshold) 
is  about  6  x  io~10  lambert. 

Now,  the  illumination  of  full  sunlight  would  be  an  intolerable 
glare  under  either  of  two  conditions :  (a)  sudden  exposure  of  an 
eye  accommodated  to  a  much  lower  mean  brightness  or  (b)  a 
steady  exposure  with  surroundings  very  much  less  bright.  The 
first  case  is  simply  a  lack  of  accommodation  due  to  lack  of  time 
for  adjustment,  the  second  is  a  similar  lack  of  accommodation 
due  to  the  impossibility  of  accommodating  to  a  bright  spot  and  a 
dark  field  at  the  same  time.  These  illustrations  indicate  the 
relation  of  glare  to  vision.  Physiologically,  glare,  in  its  broader 
interpretation,  is  the  direct  cause  of  strained  brightness  accom- 
modation. There  are  four  classes  of  strained  brightness  accom- 
modation : 

1.  Brightness  above  the  maximum  limit  of  full  accommodation. 
Full  noon  sun  on  snow,  sand  or  water  are  examples  of  excessive 
brightness  glare.  Whatever  the  nature  of  the  adaptation  of  the 
retina  to  the  brightness  of  the  image  upon  it  (rate  of  catabolism 
of  visual  purple?)  there  is  an  upper  limit  to  it.  Brighter  images 
cause  distress  and  excessively  bright  images,  long  continued,  re- 
sult in  a  temporary  loss  of  dark  adaptation  (snow  blindness) 
lasting  for  from  a  few  hours  to  a  week.  The  sole  remedy  for  con- 
ditions causing  brightness  glare  is  the  wearing  of  absorbing 
glasses,  those  transmitting  1/10  of  the  light  (/.  e.,  of  density 
unity)  are  sufficiently  absorbing  for  snow  fields.  The  solar  disk 
may  be  viewed  comfortably  through  a  screen  whose  transmission 
is  one  millionth. 

2.  Brightness  greatly  in  excess  of  that  to  which  the  eye  is  tem- 
porarily accommodated  produces  painful  glare  lasting  nearly  until 
the  retinal  accommodation  has  reached  the  new  level.     Coming 


GENERAL   REPORT   ON    GLARE  989 

out  of  a  dark  room  into  full  daylight  is  a  familiar  example  of 
temporary  glare.  A  single  short  exposure,  such  as  is  caused  by 
lightning  at  night,  cause  flash  glare.  A  succession  of  flashes 
constitutes  flicker.  All  kinds  of  glare  of  this  class  may  be  attri- 
buted to  the  lag  of  accommodation  behind  exposure.  This  lag 
is  a  real  visual  economy,  since  we  are  constantly  viewing  objects 
of  different  brightness  and  if  there  were  no  lag  (amounting  to 
from  half  a  second  to  several  minutes)  the  wear  and  tear  on  the 
accommodation  would  necessarily  be  considerably  increased. 

3.  Brightness  localized  in  a  field  of  much  lower  or  much  higher 
luminosity.  This  is  the  case  of  contrast  glare  or  spot  glare.  The 
retina  tends  to  accommodate  itself  to  that  part  of  the  image  fall- 
ing upon  the  fovea,  in  other  words  upon  that  part  of  the  field  of 
view  upon  which  the  attention  is  centered.  We  have  no  data 
at  present  on  the  distribution  of  the  accommodation  over  the 
retina  in  the  case  of  excessive  contrast  within  the  field  of  vision 
nor  on  how  this  varies  with  the  (a)  average  luminosity  of  the 
field  (b)  the  size  of  the  brighter  areas  or  (c)  the  location  of  the 
brighter  areas  with  respect  to  the  center  of  attention. 

Details  are  discerned  by  means  of  differences  in  brightness  and 
color.  Vision  is  at  its  best  when  contrasts  are  about  1  :  20,  while 
it  is  accomplished  with  effort  at  contrasts  as  low  as  98 :  100  pro- 
vided the  general  illumination  be  sufficient,  and  without  sensible 
discomfort  if  contrasts  be  less  than  1  :  100.  Contrasts  as  high 
as  1  :  10,000  are  not  rare,  in  window  frames  against  open  sky, 
illuminants  against  their  backgrounds  or  in  spots  of  specular  re- 
flection or  transmission ;  these  constitute  contrast  glare. 

The  physiological  basis  of  contrast  glare,  is,  no  doubt,  some 
sort  of  conflicting  tendency  among  the  sets  of  nerves  controlling 
retinal  adaptation.  The  means  of  control  of  the  different  parts  of 
the  retina  are  only  partly  independent,  hence  the  general  level  of 
adaptation  represents  a  compromise  between  local  tendencies  in 
different  parts  of  the  retina.  With  but  moderate  contrasts  in 
the  field,  there  is  no  effort  toward  local  adaptation.  It  is  only 
excessive  contrasts  which  tend  to  cause  the  differential  accommo- 
dation resulting  in  discomfort. 

In  general,  no  protective  glasses  can  afford  any  relief  from 
contrast  glare.     The  sole  remedy  is  to  reduce  the  contrasts  caus- 


990     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ing  it  by  keeping  excessively  bright  spots  out  of  the  field  of  view 
or  by  properly  using  diffusing  media  of  suitable  quality.  It  is 
only  in  cases  of  contrasting  fields  differing  in  hue  that  protective 
glasses  are  of  any  avail.  These  should  be  of  the  dominant  hue 
of  the  darker  part  of  the  field. 

4.  Brightness  below  the  minimum  limit  of  accommodation 
causes  a  strain  of  whatever  controls  the  accommodation,  provided 
the  object  viewed  be  given  concentrated  attention.  Reading 
dimly  illuminated  matter  is  a  familiam  example.  This  is  not  glare 
proper  but  a  cause  producing  a  related  effect. 

Our  special  report  on  the  Effect  of  Glare  on  Vision  (Report 
No.  10)  deals  at  considerable  length  with  the  various  effects  out- 
lined above  and  includes  the  quantitative  data  at  present  available. 

Some  cases  of  glare  intermediate  between  classes  1  and  4  re- 
quire special  consideration,  cases  in  which  a  bright  field  is  com- 
posed of  numerous  fine  bright  points,  granular  glare  for  short. 
Familiar  illustrations  are  sunlight  on  rough  water,  frosted  glass, 
sand  or  rain  drops,  a  starry  sky  and  the  like.  The  resolving 
power  of  the  eye  is  about  half  a  minute  of  arc,  that  is,  the  image 
of  any  object  however  small  will  have  a  diameter  of  at  least  0.002 
mm.  on  the  retina.  The  image  of  a  distant  arc  lamp,  star  or 
glare  spot  is  spread  over  this  minimum  diameter  on  the  retina, 
hence  will  appear  of  lower  intrinsic  brilliancy  and  contrast  than 
it  really  is.  In  certain  cases  this  effect  of  angular  size  of  detail 
is  of  considerable  importance. 

Another  class  of  glare  producing  retinal  strain  is  that  in  which 
the  object  of  attention  is  overlaid  with  a  veil  either  darker  or 
lighter  than  the  object  in  which  details  are  to  be  discerned.  Pro- 
jection on  a  screen  in  a  lighted  room,  reflection  from  varnished 
wood  or  glossy  paper,  a  landscape  viewed  through  a  haze  or  a 
dirty  window  upon  which  the  sun  is  shining  are  illustrations  of  a 
bright  veil ;  a  landscape  viewed  through  a  wire  screen  not  illumin- 
ated is  an  example  of  a  dark  veil. 

Such  cases  are  called  veiling  glare.  Only  specular  reflection 
from  a  glossy  surface  causes  actual  brightness  glare  of  the  nature 
of  veiling  but  all  cases  of  veiling  cause  interference  with  vision. 
The  resulting  discomfort  depends  in  large  measure  upon  the  de- 
gree of  attention  given  the  object  viewed. 


GENERAL  REPORT  ON  GLARE  991 

The  pupillary  diameter  varies  from  2  mm.  to  7  or  8  mm. ;  that 
is,  the  area  of  the  pupil  varies  in  the  ratio  of  about  i  to  15  in 
extreme  range.  The  extreme  range  of  retinal  sensibility  is  of  the 
order  of  ten  million  to  one,  so  that  in  the  total  brightness  accom- 
modation of  the  eye,  pupillary  expansion  and  contraction  play 
but  a  minor  part.  It  is  very  desirable  to  know  the  size  of  pupil 
and  retinal  sensibility  corresponding  to  each  brightness  of  field 
of  vision  and  a  sub-committee  is  at  present  engaged  in  obtaining 
this  data.  The  only  data  at  present  available  is  that  of  Nagel 
(see  Helmholtz,  phys.  Optik,  II,  264)  and  others  on  the  increase 
of  dark  adaptation  with  time.  Five  observers  obtain  data  in 
substantial  agreement.  Starting  with  ordinary  daylight  interior 
accommodation,  the  minimum  perceptible  brightness  corresponds 
to  the  flux  density  given  by  one  meter  candle.  The  reciprocal  of 
this  minimum  increases  with  time  in  the  dark  about  as  follows : 

Minutes  adaptation 0.5  4        9  04  19  31  61      (960) 

Threshold  sensibility  ...  20  75  1,850  10,400  26,000  174,000  215,000  270,000 
This  may  be  represented  by  the  equation 

log  I/I0  =  6.43  (1  —  e-°™*) 
t  being  the  time  of  dark  adaptation. 

The  effect  of  glare  on  vision  is  the  basis  upon  which  it  is  classi- 
fied and  defined.  The  fact  must  be  strongly  emphasized  that  it 
depends  not  upon  the  objective  brightness  of  the  field  viewed  but 
upon  the  subjective  brightness  sensation.  The  eye  observes 
brightness  and  variation  in  brightness  but  the  scale  reading  (sen- 
sation) is  not  proportional  to  the  stimulus  (light  flux)  over  the 
whole  range  of  the  instrument.  It  is  impossible  to  measure  di- 
rectly the  brightness  sensation  corresponding  to  each  brightness 
observed  but  relative  values  may  be  determined  by  an  indirect 
method. 

The  sensibility  of  an  instrument  is  the  derivative  of  its  scale 
reading  with  respect  to  the  stimulus.  Now,  the  photometric  sen- 
sibility curve  of  the  average  normal  eye  may  be  (Nutting,  "Ap- 
plied Optics,"  p.  127)  well  represented  by  the  function  P  =  Pw  -|- 
(1  —  Ptw)  (B/B0)«,  B  being  the  (meter-candle)  brightness  and 
B0  the  threshold  value,  and  Vm  the  minimum  perceptible  photom- 
etric difference,  about  0.017.  The  general  integral  of  this  or 
S  =  C  log  [1  +  (1  —  P»*)(B/B0)»  —  *]x/" 


992     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

gives  the  general  relation  between  brightness  sensation  S  and 
objective  brightness  B.  Over  a  wide  range  of  moderate  bright- 
nesses this  reduces  to  Fechner's  law,  S  =  K  log  (B/B0).  These 
relations  must  be  used  in  dealing  with  contrast  when  the  field  of 
lower  brightness  is  below  that  corresponding  to  a  meter-candle 
on  a  white  reflecting  surface. 

DEFINITIONS. 

Glare. — Glare  is  brightness  within  the  field  of  view  of  such  a 
character  as  to  cause  discomfort,  annoyance  or  interference  with 
vision.  As  pointed  out  above,  glare  causes  other  subjective  visual 
effects  and  impaired  vision  may  be  due  to  causes  other  than 
glare.  However,  it  does  not  appear  feasible  to  broaden  the  defi- 
nition without  making  it  include  all  forms  of  improper  or  defec- 
tive illumination. 

Brightness  Glare. — Brightness  glare  is  glare  due  to  an  excessive 
general  brightness  of  the  field  of  view.  A  brightness  approaching 
or  exceeding  that  of  white  paper  in  direct  sunlight  is  considered 
excessive.  The  upper  limit  of  comfort  for  fully  accommodated 
eyes  is  about  3  lamberts  or  1  candle  per  square  centimeter.  This 
limit  is  illy  defined  but  of  nearly  the  same  value  for  all  normal 
eyes  so  far  as  known.  If  any  quantitative  expression  is  to  be 
chosen  for  brightness  glare  probably  the  most  rational  would  be 

G*  =  log  (B/B0) 
in  which  B  is  the  brightness  causing  the  glare  to  be  specified  and 
B0  is  the  upper  limit  of  comfort.     Thus,  a  brightness  glare  of 
1  corresponds  to  a  brightness  of  30  lamberts,  a  glare  of  2  to  300 
lamberts,  and  so  on. 

Contrast  Glare. — Contrast  glare  is  glare  due  to  excessive  con- 
trasts within  the  field  of  view.  A  proper  measure  of  contrast 
glare  is  relative  total  brightness.  This  holds  for  the  moderate 
working  brightnesses.  Relative  total  brightness  is,  for  nearly 
normal  illumination, 

_B_  _  Brf-f  B5  <*Rd    +    irRs 

B'  ~~  B'd  -f-  B,  toR'd  +  irR's 

in  terms  of  specular  and  diffuse  brightness  Bs  and  B<* ,  specular 
and  diffused  reflecting  power  R5  and  Rd  and  solid  angle  w  sub- 
tended bv  the  source. 


GENERAL  REPORT  ON  GLARE  993 

A  quantitative  expression  for  contrast  glare  applicable  at  all 
brightnesses  from  the  threshold  of  vision  up  to  the  highest  that 
are  utilized  is  an  expression  for  the  difference  in  the  brightness 
sensations 

n     -Ifw  i  +Pm(B1»/B0«-i)  _    \ 
^c  ~  n     \      g   i  +  Pm  (B2"/B0«  —  i)  / 

Pm  being  the  least  perceptible  photometric  difference  (about 
0.017),  Bx  and  B2  the  brightnesses  (objective)  of  the  contrasting 
areas,  B0  the  threshold  brightness  and  n  a  constant  equal  to  about 
0.35.  The  constant  2  signifies  that  glare  begins  at  contrasts 
of  100  :  1.  This  expression  is  to  be  used  with  care  since  contrast 
glare  varies  to  some  extent  with  the  length  of  the  boundary 
along  which  contrast  occurs,  with  the  part  of  the  retina  upon 
which  the  brightest  part  of  the  image  falls,  the  degree  of  general 
accommodation  and  other  factors. 

Veiling  Glare.— Veiling  glare  is  that  cause  of  impaired  vision 
due  to  a  light  or  dark  veil  obscuring  the  field  of  view  and  of  a 
pattern  different  from  that  of  the  object  viewed.  The  veiling 
due  to  a  bright  veil  is  greater,  the  greater  the  (sensation)  bright- 
ness of  the  veil  relative  to  that  of  the  field  to  be  viewed.  If  the 
veil  is  a  network  or  a  uniformly  illuminated  area,  probably  a 
mean  brightness  would  serve  as  a  measure  of  veiling.  A  quanti- 
tative expression  for  bright  veiling  glare  that  would  serve  is  a 
statement  of  its  effect  in  reducing  contrast.  Suppose  a  veil  of 
brightness  V  overlies  a  contrast  measured  by  B/B1.     Then 

1       B        1       B    +  V 
Gv  =  log  ^ log  B,        y 

For  example,  if  on  a  glossy  printed  page,  the  contrast  between 
paper  and  ink  is  20 :  1  away  from  the  specular  angle  and  1  :  1  at 
the  specular  angle,  then  the  veiling  glare  in  the  latter  case  is  log 
20  or  1.3. 

Dark  veiling  is  difficult  to  describe  in  terms  of  brightness.  It 
involves  a  sacrifice  of  both  brightness  and  definition.  The  latter 
effect  is  so  considerable  in  proportion  to  the  first  that  a  quanti- 
tative definition  based  on  brightness  alone  is  of  little  service. 

Temporary  Glare  and  Flicker.— Temporary  glare  is  glare  caused 
by  temporary  lack  of  brightness  accommodation  of  the  retina. 
Temporary  glare  is  greater  the  greater  the  brightness  of  the  newly 


994    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

exposed  field  relative  to  that  of  the  field  to  which  the  retina  is 
accommodated.  Now,  the  only  known  means  of  estimating  the 
level  of  brightness  accommodation  (see  below)  is  by  the  magni- 
tude of  the  threshold.  If,  now,  glare  is  to  be  estimated  by  the 
ratio  of  the  new  brightness  to  which  the  eye  is  tending  to  accom- 
modate itself  to  the  brightness  to  which  it  is  already  accommo- 
dated the  temporary  glare  is  properly  measured  by 

G<  =    kg  -|s-  —  2 

where  Bx  and  B2  are  the  two  thresholds  in  question  and  the  con- 
stant signifies  that  glare  begins  at  a  ratio  of  brightnesses  of 
100:1.  This  expression  is  similar  to  that  for  contrast  glare 
(see  above)  but  simplified. 

Flicker  involves  not  only  the  ratio  of  two  brightnesses  but  the 
rate  of  accommodation.  The  brightness  sensation,  at  ordinary 
brightnesses,  rises  to  half  its  value  in  about  1/20  second,  flicker 
appears  most  pronounced  at  8  or  10  cycles  per  second,  that  is 
with  the  transition  from  dark  to  light  occupying  about  1/20  second. 
At  low  mean  brightnesses  the  rate  of  accommodation  is  very  much 
slower.  Fluctuations  in  brightness  as  slow  as  i  per  second  are 
very  disagreeable.  Experiment  shows  that  flicker  disappears  at 
a  frequency  proportional  to  the  logarithm  of  the  brightness.  No 
simple  expression  more  than  approximately  expresses  the  relation 
of  flicker  sensation  to  frequency  and  brightness. 

GLARE  IN  PRACTISE. 

Since  the  photometric  sensibility  of  the  retina  and,  therefore, 
the  sensation  of  brightness,  varies  enormously  with  the  brightness 
of  the  field  of  view,  any  criterion  for  glare  is  incomplete  unless 
the  temporary  retinal  sensibility  be  specified.  The  fact  that  this 
sensibility  varies  continuously  increases  the  difficulty  of  specify- 
ing it. 

The  only  practical  way  out  of  the  difficulty  appears  to  be  to  (i) 
specify  sensibility  in  terms  of  the  mean  level  of  brightness  to 
which  the  eye  is  accommodated  and  (2)  choose  and  name  a 
limited  number  of  those  levels  of  brightness  corresponding  to 
practical  working  conditions.  We,  therefore,  consider  practical 
lighting  problems  in  glare  from  the  standpoint  of  the  four  fol- 
lowing different  levels  of  accommodation : 


GENERAL  REPORT  ON  GLARE  995 

i.  Bright  daylight  in  the  open.  The  brightness  of  the  field  of 
view,  excluding  such  extremes  as  deep  shadows  and  specular 
reflections  of  the  sun,  ranges  from  nearly  white  objects  in  the 
sun  (2  to  10  lamberts)  and  the  open  sky  (1  lambert)  down  to 
foliage  (y2  lambert)  and  moderate  shade  (V10  lambert).  Prob- 
ably 1  lambert  is  a  fair  average  for  the  brightness  to  which  the 
eye  is  accommodated  under  this  condition  of  illumination. 

2.  Interiors  in  full  daylight.  Again  excluding  such  excessively 
bright  objects  as  those  in  direct  sunlight  and  such  dark  objects 
as  deep  shadows,  the  brightness  of  the  field  of  view  in  interiors 
on  a  bright  day  varies  from  the  sky  at  1  lambert,  white  paper 
(0.1  to  0.04  lambert)  and  walls  with  a  brightness  of  about  10 
millilamberts,  down  to  rugs,  dark  objects  and  moderate  shadows 
1  to  10  millilamberts  in  brightness.  In  this  case  10  millilamberts 
is  a  fair  average  level  of  brightness. 

3.  Interiors  artificially  illuminated.  Unshielded  illuminants 
range  in  brightness  about  as  follows :  arcs  from  10,000  to  200,000 
lamberts,  gas-filled  tungsten  lamp  filaments  5,000  to  8,000  lam- 
berts, ordinary  tungsten  200  to  500  lamberts,  carbon  filaments 
150  to  300  lamberts,  gas  mantles  50  to  200  lamberts,  acetylene 
flames  50  to  200  lamberts,  gas  flames  5  to  40  lamberts,  kerosene 
oil  flames  5  to  100  lamberts.  Frosted  lamp  bulbs  range  from 
1  to  50  lamberts  in  brightness  while  diffusing  globes  and  bowls 
vary  from  0.1  to  1  lambert.  Such  illuminants  are  supposed  to 
be  outside  the  range  of  vision  except  at  rare  intervals.  Objects 
within  the  field  of  view  vary  from  10  millilamberts  down  to  0.01 
millilambert  and  lower.  A  brightness  of  0.1  millilambert  is  about 
an  average  for  the  field  of  vision  in  interiors  at  night.  If  the 
illuminants  are  not  properly  placed  so  that  one  or  more  of  them 
is  continuously  or  frequently  within  the  field  of  view,  of  course 
the  mean  eye  adaptation  is  such  as  corresponds  to  a  higher  mean 
brightness  than  0.1  millilamberts. 

4.  Night  Street  Illumination.  The  range  of  brightness  within 
the  field  of  view  out  of  doors  at  night  is  enormous.  Excluding 
artificial  light  sources  viewed  directly  (see  preceding  paragraph) 
the  various  brightnesses  ordinarily  within  the  field  of  view  are 
roughly:  white  objects  in  full  moonlight  0.01  millilambert,  foli- 
age, roads  and  pavements  in  full  moonlight  0.0005  millilambert. 


996     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  same  objects  under  starlight  are  about  1/20  as  bright.  Objects 
can  be  just  descerned  with  full  accommodation  at  about  io-6 
millilamberts.  Considering  only  brightnesses  necessary  and  com- 
fortable to  the  eye,  probably  0.00 1  millilamberts  represents  a 
fair  average  for  night  vision  in  the  open. 

The  four  levels  of  brightness  determining  the  four  chief  levels 
of  accommodation  may  be  thus  summarized. 

Average       Preceptible         Relative 
brightness     percentage  retinal 

level  difference         sensibility 

i.  Exterior  daylight 1000  ml.  0.0176  1 

2.  Interiors  in  daylight    10  0.030  59 

3.  Interiors  at  night o.  1  0.123  1430 

4.  Exterior  at  night 0.001  0.79  22300 

The  percentage  perceptible  difference  is  the  difference  in  bright- 
ness that  is  just  perceptible  (from  data  of  A.  Konig)  expressed  as 
a  fraction  of  the  whole.  Retinal  sensibility  in  the  last  column  is 
proportional  to  the  increment  just  perceptible  calculated  from  the 
data  of  Konig.  Such  data  are  to  be  regarded  as  tentative  only. 
Your  committee  is  now  engaged  in  its  direct  determination. 

Such  data  give  a  basis  for  the  quantitative  estimation  of  glare 
under  various  conditions.  For  example,  assuming  the  above  data 
correct,  an  area  so  bright  as  to  be  blinding  in  broad  daylight  must 
be  about  60  times  as  bright  as  one  that  is  blinding  in  an  interior 
in  the  daytime  and  22,000  times  as  bright  as  a  surface  blinding 
at  night  out  of  doors.  The  light  sufficient  to  read  by,  to  just 
distinquish  objects  by  and  the  brightnesses  causing  fatigue  or 
strain  are  known  to  vary  in  somewhat  similar  proportions  at 
the  different  levels,  but  exact  data  are  not  yet  available. 

At  each  level  of  accommodation  a  number  of  brightness  sensa- 
tions may  be  denned  (such  as  dazzling,  blinding,  excessive,  un- 
comfortable, annoying,  normal,  defective,  deficient,  signal  and 
threshold)  in  terms  of  the  brightness  causing  them  relative  to  the 
mean  level.  It  may  be  desirable  ultimately  to  define  quantita- 
tively a  set  of  such  terms  but  only  after  the  relation  of  each  to 
brightness  and  angular  area  shall  have  been  investigated. 

An  important  relation  that  has  been  noted  by  several  writers 
should  be  emphasized  here,  namely  that  the  more  contrasty  the 
field  of  view  the  higher  the  level  of  illumination  demanded  by  the 
eye  for  acute,  comfortable  vision.     In  machine  shops  where  large 


GENERAL  REPORT  ON  GLARE  997 

dark  areas  are  general  and  specular  glare  common,  much  more 
light  is  required  for  good  seeing  than  in  say  a  living  room  with 
no  specular  surface,  indirect  lighting  and  light  walls  and  floors. 
Your  committee  are  not  prepared  to  state  the  relation  between 
proper  average  brightness  and  mean  contrast  but  do  not  doubt 
that  such  a  relation  exists  and  that  it  may  be  determined  and 
formulated.     Data  are  now  being  obtained  by  a  sub-committee. 

The  special  reports  prepared  by  this  committee  are  listed  below. 
Report  No.  6  was  prepared  at  the  request  of  the  National  Letter 
Carriers  Association,  No.  n  at  the  request  of  the  Automobile 
Association.  The  remaining  reports  were  prepared  solely  in  the 
interests  of  illuminating  engineering: 

REPORTS  OF  COMMITTEE  ON  GLARE. 

1.  General  Report  on  Glare. — Nature  of  various  classes  of  glare, 

the  effect  of  each  on  vision,  limits  of  tolerance  and  means 
of  suppression. 

2.  Diffusing  Media  I. — Classes  of  diffusion,  nomenclature  and 

physical  theory  of  diffusion. 

3.  Diffusing  Media  II. — Instruments  and  methods  for  measuring 

diffusion  and  theory  of  diffusion  photometry. 

4.  Papers. — Print  papers,  sizings,  fillers,  inks.     Writing  papers 

and  inks.  Typewriting  papers,  inks  and  carbons.  Draw- 
ing papers  and  India  inks.  Tracing  papers  and  cloths. 
Blue  print  papers.     Photostat  papers. 

5.  Photographic  Papers  and  Plates. — Glossy,  semi-glossy,  semi- 

mat,  velvet,  rough  and  mat  papers.  Stocks,  finished 
papers  and  developed  papers  in  three  densities.  Raw 
plates,  negatives. 

6.  Windozv  Envelopes. — Diffusion  analyses  of  various  kinds  in 

use. 

7.  Furnishings. — Walls,    ceilings,    floors,    woodwork,    fixtures, 

shades,  draperies  and  furniture;  unfinished,  finished,  and 
covered.     Brightness,  contrast  and  veiling  glare. 

8.  Projection   and   Focusing   Screens. — Washes,    cloths,    metal 

and  special  coverings.  Focusing  and  translucent  projection 
screens. 

9.  Diffusing  Glassware. — Ground,   frosted,  etched  and  flashed 

globes  and  shades. 


998     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

10.  Effects  of  Glare  on  Vision. — Excessive  and  deficient  illumin- 
ation, temporary  glare,  excessive  contrast,  veiling,  fatigue, 
annoyance,  discomfort,  loss  of  brightness  adaptation,  loss 
of  acuity,  permanent  injury. 
11.  Automobile  Headlights. — Causes  of  excessive  glare,  mini- 
mum requirements  in  lighting  and  warning.  Headlight 
regulation. 

12.  Interior  Illuminants. — Intensity,   character  and   position  of 

lighting  units. 

13.  Street  Lighting. — Character,  brightness  and  spacing  of  light- 

ing units. 

The  character  of  each  report  is  indicated  by  the  brief  outline 
of  each.  Reports  2-9  inclusive  deal  with  diffusing  media,  No.  10 
with  visual  effects  and  11,  12  and  13  with  practical  engineering 
problems.  In  Report  No.  2  are  defined  various  terms  used  in 
dealing  with  scattered  light  such  as  reflecting  power,  transmis- 
sion, opacity,  turbidity,  entrant  scatter,  exit  scatter,  optical  density 
and  specific  density,  contrast  and  gloss.  In  the  report  on  papers 
are  given  the  results  of  complete  diffusion  analyses  of  many  kinds 
of  papers,  inks,  fillers,  sizing,  etc.  Of  particular  interest  are 
gloss,  specific  density,  back  reflection  and  contrast  ratio.  Photo- 
graphic papers  are  produced  with  a  wide  variety  of  accurately 
reproducible  surfaces  such  as  rough,  textile,  mat,  semi-mat,  semi- 
glossy  and  glossy,  each  having,  in  the  finished  print,  a  wide  range 
of  diffuse  reflecting  powers.  It  is  on  account  of  the  interest 
attached  to  the  study  of  such  surfaces  that  this  report  is  included 
in  the  series. 

Window  envelopes  are  desired  as  transparent  and  as  free  from 
diffusion  as  possible,  properties  quite  the  opposite  of  those  re- 
quired of  print  papers.  The  ease  with  which  print  may  be  read 
through  the  prepared  window  is  quantitatively  defined  in  con- 
trast ratio.  The  specular  and  diffuse  reflecting  power  of  in- 
terior furnishings,  upon  which  home  and  office  comfort  so  largely 
depend  are  discussed  in  report  No.  7.  In  the  report  on  projection 
screens  (No.  8)  are  given  accurate  diffusion  analyses  of  various 
types  of  screens.  Screen  efficiency  is  defined  and  the  properties 
of  an  ideal  screen  and  of  the  best  realizable  screen  given.  Diffus- 
ing glassware  is  treated  from  both  the  laboratory  and  engineering 


GENERAL   REPORT   ON   GLARE  999 

points  of  view.  Report  No.  10,  on  the  effects  of  glare  on  vision, 
is  one  of  the  most  important  of  the  series  since  its  effect  on  the 
eye  is  the  ultimate  criterion  not  only  of  glare  but  of  good  and 
bad  lighting.  Report  No.  12  deals  with  various  engineering 
problems  in  interior  illumination  and  No.  13  deals  in  a  similar 
manner  with  street  illumination. 

A  complete  bibliography  of  glare  and  related  effects  would  be 
very  extended ;  nearly  all  the  literature  of  glare  is  readily  avail- 
able in  the  Transactions  of  our  society.  To  those  desiring  to 
read  further  on  the  subject  we  recommend  the  various  reports  of 
the  committees  on  glare,  the  papers  by  Dr.  Cobb  on  the  effect  of 
glare  on  visual  acuity,  of  Professor  Ferree  on  the  effect  of  ex- 
cessive and  deficient  illumination,  Mr.  Luckiesh  on  glare  in  its 
various  aspects,  Mr.  Cravath  on  brightness,  Mr.  Minick  on  head- 
lights and  Mr.  Sweet  on  street  illumination. 

Your  present  committee  has  felt  that  the  work  most  urgent  for 
them  to  do  lay  in  the  field  between  the  optical  laboratory  and 
illuminating  engineering  and  extending  into  both.  We  have  en- 
deavored to  secure  the  data  and  formulate  the  relations  most 
needed  by  the  illuminating  engineering  profession  in  improving 
illumination  and  lighting  practise,  leaving  to  later  committees  the 
work  of  expanding  and  popularizing  this  material. 

Your  committee  consider  that  the  line  of  progress  in  glare  re- 
search lies  in  the  further  investigation  of  adaptation  levels  of  the 
retina,  of  local  and  partial  adaptation  and  of  limits  of  tolerance 
in  proper  lighting.  Another  line  of  work  urgently  demanding 
attention  is  required  to  fill  the  gap  between  laboratory  and  prac- 
tical engineering  data. 

Nelson  M.  Black, 

J.  R.  Cravath, 

F.  H.  Gilpin, 

M.  Luckiesh, 

R.  K.  Richtmyer, 

F.  A.  Vaughn, 

P.  G.  Nutting,  Chairman. 


:i 


IOOO    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

THE  EFFECT  OF  GLARE  ON  VISION.* 


Synopsis:  What  is  known  of  the  visual  effect  of  radiation  is  out- 
lined. Retinal  phenomena,  retinal  adaptation  to  flux  density,  optic  images, 
pupillary  adaptation  and  deleterious  effects  of  radiation  are  discussed. 
The  following  subjects  are  also  discussed  briefly:  glare  and  vision;  effects 
of  excessive  brightness,  momentary  and  continuous;  conjunctivitis;  kera- 
titis; retinitis;  effects  of  excessive  contrast;  discomfort,  interference  with 
vision;  effects  of  excessive  extra  visual  radiation;  and  effects  of  veiling 
glare  and  flicker. 


INTRODUCTION. 

In  many  respects  the  viewpoint  from  which  this  report  of  the 
effect  of  glare  on  vision  is  written  must  necessarily  differ  ma- 
terially from  that  of  other  reports  in  this  series.  Many,  if  not 
all  of  these  reports  deal  to  a  greater  or  less  extent  with  definite 
quantitative  data,  on  the  basis  of  which  precise  statements  of 
facts  are  possible.  With  visual  phenomena,  however,  particularly 
in  connection  with  the  deleterious  effects  of  glare,  little  data, 
qualitative  or  quantitative,  is  to  be  found,  and  what  there  is  seems 
more  or  less  conflicting.  To  a  large  extent,  therefore,  this  re- 
port is  to  be  regarded  as  the  committee's  opinion  as  to  the  nature 
of  the  effects  of  glare  on  vision,  as  based  on  evidence  now  avail- 
able. On  account  of  the  necessity  for  brevity,  detailed  refer- 
ences have  been  omitted. 

Since  any  discussion  of  the  physiology  of  glare  must  be  very 
closely  connected  with  the  more  general  question  of  the  deleterious 
effects  of  radiation  on  vision,  a  few  introductory  statements  seem 
necessary  regarding  radiant  energy,  the  eye,  and  the  physiology 
of  vision. 

The  general  nature  of  the  propagation  of  energy  by  wave 
motion  is  assumed  to  need  no  discussion  here.  Excluding  X-ray 
radiation  the  shortest  waves  yet  observed  have  a  wave-length  of 
0.000006  cm.  From  this  point,  the  known  wave-length  extend  in 
an  unbroken  sequence  up  to  the  longest  electromagnetic  waves, 
the  length  of  which  is  measured  in  miles.  This  series  is  fre- 
quently thought  of  as  divided  into  four  parts :  ( 1 )  the  ultra- 
violet,  extending   from   the   shortest   known   waves    (excluding 

*  Report  No.  10.,  I.  E.  S.,  Committee  on  Glare,  1914-15. 


THE   EFFECT   OF   GLARE  ON    VISION  IOOI 

X-rays)  up  to  the  point  where  ordinary  vision  begins,  somewhere 
in  the  neighborhood  of  0.00004  cm.;  (2)  the  visible,  extending 
for  one  octave  from  about  0.00004  cm.  up  to  the  upper  limit  of 
vision,  approximately  0.00008  cm.;  (3)  the  infra-red,  extending 
from  here  up  to  waves  a  few  tenths  of  a  millimeter;  (4)  beyond 
this  point  begins  the  region  usually  thought  of  as  comprising  the 
electromagnetic  waves. 

Similarly,  the  known  effects  of  radiation  can  be  divided  into 
four  classes.  (1)  The  heat  effect;  (2)  the  chemical  effect;  (3) 
electric  and  electromagnetic  effects ;  (4)  the  visual  effect. 

The  division  of  the  spectrum  into  four  parts  is  obviously  quite 
artificial.  It  is  based  solely  on  the  circumstance  that  the  visual 
effect  comprises  the  octave  between  0.00004  and  0.00008  cm. 
The  same  may  be  said  regarding  the  classification  of  the  effects 
of  radiation.  It  might  be  safe  to  predict  that  when  our  knowl- 
edge of  physical  processes  is  sufficiently  extended  we  shall  explain 
all  phenomena  on  the  basis  of  the  electromagnetic  effect. 

The  heat  effect  of  radiation  throughout  the  spectrum  is  pro- 
portional to  the  energy  at  each  wave-length.  Since  in  the  spectra 
of  modern  illuminants  the  energy  is  greatest  in  the  infra-red, 
the  infra-red  waves  have  sometimes  been  called  heat  waves.  This 
classification  is  evidently  erroneous.  In  this  sense  all  zvaves  are 
heat  waves. 

The  chemical  effect  of  any  part  of  the  spectrum  is  a  function 
of  both  the  energy  contained  in,  and  the  wave-length  of,  that  part. 
In  other  words,  the  chemical  effect  is  selective.  No  definite 
statement  of  its  extent  can  be  made.  In  general  the  shorter 
visible  rays  and  the  longer  ultra-violet  rays  are  the  more  active 
chemically.  But  it  is  quite  incorrect  to  speak  of  violet  and  ultra- 
violet radiation  as  chemical  radiation.  Photochemical  effects  are 
known  well  into  the  infra-red. 

Regarding  the  electromagnetic  effect,  little  need  be  said  in  this 
connection.  Since  radiant  energy  is  itself  electromagnetic,  its 
effects  must  be  ultimately  expressed  in  those  terms. 

THE  VISUAL  EFFECT  OF  RADIATION. 
As  to  the  ultimate  nature  of  the  visual  effect,  with  which  we  are 
directly  concerned  in  this  report,  it  would  obviously  be  evading 
the  question  to  say  that  it  is  electromagnetic.     For  while  such 


1002     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

a  statement  is  probably  true,  broadly  speaking,  we  cannot  explain 
the  transformation  of  radiant  energy  into  visual  sensation  by 
means  of  what  are  now  recognized  as  electromagnetic  phenomena. 

There  are  no  reasons  for  assuming  that  the  visual  effect  of 
radiation  is  simply  a  heat  effect.  The  latter,  as  explained  above, 
is  common  to  all  parts  of  the  spectrum,  while  the  former  is 
highly  selective.  Further,  granted  that  there  might  be  in  the 
retina  a  selectively  absorbing  medium  capable  of  making  possible, 
by  temperature  changes,  the  selective  character  of  vision,  it  is 
difficult  to  conceive  of  the  myriad  of  visual  sensations  being  pro- 
duced by  thermal  phenomena.  It  is,  of  course,  true  that  a  visual 
sensation  results  from  electric  currents  in  the  optic  nerve  fibers, 
and  it  is  further  known  that  light,  falling  on  the  retina,  produces 
electric  effects  in  the  optic  nerve.  It  is  thinkable  that  the  rods  and 
cones  of  the  retina  are  sensitive  thermo-electric  receivers.  Our 
knowledge  of  thermo-electric  phenomena,  however,  does  not  point 
to  it  as  a  suitable  basis  for  a  working  theory  of  vision. 

There  remains,  as  a  basis  for  an  explanation  of  visual 
processes,  the  chemical  effect.  About  all  that  one  is  warranted 
in  saying  at  the  present  time  is  that  an  explanation  on  this  basis 
is  a  possibility.  Several  hypotheses  have  been  advanced  but  all 
are  but  little  more  than  speculation. 

Since  so  little  is  known  of  the  fundamental  processes  by  means 
of  which  radiant  energy  is  transformed  into  visual  sensation,  it 
is  evident  that  any  discussion  of  the  peculiarities  of  these  processes 
must  be  either  empirical  or  superficial. 

RETINAL  PHENOMENA. 

The  reception  of  radiant  energy  on  the  retina  is  known  to 
produce  at  least  three  results  in  the  retinal  media : 

(i)  A  change  in  shape  of  the  cones.  The  tips  of  the  cones 
recede  when  illuminated,  due  to  the  body  of  the  cone  becoming 
shorter  and  thicker.  (2)  Closely  connected  with  (1)  is  the  so- 
called  "migration"  of  the  dark  pigment.  On  exposure  to  light 
the  pigment  bearing  cells  push  up  towards  the  tips  of  the  rods 
and  cones.  Conversely,  they  recede  toward  the  base  of  the  cones 
in  darkness.  This  pigment  migration  has  been  found  in  some 
lower  animals  but  has  never  been  observed  directly  in  mammals. 
(3)  Most  significant  of  all,  the  visual  purple,  a  watery  fluid  purp- 


THE   EFFECT   OF   GLARE   ON   VISION  IOO3 

lish  in  color,  is  bleached  to  yellow  or  even  "white"  on  exposure 
to  light.  Different  wave-lengths  have  different  bleaching  powers. 
A  curve  showing  the  bleaching  power  of  various  parts  of  the 
spectrum  is  quite  similar  in  shape  and  position  to  the  luminosity 
curve.  The  chemical  or  physical  changes  corresponding  to  the 
bleaching  of  the  visual  purple  are  not  known.  Nor  is  anything 
definitely  known  regarding  the  relation  of  this  phenomena  to 
visual  sensation.  Several  hypotheses  have  been  advanced  but 
all  have  obvious  difficulties. 

Among  the  retinal  phenomena  which  may  be  observed  subjec- 
tively and  which  have  an  important  bearing  on  the  subject  of 
glare  may  be  mentioned  two : 

(1)  Retinal  adaptation,  frequently  called  light  or  dark  adapta- 
tion, is  a  phenomenon  well  known,  qualitatively  at  least,  to  every- 
one who  has  experienced  the  sensation  of  not  being  able  to  see 
when  first  entering  a  darkened  room  from  full  daylight ;  or,  the 
reverse,  the  pain  experienced  when  first  going  from  a  darkened 
room  into  full  sunlight.  Quantitatively,  retinal  sensibility  is 
defined  as  the  reciprocal  of  the  minimum  observable  (threshold) 
illumination.  In  terms  of  the  meter-candle  on  a  white  surface. 
the  retinal  sensibility  is  nearly  unity  for  the  eye  adapted  to  sun- 
light. On  entering  a  dark  room,  adaptation  is  rapid  at  first, 
then  slower  and  slower.  It  continues  until  at  the  end  of  an  hour 
it  has  reached  a  value  of  about  200,000.  That  is,  after  an  hour's 
rest  in  the  dark  the  minimum  observable  illumination  is  1/200,000 
of  what  it  is  with  the  eyes  accommodated  to  sunlight. 

The  return  from  a  condition  of  dark  adaptation  to  light  adapta- 
tion is  much  more  rapid,  being  accomplished  in  a  few  seconds. 

One  important  result  of  the  phenomena  of  adaptation  is  that, 
under  different  condition,  the  same  sensation  may  be  caused  by 
widely  different  brightnesses.  Thus,  with  the  eye  adapted  to  sun- 
light, the  threshold  sensation  is  just  caused  by  1  meter  candle 
on  a  white  surface.  But  with  the  eye  adapted  for  one  hour, 
the  same  sensation  can  be  caused  by  1/200,000  of  a  meter-candle. 
One  might  conclude  therefore,  that  with  the  sunlight  adapted  eye 
an  illumination  of  100  meter-candles  would  cause  the  same  sen- 
sation as  1/2,000  of  a  meter-candle  with  the  eye  dark  adapted. 
This  does  not  necessarily  follow.     For  with  the  eye  exposed  to 


1004     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

1/2,000  of  a  meter-candle,  it  is  no  longer  in  a  condition  of  adap- 
tation where  1/200,000  meter-candle  excites  the  threshold  sensa- 
tion, on  account  of  the  rapid  change  from  dark  toward  light 
adaptation  noted  above. 

Whatever  may  be  the  nature  of  the  processes  by  which  radiant 
energy  is  transformed  into  visual  sensation,  or  by  which  adapta- 
tion may  be  accomplished,  it  seems  reasonable  to  assume  that 
there  is  at  least  a  rough  correspondence  between  sensation  and 
the  physiological  activity  which  causes  it.  In  other  words,  the 
intensity  of  physiological  reactions  produced  by  the  reception 
of  radiant  energy  on  the  retina  depends  both  on  the  flux  density 
of  that  radiation  at  the  retina  and  on  the  state  of  adaptation  of 
the  eye. 

(2)  Brief  mention  should  be  made  of  the  formation  of  after- 
images in  the  eye.     Two  kinds  of  after-images  are  recognized. 

(a)  Positive  After-images. — If  the  eyes  be  kept  in  the  dark 
for  a  few  minutes,  and  then  suddenly  exposed  for  two  or  three 
seconds,  a  "positive"  image  of  the  field  viewed  will  be  seen.  This 
will  gradually  fade.  The  intensity  of  the  after-image  caused 
by  a  given  brightness  depends  on  the  condition  of  adaptation 
of  the  eye.  With  the  eye  fully  dark  adapted  one  may  observe 
the  positive  after-image  of  a  window  looking  out  on  a  moon- 
lighted scene.  With  the  light  adapted  eye  far  higher  intensities, 
those  usually  met  in  daylight,  are  necessary  to  produce  after- 
images. 

(b)  Negative  After-images. — These  may  be  observed  by  gaz- 
ing steadily  for  two  or  three  minutes  at  a  field  in  which  there  is 
excessive  contrast.  On  looking  at  a  white  wall  a  "negative"  after- 
image is  observed.  With  negative  after-images  thus  observed, 
not  only  are  light  and  shade  reversed,  but  colors  are  usually  seen 
complementary.  Negative  after-images  frequently  follow  a 
faded  positive  after-image. 

The  following  two  statements  may  be  made,  based  on  the  phe- 
nomena of  after-images :  ( 1 )  The  physiological  processes  set 
going  by  the  reception  of  radiation  on  the  retina  persist  for  some 
time  after  the  radiation  is  cut  off.  (Positive  after  image.)  (2) 
The  ability  of  any  part  of  the  retina  to  respond  to  a  given  stim- 
ulus depended  on  its  immediate  previous  history ;  thus,  where  one 


THE   EFFECT   OF   GEARE   ON   VISION  IOO5 

observes  the  negative  after-image  on  the  white  walls  those  parts 
of  the  retina  previously  stimulated  in  excess  of  their  surroundings 
are  not  able  to  produce  from  the  same  stimulus  as  great  a  sensa- 
tion as  their  surrounding  parts. 

Pupillary  adaptation,  as  a  result  of  varying  brightness,  is  well 
known.  Under  normal  conditions,  the  size  of  the  pupil  may  vary 
from  something  less  than  2  millimeters  to  something  over  7  milli- 
meters, causing  by  "stopping  down"  the  optical  system  of  the 
eye  a  variation  in  brightness  of  the  physical  image  found  on  the 
retina  of  from  1  to  20.  Pupillary  adaptation  is  a  function  of 
the  actual  brightness  of  the  field  viewed,  of  the  state  of  retinal 
adaptation,  and  perhaps  also  of  the  color  of  the  active  light.  It 
is  "a  reflex  act,  secondary  to  retinal  stimulation." 

MEANS  AVAILABLE  FOR  STUDYING  EFFECTS 
OF  RADIATION. 

The  above  are  some  of  the  ocular  phenomena  incidental  to 
vision.  If  one  excludes  such  unusual  cases  as  snow  blindness, 
ultra-violet  "burns,"  etc.,  which  are  seldom  if  ever  experienced 
by  the  average  individual,  we  know  of  no  structural  change  in 
eye  media  coincident  with  any  of  the  deleterious  effects  of  rad- 
iation on  vision.  These  disturbances  produced  are  largely  func- 
tional, and  they  must,  therefore,  be  studied  by  such  phenomena, 
observable  objectively  or  subjectively,  as  are  known  to  be  closely 
connected  with  the  processes  which  result  in  visual  sensation. 

For  example,  a  study  of  retinal  adaptation  gives  much  inform- 
ation regarding  the  pathological  condition  of  the  retina.  The 
following  clinical  observations  are  illustrative : 

Several  patients  (Arch.  f.  Ophth.,  vol.  82,  p.  509)  complained 
of  flickering  sensation,  inability  to  see  clearly  for  a  long  time 
after  coming  into  a  light  room  from  a  dark  room,  and  other 
general  disturbances  to  vision,  due,  apparently,  to  working  under 
improper  artificial  illumination.  A  test  of  the  time  adaptation 
curves  showed  threshold  sensibilities  far  below  normal,  indicating 
a  serious  functional  disturbance — whatever  its  nature — in  the 
retina. 

Likewise,  observation  by  means  of  after-images,  pupillary  re- 
actions, examination  of  the  light  and  color  limits  of  the  periphery 


1006     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

of  the  retina  are  some  of  the  phenomena  by  which  the  oculist  can 
study  functional  disturbances  in  the  eye. 

GLARE  AND  VISION. 
Below  will  be  briefly  summarized  some  of  the  effects  of  the 
various  recognized  types  of  glare  on  vision.  For  purposes  of 
this  report,  we  will  keep  in  mind  the  effect  of  each  of  the  several 
types  of  glare  as  follows :  (a)  Effect  on  external  and  internal 
eye  media,  (b)  effect  on  muscular  apparatus  of  the  eye,  (c)  func- 
tional disturbances  produced  in  the  retina.  The  last  is  by  far  the 
most  important. 

EXCESSIVE  BRIGHTNESS. 

Glare  due  to  excessive  brightness  may  be  of  two  kinds :  ( i ) 
momentary,  (2)  continuous. 

When  the  more  or  less  completely  dark  adapted  eye  is  suddenly 
exposed  to  a  higher  illumination,  the  eye  is  "caught  unawares" 
with  the  pupil  wide  open  and  with  the  retina  in  a  condition  to 
register  weak  light  intensities.  Excessive  retinal  stimulation  re- 
sults. This  causes  a  "blinding  sensation,"  as  a  result  of  which 
there  is  a  sudden  contraction  of  the  pupil  so  intense  as  to  be 
painful.  There  seems  also  to  be  some  reason  to  believe  that  the 
intense  stimulation  of  the  retina  causes  pain.  Very  quickly  the 
retina  adapts  itself  to  the  new  intensity — or  at  least  attempts  to 
do  so.  If  the  brightness  is  not  too  intense,  a  condition  of  com- 
parative comfort  is  soon  reached.  The  glare  is  then  said  to  have 
been  momentary.  In  probably  the  vast  majority  of  cases  there 
has  been  no  injury,  even  temporary,  except  when  the  process  be 
repeated  rapidly,  many  times  in  succession,  or  when  the  eye  is 
exposed  to  an  excessively  brilliant  momentary  flash. 

In  some  cases,  however,  the  brightness  may  be  so  intense  that 
the  sensation  of  discomfort  or  pain  does  not  disappear  after  a 
few  seconds  but  persists.  The  glare  is  then  said  to  be  continuous. 
Such  conditions  obtain  when  the  eye  is  exposed  to  the  excessive 
brightness  from  large  snow  fields,  deserts,  the  flash  of  an  electric 
switch,  etc. 

The  reduction  of  the  physiological  activity  by  both  pupillary 
and  retinal  adaptation  is  not  in  case  of  continuous  glare  sufficient 
to  reduce  the  stimulus  to  an  allowable  maximum.  There  results 
pain  due  in  part  to  the  continued  attempt  of  the  iris  to  close 


THE   EFFECT   OF  GEARE  ON   VISION  IOO7 

further ;  excessive  bleaching,  without  possibility  of  restoration  of 
the  visual  purple,  and  a  general  condition  of  muscular  strain  re- 
sulting from  squinting  and  tension  of  external  eye  muscles. 

The  effects  appear  to  be  much  more  harmful  if  the  excessive 
brightness  is  located  beneath  the  general  eye  level.  (This  might 
be  anticipated  by  a  consideration  of  the  conditions  under  which 
primitive  man  was  developed.) 

In  cases  of  continuous  glare  due  to  excessive  brightness  of  long 
duration,  there  results  such  ocular  disturbances  as  snow  blind- 
ness, desert  blindness,  etc.,  which,  in  addition  to  being  accom- 
panied by  external  irritating,  result  in  a  temporary  or  semi-per- 
manent loss  of  power  to  dark  adapt. 

Among  the  classified  disorders  recognized  by  oculists  as  arising 
from  long  continued  exposures  to  excessive  brightness  may  be 
mentioned : 

1.  Conjunctivitis. — An  inflammation  of  the  conjunctiva,  the 
membrane  covering  the  inner  surface  of  the  eyelids  and  the  outer 
surface  of  the  eyeball.  The  eyes  become  blood-shot;  there  are 
sensations  of  sandiness;  sharp,  shooting  pains;  heaviness  of  the 
eyelids ;  and  marked  dryness.  Unless  the  exposure  be  of  too  long 
duration,  "recovery  usually  follows  the  removal  of  the  cause." 

2.  Keratitis. — Inflammation  of  the  cornea,  accompanied  by 
cloudiness  and  consequent  impairment  of  vision. 

3.  Retinitis. — Inflammation  of  the  retina,  with  accompanying 
functional  disturbances. 

Sun  blindness  (solar  retinitis)  has  resulted  in  a  number  of 
cases  from  direct  observation  of  the  sun.  There  is  partial  (or 
absolute?)  blindness  of  the  central  portion  of  the  retina,  defective 
color  vision,  reduction  of  visual  acuity,  and  an  apparent  distor- 
tion of  objects  in  the  field  of  view.  Frequently,  ophthalmoscopic 
examination  of  the  retina  shows  no  change,  or  there  may  be  a 
small  orange  spot  near  the  fovea,  with  alterations  in  pigmenta- 
tion. It  is  stated  that  in  no  case  in  which  vision  was  reduced  to 
less  than  one  third  has  there  been  full  recovery  of  visual  acuity. 

Snow  blindness  may  be  so  serious  as  to  result  in  permanent 
blindness.  There  are  the  ordinary  symptoms  of  conjunctival  and 
corneal  inflammation,  spasmodic  contraction  of  the  eyelids,  fre- 
quently corneal  ulcers,  intense  deep-seated  pain  when  the  eye  is 


1008     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

exposed  to  light  (photophobia)  quivering  and  unsteadiness  of 
vision,  but  no  retinal  changes  observable  by  means  of  the  ophthal- 
moscope. 

Until  we  know  more  about  the  phenomena  of  vision  we  can 
only  speculate  on  the  ultimate  nature  of  the  retinal  disturbances 
incidental  to  the  above  diseases.  For  example,  continuous  ex- 
cessive brightness  causes  an  excessive  bleaching  of  the  visual 
purple.  Now  if  this  acts  in  an  electro-chemical  way  to  produce 
vision,  the  physiological  processes  caused  by  it  are  continuously 
over-stimulated,  as  are  likewise  the  processes  by  which  the  visual 
purple  is  renewed.  Obviously,  as  in  any  bodily  function,  what- 
ever the  nature  of  the  processes  underlying  vision,  the  excessive 
stimulation  of  any  or  all  of  them  for  a  long  period  must  result  in 
a  lowering  of  the  efficiency  with  which  they  can  be  carried  on. 
In  other  words,  the  deleterious  effects  of  excessive  brightness 
seem  to  be  primarily  due  to  continued  over-stimulation  of  the 
retinal  processes  by  visible  radiation  rather  than  to  the  presence 
of  extra-visual  radiation. 

The  obvious  remedy  for  glare  due  to  excessive  brightness  is 
the  use  of  neutral  tinted  glasses  of  suitable  density. 

EXCESSIVE  CONTRAST. 

Glare  due  to  excessive  contrasts  occurs  when  the  general  level 
of  the  brightness  of  the  visual  field  is  not  above  the  upper  limit 
for  which  the  eye  can  readily  adapt,  while  within  the  field  there 
exists  more  or  less  restricted  areas  whose  brightness  is  much 
above  this  level. 

The  brightness  of  these  areas  may  be  (i)  so  great  as  to  cause 
of  themselves,  injury  by  over-stimulation  of  restricted  areas  (as 
in  the  case  of  bare  light  sources)  or  (2)  they  may  be  such  as  to 
cause  simply  a  reduction  of  visual  acuity  and  the  ability  to  dis- 
tinguish contrasts  in  surrounding  parts  of  the  visual  field,  causing 
simply  "annoyance,  or  interference  with  vision."  (1)  depends 
in  large  part,  perhaps  entirely,  on  the  absolute  brightness  of  the 
area  concerned ;  (  for  upper  limit  of  brightness  permissible  within 
the  visual  field  see  other  reports  in  this  series) ;  on  the  retinal 
area  on  which  the  image  falls ;  and,  perhaps,  to  a  small  extent  on 
the  condition  of  adaptation  of  the  eye.  (2)  depends  quite  as 
much  on  the  condition  of  adaptation  of  the  eye  as  on  the  absolute 


THE   EFFECT   OF   GLARE  ON   VISION  IOC»9 

brightness  of  the  objects  concerned.    "Interference  with  vision" 
due  to  (2)  is  from  three  causes: 

(a)  It  is  well  known  that  an  excessively  bright  area,  even 
though  small  as  compared  with  the  whole  field,  will  cause  a  con- 
traction of  the  pupil,  thereby  reducing  the  physical  brightness  of 
the  image  of  the  whole  field  as  formed  on  the  retina.  Certain  ex- 
periments seem  to  indicate,  however,  that  this  effect  is  in  part 
compensated  for  by  increased  visual  acuity  due  to  having  the 
lens  stopped  down. 

(b)  The  eye  media  cause  a  slight  scattering  of  the  light  from 
the  excessively  bright  area,  causing  the  equivalent  of  veiling  glare 
over  the  areas  immediately  surrounding  the  bright  source. 

(c)  More  important  still,  the  existence  of  excessively  (rela- 
tively) bright  areas  within  the  field  of  vision  tends  to  shift  retinal 
adaptation  toward  that  required  for  the  brighter  area.  Whatever 
the  process  of  adaptation,  it  is  probable  that  one  part  of  the  retina 
is  affected  to  some  extent  by  the  adaptation  of  another  part.  Con- 
sequently, or  inability  to  see  detail  in  a  dark  field  in  the  fore- 
ground of  which  is  a  bright  light  source  is  in  part  to  causes 
exactly  the  same  as  those  which  make  it  impossible  to  see,  at  first, 
when  entering  a  darkened  room  from  sunlight.  That  is,  it  is 
simply  a  matter  of  adaptation. 

The  deleterious  effects  of  excessive  contrast  depend  in  part  on 
the  relative  sizes  of  the  contrasting  areas.  With  large  contrasting 
areas  (brilliantly  lighted  table  top,  with  remainder  of  room  dim) 
re-accommodation  both  pupillary  and  retinal  is  necessary  as  one 
shifts  one's  gaze  from  the  brighter  to  the  darker  area  and  vice 
versa.  If  this  re-accommodation  occurs  too  frequently  interfer- 
ence with  visual  functions  may  result.  On  the  contrary  small 
"checker-board-like"  contrasting  areas  do  not  necessitate  such  re- 
accommodation,  and  from  that  standpoint  are  less  objectionable. 

As  studied  subjectively,  we  can  divide  the  effects  of  glare  due 
to  excessive  contrast  into  two  classes: 

(1)  Ocular  discomfort.  This  manifests  itself  by  a  "sandi- 
ness"  which  "soon  passes  over  into  a  sharp,  stinging  pain,  fol- 
lowed by  a  muscular  discomfort,  an  aching  in  the  ball  of  the  eye 
which,  if  the  exposure  is  continued  long  enough  seems  to  radiate 
to  the  socket  and  the  surrounding  regions  of  the  face  and  head." 


IOIO     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

This  discomfort  is  not  felt  in  the  retina  as  a  result  of  over-stimu- 
lation, but  in  the  other  parts  of  the  eye. 

(2)  Simple  interference  with  vision,  by  reduction  of  visual 
acuity,  etc. 

Ocular  discomfort  depends  on  the  intrinsic  brilliancy  of  the 
bright  area  and  on  its  extent.  Thus,  the  ocular  discomfort  aris- 
ing from  a  500-watt  tungsten  lamp  within  the  field  of  view  is 
greatly  reduced  by  surrounding  the  lamp  by  a  suitable  translucent 
shade.  In  general,  bright  areas  within  the  field  of  view  which 
leave  persistent  negative  after-images,  are  to  be  avoided. 

Interference  with  vision,  however,  seems  to  depend  on  the  total 
light  entering  the  eye  from  the  bright  area.  Thus,  while  a  globe 
around  a  500-watt  lamp  largely  eliminates  ocular  discomfort,  it 
does  not  materially  reduce  interference  with  vision,  unless  the 
intrinsic  brightness  of  the  area  be  brought  down  to  the  general 
level  of  that  in  the  field  of  view  (under  which  condition  excessive 
contrast  no  longer  exists).  In  this  connection  it  has  been  shown 
that  if  the  interference  with  vision  be  expressed  as  a  "blinding 
effect,"  which  quantitatively  is  "the  per  cent,  increased  illumin- 
ation for  equal  clearness  of  vision  as  compared  with  conditions 
where  the  blinding  effect  is  absent,"  then  the  so-called  blinding 
effect  is  proportional  to  the  square  root  of  the  candlepower  of 
the  bright  area  (source)  in  the  field  of  view. 

Protective  neutral  tinted  glasses  may  be  of  value  in  eliminating 
ocular  discomfort  due  to  contrast  glare.  They  obviously  cannot 
materially  reduce  interference  with  vision,  since  they  simply  re- 
duce the  general  level  of  brightness  and  therefore  of  adaptation, 
but  do  not  reduce  the  contrast. 

EXCESSIVE  EXTRA- VISUAL  RADIATION. 

In  spite  of  a  great  deal  of  experimentation  and  speculation  on 
the  effect  of  extra-visual  radiation  on  eye  media  and  the  visual 
functions,  no  very  definite  conclusions  have  been  reached.  There 
is,  for  example,  much  disagreement  as  to  the  limits  of  trans- 
parency of  the  several  eye  media  in  the  ultra-violet.  One  ob- 
server states  as  follows : 

Cornea :    Transparent  above  0.295/i, ;  opaque  below. 

Lens :  Increasing  transparency  from  0.350/t  to  0.400/i ;  com- 
pletely transparent  above  0.400/x,. 


THE   EFFECT   OF   GEARE  ON   VISION  IOII 

Vitreous :  A  3/16-in.  layer  shows  a  broad  absorption  band 
from  0.250/1  to  0.280/1,  with  a  maximum  at  0.270. 

Another  observer  states  that  light  wave  lengths  shorter  than 
0.320/i  cannot  pass  the  cornea.  Another  states  that,  with  suffi- 
ciently intense  radiation,  lines  in  the  neighborhood  of  0.30  are 
distinctly  visible  as  lines. 

Less  work  has  been  done  regarding  the  transmission  in  the 
infra-red  region.  It  is  concluded  that  "the  total  energy  trans- 
mitted through  the  several  layers  of  eye  media,  as  they  exist  in 
contact  with  each  other,  is  about  the  same  as  that  transmitted 
through  an  equal  quantity  of  water." 

Ultra-violet  radiation  may  be  visible  indirectly,  by  the  fluor- 
escence which  it  produces  in  the  lens  (and  retina). 

Over-exposure  to  ultra-violet  radiation  produces  a  "burn." 
After  a  time,  perhaps  a  few  minutes,  frequently  many  hours, 
there  results  pain  in  the  eyes,  a  deep-seated  itching,  sensitivity 
to  light,  twitching  and  swelling  of  the  lids.  There  is  strong  con- 
traction of  the  pupil  and  conjunctival  discharge.  Examination 
shows  a  contraction  of  the  visual  field,  reduction  in  visual  acuity 
and  partial  or  total  loss  of  dark  adaptation.  Complete  recovery 
requires  several  days.  In  the  more  severe  cases  there  may  be 
permanent  reduction  in  visual  acuity.  One  authority  states  that 
the  source  of  the  trouble  comes  from  rays  shorter  than  0.330/*. 
Others  seem  inclined  to  put  the  limit  somewhat  lower. 

No  definite  statement  can  be  made  regarding  the  effect  of 
infra-red  radiation.  In  general,  however,  no  deleterious  effects 
comparable  to  those  due  to  ultra-violet  radiation  seem  to  have 
been  observed.  Even  in  the  case  of  radiation  comparatively  rich 
in  infra-red,  it  is  probable  that  the  absorbing  power  of  the  an- 
terior eye  media  sufficiently  protects  the  sensitive  retina  from 
injury,  except  for  the  most  intense  and  unusual  cases. 

It  is  probable  that  the  harmful  effects  of  extra  visual  radiations 
on  the  retina  cannot  be  expressed  completely  in  terms  of  the 
wave  length  and  intensity  of  the  radiation  concerned.  The  con- 
dition of  the  eye  is  a  very  important  factor.  For  example,  if  the 
eye  be  dark  adapted,  just  as  it  is  more  sensitive  to  visible  radi- 
ation, so  also  it  may  be  more  sensitive  to  the  effect  of  ultra-violet 
radiation.     It  is  possible  that,  by  reason  of  being  light  adapted, 


IOI2     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  retina  is  protected  from  the  ultra-violet  of  daylight,  while 
with  the  eye  partially  dark  adapted  there  is  insufficient  protection 
against  the  smaller  amount  of  ultra-violet  contained  in  artificial 
illuminants.  In  other  words,  the  mere  fact  that  artificial  illum- 
inants  contain  proportionally  less  ultra-violet  than  daylight  is  not 
of  itself  a  proof  that  the  ultra-violet  of  modern  light  sources  is 
not  harmful.  The  effects  of  ultra-violet  radiation  are  probably 
due  to  atomic  disturbances ;  i.  e.,  are  chemical  in  nature.  Since 
the  chemical  effect  of  radiation  is  selective,  the  intensity  of  the 
disturbances  due  to  this  cause  are  a  function  not  only  of  the 
energy  contained  in  the  radiation  itself,  but  of  the  character  of 
the  receiver.  We  may  not  be  able  to  specify  structurally,  wherein 
the  dark  adapted  eye  differs  from  the  light  adapted  eye,  but  func- 
tionally we  know  that  a  great  difference  exists. 

It  is  safe  to  say,  in  spite  of  our  lack  of  knowledge  of  the  nature 
of  the  harmful  effects  of  radiation,  that  where  the  eye  is  exposed 
to  radiations  known  to  contain  relatively  large  amounts  of  extra 
visible  radiation,  one  should  use  protective  glasses  which  cut  off, 
so  far  as  possible,  the  ultra-violet  and  infra-red.  Except  for 
esthetic  reasons  there  is  no  particular  harm  in  using  a  glass  which 
cuts  off  also  some  of  the  visible  spectrum,  if  that  be  necessary  to 
insure  complete  elimination  of  the  extra  visual  content. 

VEILING  GLARE  AND  FLICKER. 

These  conditions  which  cause  ocular  discomfort  are  dismissed 
together,  because  it  is  probable  that  a  large  part  of  the  source 
of  trouble  is  not  directly  physiological  but  is  to  a  certain  extent 
psychological.  The  connection  between  the  eyes  and  the  various 
bodily  functions  is  well  known.  To  a  layman,  this  indicates  that 
a  comparatively  slight  cause  may  seriously  disturb  the  "equili- 
brium" existing  in  our  ocular  apparatus.  Thus,  there  are  twelve 
muscles  which  rotate  the  eye-ball  in  its  socket.  Each  eye  must 
be  so  oriented  that  the  image  viewed  will  fall  on  exactly  the  same 
part  of  each  retina — an  adjustment  which  must  be  made  with  the 
highest  precision.  Evidently,  this  requires  "a  most  complicated 
and  delicately  balanced  set  of  muscles  and  nervous  connections — 
and  a  small  but  persistent  disturbing  circumstance  may  work  not 
only  great  discomfort,  but  in  extreme  cases,  such  confusion  of  the 
various  eye  movements  as  to  make  vision  well  nigh  impossible." 


THE   EFFECT   OF  GLARE  ON   VISION  IOI3 

When  we  consider  the  still  more  delicate  mechanisms  which 
operate  the  iris  and  the  lens,  it  is  safe  to  say  that  any  condition 
which,  however  little,  interferes  with  comfortable  vision  must, 
if  continued,  result  in  ill  effects.  Even  were  the  data  available, 
it  would  be  beyond  the  scope  of  the  present  report  to  analyze  the 
various  conditions  coming  under  the  above  head. 

Veiling  glare  (see  examples  mentioned  in  other  reports)  re- 
sults in  insufficient  contrast.  "The  seeing  is  bad."  One  feels 
(perhaps  unconsciously)  an  annoyance  at  not  being  able  to  dis- 
tinguish clearly,  and  with  ease,  detail  in  the  field  of  view.  These 
are  possibly  efforts  to  refocus.  The  annoyance,  mental  and  ocu- 
lar, causes  a  strained  condition  in  all  parts  of  the  visual  apparatus, 
so  that,  even  though  the  brightness  be  within  the  limits  of  toler- 
ance, and  the  radiation  reaching  the  eye  contain  no  specifically 
harmful  component,  serious  harm  of  a  more  or  less  nervous 
nature,  may  result. 

The  same  remarks  apply  to  flicker — either  in  brightness  or  in 
space.  The  general  dissatisfaction  at  not  being  able  to  see  clearly 
is  of  itself  largely  the  cause  of  the  ocular  discomfort.  In  dis- 
placement flicker  there  is  the  added  strain  on  the  external  eye 
muscles,  and  in  brightness  flicker  a  corresponding  strain  on  the 
iris  due  to  constant  attempts  at  pupillary  adaptation,  and  if  the 
range  of  brightness  be  extreme,  there  is  continual  retinal  adapta- 
tion. 

"It  is  a  great  though  often  forgotten  physiological  law  that  any 
organ,  exercised  within  its  limits,  tends  to  increase  in  power,  and 
facility,  while  if  overworked  it  becomes  less  and  less  able  to  do 
any  work  at  all.  If  a  man  habitually  uses  his  eyes  in  strong 
lights  he  decomposes  his  visual  purple  faster  than  it  can  be  re- 
generated. If  he  uses  his  ciliary  muscles  without  rest,  day  after 
day,  they  begin  to  break  down  under  the  strain  and  become  fa- 
tigued even  by  short  periods  of  use." 

Permissible  fluctuations  in  brightness  depend  on  the  adaptation 
of  the  eye  and  on  the  time  rate  of  change  of  brightness.  Thus 
10  per  cent,  "sine- wave"  changing  in  brightness  with  a  period  of 
several  seconds  would  not  be  so  objectionable  as  an  abruptly 
alternating  increase  and  decrease  of  brightness  of  the  same  period 
and  amount. 


IOI4    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

When  the  fluctuations  of  brightness  are  sufficiently  high  so  as 
not  to  give  the  sensation  of  flicker,  common  experience  seems  to 
indicate  that  there  is  no  harmful  effect.  It  has  been  shown  that 
the  optic  nerve  can  transmit  a  flickering  sensation  whose  fre- 
quencies are  far  higher  than  those,  (i.  e.,  40  or  50-light  cycles 
per  second)  at  which  vision  becomes  continuous.  This  indicates 
that  the  damping  out  of  the  flicker  must  occur  in  the  retinal 
processes,  and  hence  there  can  be  no  reflex  excitation  of  the  pupil 
or  other  ocular  apparatus  whose  functioning  depend  on  light 
sensation. 

Nelson  M.  Black, 
J.  R.  Cravath, 
F.  H.  Gilpin, 

M.  LUCKIESH, 

F.  K.  RlCHTMYER, 

F.  A.  Vaughn, 

P.  G.  Nutting,  Chairman. 


luckiesh:   yellow  light  1015 

YELLOW  LIGHT.* 


BY  M.  LUCKIESH. 


Synopsis:  A  discussion  of  the  importance  of  color  in  lighting  and 
vision  would  be  too  extensive  to  be  treated  in  a  single  paper.  However, 
inasmuch  as  most  artificial  illuminants  are  decidedly  yellow  as  compared 
with  daylight  and  as  yellow  light  has  some  distinctly  different  properties 
as  compared  with  many  other  illuminants,  a  brief  discussion  of  its  place 
in  lighting  is  presented.  The  knowns  and  unknowns,  and  the  various 
opinions  regarding  yellow  light  are  discussed  briefly  with  respect  to 
visual  acuity,  glare,  fatigue,  penetrating  power,  and  esthetic  value.  The 
procedure  involved  in  altering  the  light  from  tungsten  lamps  to  a  match 
with  the  light  from  the  kerosene  flame  and  old  carbon  incandescent  lamp 
is  presented  together  with  the  resultant  efficiencies  of  the  altered  light 
for  tungsten  lamps  operating  throughout  the  extreme  present  range  of 
luminous  efficiencies.  The  error  usually  made  in  attempts  to  simulate 
the  color  of  the  older  illuminants  by  means  of  screening  tungsten  lamps 
with  yellow  filters  is  pointed  out,  and  illustrated  by  a  comparison  of  the 
ideal  transmission  screens  for  accomplishing  this  purpose  with  ordinary 
amber  glass  of  various  densities  which  is  usually  used. 


The  importance  of  the  color  of  illuminants  and  their  surround- 
ings has  become  very  evident  to  the  lighting  expert.  In  fact  color 
is  so  influential  in  lighting  and  vision  that  certainly  the  problems 
would  often  be  extremely  simplified  if  color-vision  ceased  to  exist. 
Yet  few  persons  realize  that  the  ability  to  see  color  complicates 
the  study  of  lighting  and  vision  very  much.  A  treatment  of  the 
subject  of  color  in  its  relation  to  lighting  would  be  far  beyond 
the  scope  of  a  brief  paper,  but  inasmuch  as  the  majority  of  arti- 
ficial illuminants  are  yellowish  in  color,  yellow  light  will  be 
briefly  discussed.  There  are  many  unsolved  problems  pertaining 
even  to  this  narrowed  field  as  will  be  seen  by  the  confused  state 
of  affairs.  Any  color  phenomenon  is  so  complicated  that  the 
chief  difficulty  in  interpreting  observations  lies  in  the  absence  of 
properly  recording  or  weighing  all  the  influential  factors  found  in 
a  given  case.  Too  often  matters  of  taste  are  construed  as  gen- 
eral facts.    The  physical  problems  are  usually  easy  to  solve.    The 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,  D.   C,   September  20-23,    191 S- 

The   Illuminating   Engineering   Society   is   not   responsible   for    the   statements    or 
opinions  advanced  by  contributors. 
12 


IOl6    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

physiological  and  psychological  problems  are  more  difficult  to 
study  owing  to  the  vagueness  of  the  criteria  but  these  problems 
are  certainly  capable  of  solution.  However,  the  problems  which 
involve  merely  the  esthetic  taste  are  indeterminate.  An  attempt 
will  be  made  briefly  to  point  out  the  knowns  and  unknowns  and 
to  discuss  the  opinions  and  conclusions  of  various  observers  re- 
garding those  phenomena  which  are  of  chief  interest  in  a  discus- 
sion of  yellow  light. 

Visual  Acuity. — Some  years  ago  it  was  shown  that  mono- 
chromatic light  was  superior  to  light  of  an  extended  spectral 
character  for  the  perception  of  very  fine  detail.  An  investiga- 
tion1 showed  that  monochromatic  light  near  the  middle  of  the 
spectrum,  namely  yellow  light,  was  superior  for  the  perception 
of  fine  detail  to  monochromatic  light  of  any  other  wave-length. 
More  recently  the  author2  has  investigated  visual  acuity  in  day- 
light and  ordinary  tungsten  light.  This  problem  has  been  studied 
under  various  conditions  in  connection  with  other  work  with  the 
general  result  that  visual  acuity  was  found  to  be  practically  the 
same  under  equal  intensities  of  illumination  for  these  two  illum- 
inants.  These  tests  were  made  on  fine  parallel  lines  at  the  thresh- 
old of  discrimination.  In  some  of  the  work  by  the  author  and 
others  another  criterion  was  used,  namely  that  of  equal  read- 
ability or  clearness  of  a  page  of  type.  This  latter  criterion  ap- 
proaches more  nearly  to  the  predominating  condition  found  in 
practise  and  has  proved  to  be  sufficiently  definite  to  commend  its 
use  in  practical  investigations.  For  instance  in  reading,  the  char- 
acters are  recognized  in  groups  and  the  eye  is  not  focused  on  in- 
dividual letters  but  travels  across  a  page  in  a  series  of  jumps. 
Even  though  the  eye  did  examine  each  letter  or  portion  of  a  letter 
the  illumination  is  usually  sufficiently  high  so  that  the  size  of  the 
detail  is  far  above  the  limits  of  discrimination. 

Owing  to  the  fact  that  yellow  paper  is  often  declared  to  be 
"easier  on  the  eyes"  it  was  thought  of  interest  to  ascertain  if  there 
was  an  appreciable  difference  in  visual  acuity  when  fine  lines 
were  viewed  against  backgrounds  of  white  and  yellow  copy  paper. 

1 I,uckiesh,  M.,  The  Dependence  of  Visual  Acuity  on  the  Wave-Length  of  I,ight; 
Elec.  World,  58.  P-  "32.  19"- 

The  Influence  of  Spectral  Character  of  I,ight  on  the  Effectiveness  of  Illumination; 
Trans.  I.  E-  S.,  vol.  7.  P-  i35, 1912. 

*  I<uckiesh,  M.,  Visual  Acuity  in  White  I,ight;  Elec.  World,  Dec.  6,  1913. 


luckilsh:   yellow  light  1017 

The  illuminant  was  artificial  daylight  of  approximately  the  same 
spectral  character  as  noon  sunlight.  The  reflection  coefficients 
of  the  white  and  yellow  papers  for  this  illuminant  were  0.77  and 
0.69  respectively.  Under  equal  illumination  visual  acuity  was 
found  to  be  practically  the  same  with  a  slight  tendency  to  be  bet- 
ter with  the  yellow  copy  paper  as  a  background.  When  the  back- 
grounds were  equally  bright  visual  acuity  appeared  to  be  slightly 
but  definitely  higher  with  the  background  of  yellow  copy  paper. 
The  illumination  used  varied  from  3  to  10  foot-candles.  It  should 
be  noted  that  this  paper  was  a  pale  and  unsaturated  yellow  in 
color.  Although  there  was  no  appreciable  difference  in  acuity 
when  the  two  backgrounds  were  illuminated  to  equal  flux  den- 
sities it  is  apparent  that  the  light  reflected  from  the  yellowish 
paper,  in  which  the  blue  and  violet  rays  were  somewhat  sup- 
pressed, showed  a  slight  advantage  per  unit  of  brightness  over 
that  reflected  from  the  white  paper  in  respect  to  defining  power. 
This  does  not  necessarily  indicate  that  the  unsaturated  yellow 
light  was  better  for  revealing  fine  detail  than  any  other  unsat- 
urated color,  although  other  evidence  points  to  this  conclusion. 
Further,  with  a  given  illuminant  such  as  the  light  from  a  tungsten 
lamp,  apparently  little  advantage  is  gained  in  visual  acuity  by 
screening  out  some  of  the  visible  rays  of  short  wave-length.  If 
this  screening  were  carried  further  possibly  some  advantage 
might  appear.  It  appears  quite  likely  that,  at  the  higher  illum- 
inations where  visual  acuity  decreases  slowly  with  decreasing 
illumination,  the  reduction  in  visual  acuity  due  to  decreased  il- 
lumination, which  is  the  result  of  the  screening  process,  would 
be  more  than  overcome  by  the  increasing  definition  due  to  the 
approach  toward  monochromatism  of  the  light  passing  through 
the  screen.    This  point  is  open  to  further  investigation. 

Glare. — The  opinions  regarding  the  relation  of  the  color  of  the 
illuminant  and  glare  are  quite  conflicting.  This  state  of  affairs 
is  no  doubt  largely  due  to  the  indefiniteness  of  the  criteria  and 
the  lack  of  an  approved  method  of  measuring  the  vague  con- 
dition known  as  glare.  The  opinions  that  have  been  expressed  on 
this  point  are  usually  associated  with  headlights.  It  is  strongly 
asserted  by  some  that  a  yellowish  headlight  is  less  glaring  than 
a  white  one.    While  the  author  does  not  wish  to  be  understood 


IOl8    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

as  supporting  this  conclusion  it  has  often  appeared  to  him  that 
a  greenish-yellow  headlight  which  was  experimented  with  con- 
siderably, appeared  to  be  noticeably  less  glaring  than  a  'white' 
light  without  the  greenish-yellow  screen,  the  units  being  of  equal 
wattage.  The  greenish-yellow  screen,  however,  absorbed  about 
25  per  cent,  of  the  total  light  which  was  emitted  by  the  tungsten 
lamp  used. 

On  the  other  hand  others  have  strongly  asserted  that  yellow, 
orange  and  red  rays  contribute  more  to  the  production  of  glare 
than  the  visible  rays  of  shorter  wave-lengths.  In  fact  the  ideal 
illuminant  according  to  these  observers  is  one  that  has  even  less 
of  the  yellow,  orange  and  red  rays  than  daylight.  However,  until 
more  convincing  evidence  is  submitted  this  question  is  un- 
answered. 

Yellow  and  yellow-green  glasses  are  worn  considerably  for 
protecting  the  eyes  from  the  glare  of  daylight.  That  such  glasses 
reduce  glare  is  quite  apparent  especially  when  the  eyes  are  called 
upon  to  perceive  fine  detail.  In  the  case  of  outdoor  target- 
shooting  such  glasses  have  proved  very  helpful;  however,  in 
such  cases  the  decrease  in  glare  is  not  due,  predominantly  at 
least,  to  any  inherent  virtue  in  the  yellow  or  yellow-green  light, 
but  is  due  chiefly  to  the  great  reduction  in  brightness  of  the  broad 
expanse  of  visible  blue  sky  and  the  accompanying  decrease  in 
the  luminous  flux  entering  the  eye.  The  author  has  suggested 
the  use  of  a  greenish-yellow  light  for  illuminating  indoor  rifle- 
ranges  owing  to  the  fact  that  for  equal  brightnesses  of  the  targets 
and  their  surroundings  (and  therefore  perhaps  approximately 
equal  conditions  of  glare)  the  targets  can  be  seen  more  clearly, 
the  increased  definition  being  due  in  this  case  to  the  less  extended 
spectral  character  of  the  light.  No  definite  data  is  available  from 
such  installations.  Protecting  glasses  will  not  be  effective  in  the 
same  manner  indoors  as  outdoors,  owing  to  the  absence  of  a 
broad  area  of  high  brightness  which  is  present  in  the  latter  case. 
When  yellow  or  yellow-green  glasses  are  used  for  distant  vision, 
with  or  without  field  glasses,  the  increase  in  the  clearness  of  de- 
tails is  quite  apparent.  One  reason  for  this  is  the  partial  elim- 
ination of  the  bluish  haze  which  is  more  or  less  effective  in 
obliterating  distant  details.    Some  of  these  effects  are  not  directly 


LUCKIESH  :     YELLOW    LIGHT  IOIO, 

connected  with  the  problems  of  lighting  but  nevertheless  are 
often  confused  and  misinterpreted. 

Some  time  ago  Dr.  P.  W.  Cobb  showed  that  a  bright  light 
source  in  the  field  of  view  was  glaring  even  when  the  image  of 
this  source  fell  on  the  blind  spot  of  the  retina.  He  attributed  the 
glare  due  to  scattered  light  in  the  eye.  It  has  been  suggested  that 
blue  light  might  be  more  glaring  than  yellow  light  because  of 
the  greater  scattering  of  the  blue  rays  by  fine  particles  as  dis- 
cussed later.  However,  diffusing  media  differ  in  their  selective 
scattering  of  rays  of  light  and  little  is  known  about  the  selective 
scattering  of  the  sclerotica  or  white  exterior  coat  of  the  eye- 
ball. 

The  advantage  of  using  yellow  or  yellow-green  glasses  has 
been  shown  elsewhere.3  An  acuity  object  was  set  up  on  a  clear 
day  in  the  shade  of  a  building  in  such  a  position  that  a  large  sky 
area  was  visible  to  the  observer.  Visual  acuity  readings  were 
made  as  rapidly  as  possible  and  after  three  minutes  had  elapsed 
yellow-green  glasses  were  quickly  placed  before  the  eyes  and  the 
readings  were  continued.  At  the  end  of  three  minutes  these 
glasses  were  removed  and  readings  were  made  as  before.  At  the 
beginning  of  the  observations  only  a  slight  sensation  of  glare  was 
experienced ;  however,  as  soon  as  acuity  observations  were  begun 
the  glare  became  very  evident  and  rapidly  grew  painful.  Acuity 
was  always  better  when  the  colored  glasses  were  before  the  eyes 
and  during  the  latter  part  of  the  experiment,  which  lasted  18 
minutes,  it  was  indeed  a  great  relief  to  wear  the  yellow-green 
glasses.  The  absorption  coefficient  of  these  glasses  was  about  50 
per  cent,  yet  acuity  was  better  with  this  reduced  illumination  than 
with  the  total  light  and  the  discomfort  due  to  glare  was  practi- 
cally eliminated.  This  experiment  showed  conclusively  the  re- 
duction of  glare  attending  the  reduction  in  the  brightness  of  the 
sky  area. 

The  foregoing  provides  an  example  of  the  ease  with  which 
confusing  conditions  are  brought  about.  It  might  be  argued 
that  the  decrease  in  the  amount  of  blue  light  due  to  a  reduction  in 
the  brightness  of  the  sky  area  was  responsible  for  the  reduction 
of  glare.     However,  it  is  quite  certain  that  this  excessive  glare 

*  I,uckiesh,  M.,  Safeguarding  the  Eyesight  of  School  Children;  Trans.  I.  E.  S.,  p.  181, 
No.  2,  1915. 


1020     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

was  due  to  the  broad  expanse  of  bright  sky  in  the  visual  field 
and  was  not  related  appreciably  to  the  color.  As  previously 
stated  there  are  no  definite  data  available  relating  to  glare  and  the 
color  or  spectral  character  of  the  illuminant. 

Fatigue. — Here  again  definite  data  are  lacking  for  quite  the 
same  reasons  as  found  in  the  measurement  of  glare,  namely  the 
vagueness  of  the  condition  and  the  criteria  and  the  absence  of 
an  approved  and  thoroughly  tested  method.  It  is  perhaps  safe  to 
state  that  there  is  a  general  opinion  that  ordinary  artificial  light 
is  more  productive  of  fatigue  than  ordinary  daylight.  The  author 
is  inclined  to  believe  that  sufficient  weight  has  not  often  been 
given  to  the  fact  that  artificial  light  is  usually  judged  after  the 
eyes  have  done  a  day's  work  under  daylight.  It  has  been  con- 
tended that  the  greater  energy  absorption  in  the  eye  media4  per 
unit  of  light  for  ordinary  yellowish  artificial  illuminants  than 
for  daylight  accounts  for  eye-fatigue  under  artificial  light.  Little 
account  seems  to  have  been  taken  of  the  much  greater  intensi- 
ties of  illumination  usually  experienced  in  daytime.  If  this  con- 
tention is  correct  there  should  be  plenty  of  evidence  of  eye- 
fatigue  due  to  absorption  of  energy  in  many  cases  of  daylighting. 
Inasmuch  as  this  point  has  not  been  proved  and  as  there  are  no 
experimental  data  available  that  throw  much  light  upon  the  sub- 
ject, it  is  futile  to  discuss  it  further. 

It  has  been  contended5  that  yellow  and  orange  lights  at  high 
intensities  are  more  fatiguing  than  green  and  grenish-blue  lights. 
It  has  been  suggested  by  some  that  this  result  obtains  because  the 
yellow  rays  are  more  effective  in  bleaching  the  visual  purple  than 
rays  of  other  wave-lengths.  There  is  much  to  be  learned  about 
this  process  and  several  problems  must  be  investigated  before 
such  a  conclusion  is  tenable.  For  instance,  the  relation  of  the 
bleaching  action  to  the  amount  of  light-sensation  produced  and 
to  fatigue  must  be  known  before  such  a  contention  can  be  con- 
sidered more  than  a  hypothesis. 

The  statement  is  often  made  that  yellow  light  is  "easier  on 
the  eyes"  than  white  light.  Usually  this  is  applied  to  the  use  of 
yellow  paper;  and,  based  on  this  premise,  certain  books  have 

4  Luckiesh,  M.,  Radiant  Energy  and  the  Eye;  Elec.  World,  Oct.  25,  1913. 

Energy  Density  in  the  Eye-Media;  Elec.  World,  1915. 
6  Steinmetz,  C  P.,  Radiation,  Light  and  Illumination;  1909,  p.  265. 


luckiesh:   yellow  light  1021 

been  printed  on  yellow  paper.  There  are  so  many  variables  that 
it  is  impossible  to  draw  definite  conclusions  from  the  available 
data.  However,  it  is  well  to  distinguish  between  the  two  con- 
ditions, namely,  black  type  on  a  yellow  paper  illuminated  by 
white  light  and  black  type  on  white  paper  illuminated  by  yellow 
light.  In  general  there  will  be  a  difference  in  the  contrast  ratios 
between  the  type  and  backgrounds  in  the  two  cases.  The  ink  may 
be  assumed  to  reflect  light  non-selectively  and  therefore,  for  equal 
brightnesses  of  the  type  in  the  two  cases,  the  brightnesses  of  the 
backgrounds,  one  of  which  selectively  reflects  light,  will  be  un- 
equal. The  contrast  ratio  is  probably  of  some  importance  from 
the  standpoint  of  fatigue,  but  there  are  no  data  available  regard- 
ing this  point. 

The  author  has  used  artificial  daylight  for  several  years  for 
desk  lighting  and  it  has  been  his  experience  that  it  is  less  fatigu- 
ing than  the  light  from  a  tungsten  incandescent  lamp.  This  is 
especially  evident  when  the  daylight  must  be  reinforced  by  ar- 
tificial light.  This  experiment  was  carried  further  by  using 
clear  tungsten  lamps  and  tungsten  lamps  with  medium  and  dense 
yellow  bulbs  for  several  hours  of  reading  on  a  great  many  even- 
ings. It  is  certain  that  the  deep  yellow  light  was  more  fatiguing 
than  the  light  from  a  clear  tungsten  lamp  and  that  the  latter 
seemed  to  be  more  fatiguing  than  the  daylight.  Another  observer 
drew  the  same  general  conclusions.  The  experiments  were  made 
with  the  yellow  lamps  versus  the  clear  lamps  in  the  evening,  but 
the  comparisons  of  the  artificial  daylight  and  tungsten  light  were 
made  in  daytime  under  ordinary  working  conditions.  The  light- 
ing conditions  such  as  the  distribution  of  light,  position  of  the 
book  and  observer,  etc.,  were  such  as  would  be  termed  satis- 
factory. It  is  recognized  that  such  experiments  are  not  of  the 
character  that  would  be  pronounced  conclusive,  but  it  appears 
that  such  data  should  be  gathered  and  recorded.  As  long  as  a 
simple  method  for  testing  eye  fatigue  is  unavailable  such  ob- 
servations as  noted  above  must  govern  our  practise  and  in  all 
events  they  will  be  available  for  future  summaries. 

PENETRATING  POWER. 
Inasmuch    as    blue    rays    and    others    of    short    wave-length 
are  scattered  more  than  the  rays  of  longer  wave-length  it  is  in- 


1022     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

teresting  to  consider  the  penetrating  power  of  yellow  light  as 
compared  with  that  of  other  lights.  It  is  well  known  that  smoke 
consisting  of  fine  particles  appears  bluish  in  color  while  its 
shadow  on  a  white  surface  is  of  a  reddish  hue.  The  setting  sun 
appears  red  owing  to  the  partial  absorption  of  the  visible  rays 
of  short  wave-lengths  by  the  smoke,  dust,  etc.,  in  the  atmosphere. 
This  absorption  is  produced  largely  by  scattering  the  blue  rays 
more  than  the  rays  of  longer  wave-length  with  the  result  that  the 
skylight,  which  is  scattered  sunlight,  appears  predominantly  blue 
in  color.  In  the  same  manner  the  familiar  haze  in  the  distance 
appears  blue.  It  is  thus  seen  that  the  yellow  light  will  penetrate 
through  a  greater  thickness  of  ordinary  atmosphere  than  white 
or  bluish  light.  Obviously  deep  yellow  and  red  lights  if  they 
could  be  produced  at  a  high  efficiency  would  be  quite  satisfactory 
for  signals  that  must  penetrate  a  dust  and  smoke  laden  atmos- 
phere. In  experiments  conducted  on  a  clear  night  it  has  been 
found6  that  there  was  no  difference  in  the  penetrating  power  of 
tungsten  and  carbon  incandescent  electric  lights  for  distances  of 
a  mile. 

In  the  case  of  headlights  another  condition  is  of  interest, 
namely  that  when  the  observer  is  behind  the  headlight.  In  this 
case,  the  condition  is  different  from  that  of  an  observer  in  the  dis- 
tance trying  to  distinguish  the  signal  light.  An  automobile  or 
locomotive  driver  uses  the  light  for  illuminating  the  pathway  and 
if  a  considerable  portion  of  the  light  be  scattered  by  fog,  smoke, 
or  dust,  it  should  be  more  difficult  to  see  through  the  illuminated 
veil  than  in  the  case  of  little  or  no  scattering  of  light.  In  fact, 
the  reduction  in  the  ability  to  see  is  very  likely  due  more  to  this 
luminous  veil  than  to  the  actual  loss  of  light  in  the  projected 
beam.  This  condition  is  reproduced  by  painting  a  screen  door 
white  and  attempting  to  see  beyond  it.  It  is  well  known  that  it 
is  difficult  to  see  into  a  room  when  such  a  screen  is  highly  illum- 
inated by  daylight  on  the  side  toward  the  observer.  Owing  to 
the  fact  that  visible  rays  of  short  wave-lengths  are  scattered 
more  than  the  yellow,  orange  and  red  rays,  it  appears  that  the 
luminous  veil  in  an  atmosphere  laden  with  fog,  smoke,  or  fine 
dust  would  be  less  apparent  and  less  liable  to  obscure  vision  in 

6  Paterson  and  Dudding,  Visibility  of  Point  Sources,  National  Physical  laboratory, 
England;  Abstract  in  Elec.  World,  1913,  vol.  67,  p.  266. 


luckiesh:   yellow  light  1023 

the  case  of  a  yellow  illuminant  than  in  the  case  of  one  contain- 
ing a  relatively  greater  amount  of  rays  of  the  shorter  wave- 
lengths. Such  experiments  are  difficult  to  perform  owing  to  the 
impossibility  of  obtaining  constant  conditions  out  of  doors  and 
to  the  absence  of  a  simple  and  rapid  method  for  making  the 
observations.  However,  the  author  experimented  with  tungsten 
lamps  in  automobile  headlights  using  a  greenish-yellow  glass  over 
one  headlight  and  a  clear  glass  over  the  other.  On  several  foggy 
nights  the  experiments  were  made  and  although  the  screens  were 
used  interchangeably  on  the  two  lamps  the  four  observers  con- 
cluded that  distant  objects  in  the  fog  were  more  easily  seen  by 
means  of  the  greenish  yellow  light  notwithstanding  the  fact  that 
the  luminous  intensity  of  this  beam  was  25  per  cent,  lower  than 
that  of  the  'white'  beam  through  the  clear  screen. 

Based  upon  the  forgoing  principle  several  different  types  of 
headlights  have  been  constructed  by  various  companies.  These 
include  gold-plated  reflectors,  greenish-yellow  glass  reflectors 
backed  with  a  silver  coating,  yellow-green  bulbs  for  tungsten 
lamps,  and  greenish-yellow  lenses  in  the  aperture  of  the  re- 
flector. It  appears  that  the  latter  scheme  has  all  the  advantages 
possessed  by  the  others  and  the  additional  advantage  of  sim- 
plicity. Of  course  there  may  be  cases  where  a  glass  screen  can 
not  be  used  in  the  aperture,  such  as  in  the  extremely  powerful 
searchlights.  In  such  cases  the  observer  could  wear  the  screens 
before  his  eyes. 

The  phenomenon  known  as  the  Purkinje  effect  has  often  been 
misinterpreted  in  considering  the  penetrating  power  of  illumin- 
ants.  It  is  true  that  at  low  intensities  of  illumination  the  visible 
rays  of  short  wave-lengths  possess  a  relatively  greater  illumin- 
ating value  than  the  rays  of  longer  wave-lengths,  as  compared 
with  their  relative  values  at  high  intensities.  This  fact  is  per- 
haps worthy  of  attention,  but  it  should  be  noted  that  the  Purkinje 
phenomenon  is  usually  studied  with  the  entire  retina  dark  adapted. 
This  is  not  in  general  the  condition  found  in  practise  because  the 
foreground,  especially  from  the  point  of  view  of  an  automobile 
or  locomotive  driver,  is  usually  of  brightnesses  well  above  the 
Purkinje  region.  Some  investigators  have  found  the  Purkinje 
phenomenon  to  be  much  less  marked  in  the  case  of  the  photo- 
metric field  being  surrounded  by  a  field  of  moderate  brightness. 


1024     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

It  is  interesting  to  note  that  the  visibility  of  point  sources  of 
light  in  clear  atmosphere  has  been  shown6  to  vary  directly  as  the 
candlepower  and  inversely  as  the  square  of  the  distance.  Further, 
in  the  case  of  signals  it  must  be  remembered  that  the  central 
region  of  the  retina,  where  objects  are  seen  clearly,  is  more  sen- 
sitive to  yellow  light  than  to  blue  light. 

ESTHETIC  VALUE. 
The  esthetic  value  of  colors  is  quite  a  matter  of  taste;  there- 
fore it  is  not  surprising  to  find  a  diversity  of  opinion.  For  this 
reason  it  is  difficult  to  discuss  this  phase  of  the  subject.  Too 
often  the  illuminating  engineer  fails  to  distinguish  between  mat- 
ters of  taste  and  scientific  facts  that  are  not  affective  in  nature. 
So  that  it  appears  profitable  to  discuss  this  subject  briefly  in  order 
to  emphasize  this  point.  The  history  of  the  esthetic  value  of 
yellow  is  interesting  as  it  is  for  colors  in  general.  It  is  of  par- 
ticular interest  inasmuch  as  artificial  illuminants  were  for  many 
years  of  a  yellowish  hue  and  even  to-day  most  of  the  illuminants 
that  are  used  where  the  esthetic  taste  is  important  are  quite 
yellow  as  compared  with  daylight.  While  there  are  problems 
pertaining  to  the  affective  value  of  colors  awaiting  solution,  it 
appears  to  the  author  that  the  chief  object  of  the  lighting  expert 
in  dealing  with  the  esthetic  side  of  color  in  lighting  should  be  to 
ascertain,  and  satisfy  if  possible,  the  esthetic  taste  of  his  client 
rather  than  his  own.  It  is  the  client  who  must  be  satisfied  and 
it  is  the  client  who  is  obliged  to  live  amid  the  surroundings  whose 
appearance  is  largely  under  the  control  of  the  lighting  specialist. 
Experience  shows  that  illuminants  of  many  tints  find  a  place  in 
lighting  owing  to  the  diversity  of  taste  which  actually  exists. 
If  a  person  interested  in  lighting  prefers  the  "warmer"  tints  of 
the  older  illuminants  he  should  recognize  that  this  is  a  question  of 
personal  taste  and  should  not  enforce  upon  others  a  condition 
which  is  strictly  a  matter  of  taste.  Likewise  those  who  believe 
that  modern  illuminants  should  be  altered  in  the  other  direction 
because  they  prefer  artificial  daylight  should  take  care  that  they 
distinguish  between  those  cases  which  require  light  of  a  daylight 
quality  for  scientific  reasons  and  those  which  are  governed  only 
by  the  esthetic  sense. 

«  Paterson  and  Dudding.    Visibility  of  Point  Sources,  National  Physical  laboratory, 
England;  Abstract  in  Elec.  World,  1913,  vol.  67,  p.  266. 


luckiesh:   yellow  light  1025 

There  are  many  interesting,  conflicting,  and  amusing  state- 
ments to  be  found  regarding  the  psychological  (and  physiological) 
influence  of  color.  It  is  quite  permissible  to  express  personal 
opinions  and  convictions  regarding  the  psychological  influence 
of  color,  but  care  should  be  taken  to  label  these  "personal  convic- 
tions" in  order  that  those  less  familiar  with  the  subject  may  not 
take  the  statements  too  seriously  and  assume  that  they  are  gen- 
erally applicable.  A  common  mistake  is  made  in  expressing  a 
conclusion  involving  psychological  influence  of  a  certain  condition 
of  lighting  and  ascribing  a  reason  which  can  be  shown  to  be 
unjustified.  It  has  been  stated  by  a  lighting  specialist  that  the 
"white"  light  of  the  tungsten  lamp  caused  persons  to  be  depressed, 
to  have  a  headache  or  to  have  the  blues.  It  is  a  remarkable  fact 
that  those  persons  enjoy  life  at  all  considering  that  they  are  com- 
pelled to  live  in  daylight  for  a  large  portion  of  their  time.  Of 
course  the  appearance  of  a  color  is  very  largely  influenced  by  its 
environment  and  contrast  is  an  important  factor.  How  much  a 
purely  imaginary  contrast  can  effect  personal  taste  the  author  is 
unable  to  state;  but,  if  the  person  who  is  depressed  by  tungsten 
light  owing  to  its  "whiteness"  is  mentally  comparing  its  color 
with  that  of  the  carbon  lamp  or  another  old  illuminant,  it  is  quite 
likely  that  the  tungsten  lamp  appears  unduly  white.  But  why 
should  the  older  illuminants  be  taken  as  the  standard  for  com- 
parison? If  that  person  should  compare  carbon  and  tungsten 
lamps  side  by  side  with  daylight  relatively  little  difference  will  be 
seen  between  the  colors  of  the  kerosene,  carbon  and  tungsten 
lights.  It  is  strange  indeed  to  hear  so  little  complaining  regard- 
ing the  unesthetic  color  of  daylight.  However,  influenced  by 
these  various  appeals  for  "warmer"  illuminants,  one  is  often 
inclined  to  believe  that  the  Creator  made  a  mistake  in  designing 
the  first  and  most  universal  illuminant.  Perhaps  He  designed  the 
best  utilitarian  illuminant  leaving  it  to  man,  as  he  rose  in  the 
scale  of  intelligence,  and  developed  an  esthetic  sense,  to  provide 
his  own  luxuries. 

In  a  recent  paper  in  the  Transactions  the  use  of  amber  glass 
was  very  much  in  evidence  for  altering  tungsten  light  to  a 
"warmer"  tint.  Amber  glass  will  not  alter  tungsten  light  to 
match  any  of  the  older  illuminants  and  while  it  may  be  preferred 


1026     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

by  many  persons  it  has  a  greenish  tinge  that  is  objectionable  to 
many.  Thin  amber  glass  is  nearly  a  lemon  yellow  and  the  dense 
specimens  become  less  greenish  when  viewed  in  tungsten  light, 
but  at  no  density  will  the  ordinary  amber  glass  match  any  of 
the  older  illuminants.  Therefore,  if  light  of  an  amber  color  is 
preferred  it  is  not  because  it  imitates  the  color  of  older  illu- 
minants. Here  it  may  be  of  interest  to  refer  briefly  to  some 
experiments  conducted  in  a  study  of  color  preference.7  A  group 
of  fifteen  fairly  saturated  colored  papers  (representing  the  whole 
range  of  the  spectrum)  each  4  inches  (10.16  cm.)  square,  were 
presented  to  fifteen  observers  who  were  instructed  to  choose 
the  colors  in  the  order  in  which  they  preferred  them.  Among 
other  instructions  each  observer  was  asked  to  choose  the  colors 
for  color's  sake  alone  by  isolating  each  color  in  his  mind.  In  fact, 
he  was  told  to  "live"  and  to  "see"  each  color  individually  until  he 
was  prepared  to  make  his  choice.  Both  in  tungsten  light  and 
daylight  (the  separate  experiments  being  conducted  usually  sev- 
eral weeks  apart)  the  lemon  yellow  ranked  last  and  the  more 
reddish  yellows  ranked  about  midway  in  the  preference  order. 
The  lemon  yellow  was  placed  last  in  the  preference  order  by 
nearly  every  observer.  These  data  are  not  presented  as  proof 
that  the  average  person  does  not  like  an  amber  color  because  it  is 
a  long  step  from  this  experiment  to  lighting  conditions,  but  rather 
to  illustrate  that  the  esthetic  or  affective  values  of  colors  can  be 
studied  with  groups  of  persons. 

The  author  has  experimented  with  clear  tungsten  light,  arti- 
ficial daylight,  rose,  yellow,  blue,  red,  and  amber  lights  in  the 
home,  and  while  some  of  these  results  are  outside  the  scope  of 
this  paper,  it  may  be  of  interest  to  record  his  personal  con- 
clusions. Clear  tungsten  light  was  found  to  be  satisfactory  in 
most  cases  when  the  glass  shade  or  accessory  was  of  a  yellowish 
tint.  The  light  itself  was  satisfactory  as  far  as  the  appearance  of 
most  objects  was  concerned.  Especially  in  a  shower  over  the 
dining  room  table  it  was  satisfactory  but  largely  due  to  the  fact 
that  the  glass  shades  which  concealed  the  lamps  were  a  deep 
yellow  in  color  providing  a  low  intensity  yellow  light  for  il- 
luminating the  walls  and  ceiling  and  permitting  unaltered  light 
to  illuminate  the  table.     The  artificial  daylight  lamps  were  pleas- 

7  I/uckiesh,  M.,  Color  and  Its  Applications,  Fig.  77;  Scientific  American,  June  26,  1915. 


luckiesh:   yellow  light  1027 

ing  in  the  same  fixture  and  also  in  a  reading  lamp  with  a  yellow 
silk  shade  the  direct  light  being  unaltered  in  color.  In  a  white 
semi-indirect  bowl  in  the  living  room  slightly  rose-tinted  lamps 
were  used  for  several  months.  These  were  found  to  be  definitely 
unrestful  and  somewhat  irritating.  The  yellow  lamps  which  were 
carefully  made  to  match  a  kerosene  flame  were  the  most  satis- 
factory for  the  general  illumination  in  the  living  room  for  con- 
versational purposes,  but  not  for  reading.  The  deep  blue  light 
which  was  used  to  illuminate  the  ceiling  of  the  dining  room  in 
order  to  roughly  imitate  out  of  doors  was  quite  depressing.  The 
red,  as  is  commonly  experienced,  was  highly  unsatisfactory  for 
general  illumination  even  at  low  intensity  and  low  saturation. 
The  amber  light  was  not  as  satisfactory  as  the  unsaturated  yellow 
which  simulated  the  kerosene  flame.  These  conclusions  were 
quite  definite  in  all  these  cases  and  were  arrived  at  through  many 
experiments  and  many  months  of  observation  under  ordinary 
conditions  in  the  home.  It  should  be  noted  that  the  rugs  and 
paintings  in  the  room  lost  much  of  their  beauty  under  the  yellow 
illuminants  which  suggested  the  possibility  of  using  tungsten 
lamps  with  both  clear  and  yellow  bulbs  on  separate  circuits.  This 
scheme  was  tried  and  has  been  used  for  a  year  with  considerable 
satisfaction. 

SIMULATING  OLD  ILLUMINANTS. 

The  present  efficiency  of  illuminants  makes  it  possible  to  vary 
their  color  to  suit  the  requirements  by  the  use  of  colored  screens 
and  yet  enjoy  the  advantage  of  a  fairly  high  efficiency.  The 
quality  of  the  tungsten  light  has  been  altered  to  match  in  spectral 
character  various  kinds  of  daylight.  Owing  to  the  fact  that  many 
have  expressed  a  desire  to  simulate  the  color  of  the  older  illum- 
inants, considerable  attention8  has  been  given  to  this  subject. 
The  transmission  of  ideal  screens  for  converting  the  light  from 
vacuum  tungsten  lamps  of  various  luminous  efficiencies  to  the 
same  spectral  character  of  the  old  carbon  incandescent  lamps 
(3.1  watts  per  mean  horizontal  candle)  and  of  the  kerosene  flame 
have  been  computed  and  the  resulting  luminous  efficiencies  have 
been  determined.  In  Fig.  1  Curve  Or  represents  the  transmission 

8  I,uckiesn,  M.,  Simulating  Old  Illuminants;  Elec.  Review  and  W.  E.,  July  24,  1915, 
p.  161. 


1028     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


of  the  ideal  screens  for  total  light  for  converting  the  light  from 
vacuum  tungsten  lamps  operating  at  various  efficiencies  into  light 
of  the  same  spectral  character  as  that  of  the  carbon  incandescent 


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Fig.  i. — Showing  the  transmission  of  colored  screens  for  use  with  the  vacuum  tungsten 
lamps  for  simulating  old  illuminants;  also  showing  the  luminous  efficiency  of  the 
altered  light. 


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Fig.  2.— Data  similar  to  that  in  Fig.  i  but  for  the  gas-filled  lamp. 

lamp.  Curve  Kt  is  a  corresponding  curve  for  the  ideal  screens 
which  convert  the  light  from  vacuum  tungsten  lamps  into  light 
of  the  same  spectral  character  as  the  kerosene  flame.    On  com- 


luckiesh:   yellow  light 


1029 


bining  the  transmission  of  the  ideal  screen  in  any  case  with  the 
luminous  efficiency  of  the  unscreened  illuminant,  the  luminous 
efficiency  of  the  altered  light  is  obtained.  Curve  CE  represents 
the  final  luminous  efficiencies  of  the  vacuum  tungsten  lamp  after 
it  has  been  screened  to  match  a  carbon  lamp  in  color.  KE  shows 
a  similar  data  when  the  tungsten  lamp  has  been  screened  to  match 
the  kerosene  flame.  In  Fig.  2  the  corresponding  data  are  given 
for  the  gas-filled  lamp. 

In  Fig.  3  curve  C  represents  the  spectral  transmission  curve  of 
the  ideal  screen  for  altering  the  light  from  a  vacuum  tungsten 
lamp,  operating  at  7.9  lumens  per  watt,  to  a  spectral  match  with 


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Fig.  3.— Ideal  screens  for  tungsten  lamp  (vacuum)  operating  at  7.9  lumens  per 
watt  compared  with  common  amber  of  various  densities. 

the  light  from  the  carbon  incandescent  lamp  under  consideration 
between  0.40/i  and  0.70/1,  the  transmission  being  assumed  to  be 
100  per  cent,  at  0.7071,  the  practical  long-wave  limit  of  the  visible 
spectrum.  Curve  K  is  a  similar  curve  of  an  ideal  screen  for 
matching  the  spectrum  of  the  kerosene  flame.  Curves  C  and  K' 
in  Fig.  4  are  similar  curves  of  corresponding  ideal  screens  for  the 
gas-filled  tungsten  lamp  operating  at  22  lumens  per  watt.  Similar 
computations  have  been  made  for  tungsten  lamps  operating  at 
various  efficiencies,  which  data  have  been  used  in  plotting  the 
curves  shown  in  Figs.  1  and  2. 

In  producing  practical  colored  screens  for  the  foregoing  pur- 


IO3O    TRANSACTIONS  OF  II^UMINATING  ENGINEERING  SOCIETY 


poses  the  obvious  beginning  is  to  use  a  yellow  pigment.  No  per- 
manent pigment  has  been  found  which  alone  will  suffice.  This 
is  not  surprising  to  one  familiar  with  coloring  elements,  but  it  has 
not  usually  been  recognized  in  practise.  Most  so-called  yellow 
pigments  have  a  greenish  tinge  in  the  lesser  densities  and  the 
author  is  not  aware  of  any  permanent  yellow  pigment  that  matches 
a  spectral  yellow  in  hue,  or  that  at  any  density  will,  when  used 
with  the  tungsten  lamp,  match  the  unsaturated  yellow  of  the  old 
illuminants.  Usually  a  pigment  which  is  given  the  name  of 
amber  is  considered  satisfactory.  Of  a  number  of  yellow  pig- 
ments examined  (and  these  represent  perhaps  all  the  permanent 


0.+&U. 


t66v&-  /-<~nfM 


Fig.  4. — Ideal  screens  for  tungsten  lamp  (gas-filled)  operating  at  22  lumens  per 
watt  compared  with  common  amber  of  various  densities. 

yellow  pigments)  none  was  found  to  be  satisfactory  alone.  An 
example  which  is  approximately  representative  of  this  group  of 
yellow  pigments  is  shown  by  the  so-called  amber  glass  of  four 
different  densities  in  Figs.  3  and  4.  The  numbers  on  the  curves 
represent  the  relative  amounts  of  coloring  matter  present  per  unit 
of  surface  area  of  the  amber  glasses.  In  general  the  glasses  are 
seen  to  transmit  green  rays  too  freely.  In  order  to  make  this 
point  clear  the  spectral  transmission  curves  of  the  ideal  screens 
C  and  K  in  Fig.  3  have  been  plotted  equal  to  unity  of  all  wave- 
lengths in  Figs.  5  and  6  respectively,  and  the  transmission  of  the 
amber  glasses  were  made  equal  to  unity  at  o.yoyi,  the  practical 


LUCKIESH  :     YELLOW    LIGHT 


IO3I 


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Fig.  5-— Showing  the  ratio  of  transmission  of  amber  glass  (various  densities)  to  that  of 
an  ideal  screen  for  converting  the  light  from  a  tungsten  lamp  operating  at  7.9  lumens 
per  watt  to  the  same  spectral  character  as  that  from  the  carbon  lamp. 


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Fig.  6. — Showing  the  ratio  of  transmission  of  amber  glass  (various  densities)  to  that  of  an 
ideal  screen  for  converting  the  light  from  a  tungsten  lamp  operating  at  7.9  lumens  per 
watt  to  the  same  spectral  character  as  that  from  the  kerosene  flame. 


13 


1032     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

limit  of  the  visible  spectrum.  It  is  thus  seen  that  no  density  of  a 
so-called  amber  glass  will  suffice  for  the  purpose  under  consid- 
eration. 

These  curves  for  an  average  yellow  pigment  have  been  pre- 
sented to  illustrate  that  it  is  not  an  extremely  simple  matter  to 
simulate  the  color  of  the  older  illuminants  by  using  colored 
screens  with  tungsten  lamps.  However,  inasmuch  as  the  re- 
quirements do  not  demand  more  than  a  close  approximation,  one 
familiar  with  pigments  and  color  mixture  readily  can  produce  a 
proper  coloring.  The  match  can  be  subjective  if  the  spectral 
character  of  the  altered  light  does  not  vary  too  much  from  the 
illuminants  to  be  matched.  Satisfactory  colorings  have  been  made 
for  matching  the  kerosene  flame  by  means  of  the  tungsten  lamp 
and  on  viewing  this  lamp  in  comparison  with  the  common  amber 
lamps  the  truth  of  the  foregoing  is  strikingly  evident.  That  is, 
the  ordinary  amber  lamps  appear  very  different  from  the  unsatu- 
rated yellow  of  the  properly  colored  lamps. 

It  has  long  appeared  to  the  author  that  illuminating  glassware 
which  largely  is  practically  colorless,  if  properly  tinted  an  un- 
saturated yellow  instead  of  the  common  greenish-yellow,  would 
meet  with  the  approval  of  many  users.  For  instance,  the  ap- 
pearance of  a  semi-indirect  bowl  of  the  proper  tint  would  satisfy 
the  esthetic  taste  of  those  who  desire  the  "warmer"  tints,  and  if 
the  walls  and  ceiling  were  properly  tinted  clear  tungsten  lamps 
would  be  satisfactory.  It  has  been  shown9  that  the  color  of  the 
surroundings  alter  considerably  the  useful  light  by  selective  re- 
flection. In  fact  it  was  shown  that  with  the  so-called  indirect 
and  semi-indirect  systems  a  yellow  tinge  in  the  color  of  the  walls 
and  ceiling  altered  the  tungsten  light  which  reached  the  useful 
plane  to  a  yellowish  hue  more  saturated  than  that  of  the  older 
illuminants.  This  alteration  by  selective  reflection  can  be  utilized 
in  many  cases  of  so-called  indirect  and  semi-indirect  systems  and 
in  the  case  of  the  latter  the  bowl  can  be  properly  tinted.  In  the 
case  of  direct  units  it  is  more  difficult  to  obtain  the  "warmer" 
light  without  coloring  the  lamp.  However,  as  shown  in  the  case 
of  the  shower,  if  the  shades  are  deep  enough  and  of  the  desired 
color  the  results  can  be  made  pleasing.     However,  it  is  not  the 

»  IyUckiesh,  M.,  The  Influence  of  Colored  Surroundings  on  the  Color  of  the  Useful 
Light;  Trans.  I.  E.  S. 


LUCKIESH  :     YELLOW   LIGHT  IO33 

intention  of  the  author  to  discuss  fully  this  phase  of  the  subject. 
An  attempt  has  been  made  to  point  out  briefly  the  place  of 
yellow  light  in  the  problems  of  lighting  and  vision.  There  are 
many  conflicting  opinions  and  a  lack  of  data  on  some  questions. 
The  chief  reasons  for  the  confusion  appears  to  be  due  to  misin- 
terpretation of  results  by  the  lack  of  careful  analysis  of  the  con- 
ditions. It  has  appeared  worth  while  to  record  the  results  that 
have  been  obtained,  to  summarize  the  opinions  and  conclusions 
of  others  and  to  discuss  briefly  the  theory  underlying  certain 
phenomena.  Many  of  the  questions  involved  in  the  foregoing 
discussion  have  arisen  from  time  to  time  and  it  is  to  be  hoped  data 
will  be  presented  by  others  which  will  aid  in  clarifying  the  con- 
fusion now  existing.  It  is  further  to  be  hoped  that  the  illumin- 
ating engineer  will  be  more  analytical  in  drawing  conclusions  and 
recording  observations  concerning  such  phenomena  as  are  dis- 
cussed in  the  foregoing  paragraphs. 

OTHER  REFERENCES. 

LUCKIESH,   M. 

Color  and  Its  Applications,  New  York,  Chapters  VI  and  XL 
Cobb,  P.  W. 

Physiological  Points  Bearing  on  Glare. 
Trans.  I.  E.  S.,  1912,  6,  p.  164. 

The  Psychology  of  Yellow. 

Pop.  Sci.  Monthly,  1906,  68,  p.  456. 
Jastrow,  J. 

The  Popular  Esthetics  of  Color. 

Pop.  Sci.  Monthly,  1897,  50,  p.  361. 


DISCUSSION. 

Mr.  J.  R.  Cravath  :  I  am  very  glad  Mr.  Luckiesh  has  ex- 
ploded a  bomb  under  a  lot  of  nonsense  that  has  been  talked  about 
matters  of  color  in  connection  with  illumination  engineering,  and 
shown  where  the  line  of  demarcation  is  between  taste  and 
scientific  fact.  There  has  been  a  great  deal  said  about  color  which 
is  purely  a  matter  of  personal  opinion. 

Dr.  J.  W.  ScherESCHewsky:  It  seems  to  me  that,  consider- 
ing the  matter  on  physiological  grounds,  there  can  be  no  reason 
whatever  for  asking  for  a  yellowish  tone  in  artificial  illuminants. 
The  nearer  they  approximate  the  spectral  composition  of  day- 


1034    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

light,  the  better  they  are  for  seeing  purposes.  I  think  possibly 
one  reason  why  we  have  found  kerosene  light,  for  instance,  agree- 
able, is  that  at  the  low  intensities  at  which  kerosene  lights  are 
usually  employed,  the  eye  perhaps  finds  it  a  little  more  able  to 
adapt  itself  to  the  luminous  intensity  involved.  It  seems  per- 
haps— I  don't  know — that  this  is  a  subject  for  future  investiga- 
tion. There  is  some  internal  evidence  to  the  effect  that  the 
shorter  wave-lengths  will  tend  to  produce  a  state  of  hyperadap- 
tation,  that  they  are  stimulators  of  adaptation.  That  is  to  say, 
when  we  have  high  intensities,  we  will  get  a  little  better  adapta- 
tion to  those  intensities  if  the  percentage  of  blue  light  in  the 
source  approximates  daylight.  On  the  other  hand,  in  very  high 
intensities  in  which  the  yellow  component  is  more  in  evidence, 
there  may  not  be  that  physiological  stimulus  to  complete  adapta- 
tion which  blue  wave-length  seem  to  bring  forth.  On  the  other 
hand,  where  we  use  low  intensities,  as  in  the  case  of  kerosene 
light,  the  eye  is  perhaps  a  little  bit  more  sensitive  to  the  light 
under  those  circumstances ;  and  consequently  with  that  low  inten- 
sity, we  find  the  light  agreeable  to  read  by;  but  I  think  on  the 
whole  that  we  are  advancing  toward  the  natural  trend  which 
illuminating  engineering  ought  to  take,  where  our  whole  aim  will 
be  to  reproduce,  as  nearly  as  we  can,  the  natural  composition  of 
daylight  and  raise  the  intensity.  I  cannot  see  any  real  object  in 
trying  to  produce  warm  tones  except  simply  the  psychological 
association  with  firelight  which  was  the  symbol  for  warmth  and 
comfort  in  the  early  days  when  men  had  a  much  harder  struggle 
to  live  than  they  have  now. 

Mr.  G.  H.  Stickney:  In  practical  illuminating  engineering, 
questions  relating  to  the  color  of  light  arise  in  quite  a  number  of 
problems.  It  is  not  surprising  that  there  is  more  or  less  confusion 
as  to  whether  the  color  differences  affect  the  physiological  action 
of  the  eyes  or  the  mental  processes,  especially  as  both  are  quite 
susceptible  to  suggestion.  This  is  rather  borne  out  by  the  dif- 
ferences of  opinion  among  different  individuals  or  communities, 
while  those  who  are  closely  associated  seem  inclined  to  agree  one 
way  or  another. 

In  street  lighting,  for  example,  some  people  think  they  can  see 
much  better  by  a  white  light  than  by  one  having  a  slightly  yellow 


YELLOW   LIGHT  IO35 

tint.  On  the  other  hand,  others  claim  they  can  see  fully  as  well 
by  the  yellow  tinted  light  and  prefer  it  on  account  of  its  pleasing 
color.  Personally,  I  have  been  unable  to  discover  any  apprecia- 
ble difference,  traceable  to  color,  in  the  seeing  value  of  light  from 
the  high  efficiency  incandescent  lamps  or  the  white  or  even 
slightly  bluish  lights.  I  believe  that  such  differences  are  more 
readily  explained  by  variations  in  intensity,  direction  or  glare. 

Again,  we  sometimes  hear  that  white  light  from  street  lamps 
is  preferable  for  use  in  conjunction  with  incandescent  lighted 
show  windows.  My  own  observation  has  been  that  the  most 
pleasing  effect  is  obtained  when  both  are  approximately  the  same 
color.  When  two  such  colors  of  light  are  mingled  so  as  to  em- 
phasize the  simultaneous  contrast,  I  have  noticed  that  if  the  white 
light  is  more  brilliant,  the  yellow  light  looks  dingy;  or  if  the  yel- 
low light  predominates  it  looks  warm  and  pleasing,  while  the 
white  lights  appear  cold  and  blue.  Still  I  am  not  sure  but  what 
there  are  conditions  under  which  it  might  be  desirable  to  combine 
the  two  colors  of  light. 

In  store  lighting  we  sometimes  find  a  compromise  necessary. 
White  light  is  unquestionably  preferable  for  the  selection  of 
colored  materials  for  daylight  use.  On  the  other  hand,  most  store 
managers  seem  to  prefer  the  appearance  of  the  store  under  in- 
candescent illumination,  and  even  where  colored  materials  are 
sold  they  often  consider  the  warm  homelike  effect  of  the  yellow 
tinted  light  more  important  than  the  degree  of  color  matching 
quality  obtainable  with  any  practical  illuminants. 

Another  phase  of  this  question  arises  in  connection  with  head- 
lights for  automobiles,  etc.  It  has  sometimes  been  thought  ad- 
visable to  use  yellow  screens  in  connection  with  incandescent 
headlights  to  reduce  the  glare.  This,  of  course,  has  to  be  con- 
sidered from  two  standpoints.  To  the  approaching  observer 
glare  does  not  seem  to  be  reduced  to  any  greater  extent  than  has 
the  illumination ;  on  the  other  hand,  to  the  driver  behind  the  head- 
lights there  is  undoubtedly  a  reduction  of  halation  especially  on 
damp  or  foggy  nights.  Beyond  the  reduction  of  this  diffractive 
halation,  I  doubt  if  there  is  any  advantage  to  be  gained  in  cutting 
down  the  illumination  by  the  use  of  any  form  of  color  subtractive 
screen. 


IO36     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

A  Member:  Some  fifteen  years  ago  I  carried  on  a  series  of 
experiments  with  a  view  to  determining  the  best  light  for  the  eyes, 
taking  as  the  criterion,  the  ease  with  which  reading  could  be  done, 
and  after  going  over  quite  a  range  of  colors,  I  decided  on  the 
yellow-green.  Experiments  were  carried  on  in  a  closed  room  at 
night  and  with  a  light  source  out  of  the  range  of  vision. 

Dr.  J.  W.  ScherEschewsky:  I  forgot  to  mention  the  range 
of  personal  preference  of  individuals  with  regard  to  the  refrac- 
tion of  the  eye.  It  seems  to  me  that  the  refraction  of  the  eye 
often  has  a  marked  influence  on  the  kind  of  light  and  the  kind 
of  colors  individuals  prefer.  Persons  who  have  a  tendency  to 
hyperopia  are  naturally  inclined  to  prefer  colors  at  the  short  end 
of  the  spectrum,  whereas  myopes  prefer  longer  wave-lengths 
which  can  be  focused  with  greater  ease  on  the  retina;  so  I 
think  that  the  preference  really  lies  in  the  state  of  refraction  of 
the  eye  of  the  individual  concerned. 

Mr.  W.  A.  Durgin:  If  the  use  of  white  or  yellow  light  is 
only  a  matter  of  personal  preference,  as  this  paper  rather  indi- 
cates, the  immediate  problem  of  light  supply  becomes  a  deter- 
mination of  the  present  preponderance  of  that  preference.  My 
personal  experience  seems  to  indicate  a  majority  choice  of  yel- 
low light.  In  the  offices  of  Commonwealth  Edison  Company  of 
Chicago,  where  1,200  employees  work  under  a  distinctly  yellow 
flux,  at  least  sixty  have  come  forward  with  expressions  of  ap- 
proval, whereas  none  has  expressed  dissatisfaction.  This,  how- 
ever, is  only  an  indication.  Widespread  observation  is  needed, 
and  the  accumulation  of  such  preference  data  should  be  made  a 
part  of  all  illumination  testing  programs. 

Dr.  Charles  P.  Steinmetz:  The  subject  matter  of  Mr. 
Luckiesh's  paper  on  the  effect  of  the  quality  of  color  on  the  ease 
of  the  eye  is  a  very  interesting  one  and  very  well  worth  careful 
consideration  and  study,  especially  since  the  experimental  evi- 
dence of  different  observers  not  infrequently  directly  contradicts, 
and  even  the  conclusions  of  one  and  the  same  observer  under  dif- 
ferent conditions  are  not  infrequently  entirely  contradictory. 
Now  the  reason,  the  way  I  look  at  it,  is,  that  the  easiest  light  is 
the  light  that  is  least  fatiguing  to  the  eye.  Now  at  times  it  de- 
pends on  the  conditions,  whether  fatigue  will  occur  with  one 


YELLOW   LIGHT  IO37 

color  of  light  or  another  color.  I  do  not  believe  there  is  any  par- 
ticular color  of  light  which,  by  itself,  is  less  or  more  fatiguing 
than  another,  but  the  question  depends  entirely  on  the  relation 
of  the  color  of  the  light  to  the  color  of  the  objects  which  are  dis- 
tinguished and  the  purpose  for  which  we  desire  to  distinguish 
them.  If  there  is  any  special  quality  in  the  light  by  itself,  we 
would  naturally  expect  that  in  the  middle  of  the  spectrum,  which 
is  about  between  53  and  54  microcentimeters,  the  light  would  be 
the  easiest.  Now  then,  we  use  light  to  distinguish,  and  where 
the  observer  of  the  light  is  to  distinguish  objects  sharply,  as  for 
instance,  in  reading  and  calculating  and  doing  exact  work,  there 
naturally  that  light  will  be  the  least  fatiguing  which  gives  the 
sharpest  distinction,  that  is,  which  exaggerates  contrast ;  and  that, 
indoors,  is  a  short  wave  light,  the  white  or  the  bluish  green. 
Where  the  purpose  is  to  rest  the  eye,  that  is,  not  to  give  strong 
contrast  and  thereby  irritate  the  eye  by  continuously  seeing  ir- 
relevant things,  but  merely  to  show  enough  contrast  to  be  able  to 
walk  around  and  see  the  room,  as  for  general  indoor  illumination, 
there  the  light  will  be  the  least  fatiguing  which  reduces  the  con- 
trast. Now  you  see  that  depends  on  whether  you  arrange  your 
experiment  in  trying  the  restfulness  of  light  under  conditions  of 
exact  detail  work  or  under  conditions  of  resting  after  the  day's 
work  in  your  room ;  obviously  exactly  opposite  conclusions  about 
the  color  of  the  light  may  be  obtained.  Furthermore,  the  restful 
light,  which  reduces  contrast  so  much  that  when  you  are  nervous 
or  irritated,  you  feel  that  it  is  restful,  will  usually  be  the  long 
wave-light,  yellow  or  orange-yellow,  because  the  predominant 
doors,  where  the  predominant  colors  are  blue  and  green,  the 
was  pointed  out  by  Mr.  Luckiesh  is  very  irritating  because  it  is 
intensified  by  contrast  with  the  different  kinds  of  light;  while  out 
doors,  whwere  the  predominant  colors  are  blue  and  green,  the 
short  waves,  the  blue  sky  is  not  irritating,  while  if,  under  certain 
atmospheric  conditions  you  have  a  yellowish  sky,  you  feel  un- 
comfortable. You  cannot  speak  of  a  definite  color  of  light  as 
having  a  definite  effect,  but  it  is  all  relative.  Monochromatic 
light  allows  the  eye  to  focus,  because  you  get  a  definite  focus, 
but  where  a  definite  distinction  is  not  wanted,  monochromatic 
light  is  not  wanted ;  otherwise  chromatic,  light,  by  distorting  the 
color  effect,  is  irritating  to  the  eye;  it  means,  in  short,  that  the 


IO38     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

effect  of  color  of  light,  in  its  effect  on  the  eye,  is  entirely  a  relative 
condition  dependent  on  the  surrounding  objects  in  their  color 
character  and  the  purposes  for  which  you  desire  to  see. 

Mr.  M.  Luckiesh  (In  reply)  :     I  gathered  together  these  con- 
flicting conclusions  with  the  hope  that  with  closer  attention  by 
lighting  engineers  the  questions  will  be  answered  eventually.    The 
last  sentence  in  the  paper  brings  forth  a  vital  point  in  future  pro- 
cedure.    There  is  little  to  add  to  the  discussions  by  various 
members.    I  should  like  to  bring  out  one  point  in  connection  with 
Mr.  Durgin's  remarks.    He  has  exhibited  here  a  unit  consisting 
of  amber  glass  cased  with  opal  glass.    When  the  unit  is  lighted 
the  bowl  appears  a  decidedly  amber  color.     He  mentioned  that 
quite  a  number  of   employees   "have  come   forward   with  ex- 
pressions of  approval  wheras  none  has  expressed  dissatisfaction." 
Inasmuch  as  only  a  portion  of  the  light  (the  direct  component)  is 
altered  by  the  amber  glass,  I  wonder  whether  the  employees  in 
expressing  approval  were  influenced  by  the  color  of  the  light  unit 
or  the  actual  color  of  the  light  which  they  use.    These  are  prob- 
ably two  different  colors,  the  light  which  they  use  consisting  of 
the  altered  direct  component  plus  the  indirect  component  which 
is  altered  by  reflection  from  the  walls  and  ceiling.     I  have  shown 
that  the  alteration  due  to  colored  surroundings  is  considerable 
(Trans.  I.  E.  S.,  vol.  8,  1913,  p.  62).     This  illustrates  a  point 
from  which  much  confusion  may  arise.     A  danger  in  using  the 
opinions  of  laymen  is  that  these  opinions  may  be  influenced,  as  is 
possible  in  this  case,  by  the  impressions  gained  by  looking  at  the 
lighting  unit  instead  of  through  a  consideration  of  the  light  that 
actually  reaches  their  working  planes.    It  may  be  in  this  case  that 
no  such  errors  exist;  nevertheless,  this  is  a  very  common  error 
among  those  who  use  light.     In  considering  this  entire  subject, 
one  should  be  careful  to  make  a  complete  analysis  of  the  con- 
ditions and  when  using  the  opinions  of  laymen,  one  should  be 
certain  that  the  opinions  are  based  upon  such  an  analysis.    An- 
other danger  in  using  opinions  of  laymen  is  that  there  is  often  a 
decided  tendency  of  such  observers  to  form  opinions  that  they 
believe  are  desired  by  their  superiors.     These  are  examples  of 
pitfalls  that  are  well  known  and  thoroughly  considered  by  the  in- 
vestigator. 


MILLAR:    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO39 

THE  EFFECTIVE  ILLUMINATION  OF  STREETS.* 

BY  PRESTON   S.   MILLAR. 

Synopsis:  This  paper  mentions  the  dependence  of  effectiveness  in 
street  lighting  upon  municipal  appropriations  and  efficient  lamps,  but  dis- 
cusses more  particularly  those  aspects  of  effectiveness  which  are  dependent 
upon  skilful  utilization  of  the  light  to  produce  the  most  effective  illumina- 
tion. There  are  included  a  classification  of  streets,  a  statement  of  the 
objects  of  street  lighting  and  the  elements  of  vision  under  street  lighting 
conditions.  The  paper  emphasizes  three  considerations  which  are  some- 
times neglected  in  street  lighting  discussions;  namely,  the  silhouette  effect, 
specular  reflection  from  street  pavements,  and  glare.  The  remainder  of 
the  paper  is  given  over  to  a  presentation  of  the  variables  upon  which  the 
effectiveness  of  street  illumination  depends,  and  upon  the  influence  which 
each  feature  of  the  installation  exercises  through  these  several  variables. 
As  a  part  of  this  discussion  illuminating  efficiency  values  for  the  several 
modern  street  illuminants  are  given.  The  appendix  includes  statistics  and 
photographs  of  some  very  recent  installations  which  illustrate  the  latest 
trend  in  street  lighting. 

Improvement  in  street  lighting  involves  (i)  larger  municipal 
appropriations;  (2)  more  efficient  lamps  and  accessories;  (3) 
greater  skill  in  application. 

FACTORS  INFLUENCING  IMPROVEMENTS. 

Larger  Municipal  Appropriations. — The  public  is  gradually 
becoming  acquainted  with  the  advantages  of  more  liberal  use  of 
light.  Use  of  the  streets  at  night  is  becoming  more  general 
throughout  a  greater  number  of  hours.  Requirements  for  good 
street  lighting  are  becoming  greater  as  traffic  becomes  denser  and 
as  traffic  speed  increases.  Also  the  advertising  value  of  exten- 
sively employed  light  is  commanding  appreciation  in  mercantile 
lines.  These  things  combined  are  leading  to  larger  municipal  ap- 
propriations. Larger  appropriations  mean  betterment  in  street 
illumination  because  the  mere  addition  of  lamps  with  no  increase 
in  lighting  efficiency  and  no  greater  skill  in  application  usually 
improves  conditions.  The  greatest  single  obstacle  to  satisfactory 
street  illumination  is  lack  of  funds. 

More  Efficient  Lamps  and  Accessories. — The  last  two  years 
have  witnessed  increases  of  25  to  50  per  cent,  in  efficiencies  of 
street  illuminants,  the  gas-filled,  tungsten  incandescent  lamp  and 
the  magnetite  arc  lamp  having  progressed  contemporaneously. 
At  the  present  time  in  the  magnetite  lamp  of  medium  and  high 

*  A  paper  read  at  a  joint  meeting  of  the  American  Institute  of  Electrical  Engineers 
and  the  Illuminating  Engineering  Society,  at  a  convention  of  the  former  organization 
held  June  29  to  July  2,  1915,  at  Deer  Park,  Md. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


IO4O     TRANSACTIONS  OF*  ILLUMINATING  ENGINEERING  SOCIETY 

power,  in  the  gas-filled  lamp  of  low,  medium  and  high  power, 
and  in  the  flame  arc  lamp  of  high  power  there  are  available  il- 
luminants  having  efficiencies  four  or  five  times  greater  than  those 
of  various  types  of  enclosed  carbon  arc  lamps  which  were  the 
principal  street  illuminants  in  this  country  a  few  years  ago. 
Some  advance  has  been  made  also  in  the  design  of  lamp  equip- 
ments, notable  among  which  are  the  prismatic  refractor  and  a 
variety  of  light  density  translucent  glassware  which  combines 
fairly  good  diffusion  with  high  transmission.  These  improve- 
ments in  the  materials  of  street  illumination  combined  with  the 
increased  sums  which  municipalities  are  appropriating  make 
possible  a  very  general  improvement  in  street  lighting. 

Skill  in  Application. — Recently  installed  systems  are  almost 
invariably  superior  to  the  systems  which  they  replace.  Usually 
the  improvement  is  due  in  part  to  greater  skill  on  the  part  of 
the  engineers  in  charge.  City  engineers,  central  station  engineers 
and  manufacturers  are  better  acquainted  with  the  problems  and 
have  acquired  more  skill  in  meeting  them.  The  result  is  street 
illumination  of  greater  effectiveness.  Notwithstanding  this  ad- 
vance there  are  but  few  principles  of  street  illumination  which 
are  regarded  as  thoroughly  established.  Although  the  subject 
has  received  perhaps  more  than  a  fair  share  of  discussion  and 
study,  it  is  still  enveloped  in  much  uncertainty.  In  the  literature 
and  in  practise  there  is  much  which  indicates  differences  of 
opinion  in  regard  to  principles  of  fundamental  importance.  It 
must  be  admitted  that  progress  in  the  conception  of  correct  prin- 
ciples is  slow.  Yet  there  is  progress  and  it  may  be  that  by  the 
time  most  street  lighting  is  made  good,  those  of  us  who  talk  and 
write  of  the  principles  may  reach  an  agreement  as  to  what  con- 
stitutes good  street  lighting. 

It  is  the  purpose  of  this  paper  to  discuss  the  variables  of  street 
illumination  and  the  principles  underlying  the  best  use  of  modern 
illuminants  and  accessories  under  modern  conditions  in  this 
country.  Therefore,  matters  pertaining  more  especially  to  the 
third  factor  entering  into  improvement  in  street  illumination,  as 
enumerated  in  the  opening  paragraph1,  will  be  discussed  first. 

1  This  paper  may  be  regarded  as  a  continuation  of  the  discussion  presented  by  the 
author  before  the  1910  convention  of  the  Illuminating  Engineering  Society  under  the 
title  "  Some  Neglected  Considerations  Pertaining  to  Street  Illumination  ".  Trans.  I.  E. 
S.  Vol.  v,  p.  653. 


MILLAR:    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO4I 

CLASSIFICATION  OF  STREETS. 
For  the  purposes  of  this  discussion  the  following  classification 
of  streets  is  adopted: 

Class  Description 

la  Metropolitan  thoroughfares  of  greatest  distinction, 

it  Important  city  streets  largely  traveled  at  night. 

2a  Business  streets  not  largely  traversed  at  night. 

2b  City  residential  streets. 

3a  Suburban  residental  streets. 

3b  Suburban  thoroughfares. 

It  will  be  apparent  that  requirements  for  street  illumination 
are  diverse  as  among  these  different  classes  of  streets.  For 
example,  the  ia  class  of  streets  is  distinguished  by  a  requirement 
for  dignified,  pleasing  fixtures  and  for  lamps  and  illumination 
which  should  be  of  fairly  high  intensity,  lighting  building  fronts 
as  well  as  street.  Streets  of  the  lb  class  are  likely  to  be  char- 
acterized by  much  show-window  and  sign  lighting  which 
augments  the  street  illumination  during  the  hours  of  greatest 
traffic.  Here  intensities  are  likely  to  be  highest,  and  the  ordinary 
fundamental  requirements  of  street  lighting  are  supplemented 
by  the  desirability  for  recognizing  acquaintances  in  the  passing 
throng  and  for  detailed  vision,  approaching  that  common  to  in- 
teriors at  night. 

In  streets  of  the  2a  class  a  moderate  intensity  of  illumination 
which  lights  building  fronts  as  well  as  street  is  customary. 
Policing  purposes  and  good  seeing  conditions  for  the  occasional 
pedestrian  are  the  principal  desiderata.  In  streets  of  the  2b 
class  it  is  usually  desirable  to  keep  the  light  upon  the  street  sur- 
face, avoiding  brilliant  illumination  of  the  upper  stories  of  resi- 
dence fronts  and  providing  fairly  good  lighting  for  the  low  den- 
sity vehicular  and  pedestrian  traffic. 

In  streets  of  the  3a  class  it  is  likewise  desirable  to  keep  the 
light  upon  the  street,  illuminating  the  sidewalks  well  to  serve  the 
purposes  of  pedestrians.  In  streets  of  the  3b  class,  which  are 
the  important  automobile  highways  connecting  populous  centers, 
the  principal  requirement  is  that  of  the  automobile  driver.  Here 
the  most  difficult  problems  of  street  illumination  are  encountered. 

The  discussion  in  this  paper  is  applicable  in  varying  degree  to 
streets  of  these  six  classes. 


1042     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

OBJECTS  OF  STREET  ILLUMINATION. 
From  several  points  of  view  the  objects  of  street  illumination 
may  be  stated  in  somewhat  different  ways.  The  point  of  view 
of  the  motorist  differs  from  that  of  the  pedestrian,  which  in  turn 
differs  from  that  of  the  police  commissioner  and  from  that  of 
the  merchant.  When,  however,  one  assembles  the  considerations 
growing  out  of  all  these  viewpoints,  those  of  first  importance 
appear  to  fall  within  the  comprehensive  classification  presented 
by  the  National  Electric  Light  Association  Street  Lighting  Com- 
mittee in  1914  which  is  as  follows: 

Fundamental  Purposes  to  be  Served  by  Street  Illumination. 

1.  Discernment  of  large  objects  in  the  street  and  on  the  sidewalk. 

2.  Discernment  of  surface  irregularities  in  the  street  and  on  the  side- 

walk. 

3.  Good  general  appearance  of  the  lighted  street. 

It  would  appear  that  in  proportion  as  these  three  purposes  are 
served  the  street  illumination  will  be  regarded  as  satisfactory, 
and  it  may  be  concluded  that  no  street  lighting  installation  which 
serves  these  three  purposes  reasonably  well  can  be  regarded  as 
unsatisfactory.  The  weight  to  be  given  each  will  vary  in  dif- 
ferent streets  though  in  a  general  way  it  is  probable  that  the  pur- 
poses are  served  in  the  order  named.  It  is  possible  to  install  at 
a  low  cost  a  system  which  will  reveal  large  objects  (Purpose  No. 
1 )  while  failing  to  serve  the  two  other  purposes.  With  increased 
appropriations  or  more  efficient  illuminants,  large  objects  may  be 
revealed  to  better  advantage  and  surface  irregularities  (Purpose 
No.  2)  may  also  be  revealed  although  the  third  object  may  not 
be  served.  With  still  larger  appropriations  and  still  more  ef- 
ficient illuminants,  discernment  may  be  improved  and  a  pleasing 
appearance  for  the  street  (Purpose  No.  3)  by  day  as  well  as  by 
night  may  be  had.  All  three  objects  may  be  served  when  appro- 
priations are  adequate. 

Process  of  Seeing. — In  streets  at  night  objects  are  seen  by 
reason  of  contour,  relief,  shadow  or  color. 

One  perceives  the  contour  of  objects  when  they  are  markedly 
different  in  brightness  from  their  background.  Since  most  large 
objects  on  the  street  at  night  are  darker  than  their  background 
they  are  usually  perceived  as  silhouettes. 


MILLAR:    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO43 

Contrasts  in  relief  are  perceived  when  the  exposed  surface  of 
an  adequately  illuminated  object  presents  areas  of  different  re- 
flecting powers,  or  elements  which  are  more  or  less  favorably 
inclined  with  respect  to  incident  light,  or  elements  which  lie  in 
the  shadow  of  other  elements  of  the  surface. 

Small  objects  may  be  perceived  by  reason  of  their  shadows 
occasioned  by  the  interception  of  sharply  inclined  rays  of  light. 
Shadows  of  large  objects  are  not  always  of  value  in  promoting 
discernment  and  are  often  misleading,  as  in  case  of  the  shadow 
of  a  telegraph  pole  thrown  across  the  sidewalk. 

Color  contrasts  are  not  usually  relied  upon  since  in  installa- 
tions where  discernment  is  at  all  difficult,  color  is  usually  lost  and 
objects  are  perceived  more  readily  by  other  means. 

The  several  kinds  of  contrast  perception  are  suggested  in  the 
accompanying  series  of  photographs  of  test  targets.  These  have 
been  located  successively  in  six  representative  positions  between 
lamps  in  the  street  shown  in  Figs.  8  and  9.  Fig.  ia  shows  the 
lighting  effects  by  the  centrally  mounted  lamps  shown  in  Fig.  8. 
Fig.  ib  corresponds  with  Fig.  9.  The  targets  are  of  substantially 
the  same  color  as  the  street  surface.  It  is  to  be  noted  that  those 
which  are  most  clearly  revealed  receive  the  least  light  and  are 
silhouetted  against  their  background.  Those  least  distinctly  re- 
vealed receive  on  the  observed  surfaces  about  the  same  light  as 
their  background. 

Contrast  perception  is  the  ruling  visual  process  with  which 
street  illumination  is  concerned.  To  increase  contrasts  on  sur- 
faces to  be  seen  is  to  better  conditions  for  vision,  a  consideration 
often  ignored. 

In  much  of  the  literature  of  street  illumination,  curves  of 
illumination  intensity  form  the  principal  basis  of  judgment  as 
to  effectiveness.  There  is  a  tendency  to  over-emphasize  the  im- 
portance of  incident  light  to  the  prejudice  of  other  important 
considerations.  Three  of  the  principal  considerations  which  are 
not  emphasized  directly  by  study  of  illumination  intensity  curves 
are  presented  in  the  following  paragraphs. 

Silhouette  Effect.2— When  the  writer  directed  attention  to  the 

*  Millar,  Preston  S.,  An  Unrecognized  Aspect  of  Street  Illumination;  Trans.  I.  E.  S., 
vol.  V  (1910),  page  456. 


1044     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

silhouette  effect  in  1910,  there  existed  but  little  appreciation  of 
its  importance.  During  the  five  years  which  have  intervened 
there  has  gradually  developed  a  greater  appreciation  of  the  ex- 
tent to  which  it  enters  into  conditions  of  visibility  in  street  illum- 
ination. Yet  its  very  general  applicability  even  now  is  un- 
recognized by  some  engineers.  There  is  an  impression  that  only 
in  lighting  of  very  low  intensity  is  it  the  prevailing  method  of 
discernment.  As  a  matter  of  fact  the  silhouette  effect  is  pro- 
nounced whenever  there  are  bright  street  or  building  back- 
grounds. A  photographic  under-exposure  of  any  street  in  the 
daytime  shows  objects  as  silhouettes.  The  casual  glance  of  an 
automobile  driver  corresponds  roughly  with  such  an  under- 
exposure. The  majority  of  observations  of  large  objects  on  the 
street  in  our  more  intensely  lighted  thoroughfares,  especially  in 
the  practise  of  automobile  drivers,  falls  under  this  heading,  be- 
cause a  driver  is  concerned  primarily  with  avoiding  obstacles  and 
usually  looks  carefully  enough  only  to  detect  the  presence  of 
pedestrians  and  other  objects.  Usually  he  sees  these  as  dark  ob- 
jects silhouetted  against  the  lighter  street  surface  or  building  sur- 
faces. The  pedestrian  too  obtains  distant  views  of  large  objects 
as  silhouettes,  but  as  he  moves  more  slowly  and  approaches  ob- 
jects more  closely,  he  has  opportunity  for  closer  observation,  and 
in  the  more  brightly  lighted  streets  supplements  discernment  by 
silhouette  with  actual  observation  of  surfaces  in  relief. 

Figs.  6a  and  6b  show  illustrations  made  from  the  original  sil- 
houette photograph  illustrating  the  importance  of  this  effect  in 
street  lighting. 

Nature  of  Street  Pavement. — Modern  streets  which  require 
greatest  care  in  lighting  are  traversed  by  automobiles.  The 
majority  of  them  are  paved  with  asphalt,  asphalt  block,  wooden 
block,  treated  macadam,  etc.  As  a  result  of  automobile  traffic 
such  pavements  become  oiled  and  polished.  The  high  spots  of 
the  pavement  then  reflect  specularly.  Fig.  4  is  a  night  view  of  a 
part  of  Columbus  Circle,  New  York  City.  The  pavement  is  of 
wooden  block.  The  street  in  the  immediate  foreground  of  the 
picture  is  not  traversed  by  vehicles.  The  pavement  in  the  outer 
ring  of  the  circle,  which  appears  in  the  middle  of  the  photograph, 
is  traversed  by  vehicles  and  has  become  polished  in  the  manner 


icIH 


Fig.  ia.— Test  targets  in  six  representative  locations  as  illuminated  by  centrally  mounted 
lamps  as  shown  in  Fig.  8.  Illustrating  reliance  upon  contrasts  and  different  kinds  of 
contrasts  presented  to  view. 


Fig.  ib.— Test  targets  in  six  representative  locations  as  illuminated  by  lamps  mounted  as 
shown  in  Fig.  9.  Illustrating  reliance  upon  contrasts  and  different  kinds  of  contrasts 
presented  to  view. 


MILLAR:    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO45 

described.     It  reflects  specularly  and  its  brightness  as  viewed  is 
due  largely  to  distant  lamps. 

Fig.  2  shows  measurements  of  horizontal  illumination  intensity 
and  of  brightness  at  the  angle  of  an  automobilist's  view.  The 
broken  line  shows  horizontal  foot-candles  as  measured  on  East 
80th  Street,  New  York  City.  This  has  an  ordinary  asphalt  pave- 
ment and  is  illuminated  by  multiple  enclosed  arc  lamps  365  ft. 
(101.15  m.)  apart.    The  continuous  line  shows  brightness  values. 


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Fig.  3. — Curves  of  brightness  and  illumination  intensity. 

It  will  be  noted  that  whereas  the  foot-candles  vary  in  the  ratio 
of  46  to  1,  the  brightness  varies  in  the  ratio  of  8  to  i.  This  is  a 
street  in  which  automobile  traffic  forms  but  a  small  part  of  the 
total  traffic. 

Fig.  3  shows  corresponding  data  for  upper  Seventh  Avenue, 
New  York  City,  which  is  a  street  largely  traversed  by  automo- 
biles.    The  street  is  paved  with  block  asphalt.     The  horizontal 


IO46     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

foot-candles  vary  in  the  ratio  of  10  to  1 ;  the  effective  bright- 
ness varies  in  the  ratio  of  2  to  1.  The  impression  of  uniformity 
which  one  derives  from  a  trip  through  the  street  is  expressed  by 
this  brightness  ratio  rather  than  by  the  foot-candles  ratio.  On 
this  street,  which  is  of  the  boulevard,  central  parkway  type,  there 
are  three  lines  of  lamps.  The  linear  spacing  of  the  lamps  is  about 
125  ft.  (38.1  m.).  As  the  street  is  fairly  level,  a  great  number  of 
these  lamps  is  within  view  at  a  given  time.  The  street  surface 
consists  largely  of  small  polished  areas  which  reflect  specularly 
In  driving  through  the  street  one  sees  reflected  in  these  small 
polished  areas  imperfect  images  or  part  images  of  distant  lamps. 
Notwithstanding  the  rather  wide  spacing  and  marked  non- 
uniformity  of  illumination  intensity,  the  effect  is  one  of  remark- 
able uniformity  of  lighting.  In  driving  one  looks  at  the  street 
surface  200  ft.  (60.56  m.)  or  more  away,  and  the  surface  which 
he  sees  is  rendered  bright  by  lamps  which  may  be  one  quarter, 
one  half  or  even  one  mile  away.  Consequently  the  surface  be- 
tween lamps  viewed  from  this  angle  is  almost  if  not  quite  as 
bright  as  is  the  surface  near  or  directly  under  the  lamps. 

Any  street  which  is  largely  traversed  by  automobiles,  and 
which  has  pavement  of  the  types  named  above,  is  likely  to  ap- 
pear rather  dark  because  of  the  oil  which  is  deposited  upon  it 
from  automobiles.  It  is,  however,  a  most  favorable  surface  for 
street  lighting  purposes  because  of  its  tendency  to  reflect  spec- 
ularly. It  was  found  that  Seventh  Avenue,  New  York  City,  de- 
scribed above,  has  three  to  four  times  the  effective  brightness  per 
lumen  of  incident  light  of  another  prominent  thoroughfare  which 
is  paved  with  Belgium  block. 

Fig.  11,  which  will  be  referred  to  in  another  connection,  is  an 
additional  example  of  this  effect  as  encountered  in  a  country  road 
paved  with  treated  macadam.  Here  lamps  are  spaced  500  to 
900  ft.  (152.4  to  274.37  m.)  apart.  The  roadway  between  lamps, 
from  the  driver's  point  of  view,  is  well  illuminated ;  due  in  part 
to  its  specular  character. 

Recognition  of  the  fact  that  modern  streets  are  likely  to  be 
characterized  by  more  or  less  of  this  specular  quality  necessitates 
important  alterations  in  some  of  the  theories  regarding  street 


MILLAR :    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO47 

lighting  which  have  prevailed  in  the  past  and  which  are  held  at 
the  present  time  by  some  engineers. 

Relation  Between  Lamps  and  Street  Surface. — The  effect  of 
glare  in  street  illumination  is  dependent  primarily  upon: 

1.  The  extremes  of  contrast  within  view;  that  is,  contrast 

in  brightness  between  the  light  source  and  the  illum- 
inated surfaces. 

2.  The  visual  angle  separating  the  glaring  source  from  the 

observed   surfaces. 

3.  The  portion  of  the  field  of  view  which  is  illuminated. 
Glare  militates  against  good  street  illumination,  first  in  de- 
creasing ability  to  see,  and  second,  in  rendering  unpleasant  the 
appearance  of  the  installation  and  the  street.     Insofar  as  it  re- 
duces visual  power  it  manifests  itself  in  three  ways : 

First,  actual  diminutions  in  ability  to  perceive  small  contrasts 
in  the  presence  of  a  bright  light  source.  Second,  distraction  of 
attention  as  a  result  of  which  small  contrasts  may  not  be  per- 
ceived when  viewed  casually.  Third,  a  temporary  dazzling  ef- 
fect which  persists  for  a  few  moments  after  a  bright  light  source 
is  viewed  directly. 

Figs.  6a  and  6b  illustrate  the  effect  of  glare.  In  Fig.  6b  a  black 
spot  covers  the  nearby  light  source.  In  Fig.  6a,  the  presence  of  the 
light  source  distracts  attention  from  the  automobile  and  the  view 
is  rendered  less  pleasant.  In  fact  there  is  a  little  discomfort  in- 
volved in  looking  at  the  automobile.  Nevertheless  if  one  delib- 
erately dispells  the  idea  of  the  glaring  source  from  his  mind  and 
concentrates  on  the  automobile,  it  can  be  seen  in  the  picture  just 
as  well  as  when  the  tab  covers  the  light  source.  This  picture 
further  illustrates  the  importance  of  securing  adequate  separa- 
tion beween  the  light  source  and  the  observed  object,  the  dis- 
traction due  to  the  light  source  being  greater  relatively  when  the 
picture  is  held  at  a  distance  from  the  eye  and  the  visual  angle 
between  the  source  and  object  is  decreased. 

If  a  single  brilliant  light  source,  as  a  bare  gas-filled  tungsten 

lamp  is  located  over  a  dirt  road  in  the  country,  the  glare  is  very 

bad.    If  the  lamp  is  raised  to  a  greater  height  or  moved  to  one 

side  of  the  road,  or  if  the  lamp  is  enclosed  in  a  diffusing  globe, 

14 


IO48     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

the  glare  is  lessened.  If  a  number  of  additional  lamps  are  strung 
beyond  it  along  the  road,  the  glare  is  further  reduced.  If  the 
lamps,  instead  of  being  located  over  a  dirt  road,  are  located  over 
a  treated  macadam  road,  or  better  still,  over  an  asphalt  road,  the 
glare  is  less  serious.  Light  colored  buildings  along  the  street  also 
assist  in  reducing  the  glare.  In  short,  anything  which  reduces  the 
contrast  between  the  light  source  and  the  road  surface,  or  which 
increases  the  illuminated  area  within  view,  or  which  separates  the 
bright  light  source  from  the  road  surface,  reduces  the  effect  of 
glare. 

Sweet  in  19103  studied  that  part  of  the  effect  of  glare  which  is 
a  measureable  reduction  in  the  ability  to  see,  using  a  single  light 
source  in  a  dark  room.  He  found  under  these  exaggerated  con- 
ditions that  a  large  reduction  in  visual  power  could  be  traced  to 
the  presence  of  a  bright  light  source  close  to  the  center  of  the 
field  of  vision.  In  19144  working  with  others  on  the  campus  of 
the  University  of  Wisconsin,  he  pursued  his  researches,  and  has 
given  preliminary  publication  to  some  very  interesting  results. 
In  this  latter  research  he  employed  from  two  to  four  lamps 
mounted  at  various  heights  and  with  various  spacing  intervals 
over  a  dirt  road  about  350  ft.  (106.68  m.)  long,  with  surroundings 
of  low  light-reflecting  power.  It  is  not  proposed  at  this  time  to 
enter  into  a  discussion  of  these  tests,  but  it  may  be  noted  that 
the  only  conclusions  which  they  can  indicate  are  those  which 
would  apply  to  a  short  stretch  of  dirt  road  with  surroundings  of 
low  light-reflecting  power.  The  modifications  introduced  by 
street  pavements  of  better  reflecting  qualities,  by  buildings  along 
the  street,  and  by  a  greater  length  of  illuminated  street,  have  no 
part  in  this  research.  This  is  a  serious  limitation,  because  the 
effect  of  glare  in  street  lighting  is  very  largely  reduced  by  each  of 
these  three  factors.  The  two  researches  make  available  informa- 
tion which  has  its  bearing  upon  street  lighting  principles.  If, 
however,  the  data  are  considered  without  due  regard  to  the  lim- 
itations under  which  the  tests  were  made,  there  is  danger  of  form- 
ing an  exaggerated  idea  of  the  importance  of  adopting  measures 
which  will  reduce  the  effect  of  glare  by  decreasing  the  bright- 

»  An  Analysis  of  Illumination  Requirements  in  Street  lighting,  Journal  of  Franklin 
Institute,  1910. 

*  Electrical  Review  and  Western  Electrician,  March  6,  1915. 


I  0^% 


Fig.  4.— view  in  Columbus  Circle,  New  York  City.  Note  specular  reflection  from  that 
part  of  pavement  which  is  traversed  by  automobiles;  also  absence  of  specular  reflec- 
tion from  immediate  foreground  where  there  is  no  automobile  traffic. 


Fig.  5.— Sixteenth  street,  Washington,  D.  C,  100-cp.  mazda  lamps  over  curbs 
and  dark  area  in  middle  of  street. 


Fig.  6a. — For  a  demonstration  of  the  importance  of  separating  the  glaring  source  from 
the  observed  object  hold  the  picture  nearer  to  or  further  from  the  eyes,  as  the  distance 
from  the  picture  to  the  eyes  becomes  greater  the  visual  angle  of  separation  becomes 
less  and  the  glare  effect  is  magnified. 


Fig.  6b. — Original  street  lighting  silhouette  picture.  Illustrating  importance  of  bright 
street  surface  and  showing  how  the  automobile  is  discerned  because  the  street  surface 
beyond  it  is  bright,  not  because  the  light  falling  upon  it  renders  it  visible.  For  a 
demonstration  of  glare  see  Fig.  6a. 


I  o  14  S" 


Fig.  7. — Magnetite  lamps  in  2S-ineh  globes  as  used  in  Washington,  D.  C. 


4ft* 

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1 

s                        1 — 

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Figs.  8  and  9. — Center  versus  curb  mounting  in  same  street. 


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Fig.  io. — View  of  country  automobile  road.     I,amp  wrongly  located  on  inside  of 
curve.     Glare  obscures  view  of  road  beyond. 


Fig.  ii. — View  of  same  road  shown  in  Fig.  io.  I<amp  on  side  of  curve  replaced  by 
lamp  in  the  left  of  view.  Change  of  location  enables  roadway  to  be  seen.  Note 
specular  reflection  from  roadway  due  to  lamps  6oo  and  1,000  feet  away.  Excellent 
conditions  for  driving  with  large  illuminants  (Magnetite  arc  lamps  with  refractors), 
widely  spaced. 


MILLAR :    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO49 

ness  of  light  sources  to  low  values.  Since  the  problem  is  really 
one  of  reducing  contrast  between  the  light  source  and  the  illum- 
inated surfaces,  the  more  constructive  way  of  accomplishing  the 
desired  end  is  to  increase  the  brightness  of  the  illuminated  sur- 
faces rather  than  to  dim  the  light  sources  unduly.  Excessive 
brightness  of  light  sources  must  of  course  be  reduced.  It  is 
common  experience  that  a  simple  diffusing  globe  accomplishes 
this  reasonably  well  under  most  conditions.  Too  great  reduction 
in  the  brightness  of  the  light  source  is  unsatisfactory  psychologi- 
cally. We  like  a  bright  light  source— we  are  dissatisfied  with 
illumination  in  which  a  bright  light  source  is  not  visible.  There- 
fore the  thing  to  do  is  to  eliminate  glare  by  increasing  the  bright- 
ness of  the  street  surface  and  where  desirable  that  of  surround- 
ings, and  by  reducing  the  brightness  of  the  light  sources  mod- 
erately throughout  the  angles  at  which  they  are  viewed. 

With  these  considerations  concerning  the  importance  of  the 
silhouette  effect,  specular  reflection  from  pavements  and  glare 
well  in  mind,  a  discussion  of  the  variables  of  street  illumination 
and  of  the  several  factors  which  the  engineer  must  study  in 
planning  a  street  lighting  installation  are  next  in  order. 

ILLUMINATION  VARIABLES. 

The  effectiveness  of  street  illumination  depends  upon  the  fol- 
lowing : 

(1)  Intensity  of  light  upon  the  street— there  is  no  single 
measure  of  intensity  which  serves  all  purposes.  The  average 
horizontal  intensity  upon  the  street  surface  is  most  nearly  satis- 
factory. (2)  Brightness  of  street  surface— adopting  automo- 
bilist's  viewpoint  as  to  angle  and  direction.  (3)  Relation  between 
lamps  and  street  surface — visual  angle  between  the  two  and  ex- 
tremes of  contrast  encountered.  (4)  Contrasts  produced  on  the 
street  surface  and  on  objects  on  the  street— this  is  largely  a 
function  of  the  direction  of  the  light.  (5)  Portion  of  total  field 
of  view  illuminated— this  may  be  affected  either  by  the  number 
of  lighted  lamps  within  view  or  by  the  area  of  surface  which  is 
illuminated.  (6)  Appearance  of  installation  and  of  street  by 
day  and  by  night— lamps,  fixtures,  light  distribution,  etc. 


IO5O     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

INSTALLATION  FACTORS. 
Each  of  the  foregoing  variables  upon  which  street  lighting  ef- 
fectiveness depends  is  affected  by  four  or  more  principal  instal- 
lation factors.  These  are  listed  in  the  first  column  of  Table  I, 
in  which  the  variables  are  given  as  column  headings.  The  pur- 
pose in  presenting  this  table  is  to  emphasize  the  complexity  of  the 
street  illumination  problem  and  to  indicate  the  manner  in  which 
the  several  elements  are  interconnected.  Consider,  for  example, 
street  surface  brightness  as  a  variable  in  street  illumination.  The 
table  indicates  that  brightness  depends  upon  the  power  of  the 
lighting  units,  the  number  of  lighting  units  per  mile,  the  kind  of 
lighting  accessories  employed,  the  location  of  lighting  units,  the 
nature  of  the  street  pavement  and  the  nature  of  the  surroundings. 
Alteration  in  any  one  of  these  conditions  may  influence  the 
brightness  of  the  street  and  therefore  the  effectiveness  of  the 
street  illumination.  An  engineer  who  considers  any  one  in- 
stallation condition  must  appreciate  that  his  decision  may  be  far- 
reaching  in  its  influence  upon  the  effectiveness  of  the  lighting, 
since  every  installation  factor  influences  a  number  of  these  varia- 
bles. Every  street  presents  its  own  problems,  and  the  utmost  ef- 
fectiveness of  street  illumination  for  a  given  expenditure  is  had 
when  each  factor  is  applied  with  due  regard  to  the  relations  set 
forth  in  this  table. 

TABLE  I.— Effectiveness  of  Street  Illumination. 

Variables 

Influences  through  which  factors  operate 

Relation  Portion  Appearance 

between  of  field      ofinstall- 

Installation                   Intensity     Bright-       lamps  of  view     ation  and 

factors  which  deter-             of  light         ness      and  street  Contrasts  ilium-     street,  day 

mine  effectiveness             on  street    of  street    surface**    on  street  inated      and  night 

Power   of   lighting 

units    *  *  *  «  * 

Number  of  lighting 

units  per  mile  -•  *  *  *  * 

Kind  of  accessor- 
ies    *  *  *  *  * 

Kind  of  mount  ••  • 

Location  of  light- 
ing units *  * 

Nature    of     pave- 
ment   *  *  * 

Nature     of     sur- 
roundings    *  *  * 

**  Visual  angle  and  extent  of  contrast. 

1  Visibility  not  ratio  of  reflection  coefficients. 


TABLE  II-LIGHT  PRODUCING  EFFICIENCIES  OF  MODERN  STREET  ILLUMr 


ASSOCIATION  OF  EDISON  ILLUMINATING  COMPANIES  LAMP  O  TREF 

(ARC  LAMPS  BUMMER   1914— MAZDA  I. 


tee  arc  1  van- 
00s    makes   of 


:e  and 
metallic  flame 
(standard 
I  pc — ^  :  lac 
interred  "or- 
n  omental " 


i»ksvrii-tu>n  OP  lamp  v\i>  Bfll  ii'Mi  \r 


Mr.AN   Initial  VAI.ueH 


->  amp.  a.  c.  compensator,  clear  globes,  white  (lame  electroile  . 
;  10  amp.  a.  c.  compensator,  clear  globes,  white  ilunic  elect!  ide 


G.  E.  magnetite  4  amp.,  standard  electrode,  clear  globe 

G.  E.  magnetite  4  amp  ,  high  efficiency  electrode,  clear 

G.  E.  magnetite  5  amp.,  standard  electrode,  clear  glol>e 

G.  E.  magnetite  5  amp.,  high  efficiency  electrode,  clear  globe-  ■  ■ 

G.  E.  magnetite  6.6  amp.,  standard  electrode,  clear  globe 

G.  E.  magnetite  6.6  amp.,  high  efficiency  electrode,  clear  globe  . 


Westg.  metallic  flame  4  amp.,  standard  electrode,  clear  globe 

Westg.  metallic  flame  4  amp.,  high  efficiency  electrode,  clear  globe 


loo-watt  multiple 

200     "  "         

3°o    "  "         

400     "  "         

500     "  "         

7SO     "  "         

1,000     "  "         

60-cp.  6.6  amp.  series 

100  "    6.6     "         "       

250  "    6.6     "         "       

400  "    6.6     "         "       

600-cp.  20-amp.  series  compensator 

1,000  '*    20     "  "                 '• 


93 
200 
300 
400 
57S 
938 
1, 3°° 


200 
320 


480 
800 


1,170 
2.513 
3.767 
5,026 
7.225 
11,787 
'6.335 


574 
1,005 

2.513 

4.021 


6,031 
10,053 


100 
200 
300 
400 
500 

75° 
1,000 


444 

73 
■83 
300 


32it 
5<>4t 


' I      ,-.  : 


767 

681 


238 
370 

459 
609 
693 
937 


0.97 
0.91 
0.91 
094 


o.67J 
o.63t 


11. 7 
125 
12.5 
125 
14.4 
'5-7 
16.3 


I3I 
■3-8 
134 


18.8* 
•9-9t 


265 
326 


9.638 
8,557 


2,991 
4.649 
5.768 
7.655 
8,708 
11,774 


3.310 
4,100 


3'o 
323 
39o 
371 
5" 
5"9 


299 
306 


18.5 
17.8 


965 
14.4 
14.8 
20.6 
17.0 
23-  ■ 


1 1.1 
'34 


0.68 
0.74 


ittaper     ; 
audit       v 


s*> 


la. 

-   :■ 


Curve  P.  or  C 
"  B  or  C 
"  BorC 
"  BorC 
•'  BorC 
"      BorC 


No  material  chan .  -  in  cp.  throagboat  trial  has  keea  aaaem 


Curve  D 
"       D 


--- 


Dsnal  fixture!  and  con- 
tainers absorb  from  7  to 
35  per  cent,  of  tin-  light 
given  by  the  lamp. 


F,  GorH 
F,  GorH 
F.GorH 
F,  GorH 
F,  GorH 
F.GorH 
F.GorH 


F.GorH 
F.GorH 
F.GorH 
F,  G  or  H 


84 
180 

270 
360 
5'8 

S45 
1,170 


7S 
196 

3H 


1,056 

98 

I 

2.262 

196 

I 

3.393 

294 

I 

4.534 

392 

I 

6.509 

490 

0 

10.618 

1 

0 

14.700 

980 

10.8 

1-5 

'-5 

: 

5-o 


9S0 

2.46.; 
3.946 


0.99 
0.96 
o-95 


3-« 

- 
2.9 


E,  F.GorH 
E.F.GorH 


5.554 
9.047 


5  =  I  I 


1  Total  Inmens  =  scp  /  <v 

1  laBif  11  (I,)  =  o.o5  acp.,  approx. 


average  eandlepom 
Dpensator. 


1 1  ril.  t.  '1  i.mying  up  to  20  per  cent,  of  these  values. 


Flame  arc  lamp,  clear  globes 


Curve  H 
Magiiiliir.-reflector  and  clear  glolx 


II    LIGHT  PRODUCING  EFFICIENCIES  OF  MODERN  STREET  ILLUMINANTS 


LXMINATING  C 


OMPANIES  LAMP  COMMITTEE  DATA  ON  STREET  ILLUMINANTS 


MA/PA  LAMPS  WINTliR  19M) 


,\M  u:i     I  


■  Lmsrnva  Sskvick 


D  s* 


.  POV  sum  i  i   l.uiii  ]  in.,  si  u  \  u  i 


709 
580 


7288 


O.74 
0-77 


17.O 
16.3 


73% 
79% 


9-<S 

14-4 

J0.6 

II. 1 

57 


Curve  B  or  C 
•  B  or  C 
"  B  or  C 
••  BorC 
••  BorC 
•'      B  or  C 


No  material  change  in  cp.  throughout  trim  has  been  observed. 


113 
0.94 


:-.r.i    00B- 
■' the  light 


Curve  E.F.GorH 

•  E.F.GorH 

"  E.F.GorH 

"  E.F.GorH 

••  E.F.GorH 

"  E.F.GorH 

"  E.F.GorH 


84 
180 
270 
360 
5>8 
845 
1,170 


E.F.GorH 
E.F.GorH 
E.F.GorH 
E.F.GorH 


45-7 

78 
196 
3M 


E.F.GorH 
E.F.GorH 


1,056 
2,262 
3.393 
4,524 
6,509 
10,618 
14.700 


2,463 
3,946 


5.554 
9.°47 


196 
294 
392 
490 
735 
980 


45-3 
74-5 

187 

306 


33'J 
520$ 


099 
0.96 
0.95 
0.97 


o-75t 
0.725: 


10.8 
II-5 


n-5 
13-3 


12.7 
13- 1 
13-2 


i6.8t 

I7-4t 


3655 


130  lir.  per  trim 
80  lir    |>er  trim 


!.■  i«rmit 
assign  incnt. 


317  lir.  per  trim 


MANUI'AI  TURK1 


General  Electric  Co.  approves  assignment  of  values  ;  reports  latest  lamp  with  compensator  consumes  | 
•  type  without  compensator :  scp.  890-total  lumens  11190— watts  465— w.-r 
lumens  per  w.  24. 

Westinghouse  Electric  &  Manufacturing  Company  reports  for  1915  lamp  electrode  life  of  130  hours  ana.  wit  hoot  coss- 
inglier  efficiency  as  follows:   scp.  initial  770— total  lumens  9676;  throughout  life  (average;  scp.  640;  total 
lumens  8,041     terminal  watts  initial  445,  average  throughout  life,  442;  w.p.c.  initial  0.58,  throughout  life  0.69;  harness 
per  watt  initial  21  7.  throughout  life,  18.2. 

National  Carbon  Company  reports  for  flame  arc  lamp  as  a  type,  16.9  lumens  per  watt  (w.p.c.  0.74)  tnroogboot  nfe. 
with  lamp  equipped  with  light  diffusing  glass-ware. 


Data  insufficient  to  permit  assignment.  See  manufacturer's  statement. 


G.  B.  Co.  approves  assignment  of  va 
G.  E.  Co.  approves  assignment  of  val 
r,  B.  Co.  approves  assignment  of  val 
G.  E.  Co.  approves  assignment  of  va 
G.  E.  Co.  approves  assignment  of  va 
('..  11.  Co.  approves  assignment  of  va 


lues.  States  electrode  lives  are  for  two  sizes,  respectively  230  and  350  hr. 

lues.  States  electrode  life  is  180  hours. 

hies.  States  electrode  lives  are  for  two  sizes,  respectively  150  and  225  br. 

lues.  States  electrode  lives  are  for  two  sizes,  respectively  125  and  150  hr. 

lues.  States  electrode  life  is  no  hours. 

lues.  States  electrode  life  is  75  hours. 


G.  E.  Co.  states  sliglulv  higher  candlepower  and  efficiency  obtained  in  inverted  "  ornamental "  type  of  lamp. 


Westinghouse  Elec.  &  Mfg.  Co.  approves  assignment  of  values  and  claims  250  to  275  ho 
Westinghouse  Klec.  &  Mfg.  Co.  approves  assignment  of  values 


Approximate  values  for  the  Summer  of  1915. 


Initial  watts  per  enudle  Initial  lumens  per  watt 


0.96 
0.88 
0.82 
O.82 
O.82 
O.76 
0.71 


0.9I 
0.76 
0.75 


0.63? 
o.6it 


13" 
14.3 
15-3 
15-3 
15-3 
16.5 
17-7 


12.6 
13-8 
•6.5 
16.7 


I9-9J 

20.6J 


Ap^  roximate  average  life  under  correct  operating  conditions 


1,000  hours 

1,000  " 

1,000  " 

1,000  " 

1,000  " 

1,000  " 

1,000  " 


Curve  D 
Metallic  flame— reflector  and  clear  globe 


Curve  E 
Mazda  with  diffusing  globe 


Curre  H 
MAidn  with  diffusing  jcloc* 


MILLAR:    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO5I 

In  attempting  to  discuss  these  several  elements  of  the  problem 
it  is  necessary  to  generalize,  and  this  in  spite  of  the  fact  that  the 
great  differences  in  streets  of  the  several  classes  listed  on  another 
page  made  generalization  difficult.  Nevertheless  it  is  hoped 
that  a  general  discussion  of  the  influence  of  each  factor  upon  the 
several  variables  will  be  of  value,  particularly  since  it  is  pro- 
posed to  note  principally  those  features  in  which  recent  experi- 
ence has  suggested  some  new  consideration. 

She  of  Lighting  Units  and  Spacing  Intervals. — There  is  now  a 
general  tendency  toward  the  adoption  of  more  powerful  lamps  of 
one  of  the  three  types  listed  in  Table  II.  These  data  are  available 
through  the  courtesy  of  the  Lamp  Committee  of  the  Association 
of  Edison  Illuminating  Companies;  in  large  measure  they  are 
authoritative  for  lamps  of  the  period  stated  and  equipped  as 
indicated. 

Of  the  above  illuminants  the  flame  arc  lamp  and  the  multiple 
gas-filled  tungsten  lamp  depreciate  in  candlepower  20  to  25  per 
cent,  throughout  life.  The  magnetite  lamp  and  the  series  gas- 
filled  lamps  do  not  change  materially  throughout  life. 

Large  versus  Small  Illuminants. — The  cluster  of  lamps  em- 
ployed so  largely  in  "ornamental  or  white  way"  lighting  during 
the  past  five  years  has  yielded  in  favor  in  most  recent  installa- 
tions to  the  single  illuminant  or  less  frequently  to  twin  illumi- 
nants on  one  post. 

The  effectiveness  of  the  lighting,  other  things  being  equal,  is 
dependent  upon  the  choice  as  between  many  small  lighting  units 
and  few  large  lighting  units.  In  favor  of  the  small  illuminants 
it  is  urged  that  greater  uniformity  results  from  their  use;  that 
they  may  be  mounted  lower,  thus  avoiding  shadows  from  trees, 
etc. ;  and  it  is  added  that  when  small  illuminants  are  mounted 
low,  a  larger  percentage  of  their  total  flux  is  distributed  over 
the  street  surface.  On  the  other  hand,  it  is  argued  in  favor  of 
large  illuminants  that  they  are  relatively  less  costly  per  mile,  and 
that  usually  the  appearance  of  a  street  lighted  by  them  is  more 
pleasing. 

There  are  two  considerations  not  usually  urged  in  this  con- 
nection. The  first  is  discussed  in  more  detail  under  the  subject 
of  location  of  lighting  units.     Large   illuminants  are   favored 


IO52     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

from  this  viewpoint  because  they  may  be  placed  well  out  over 
the  middle  of  the  street,  where  the  specular  reflection  from  street 
surfaces  allows  the  light  to  be  applied  in  a  more  favorable  direc- 
tion than  that  from  small  illuminants  which  usually  are  mounted 
low  over  the  curb.  Fig.  11  is  an  excellent  illustration  of  the 
advantageous  use  of  large  units  in  lighting  a  country  road.  The 
lamps  are  placed  500  to  900  ft.  (152.4  to  274.32  m.)  apart  and 
18  to  25  ft.  (5.48  to  7.60  m.)  high.  The  effect  is  good  for  auto- 
mobile driving  purposes.  An  example  of  ineffective  use  of  small 
illuminants  will  occur  to  all  who  can  visualize  a  wide,  wet  street 
with  lamps  over  both  curbs.  The  lighting  of  the  street  surface 
consists  of  a  few  bright  streaks  near  the  curbs,  while  the  middle 
of  the  street  is  dark.  Fig.  5  illustrates  this  effect  upon  a  dry 
pavement.  As  modern  street  pavements  are  extended,  and  auto- 
mobile traffic  increases,  the  advantages  of  mounting  lamps  well 
over  the  center  of  the  street  tend  to  increase,  and  the  disadvan- 
tages of  small  illuminants  mounted  low  over  the  curbs  tend  to 
become  more  apparent. 

The  second  consideration  was  brought  out  prominently  last 
year  by  the  Street  Lighting  Committees  of  the  National  Electric 
Light  Association  and  the  Association  of  Edison  Illuminating 
Companies.  It  was  shown  that  within  reasonable  limits,  uni- 
directional light  is  to  be  preferred  to  multi-directional  light 
because  it  enhances  contrasts  upon  which  discernment  is  depend- 
ent. Objects  and  surface  irregularities  are  seen  more  surely  by 
uni-directional  light  than  by  light  coming  from  a  number  of 
directions.  From  this  it  follows  that,  other  things  being  equal, 
the  revealing  power  of  a  few  large  illuminants  is  greater  than  that 
of  many  small  illuminants,  especially  if  the  latter  are  staggered 
along  both  curbs. 

While  these  considerations  do  not  clearly  indicate  the  desira- 
bility of  large  units,  they  do  add  weight  to  the  arguments  in  their 
favor. 

LIGHTING  ACCESSORIES. 

Improved  Distribution. — The   most   desirable   distribution   of 

light  depends  largely  on  the  nature  of  the  street  surface  and  on 

the  character  of  the  street.     Hence  there  is  no  such  thing  as  a 

correct  distribution  characteristic  for  all  street  lighting.     The 


Fig.  12.— Adjustable  temporary  installation  employed  in  New  York  City  to 
determine  best  location  for  lamps. 


Fig.  13.— Carlisle,  Pa.,  600-cp.  mazda  C  lamps  in  prismatic  refractor  units. 


Fig.  14. 


-Fourteenth  street,  Washington,  D.  C,  100-cp.  mazda  C  lamps  about  10  feet  above 
curb  and  spaced  at  intervals  of  80  feet  along  each  curb. 


Fig.  15.— Lake  Avenue,  Rochester,  500- 
watt  mazda  C  lamps,  mounted  17 y2 
feet  above  curb,  spaced  at  average 
intervals  of  225  feet. 


Fig.  16. — Main  street,  Rochester,  6.6-amp. 
magnetite  lamps.  Located  14^  feet 
above  curb  and  spaced  at  100  ft.  in- 
tervals along  each  curb. 


MILLAR:    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO53 

prismatic  refractor  is  successful  in  providing  a  distribution  char- 
acteristic which  for  a  vertical  plane  conforms  to  the  theoretical 
requirements  as  laid  down  by  some  engineers.  In  other  forms 
it  will  doubtless  provide  different  distributions  as  required.  It 
is  an  admirable  device  so  far  as  re-direction  of  light  is  concerned. 
However,  it  is  objectionable  in  some  forms  because  of  excessive 
brightness,  due  to  its  small  size.  Also  when  combined  with  the 
casings  with  which  it  is  usually  employed,  its  appearance  is  not 
attractive.  Probably  in  the  evolution  of  this  useful  device  these 
objections  will  be  overcome. 

The  same  considerations  which  underlie  the  design  of  the  re- 
fractor, namely  the  desire  to  increase  the  intensities  on  the  street 
surface  at  a  distance  from  the  lamps,  would  appear  to  favor  the 
adoption  of  asymmetrical  horizontal  distributions  whereby  light 
which  normally  is  delivered  upon  surfaces  lying  along  the  sides 
of  the  street  is  directed  upon  the  street  surface.  Lighting  ac- 
cessories to  accomplish  this  purpose  have  been  devised,  but  thus 
far  have  not  received  the  extensive  trial  which  their  theoretical 
advantages  would  appear  to  warrant. 

Diffusing  Globes. — The  employment  of  diffusing  globes  to 
decrease  brightness  of  light  sources  in  the  street  has  become  more 
general  in  recent  years.  Perhaps  the  extreme  example  in  the 
way  of  increased  size  of  such  globes  is  found  in  the  Washington, 
D.  C,  installation  of  ornamental  magnetite  lamps,  in  which  23-in. 
(58.4  cm.)  built-up  alabaster  globes  of  rather  high  density  are 
employed.  (See  Fig.  7.)  As  compared  with  the  use  of  a  clear 
globe  or  of  a  lamp  with  no  globe,  a  diffusing  globe  of  fairly 
large  size  is  usually  desirable  because  it  improves  the  appearance 
of  the  lighting  unit,  renders  the  appearance  of  the  street  more 
pleasing  and  promotes  good  conditions  of  visibility. 

It  is  desirable  to  secure  the  best  possible  balance  between  low 
light  absorption  and  good  diffusion  when  selecting  diffusing 
globes.  Test  data  on  these  two  characteristics  are  of  importance 
and  should  not  be  neglected.  Because  of  neglect  of  simple  and 
inexpensive  tests  of  commercially  available  glassware,  globes 
are  being  installed  which  do  not  accomplish  the  purposes  in  view 
so  well  as  would  other  glassware.  These  either  absorb  a  larger 
percentage  of  light  than  is  necessary  to  secure  the  desired  degree 


1054    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

of  diffusion,  or  else  diffuse  less  well  than  need  be,  considering 
the  amount  of  absorption. 

Protection  for  the  Byes. — At  first  glance  it  would  appear  that 
street  lighting  purposes  would  be  served  admirably  by  a  lighting 
accessory  which  would  concentrate  a  large  proportion  of  the 
light  flux  upon  the  street  surface  while  directing  but  little  light 
at  those  angles  which  fall  near  the  center  of  a  field  of  vision  in 
a  given  installation.  However,  certain  difficulties  operate  against 
the  success  of  such  a  scheme.  With  practicable  mounting  heights, 
spacings  have  to  be  short  if  this  is  to  be  successful  in  illumin- 
ating the  entire  length  of  the  street.  The  general  direction  of  the 
light  in  such  an  installation  is  much  more  largely  downward 
than  is  usually  the  case.  Wherever  there  are  sufficiently  short- 
interval  spacings  to  allow  of  such  an  installation,  there  usually 
exists  a  requirement  for  lighting  the  building  fronts.  In  such 
installations  the  relatively  high  intensities  on  the  street  surface, 
together  with  the  large  areas  of  considerable  brightness  which 
present  themselves  to  view,  render  the  glare  negligible  when 
ordinary  diffusing  globes  are  used.  That  is  to  say,  in  the  only 
installations  where  it  is  practicable  to  use  such  devices,  their 
eccentric  distribution  characteristics  are  unnecessary.  Where 
the  surroundings  are  such  that  the  lighting  of  building  fronts  is 
undesirable  or  unnecessary,  spacings  are  usually  too  great  to 
admit  of  the  use  of  such  devices,  because  their  illuminating  range 
is  too  small.  Also  considerations  of  street  surface  characteristics, 
discussed  elsewhere,  suggest  that  suppression  of  light  at  say  8o° 
may  do  more  harm  by  lessening  the  pavement  brightness  than  can 
be  compensated  by  decreased  brightness  of  source. 
LOCATION  OF  LIGHTING  UNITS. 

Comprehended  under  this  heading  are  such  subjects  as  height, 
transverse  location  and  spacing.  In  most  city  installations  these 
aspects  are  standardized  for  a  particular  street.  In  lighting  of 
interurban  roadways,  lamps  are  sometimes  located  in  accordance 
with  best  judgment,  varying  considerably  in  all  these  particulars. 

Location  Transverse  of  Street. — As  between  center  and  curb 
locations  there  is  a  considerable  difference.  In  the  first  place 
with  lamps  located  over  each  curb,  the  street  appears  much  wider, 
as  is  illustrated  by  a  comparison  of  Figs.  8  and  9  which  are  alter- 


Fig.  i7._ Federal  street.  Pittsburgh.    Series  a.  c.  flame  arc  lamps,  white   light  carbons" 
Lamps  mounted  24  feet  above  curb  and  spaced  at  average  intervals  of  69  feet. 


Fig.  18.— Fifth  Avenue.  New  York,  400-watt  mazda  C  lamps  on  twin  posts  mounted  19  feet 
above  curb  and  spaced  at  about  100  foot  intervals  along  both  curbs  with  extra  lamps 
at  cross-street  intersections. 


Fig.  19. — Pennsylvania  Avenue,  Washington,  D.  C,  6.6-amp.  magnetite  lamps  as  illus- 
trated in  Fig.  7.  Mounted  15  feet  above  curb,  spaced  at  50  It.  intervals  along  both 
curbs. 


Fig.  20.— Fifth  Avenue,  Pittsburgh,  6.6-amp.  magnetite  lamps,  mounted  18  feet  above  the 
curb,  spaced  at  approximately  80  ft.  intervals  along  each  curb. 


MILLAR:    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO55 

nate  test  installations  of  the  N.  E.  L.  A.  and  A.  E.  I.  C.  Street 
Lighting  Committees. 

In  the  lighting  of  important  city  streets  this  is  usually  a  desir- 
able condition.     The  lamps  mounted  over  the  curbs  likewise  illu- 
minate the  sidewalks  and  the  fronts  of  buildings  better.     (See 
Figs.  18  and  19.)     When,  however,  the  lighting  of  the  roadway 
becomes  of  first  importance,  as  in  streets  of  the  3b  class,  the  best 
use  may  be  made  of  the  light  by  locating  the  lamps  as  nearly  as 
practicable  over  the  roadway  so  as  to  take  full  advantage  of  all 
specular  reflection  from  the  street  surface.    (See  Figs.  11  and  5.) 
Height. — In  regard  to  height  of  lamps  there  is  also  a  wide 
difference  in  requirements,  depending  upon  the  character  of  the 
street.    In  some  of  the  latest  practice,  powerful  lamps  are  located 
14  to  18  ft.  (4.27  to  5.48  m.)  over  the  curbs  on  business  streets. 
These,  however,  are  backed  by  light  colored  buildings  and  the 
entire  surrounding  is  so  brightly  lighted  that  the  glare  is  not  bad. 
With  lamps  over  the  middle  of  the  street  the  background  is 
usually  the  dark  sky,  and  usually  there  are  not  light  colored 
buildings  to  relieve  the  general  darkness.    Under  these  conditions 
the  opportunity  for  glare  to  become  serious  is  considerable  and 
it  is  therefore  necessary  to  locate  the  lamps  rather  high.     The 
improvement  realized  in  increasing  the  height  of  lamps  of  mod- 
erate power  from  18  to  20  ft.  (5.48  to  6.09  m.)  is  considerable, 
while  the  improvement  in  increasing  the  height  from  say  27  to 
30  ft.  (8.22  to  9.14  m.)  is  not  very  great.     The  curve  of  glare 
falls  off  rapidly  with  increasing  separation  when  the  separation 
between  the  light  source  and  the  observed  surface  is  only  a  few 
degrees.     Around  a  lamp  which  has  a  dark  background  there  is 
a  zone  of  halation  within  which  objects  tend  to  become  invisible. 
Once  outside  this  zone,  the  glare  effect  falls  off  less  rapidly.     It 
is  very  important  to  mount  the  lamps  high  enough  to  insure  that 
the  separation  from  the  street  surface  is  at  least  sufficient  to 
avoid  this  zone  of  serious  glare. 

Power  of  Unit  as  Related  to  Glare.— Other  things  being  equal, 
the  objectionable  effects  of  glare  are  greater  when  the  lighting 
units  are  more  powerful.  Hence  it  is  approved  practise  to  mount 
the  more  powerful  units  higher  than  less  powerful  units. 

Such  a  lack  of  separation  is  responsible  for  the  serious  glare 


IO56     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

illustrated  in  Fig.  10.  An  arc  lamp  is  located  over  the  inside  of 
a  curve  in  a  road  obscuring  the  roadway  beyond.  The  angle  of 
separation  between  lamp  and  roadway  is  about  30.  Fig.  11 
shows  the  same  road  but  with  a  lamp  located  over  the  outside  of 
the  curve  and  separated  from  the  distant  roadway  by  about 
200  when  viewed  as  in  driving.  It  must  be  recognized  that 
a  bright  light  source  obscures  its  immediate  background.  This 
obscuration  is  greater  if  the  light  source  is  brighter  or  more 
powerful,  and  is  less  if  the  background  is  brighter.  In  country 
road  or  park  drive  lighting  such  obscuration  is  often  very  seri- 
ous. The  illustrations  in  Figs.  10  and  11  indicate  one  good  way 
of  overcoming  this  difficulty.  Recognizing  the  truth  that  under 
such  conditions  the  bright  light  sources  will  obscure  a  certain 
region  of  the  field  of  view,  the  source  is  so  located  that  the  back- 
ground which  it  obscures  is  one  which  it  is  not  important  to  see 
and  that  the  surface  which  it  is  desired  to  see  is  sufficiently 
separated  from  the  glaring  light  source  to  avoid  difficulty. 

Spacing. — All  features  of  an  installation  should  be  treated  in 
such  a  way  as  to  avoid  dark  areas  between  lamps,  coupled  with 
low  mountings  for  very  bright  and  powerful  lamps.  To  avoid 
ineffective  results  due  to  multi-directional  light  which  reduces 
contrasts,  spacings  need  to  be  greater  when  the  lamps  are  stag- 
gered along  both  curbs  than  when  they  form  a  line  along  one 
side  or  over  the  middle  of  the  street.  The  best  spacing  would 
appear  to  be  contingent  upon  the  kind  of  pavement  employed 
and  the  nature  of  the  surroundings.  All  the  other  factors  should 
be  so  handled  that  in  driving  one  will  not  encounter  the  bad  con- 
dition of  a  bright  light  source  preventing  an  adequate  view  of 
the  surface  of  the  street  beyond  it. 

Fig.  12  illustrates  the  very  excellent  practise  which  is  some- 
times followed  in  the  City  of  New  York,  in  locating  lamps  for 
street  lighting.  Lamps  which  are  temporarily  installed  may  be 
raised  and  lowered ;  those  mounted  from  the  mast  arm  post  may 
be  placed  nearer  to  or  farther  from  the  curb,  and  those  in  the 
center  parkways  may  be  moved  about  at  will,  the  posts  being 
mounted  in  rock-ballasted  barrels.  A  crew  of  men  locate  the 
lamps  in  the  trial  installation  as  directed  by  the  engineers  in 
charge  and  the  locations  which  appear  to  give  the  best  illumi- 


MILLAR:    THE  EFFECTIVE  ILLUMINATION  OF  STREETS      IO57 

nating  effects  are  arrived  at.  Photometric  tests  are  then  made 
to  show  the  results  obtained  and  to  afford  a  basis  for  the  plan- 
ning of  other  installations. 

THEORETICAL  CONSIDERATIONS  WHICH  HAVE  NOT  BEEN 
DEMONSTRATED. 

Color. — In  street  illumination  where  intensities  are  low,  it  is 
believed  by  some  engineers  that  white  light  is  more  effective  than 
yellow  light.  According  to  this  view,  objects  are  revealed  with 
greater  definition;  smaller  contrasts  may  be  perceived,  and  there 
is  less  suggestion  of  haziness  in  the  atmosphere  when  white  light 
is  employed.  In  accordance  with  the  Purkinje  effect  there  would 
appear  to  be  some  basis  for  this  theory,  since  it  is  well  known 
that  in  intensities  of  the  order  of  o.oi  foot-candle,  we  see  almost 
exclusively  by  red  vision  and  the  maximum  of  the  ocular  lumi- 
nosity curve  is  removed  toward  the  blue  end  of  the  spectrum. 
Whether  or  not  this  effect  is  present  in  street  lighting  is  one  of 
the  interesting  subjects  of  speculation  at  the  present  time. 

Whether  or  not  white  light  possesses  advantage  for  low  in- 
tensity street  lighting  due  to  ocular  peculiarities,  it  is  certain 
that  it  is  preferred  by  many  for  high-class  street  lighting  on  the 
ground  that  it  is  more  suitable,  pleasing  and  dignified  than  is 
yellow  light.  This  is  perhaps  a  matter  of  color  association,  and 
is  surely  a  matter  of  taste.  It,  therefore,  hardly  finds  place  in  a 
discussion  of  this  kind,  and  is  merely  mentioned  in  passing. 

"Animation"  of  Light  Source. — It  has  been  suggested  that  the 
slight  fluctuation  of  light  which  characterizes  arc  lamps  possesses 
some  advantage  for  street  lighting  purposes  over  the  steady  glow 
of  the  incandescent  lamp.  So  far  as  the  writer  knows,  no  dem- 
onstrations have  been  undertaken,  and  it  has  not  been  shown 
that  this  speculation  has  any  basis  in  fact. 

GENERAL  STATUS  OF  THE  PROBLEM  OF  STREET 
ILLUMINATION. 

There  is  an  important  consideration  suggested  in  the  first  para- 
graph of  this  paper.  As  more  money  is  expended  on  street  light- 
ing and  as  more  efficient  lamps  are  made  available,  the  intensities 
of  light  in  streets  become  greater.  As  the  intensities  increase,  the 
requirements  for  the  best  possible  application  of  light  to  promote 


IO58     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

good  visibility  conditions  become  less  severe  and  the  requirements 
for  application  which  improve  the  appearance  of  the  street  become 
more  urgent.  From  the  standpoint  of  rendering  visible  the 
street  and  objects  upon  it,  the  lighting  of  suburban  automobile 
roads  where  but  little  money  is  available  for  installation  and 
operation  offers  the  best  test  for  the  engineer's  skill.  In  first- 
class  streets  we  have  already  progressed  to  the  point  where 
esthetics  assume  large  importance.  This  does  not  mean,  how- 
ever, that  the  problems  of  street  lighting  are  becoming  less  dif- 
ficult; it  means  simply  that  the  problems  are  becoming  more  in- 
volved, and  broader  comprehension  of  the  fundamental  prin- 
ciples of  street  illumination  is  becoming  more  essential. 

Appendix. — In  the  appendix  will  be  found  some  statistics  of 
very  recent  installations  in  streets  of  several  classes  showing 
practise  in  this  country  as  of  the  early  part  of  1915.  These  are 
accompanied  by  a  few  photographs. 

Acknowledgment. — The  author  wishes  to  express  his  indebt- 
edness to  a  number  of  gentlemen  who  have  kindly  supplied  some 
of  the  photographs  and  statistics  which  are  utilized  in  this  paper, 
and  who  are  too  numerous  to  permit  of  individual  mention  in 
this  connection. 

DISCUSSION. 

Mr.  G.  H.  Stickney  :  There  is  more  difference  of  opinion  as 
to  what  is  the  best  practise  in  street  lighting  than  in  any  other 
class  of  lighting  problems.  This  is  due  in  part  to  the  efforts  to 
classify  a  wide  variety  of  demands  into  one  or  two  groups  of 
practise,  at  the  same  time  putting  the  extreme  emphasis  on  the 
cost.  Since  the  disagreement  originates  with  the  ultimate  light- 
ing effects,  the  lack  of  agreement  as  to  the  methods  of  producing 
such  effects  is  not  surprising. 

The  careful  analysis  presented  in  Mr.  Millar's  paper,  while 
not  furnishing  a  solution  of  the  problems,  is  an  important  aid 
in  that  direction,  through  clearly  denning  some  of  the  funda- 
mental facts  which  have  not  been  generally  recognized. 

One  of  the  most  important  divergences  in  practise  is  that  be- 
tween the  large  and  small,  or  the  high  power  and  low  power 
lighting  units.    There  seems  to  be  little  doubt  but  that  the  larger 


THE   EFFECTIVE   ILLUMINATION   OF   STREETS  IO59 

units  are  generally  better  for  high  intensity  lighting,  and  the 
smaller  units  more  economical  for  low  intensity  lighting.  The 
majority  of  our  street  lighting  problems,  however,  fall  in  a  class 
of  intermediate  intensities,  where  there  is  considerable  question 
as  to  which  size  of  unit  will  give  the  best  effect  for  the  least  cost. 
Good  lighting  can  be  produced  from  either.  The  latest  tendency 
seems  to  be  to  follow  the  logical  practise  of  applying  units  of 
intermediate  power.  v 

We  often  note  the  tendency  to  measure  the  value  of  street 
lighting  units  in  terms  of  their  efficiencies.  Although,  all  else 
being  equal,  this  would  be  a  fair  measure,  practically,  there  are 
other  considerations,  such  as,  maintenance  cost,  adaptability, 
convenience,  appearance,  steadiness,  etc.,  which  often  outweigh 
a  considerable  difference  in  efficiency.  This  has  been  illustrated 
in  the  transition  from  the  open  arc  to  the  enclosed  arc,  and  also 
in  the  remarkable  spread  in  the  incandescent  cluster  light,  which 
despite  its  notorious  inefficiency  enjoyed  an  almost  unprece- 
dented popularity.  This  cluster  lighting  was  never  viewed  with 
high  favor  by  engineers,  and  while  it  is  now  giving  way  to  more 
economical  and  artistic  single  light  posts  its  former  popularity 
should  be  recorded  as  the  vote  of  the  public  in  favor  of  more 
ornamental  street  lighting. 

Referring  again  to  the  efficiency  question,  it  must  be  remem- 
bered that  to-day  the  item  of  electric  energy  consumed  repre- 
sents only  about  20  to  25  per  cent,  of  the  cost  of  street  lighting 
service,  so  that  even  large  gains  in  efficiency  represent  relatively 
small  savings.  Such  gains  can,  therefore,  usually  be  more  profit- 
ably taken  up  in  raising  the  standard  of  lighting. 

The  practise  of  oiling  the  road  and  street  surface  has  had  a 
very  important  relation  to  street  lighting  practise.  Due  to  the 
blackening  of  the  surface,  streets  which  were  formerly  quite  sat- 
isfactorily lighted  become  dull  and  dingy  looking.  While  the 
glint  effect  of  such  streets  is  valuable  to  the  automobilist  in  dis- 
cerning objects,  the  black  surface  absorbs  so  much  light  that  it  is 
very  difficult  to  produce  a  pleasing  and  cheerful  lighting  effect 
and  much  more  light  is  required  than  in  the  case  of  light  colored 
pavements  such  as  asphalt.  It  can  hardly  be  expected  that  the 
color  of  pavements  will  always  be  selected  to  facilitate  street 


IO60     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

lighting,  but  there  are  many  cases  in  which  it  would  be  desirable 
to  consider  the  street  lighting  in  this  connection. 

Prof.  Dugald  C.  Jackson:  This  paper  is,  I  hope,  a  fore- 
runner of  other  papers  to  be  given  at  joint  meetings  of  the  two 
societies  which  are  here  to-night.  Papers  of  a  similar  nature 
have  been  given  by  Mr.  Millar  and  other  authors  before  the 
meetings  of  the  Illuminating  Engineering  Society,  but  these 
papers  have  not  been  given  the  general  attention  of  electrical  en- 
gineers that  the  subject  warrants. 

There  are  certain  features  of  this  paper  which  impressed  me 
very  much  and  of  which  I  will  speak.  To  begin,  the  paper  refers 
to  the  change  of  attitude  of  engineers  who  have  to  do  with  street 
lighting,  which  has  turned  them  from  the  enclosed  series  arc 
lamp  to  other  types  of  lamps,  and  for  myself  I  want  to  express 
very  great  satisfaction  in  that.  I  have  always  believed  that  the 
enclosed  series  arc  lamp  (especially  when  operated  on  alternat- 
ing current)  was  one  of  the  mistakes  of  electrical  engineers,  and 
that  it  arose  by  allowing  the  question  of  the  cost  of  maintenance 
of  a  particular  machine  or  piece  of  apparatus  to  take  the  place  of 
consideration  of  the  real  effectiveness  of  its  service.  Fortu- 
nately, electrical  engineers  and  others  are  now  turning  their  atten- 
tion to  more  satisfactory  illuminants,  i.  e.,  more  satisfactory  when 
judged  broadly,  and  not  solely  from  the  standpoint  of  how  many 
hours  a  particular  lamp  may  be  burned,  or  how  much  labor  may 
be  requisite  to  maintain  the  structure. 

On  the  other  hand,  I  believe  we  are  likely  to  be  misled  by  the 
charm  of  simplicity  in  the  mazda  lamp  and  perhaps  go  too  far 
in  utilizing  the  slightly  yellowish  light  for  illuminating  important 
streets.  Certainly  in  the  great  streets  of  our  cities  most  in- 
dividuals are  more  pleased  with  the  white  light  than  with  the 
yellowish  light.  There  is  no  question  about  the  possibility  of 
lighting  streets  and  roads  with  mazda  lamps  of  large  candle- 
power  very  satisfactorily,  but  a  white  light  is  to  more  of  us  more 
satisfactory,  more  enspiriting,  which  is  a  feature  of  real  import- 
ance in  a  city  street  in  the  major  business  district.  The  yellowish 
light,  however,  probably  serves  the  purpose  with  full  satisfaction 
in  the  residence  and  also  perhaps  in  less  occupied  business  streets. 

In  my  opinion,  the  question  of  large  versus  small  units  will 


THE  EFFECTIVE   ILLUMINATION   OF   STREETS  I06l 

work  itself  out.  I  am  convinced,  that  the  large  units  are  bound 
to  be  used  for  the  important  streets  of  a  city.  The  American 
cities  must,  like  the  foreign  cities,  become  convinced  that  they 
need  floods  of  illumination  in  the  regions  of  great  mercantile 
activity,  although  they  do  not  need  so  much  light  elsewhere.  To 
secure  real  flood  illumination,  large  lamp  units  must  be  used. 

There  are  few  objects  more  graceful  and  beautiful  than  a  pair 
of  fine  white  lights  on  a  graceful  post,  when  these  lights  are  prop- 
erly protected  by  a  fairly  lafge  white  diffusing  globe — the  globe 
being  large  enough  so  that  any  spot  in  the  tremendous  amount  of 
light  that  may  be  given  off  may  not  have  any  serious  effect  on 
the  eye.  On  the  other  hand,  there  are  cases  where  sincere  effort 
has  been  made  to  get  rid  of  glare  according  to  the  mistaken  ideas 
of  some  man  who  put  up  the  system,  in  which  rows  of  large  in- 
tense lights,  with  diffusing  globes,  placed  22  or  24  ft.  (6.70  or 
7.31  m.)  high,  150  to  250  ft.  (45.72  or  76.20  m.)  apart,  down 
miles  of  road  make  a  nightmare  to  travelers  on  account  of  the 
physiological  effect  of  the  continuous  rows  of  illuminants  on  each 
side,  which  affect  the  eye  with  great  discomfort. 

One  of  the  most  pleasing  results  of  the  recent  work  of  illumina- 
ting engineers  in  this  country  is  the  attention  which  is  being 
turned  towards  the  use  of  graceful  lamp  posts  in  the  cities.  I 
here  avoid  the  use  of  the  words  "decorative  posts,"  because  the 
phrase  "decorative  lighting"  has  covered  such  a  multitude  of 
sins  by  way  of  ugliness  during  the  last  few  years.  Graceful  posts 
are  coming  into  style.  The  old  mounting  of  an  arc  lamp,  or 
some  other  lamp,  on  a  strip  of  iron,  fastened  by  a  lag  screw  to 
a  crooked  wooden  pole,  which  otherwise  carried  crossarms  and 
wires,  was  a  poor  sort  of  expedient  for  supporting  the  street 
lamps,  but  if  our  cities  can  recognize  the  worth  of,  and  spend  the 
money  necessary  to  secure  graceful  posts,  I  am  sure  that  they 
will  be  improved  and  made  happier  as  places  for  living. 

Mr.  Walter  R.  Moulton  :  Referring  to  the  discerning  of 
surface  irregularities  in  streets,  I  have  in  mind  one  interesting 
example  in  Baltimore  where  a  water-front  street  about  100  ft. 
wide  is  paved  with  Belgian  block  and  is  lighted  by  means  of 
luminous  magnetite  arcs  on  standards  located  on  safety  islands 
down  the  center  of  the  street.     The  rough  spots  in  the  street  are 


IO62     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

brought  out  very  distinctly  by  the  shadows  cast  and  also  by  the 
increased  intensity  of  illumination  on  the  face  presented  to  the 
source  of  light.  Because  of  the  nature  of  the  paving,  one  would 
hardly  expect  to  find  surface  reflection,  but  objects  do  stand  out 
in  silhouette  as  the  granite  blocks  are  worn  quite  smooth  and  there 
seems  to  be  reflection  from  each  individual  block.  The  condi- 
tions of  the  street  also  illustrate  very  forcibly  the  advantage  of 
illuminants  on  one  side  of  the  roadway  only  as  this  condition  is 
quite  analagous  to  such  a  road. 

The  effect  of  street  paving  on  the  illumination  of  a  street  was 
very  plainly  shown  when  the  paving  on  both  Howard  and  Eutaw 
Streets  in  Baltimore  was  changed  from  Belgian  block  to  sheet 
asphalt.  The  location  of  luminous  arc  lamps  was  not  changed, 
but  after  the  completion  of  the  asphalt  paving  the  lighting  condi- 
tion of  the  street  seemed  to  be  greatly  improved.  Another  in- 
teresting effect  of  street  surface  is  found  on  the  Fallsway,  which 
is  a  new  concrete  structure.  The  entire  surface  of  the  road,  the 
sidewalks  and  a  3  ft.  wall  on  either  side  are  of  concrete  and 
lighted  by  means  of  luminous  magnetite  arc  lamps  similar 
to  the  downtown  business  streets.  This  roadway  has  been  in 
use  about  nine  months  and  at  the  present  time  has  absolutely  no 
specular  reflection  from  its  surface.  The  surface  of  the  street, 
however,  seems  very  well  illuminated  and  the  diffuse  reflection 
from  the  light  colored  surface  seems  to  replace  specular  reflection 
very  well  in  improving  the  apparent  illumination  of  a  street. 

Specular  reflection  from  the  surface  illumination  is  important 
in  other  outdoor  lighting  than  street  illumination.  There  is  a 
large  municipal  bathing  pool  in  Baltimore,  covering  over  two 
acres,  which  is  used  at  night  as  well  as  in  the  daytime.  A  number 
of  incandescent  lamp  standards  are  located  around  the  pool  and 
also  on  platforms  and  pedestals  in  the  center  of  the  pool  itself. 
The  general  illumination  is  very  good,  but  ability  to  see  objects 
on  the  surface  of  the  water  is  entirely  due  to  the  specular  reflec- 
tion of  the  lights  on  the  surface. 

The  excessive  brightness  of  a  prismatic  refractor  unit  combined 
with  a  high  candlepower  lamp  is  forcibly  illustrated  by  the  diffi- 
culty experienced  in  attempting  to  photograph  such  installations. 
Would  this  not  indicate  that  such  units  are  brilliant  enough  to 


THE  EFFECTIVE   ILLUMINATION   OF   STREETS  1063 

interfere  considerably  with  vision  and  would  it  not  also  seem 
to  point  out  that  their  size  should  be  increased  ? 

The  commercial  value  of  lavish  application  of  street  lighting 
in  the  downtown  section  is  well  illustrated  in  Baltimore  where 
over  1000  luminous  magnetite  are  "white-way"  lamps  have  been 
installed.  At  night  the  business  section  of  the  city  is  made  very 
prominent,  it  shows  up  quite  strongly  from  the  hilly  sections 
surrounding  the  city  and  especially  so  from  the  bay.  The  illumi- 
nation in  the  sky  from  a  distance  is  quite  strong  and  the  tall 
buildings  stand  out  quite  prominently  against  the  sky  as  the  en- 
tire face  of  the  building  is  illuminated. 

This  latter  feature  of  lighting  the  building  fronts  is  one  that 
should  not  be  overlooked.  The  civic  buildings,  namely  the  Court 
House,  Post-office  and  City  Hall  are  located  on  three  consecutive 
blocks  with  wide  streets  on  either  side  and  a  plaza  on  each  end 
and  between  the  buildings.  There  are  several  well  designed 
office  buildings  facing  the  civic  buildings.  The  generous  use  of 
white-way  lamps  in  this  section  makes  these  buildings  quite 
prominent,  especially  as  they  are  of  light  colored  stone,  the  Court 
House  being  of  white  marble.  This  section  is  made  really  more 
attractive  at  night  than  it  is  in  the  daytime. 

The  esthetic  effect  of  lighting  standards  or  posts  throughout 
the  city  is  quite  important.  If  possible  one  typical  design  should 
be  carried  out.  In  Baltimore  a  special  design  standard  was  de- 
veloped for  use  with  the  luminous  arc  white-way  lamps.  This 
same  design  has  since  been  carried  into  the  residence  sections  for 
use  with  the  incandescent  lamps  and  round  globes  and  it  has  also 
been  carried  into  the  parks.  There  are  a  great  number  of  bridges 
in  and  around  the  city  and  this  same  design  standard  has  been 
scaled  down  and  is  to  be  found  along  the  side  wall  of  bridges. 
Thus  there  is  a  harmonious  effect  produced  that  is  very  pleasing. 
A  contrast,  however,  has  been  made  in  Roland  Park,  an  exclusive 
suburban  section,  where  a  special  design  corner  post  has  been  de- 
veloped, supporting  a  rustic  lantern  and  also  supporting  name 
plates  for  each  street. 

The  beauty  spots  of  a  city  can  be  made  prominent  and  their 
artistic  value  greatly  enhanced  by  good  street  lighting.  This  is 
especially  true  of  the  small  squares  and  parks  to  be  found  in  any 
15 


I064     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

large  city.  The  bright  street  lighting  surrounding  the  small 
park  serves  as  a  background  against  which  the  dark  foliage  of  the 
trees  shows  up  very  strongly  in  silhouette.  Often  a  dainty  lace- 
like effect  is  obtained.  The  lights  in  the  small  park  itself  serve 
very  well  to  bring  out  the  beauty  of  well- formed  trees  or  banks 
of  shrubbery.  The  variations  of  light  and  shade  are  such  as  to 
make  the  park  of  untiring  interest. 

Mr.  H.  H.  Magdsick:  Mr.  Millar  has  shown  clearly  what 
factors  determine  the  effectiveness  of  the  illumination  in  streets 
with  characteristics  typical  of  our  main  thoroughfares.  For  such 
streets,  where  the  requirements  of  the  driver  of  a  vehicle  form 
the  major  consideration,  the  importance  of  these  factors  can 
scarcely  be  over  emphasized.  The  discussion  would  not  appear 
to  apply  with  equal  force  to  most  residence  districts,  which  con- 
tain a  large  proportion  of  the  total  mileage  of  streets  we  have  to 
light,  where  the  safety  and  convenience  of  the  pedestrian  are 
primary.  In  serving  these  the  incident  light  is  of  far  greater 
importance  than  in  the  other  class  of  streets  and  the  silhouette 
effect,  specular  reflection  from  street  surface,  etc.,  are  of  lesser 
value.  With  the  funds  now  available  for  street  lighting  in  some 
cities  a  sufficiently  high  intensity  can  be  provided  at  all  points 
on  the  street  to  meet  these  requirements  satisfactorily  when 
modern  equipment  is  employed. 

It  is  pointed  out  in  the  paper  that  a  bright  light  source  inter- 
feres with  vision  most  when  the  angle  of  separation  between  the 
lisrht  source  and  the  surface  viewed  is  small.  This  effect  is  to 
some  extent  decreased  by  mounting  the  unit  at  a  greater  height ; 
but  considerations  of  cost,  inefficiency  and  possible  obstruction 
of  light,  limit  this  method.  It  is  not  generally  recognized  that 
much  the  same  result  can  be  secured  by  the  use  of  prismatic 
refractor  equipment  so  installed  as  to  direct  the  maximum  candle- 
power  at  an  angle  of,  say,  Jo°  from  the  vertical,  with  a  con- 
siderably reduced  intensity  at  the  higher  angles,  which  are  viewed 
when  the  angle  of  separation  from  the  illuminated  surface  is 
small.  The  use  of  this  equipment  likewise  increases  the  bright- 
ness of  the  street  surface.  A  sufficient  intensity  is  still  emitted 
at  the  higher  angles  to  satisfy  the  desire  for  some  brightness  in 
the  illuminant  and  to  aid  vision  when  specularly  reflected;  how- 


THE   EFFECTIVE   ILLUMINATION    OF    STREETS  IO65 

ever,  it  should  be  borne  in  mind  that  onlv  certain  classes  of  street 


City  and  Street 


Descriptio 


Width  of 

roadway 

in  feet 


Pittsburgh,  Pa. 
Fifth  Avenue 

Pittsburgh,  Pa. 
Federal  .Street   . 

Chicago,  Illinois 
Dearborn  Street 

Rochester,  N.  Y. 
Main  Street    .   . 


Hartford,  Conn. 
Main  Street     . 

Washington.  D.  C. 
Pennsylvania,  Av 


New  York,  N.  Y. 
Fifth  Avenue. 
(25  to  58  Sts.) 

Corning,  N.  Y. 
Market  Street 


Rochester.  N.  Y. 
Lake  Avenue 


Milwaukee,  Wis. 
Grand  Avenue 


New  York,  N.  Y. 
Seventh  Ave. 
(no  to  136  Sts.) 


Chicago,  Illinois 
Troy  Street     .   .    . 

Washington,  D.  C. 
Sixteenth  Street  . 


36 
47 
42 
80 


90  ft.  bet 
bldg.  lines 

109 


92 


36 


Accessories 


<oft. 
(160  ft.  bet 
bldg.  lines) 


Bu  Medium    alabaster 
I    globes 

BuA^ba  globes 
BuAlba  globes 
BuAlabaster  globes 

Kovulux,  Form  1. 


Alfe-inch  segmented 
Alabaster  globe 
— dense  upper,  me- 
dium lower  hemi- 
sphere 

BuLight  Carrara  globes 


BuC 


R.  I.  globe  and 
translucent  glass 
reflectors 


Re  Alabaster  globes 


Light    alabaster 
Bv    globes 


A]  Special 


ventilated 
unit — light  Carrara 
globe 


R<Alba  globes 


Ra6-inch  Alba  globes 


Building 
fronts 
lighted  ? 


Yes 


Well 


ngnt  sources  are  still  visible,  although  in  many  cases  the  intrin- 
sic brilliancy  is  reduced  by  diffusing  globes.  Nevertheless,  the 
lamps  are  conspicuous,  and  I  have  yet  to  see  a  globe  which  does 


I  6  t>  41 


APPENDIX 


:.  Street 


^Hftmrgh.  Pa. 
^^Btb  Avenue 

^^■■rgh. 
^^hl  Street 

^^■go.  Illinois 
^^^Eborn  Street 

^^^K  Street    .   . 


^^^■rd.  Conn. 

f  Main  Street     .    . 

Washington.  D.  C. 
Pennsylvania,  Av 


^Vork.  X.  Y. 
Tnne. 

Corning.  X.  Y. 
-ket  Street 


Ro  -ester.  N".  Y. 
Lake  Avenue 

■Uiraukee.  Wis. 
^^■and  Avenue 


Mew  York.  K.  Y. 
^Berenth  Ave. 

to  136  Sts.) 


^■Ingo.  Illinois 


Description  of  Street 


Width  of 

n  adway 

in  feet 


Kind  of  buildings 


36 
47 

42 
-.0 


90  ft.  bet 
bldg.  lines 

109 


Business  structures 
Business  structures 
Business  structures 
Business  structures 

All  kinds 


60  Business  structures 


Business  structures 


50 
92 

So 

5fi 


soft. 
'160  ft.  bet 
bldg.  lines). 


Residences 


Business  structures 


Apartment  build- 
ings 


Residences 


Residences 


Installation 


No.  of 
lighting  units 


50 

90 


Approx.  82 
(twin  lamp) 

123 


200  (2  per  post) 


56 


79 


246 


Linear  spacing 

if  feet 
along  one  curb 


Approx.  80 
69 
94 


400 
92 


Height 
in  feet 


18 

24 

25 

14  ft.    6  in. 

14 
15 

19 
13  ft.    6  in. 

17  ft.    6  in. 
19  ft.  10  in. 


10  ft.    3  in. 


Location 


Both  curbs -opposite 

Both  curbs— staggered 

Both  curbs— staggered 

Both  curbs— o  p  p  o  s  i  t  e, 
main  section-staggered 
outside. 

Both  curbs— staggered 
Both  curbs— staggered 

Both  curbs— staggered 

Both  curbs— opposite 

Both  curbs — staggered 
Both  curbs— opposite 


In  center  of  block  (on 
center  isle)  On  curb  of 
intersecting  streets  at 
house  line  of  cross  street 
intersection 

East  curb  only 


Both  curbs — staggered 


Kind  of  mount 


Brackets  on 
trolley  poles 

Ornamental  posts 
Ornamental  posts 
Ornamental  posts 


Twin  lamp  orna- 
mental posts 

Ornamental  posts 


Twin  lamp  orna- 
mental posts 


Ornamental  posts 

Ornamental  posts 

Bracket  on 
trolley  pole 

Ornamental  posts 


Ornamental  posts 


Lamps 


6.6-amp.  d-c.    ornamental 
luminous  arc 

a-c.  series  flame  arc  white 
electrodes 

a-c.  series  flame  arc  lamps 


6.6-amp.    inverted    magne 
tite 


600-cp.  mazda  C. 


6.6-amp.  inverted  magne- 
tite— stand,  elect. 


120-volt,  400-watt  multiple 
mazda  C. 


400-cp.,  15-amp.  mazda  C. 


1000-cp.  mazda  C. 


4.0-amp.  d-c.  series  orna- 
mental luminous  arc — 
long  life  electrodes 

120-volt,  aoo-watt  multi- 
tiple  mazda  C. 


600-cp.  mazda  C. 


5.5-amp.   series  mazda   C. 
approx.  75  watts 


Accessories 


Medium    alabaster 
globes 

Alba  globes 
Alba  globes 
Alabaster  globes 

Novulux,  Form  1. 


23-inch  segmented 
Alabaster  globe 
— dense  upper,  me- 
dium lower  hemi- 
sphere 

Light  Carrara  globes 


C.  R.  I.  globe  and 
translucent  glass 
reflectors 

Alabaster  globes 


Light    alabaster 
globes 


Special  ventilated 
unit — light  Carrara 
globe 


Alba  globes 
ih-inch  Alba  globes 


Building 
lighted! 


Yes 


7a 


Well 


Yes 


THE   EFFECTIVE   ILLUMINATION   OF   STREETS  1065 

ever,  it  should  be  borne  in  mind  that  only  certain  classes  of  street 
surfaces  reflect  specularly  to  any  considerable  extent.  A  study 
of  the  streets  in  many  large  and  small  cities  has  shown  that  this 
is  a  negligible  factor  in  the  illumination  of  a  large  proportion  of 
the  total. 

In  Table  II  the  average  life  of  series  mazda  C  lamps  under 
correct  operating  conditions  is  given  as  1000  hours.  It  may  be 
noted  that  while  the  manufacturers  have  made  guarantees  on 
this  basis  to  cover  a  large  range  of  street  lighting  circuits  and 
operating  conditions,  the  actual  performance  in  service  as  re- 
ported in  the  technical  press  and  at  a  convention  of  electrical 
associations  shows  that  the  manufacturers'  rated  life  of  1350  is 
conservative. 

Mr.  W.  H.  Pratt  :  There  is  an  observation  which  I  have 
made,  and  which  has  rather  been  thrust  upon  me  in  reference  to 
street  lighting,  which  I  would  like  to  offer  for  what  it  is  worth. 
There  is  a  strip  of  boulevard,  some  four  or  five  miles  long,  over 
which  I  frequently  drive  in  the  evening,  and  it  is  illuminated  so 
that  it  works  satisfactorily,  so  far  as  the  visibility  of  objects  on 
the  road  are  concerned.  The  sources  of  illumination  are  mod- 
erate sized  units,  spaced  very  regularly.  I  find  that  when  some- 
what tired,  especially  when  driving  over  this  road,  there  is  a 
very  painful  effect  due  apparently  to  the  very  regular  passage  of 
sources  of  light  before  the  eyes.  I  wonder  if  this  might  not  be  a 
factor  at  times  to  be  considered  in  determining  whether  large  or 
small  units  shall  be  used.  The  effect  is  very  noticeable  and  some- 
times is  really  extremely  painful.  I  can  easily  understand  how 
under  the  circumstances  a  driver  might  be  led  to  make  serious 
mistakes  from  that  cause.  It  has  a  somewhat  hypnotic  effect, 
definitely  associated  with  the  very  regular  passage  at  rather  fre- 
quent intervals  of  the  light  sources  through  the  field  of  vision. 

Dr.  John  B.  Whitehead:  We  have  been  shown  in  very  con- 
vincing and  beautiful  fashion  the  importance  of  specular  reflec- 
tion and  the  value  of  a  highly  reflecting  surface  in  streets  and 
roadways.  I  notice  in  all  the  pictures  and  in  the  model  that  the 
light  sources  are  still  visible,  although  in  many  cases  the  intrin- 
sic brilliancy  is  reduced  by  diffusing  globes.  Nevertheless,  the 
lamps  are  conspicuous,  and  I  have  yet  to  see  a  globe  which  does 


1066     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

not  in  some  measure  give  the  disagreeable  impressions  generally 
associated  with  glare.  I  remember  also  that  when  Mr.  Millar 
showed  us  a  lantern  slide  in  which  an  attempt  was  made  to 
illuminate  a  road  with  concealed  sources,  the  slide  indicated  that 
the  result  was  an  extremely  poor  one  and  not  to  be  compared 
with  that  which  had  been  obtained  by  these  methods  which  he 
endorses.  The  question  arises,  as  to  whether  the  distribution 
curves  of  various  reflectors  which  conceal  the  source  completely 
have  been  studied  in  their  relation  to  the  angle  of  incidence  of 
the  light  upon  the  road  surface.  In  other  words,  would  it  not 
be  possible  to  get  a  considerable  amount  of  scattered  reflection 
at  high  angles  of  incidence? 

Mr.  Peter  Junkersfeld  :  Most  of  our  discussion  this  evening 
has  been  on  the  illumination  of  streets,  largely  from  the  viewpoint 
of  the  pedestrian  on  the  street,  or  the  people  using  automobiles  on 
the  street,  or  the  general  illumination  of  the  street.  There  is 
one  other  party  whose  interest  should  be  considered,  and  that  is 
the  resident  along  the  street,  and  particularly  the  resident  whose 
home  is  opposite  some  of  these  high  candlepower  lamps.  I  have 
in  mind  an  installation  of  3,000  or  4,000,  600- candlepower  type  C 
mazda  lamps  in  Chicago,  installed  under  the  direction  of  Mr.  Ray 
Palmer.  That  system  of  lamps  was  installed  on  tubular  iron 
poles,  using  tubular  iron  poles  also  between  the  poles  supporting 
the  arc  lamps,  and  the  lighting  is  very  satisfactory  from  the  stand- 
point of  street  illumination.  A  great  many  complaints,  however, 
have  arisen  from  residents  on  the  street.  These  high  candle- 
power  lamps  shine  into  the  second  and  third  story  windows, 
particularly  in  the  summer  time,  when  people  do  not  want  their 
shades  down,  but  want  them  part  way  up,  so  that  they  can  get 
as  much  air  as  possible,  and  it  is  quite  objectionable  from  their 
standpoint.  Many  complaints  have  come  in  and  in  some  places 
the  residences  along  the  street  have  taken  matters  into  their  own 
hands  and  painted  the  sides  of  the  globes.  It  finally  resulted  in 
the  passage  of  an  ordinance  under  which  any  resident  along  the 
street  may  have  a  special  shade  put  on  the  lamp  by  paying  $2 
per  lamp  and  $1  per  year  in  advance  for  the  maintenance  of  the 
shade.  It  probably  is  not  sufficient  to  cover  the  cost,  but  serves 
as  a  deterrent  against  unnecessary  shading.  The  lamps  are 
mounted  on  poles,  25  ft.  (7.62  m.)  above  the  surface  of  the  street. 


THE   EFFECTIVE   ILLUMINATION   OF   STREETS  I067 

In  other  sections  of  the  city  where  wires  are  put  under  ground 
by  common  consent  the  small  unit  lamps  on  low  poles,  10  or  12  ft. 
(3.04  or  3.65  m.)  high,  have  been  installed,  and  that  system,  from 
the  point  of  view  of  the  residents,  is  very  much  more  satisfactory 
and  at  the  same  time  gives  very  good  street  illumination. 

I  would  add  a  word  to  what  Mr.  Stickney  said  and  possibly 
also  to  what  Prof.  Jackson  said,  and  that  is,  after  all,  this  whole 
matter  of  street  lighting  must  be  a  matter  of  compromise.  There 
are  many  other  things  which  are  to  be  considered  besides  illumin- 
ation. The  staggering  of  lamps  improves  the  illumination  in 
many  cases.  That  means,  however,  considerable  increase  in  cost 
in  installation,  whether  the  wires  are  overhead  or  underground, 
because  the  wires  must  cross  back  and  forth  across  the  street, 
or  else  there  will  have  to  be  two  lines  of  poles.  There  are  a 
great  many  other  factors  of  that  kind  that  must  be  taken  into 
consideration  in  every  individual  system. 

Mr.  Allen  T.  Baldwin  :  In  the  author's  paper,  in  the  para- 
graph entitled  "Power  of  Lighting  Units,"  reference  is  made  to 
the  depreciation  in  candlepower  of  the  flame  arc  and  multiple 
mazda  lamps.  A  depreciation  of  20  to  25  per  cent,  is  claimed  for 
each  unit  mentioned.  Insofar  as  the  enclosed  type  of  flame  arc 
lamp  is  concerned,  we  have  found  at  our  laboratories  that  15  to 
20  per  cent,  is  the  average  depreciation  when  measured  as  the 
part  of  the  total  light  flux  that  is  lost  through  absorption  by 
dirty  glassware.  For  white  flame  carbons  the  lower  value  is 
nearer  the  true  average. 

The  light  absorption  arises  from  two  causes:  the  etching  of 
the  globe  and  the  adherence  to  the  globe  of  deposits  from  the 
arc.  The  loss  of  light  as  the  result  of  etching  is  the  smaller  loss 
of  the  two.  It  will  probably  not  exceed  5  to  10  per  cent.,  and  a 
test  recently  completed  on  a  globe  that  had  been  in  service  over 
700  hours  showed  that  it  was  capable  of  transmitting  96  per  cent, 
of  the  light  transmitted  by  such  globes.  The  test  was  made  in 
such  a  way  that  this  loss  was  that  known  to  be  due  to  etching 
alone.  Studies  have  shown  that  the  etching  and  deposits  are 
least  in  that  part  of  the  globe  where  it  is  desirable  to  have  the 
best  light  transmission.  At  the  end  of  the  trim  life  the  loss  at 
8o°  from  the  vertical  is  approximately  5  per  cent.,  while  at  io° 
from  the  vertical  the  loss  approaches  40  per  cent,  or  more. 


1068    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

A  comparison  of  the  distribution  curves  of  the  lamp  at  the 
beginning  and  end  of  the  life  will  show  that  the  distribution  has 
been  changed  in  a  beneficial  way.  The  deposit  in  the  bottom  of 
the  globe  acts  as  a  reflecting  surface  and  extends  the  values  along 
the  horizontal  at  the  expense  of  the  light  directly  along  the 
vertical.  These  facts  point  out  that  the  candlepower  deprecia- 
tion is  best  determined  as  the  loss  of  total  light  flux  rather  than 
that  in  any  given  direction.  In  reality  the  increase  in  efficiency 
of  the  lamps  gained  by  eliminating  globe  etching  and  deposit 
would  hardly  be  enough  to  warrant  more  than  passing  attention. 

In  connection  with  this  subject  it  is  interesting  to  note  that  it 
seems  to  be  an  inherent  tendency  of  white  flame  carbons  to  give 
an  increase  in  candlepower  as  they  are  consumed,  but  not  to  a 
sufficient  extent  to  counteract  the  losses  just  referred  to. 

Mr.  L.  D.  Nordstrum  :  The  point  Mr.  Jackson  brought  up  in 
regard  to  the  difference  in  illumination  which  might  come  about 
when  different  types  of  lamps  were  used,  I  have  had  brought  to 
my  attention  several  times  in  the  fact  that  we  have  two  different 
installations  in  Fort  Wayne,  practically  a  duplicate  form  of 
installation  outside  of  the  light  sources  used.  The  old  lighting 
system  used  the  usual  type  of  single  unit  placed  on  street  corners, 
usually  in  the  center  of  the  street.  Some  two  miles  of  the  main 
streets  were  changed  over  to  what  we  called  ornamental  lighting. 
The  poles  were  placed  on  the  curbs  on  each  side  of  the  street  and 
staggered.  They  carried  a  double  crossarm  with  a  lamp  on  each 
end  and  a  fifth  lamp  in  the  center  of  the  pole  with  ioo-watt 
mazda  lamps  in  each  globe.  This  had  been  installed  about  a 
year,  and  then  for  about  the  same  distance  a  new  form  of  light- 
ing was  carried  out,  the  same  method  of  pole  installation,  and 
poles  about  the  same  height,  in  which  we  used  4-ampere  magnetite 
lamps.  I  think  that  everybody  is  agreed  that  the  magnetite 
installation  gives  much  better  illumination.  Something  like  seven 
or  eight  months  ago  we  had  in  the  evening  a  very  dense  fog. 
These  two  installations  happen  to  be  along  the  same  street,  so  that 
they  could  be  compared,  and  in  this  dense  fog  the  light  from  the 
mazda  lamps  seemed  to  be  entirely  blotted  out.  One  could  see 
the  mazda  lamps  about  a  block  away.  Going  down  that  portion 
of  the  street  having  the  magnetite  installation  one  could  see 


THE  EFFECTIVE   ILLUMINATION   OF   STREETS  1069 

the  magnetite  lamps  strung  out  along  the  street  a  fairly  good 
distance  away,  for  several  blocks,  at  least ;  whereas  with  the  par- 
tially yellow  light  from  the  mazda  lamps  the  illumination  was 
not  nearly  so  effective. 

Mr.  J.  D.  Mortimer  "(By  letter):  Skill  in  the  design  and 
application  of  equipment  for  the  illumination  of  streets  has  not 
progressed  as  rapidly  as  has  the  design  of  illumination  for  build- 
ing interiors.  Attention  to  this  branch  of  engineering  has  been 
spasmodic.  With  the  many  interests  involved,  the  practical  de- 
sign of  a  system  of  street  lighting  requires  many  more  comprom- 
ises between  scientific  principles,  politics  and  finances  than  usually 
occur  in  other  engineering  undertakings.  Where  the  relative 
importance  of  the  different  factors  measuring  the  effectiveness 
of  street  illumination  is  still  in  dispute,  it  is  not  surprising  that 
every  engineer  possessed  of  a  street  lighting  client,  differs  from  all 
other  engineers.  It  is  hoped  that  Mr.  Millar's  analysis  will  ma- 
terially assist  in  reconciling  the  less  important  differences  and 
concentrate  future  discussion  on  the  remaining  few  but  important 
factors. 

Efficiency  and  size  of  lighting  equipment,  character  of  distribu- 
tion of  illumination,  intensity,  street  surfaces,  glare,  spacing, 
mounting  height  and  appearance,  are  all  of  importance  in  the 
design  of  a  street  lighting  system.  They  all  have  some  bearing 
on  the  ideal  scheme.  No  design  can  be  said  to  be  completed  until 
it  is  known  what  the  annual  costs  of  operation  will  be.  Assum- 
ing that  the  ideal  plan  can  be  laid  down,  the  question  arises,  are 
the  improvements  worth  the  cost?  The  increment  cost  of  small 
improvements  in  illumination  should  not  exceed  their  value. 
Value  depends  upon  time,  place  and  the  state  of  public  opinion. 
There  will  be  fashions  in  street  lighting  as  there  are  in  archi- 
tecture, street  cars,  politics,  and  hats.  Fashion  alone  will  con- 
demn as  obsolete  any  system  installed  to-day  long  before  it  has 
served  its  mechanically  useful  life.  This  fact  has  a  bearing  on 
extent  to  which  effective  illuminating  value  may  be  created  by 
additional  costs.  The  costs  may  be  added  for  a  period  of  several 
years  and  the  value  rapidly  depreciate  after  its  novelty  has  worn 
off.  The  financial  factor  in  a  subject  as  commercial  as  street 
lighting,  is  yet  one  of  the  most  important,  and  no  study  can  be 


IO7O    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

said  to  approach  completeness  that  does  not  incorporate  the 
monetary  aspects  as  an  essential  part. 

Mr.  F.  C.  Piatt  (By  letter):  Mr.  Millar  calls  attention  to 
three  means  by  which  street  lighting  can  be  improved,  ( I )  larger 
municipal  appropriations;  (2)  more  efficient  lamps  and  access- 
ories; (3)  greater  skill  in  application.  To  this  list  I  would  add  a 
fourth  item  which  is  extremely  important,  even  more  so  than  the 
obtaining  of  more  efficient  lamps :  this  is  to  procure  lamps  and  ac- 
cessories having  a  lower  first  cost  and  lower  cost  of  operation. 

For  the  ordinary  magnetite  or  carbon  arc  or  large  size  type  C 
mazda  lamp  the  cost  of  energy  amounts  to  about  25  per  cent,  of 
the  total  cost  of  service  (including  interest,  depreciation,  etc.^ 
while  the  fixed  charges  and  operating  expenses  comprise  the  re- 
maining 75  per  cent.  Hence  it  is  evident  that  if  a  10  per  cent, 
reduction  in  first  cost  and  operating  expense  can  be  made,  the 
total  cost  will  be  lowered  as  much  as  by  a  30  per  cent,  improve- 
ment in  efficiency. 

The  mazda  series  lamp  has  made  rapid  progress  in  spite  of  the 
existence  of  the  magnetite  arc  largely  because  the  cost  of  the 
lamp  and  reflector  is  much  lower  than  the  arc  lamp.  Also  the 
constant  current  transformer  is  much  cheaper  than  the  magnetite 
rectifier. 

In  regard  to  the  question  of  large  versus  small  illuminants,  it 
may  be  of  interest  to  see  exactly  what  the  effect  is  from  a  cost 
standpoint  if  the  size  of  the  units  is  varied.  The  only  system  in 
which  the  size  of  units  can  be  practically  varied  is  that  using 
mazda  series  lamps,  as  with  the  arc  lamps  the  only  variation  is 
from  large  to  larger  candlepower,  no  small  units  being  available. 

The  most  valid  argument  against  wide  spacing  of  lamps  is  the 
practical  necessity  where  blocks  are  short  of  locating  a  lamp  at 
least  at  every  street  intersection  to  serve  as  a  marker  as  well 
as  to  supply  some  illumination  along  every  road  traversed. 
Crooked,  and  tree  lined  roads  also  call  for  closer  spacing  and 
smaller  units. 

In  Mr.  Millar's  paper  considerable  attention  is  given  to  the 
question  of  lighting  for  motorists  particularly  on  suburban  roads. 
I  do  not  see  that  the  motorist  should  be  given  much  consideration 
except  to  so  place  the  street  lamps  as  to  avoid  serious  glare,  and 
to  insure  that  road  intersections  are  well  marked.    The  headlights 


THE  EFFECTIVE  ILLUMINATION   OF  STREETS  IO7I 

of  a  motor  car  are  much  better  for  showing  road  irregularities 
than  any  lighting  system  could  possibly  be,  due  to  the  shadows 
obtained  from  the  lights  close  to  the  ground. 

The  principal  object  in  lighting  suburban  roads  to  my  mind  is 
to  insure  safety  to  the  pedestrian  or  other  traveler  without  light. 
This  also  applies  largely  to  the  lighting  of  city  streets,  where  the 
more  pleasing  effect  and  better  conditions  for  pedestrians  secured 
by  curb  lighting  seem  more  important  than  the  lack  of  specular 
reflection  which  might  aid  the  motorist. 

Mr.  Preston  S.  Millar  (In  reply)  :  Prof.  Jackson  has  em- 
phasized the  possibilities  of  further  intensive  study  and  develop- 
ment in  the  illumination  field.  His  point  appears  to  be  well 
taken.  Those  who  have  visited  the  Exposition  at  San  Francisco 
have  derived  a  great  deal  of  inspiration  in  this  connection. 

Replying  to  the  question  regarding  the  measurement  of  effec- 
tive brightness,  it  should  be  stated  that  the  measurements  were 
made  about  five  years  ago  and  were  rather  crude.  After  a  few 
trials,  we  determined  the  usual  angle  of  an  automobilist's  view 
of  the  street  surface,  arriving,  if  my  recollection  is  correct,  at  2° 
as  a  typical  angle.  With  a  photometer  we  then  measured  the 
brightness  of  arbitrarily  selected  patches  of  street  surface  at  such 
angle. 

Due  to  the  great  increase  in  automobile  traffic  during  these 
past  five  years  and  to  the  more  general  adoption  of  modern 
pavements,  the  departure  of  the  brightness  curve  from  the  curve 
of  incident  light  is  probably  now  greater  than  was  found  to  be 
typical  five  years  ago. 

Mr.  Moulton  has  shown  that  the  prismatic  refractors  employed 
in  Baltimore  are  so  bright  as  to  spoil  the  photographic  effect 
by  reason  of  excessive  halations.  It  would  appear  to  be  proper 
to  ask  if  these  refractors  are  not  also  so  bright  as  to  spoil  the 
illuminating  effect.  In  one  of  the  views  which  he  has  shown 
there  is  an  illustration  of  the  lighting  of  a  public  building  by 
magnetite  lamps  along  the  curb.  It  is  to  be  observed  that  the 
lower  stories  of  the  building  were  lighted  nicely,  but  the  upper 
stories  were  not  well  lighted.  If  these  lamps  could  be  moved 
across  the  street  from  the  building,  securing  a  greater  distance 
and  a  better  angle  of  incident  light,  the  general  lighting  of  the 
front  of  the  building  would  probably  be  better. 


IO/2     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Mr.  Magdsick  has  dwelt  upon  the  point  of  view  of  the  pedes- 
trian as  opposed  to  that  of  the  automobilist.  I  am  not  sure 
that  these  viewpoints  are  essentially  different.  In  the  proposed 
lighting  of  a  Cleveland  street  which  he  has  described,  I  think 
we  arrive  at  that  class  referred  to  in  the  paper  in  which  esthetic 
considerations  are  of  first  importance.  In  such  problems  most 
of  the  questions  discussed  in  the  paper  are  of  relatively  less 
importance  because  there  is  so  much  light  available  that  appli- 
cation to  secure  the  best  visibility  is  unnecessary. 

Dr.  Whitehead  has  suggested  that  it  might  be  possible  to 
obtain  the  advantages  which  come  with  specular  reflection  from 
street  surface  and  still  avoid  all  glare  effect.  I  think  he  will 
find  that  in  cases  where  we  have  to  take  advantage  of  specular 
reflection  the  spacings  are  so  great  that  light  must  be  allowed 
to  emanate  from  the  lamp  at  such  a  high  angle  that  it  will  pro- 
duce some  glare.  When  the  spacing  is  so  short  that  the  glare 
effect  can  be  suppressed,  there  is  so  much  light  that  ordinary 
exposure  of  lamps  in  diffusing  glassware  does  not  produce  much 
glare.  The  work  of  Mr.  A.  J.  Sweet  may  be  consulted  with 
profit  in  this  connection. 

Mr.  Junkersfeld's  citation  of  objection  on  the  part  of  residents 
to  light  on  the  uoper  stories  of  houses  is  mentioned  in  the  paper 
as  well. 

Mr.  Baldwin  implies  that  the  depreciation  during  life  shown 
for  flame  arc  lamps  is  a  bit  too  high.  We  have  received  criticisms 
from  others  that  it  is  a  trifle  too  low.  If  we  may  be  permitted 
to  average  these  criticisms,  we  will  conclude  that  the  figures 
shown  in  the  paper  are  probably  substantially  typical. 

Mr.  Mortimer's  discussion  emphasizes  the  monetary  aspects 
of  street  lighting  as  fundamentally  important.  To  this  no  ex- 
ception can  be  taken.  They  are  of  transcending  importance.  He 
states  that  the  increment  cost  of  small  improvements  in  illumina- 
tion should  not  exceed  their  value.  "Value  depends  upon  time, 
place  and  state  of  public  opinion."  I  like  to  think  that  it  is  ap- 
praisal rather  than  value  that  depends  upon  time,  place  and  state 
of  public  opinion.  For  the  value  of  an  improvement  it  seems  to 
me  is  measured  in  the  added  effectiveness  of  the  lighting.  Again, 
I  like  to  think  that  it  is  the  opinion  of  public  representatives  rather 


THE   EFFECTIVE   ILLUMINATION   OF   STREETS  IO/3 

than  public  opinion  which  determines  the  appraisal.  Discussions 
of  this  kind  should  promote  ultimate  consensus  regarding  ef- 
fectiveness and  should  hasten  the  time  when  appraisal  of  street 
lighting  values  by  public  representatives  and  public  utility  repre- 
sentatives will  be  in  agreement. 

Mr.  Piatt  deprecates  the  consideration  given  in  the  paper  to  the 
requirements  of  automobilists,  stating  that  headlights  furnish  the 
best  lighting  for  his  purposes  and  that  therefore  street  lighting  in 
suburban  roads  should  be  designed  principally  for  the  purposes  of 
pedestrians.  Within  the  city  limits  of  some  large  cities  the  em- 
ployment of  headlights  is  not  permitted.  It  is  preferable  to  avoid 
the  use  of  headlights  in  much  traveled  streets,  and  it  is  entirely 
practicable  to  do  so  if  the  street  lighting  is  reasonably  effective. 
Investigation  has  shown  that  large  differences  in  the  effectiveness 
of  street  lighting  do  not  interfere  seriously  with  the  progress  or 
safety  of  the  pedestrian.  They  do  affect  the  motorist  seriously. 
The  motorist's  requirements  are  most  difficult  to  meet  and  as  the 
result  of  failing  to  meet  them  is  likely  to  be  very  disastrous,  the 
lighting  of  suburban  roads  should  be  designed  largely  with  his 
requirements  in  view. 

Mr.  Charles  F.  Lacombe  (By  letter)  :  Mr.  Millar's  paper 
takes  up  the  factors  necessary  for  the  improvement  of  street 
lighting,  the  first  two  of  which  have  been  long  hoped  for  and 
much  discussed,  while  the  third  describes  the  variable  factors 
which,  while  known  to  those  who  have  worked  on  the  streets  in 
designing  street  lighting,  have  not  been  so  carefully  described  and 
analyzed  before. 

Municipal  appropriations,  of  course,  limit  the  extent  and  quan- 
tity of  illumination  that  can  be  obtained.  As  this  item  of  a  city's 
expenditures  increases  with  its  growth  and  develops  increased 
business  with  load  characteristics  favorable  to  the  producer,  the 
city  is  entitled  to  a  fair  share  of  the  increased  efficiency  of  the 
light  sources  used  without  additional  expense.  A  liberal  policy 
of  this  kind  on  the  part  of  the  contracting  company,  with  reason- 
able appropriations  and  a  fair  length  of  contract  on  the  city's 
part,  would  go  far  towards  the  improvement  of  street  lighting  in 
the  United  States.  If  a  city  were  shown  what  could  be  done  in 
increasing  the  illumination  by  the  use  of  the  recent  highly  efficient 
lamps  for  about  the  same  amount  of  energy,  there  is  little  doubt 


1074    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

that  a  term  contract  could  be  obtained  justifying  the  expense  of 
changed  equipment  and  a  considerable  volume  of  increased  busi- 
ness would  ultimately  result  from  the  extension  of  the  improved 
illumination  so  exhibited. 

Speaking  comparatively  the  more  efficient  lamps  and  accessories 
have  arrived.  The  improved  flaming  and  luminous  arc  lamps  and 
the  gas-filled  tungsten  lamp  give  the  illuminating  engineer  light- 
ing appliances  of  wide  range  that  he  has  never  had  before  in  such 
completeness.  This  is  due  to  the  adaptability  of  the  present 
lamps  to  all  grades  of  illumination  desired,  largely  resulting  from 
the  divisibility  of  the  series  gas-filled  and  multiple  vacuum  tung- 
sten lamps  throughout  the  lower  ranges  of  intensity.  A  few 
years  ago  we  had  to  work  with  only  the  indivisible  arc  lamp  sup- 
plemented by  the  inefficient  carbon  incandescent  lamp;  the 
present  range  of  resources  in  new  and  improved  lighting  units 
should  prove  a  great  incentive  to  the  spread  of  good  illumination 
on  streets. 

It  is  worth  while  to  call  attention  to  the  availability  of  the  60, 
80  and  100-candlepower  series,  gas-filled  and  vacuum  multiple 
lamps  for  street  lighting  on  several  classes  listed  by  Mr.  Millar. 
My  remarks  on  this  are  based  on  prices  prevailing  in  New  York 
city  recently.  In  these  smaller  sizes  of  the  tungsten  lamp,  we 
now  have  new  units  of  an  efficiency  which  can  be  economically 
used  to  replace  enclosed  arc  lamps  or  gas  lamps  on  residence  or 
similar  streets.  Such  lamps  may  be  used  to  advantage  on  streets 
of  classes  2b  and  3a  and  are  also  available  in  many  cases  for 
classes  2a  and  3b. 

By  choosing  the  proper  sizes  for  a  given  height  and  spacing, 
excellent  results  can  be  obtained.  With  a  reasonable  height,  say 
14  to  16  ft.  (4.26  to  4.87  m.),  using  good  sized,  white,  slightly 
inclined  reflectors  and  carefully  arranging  the  reflector,  lamp  and 
socket  so  that  the  light  source  is  well  up  towards  and  in  proper 
focus  with  the  reflector,  glare  can  be  diminished.  This  is  partic- 
ularly important  in  the  use  of  gas-filled  series  lamps.  Another 
form  of  reflector  can  be  used  to  keep  the  direct  rays  of  the  light 
from  the  stoops  or  windows  of  houses.  In  fact  the  line  of  direct 
illumination  can  be  controlled  as  to  height  within  reasonable 
limits. 

The  use  of  two,  three  or  four  of  these  lamps  within  the  old 


THE  EFFECTIVE  ILLUMINATION   OF  STREETS  10/5 

spacings  for  enclosed  arc  lamps  can  usually  be  accomplished  at 
a  slightly  less  annual  cost  and  improve  the  lighting  without  sac- 
rificing the  unidirectional  effect  which  the  tests  made  under  Mr. 
Millar's  direction  for  the  National  Electric  Light  Association  and 
the  Association  of  Edison  Illuminating  Companies  have  shown 
to  be  quite  important.  When  gas  lamps  can  be  replaced  by  series 
gas-filled  tungsten  lamps  on  line  and  lamp  poles,  the  annual  cost 
is  decreased  with  a  large  gain  in  illumination.  On  city  streets 
with  underground  service  several  methods  of  installation  can  be 
utilized  either  with  new  or  old  equipment  which  will  give  in- 
creased illumination  at  a  less  annual  cost  per  candle  and  at  an 
equal  or  slightly  increased  cost  of  installation,  compared  with  the 
cost  of  old  equipment,  depending  on  the  economy  of  construction. 

An  installation  of  this  kind  as  generally  described,  using  over- 
head construction,  was  made  by  the  writer  about  a  year  ago  and 
afterward  largely  used  in  New  York  city.  In  this  case  ioo-can- 
dlepower  gas-filled  lamps  at  a  height  of  14  ft.  6  in.  (4.44  m.) 
from  the  road  and  spaced  120  ft.  (36.57  m.)  apart  using  white 
enameled  reflectors  (slightly  inclined)  gave  in  minimum  foot- 
candles,  measured  on  a  horizontal  plane  near  the  street  surface, 
0.0146;  maximum  0.551  and  average  of  about  0.071,  over  a  street 
and  side  walk  46  ft.  (14.02  m.)  wide.  It  proved  very  satisfactory 
for  a  3a  street,  much  more  so  than  series  enclosed  6.6-ampere 
carbon  lamps  and  at  a  slightly  smaller  expense.  The  lamps  in  this 
case  were  placed  on  one  side  of  the  street  only.  In  other  cases  the 
lamps  were  placed  on  both  sides  and  staggered,  the  spacing  being 
from  85  to  150  ft.  (25.90  to  45.72  m.)  apart  along  the  curb,  and 
very  satisfactory  results  were  obtained.  The  lamps  were 
mounted  on  line  poles.  Wherever  these  arrangements  were 
used  on  2b  and  3a  streets  they  were  preferred  by  the  inhabitants 
to  enclosed  carbon  arc  lamps.  They  also  proved  satisfactory  on 
many  suburban  boulevards  or  thoroughfares  designated  as  3b  in 
the  paper  under  discussion,  and  over  fifteen  thousand  of  these 
small  lamps  are  now  in  use  in  New  York. 

Medium  sized  gas-filled  lamps  are  available  for  all  grades  of 
lb,  2a  and  3b  streets  for  all  kinds  of  spacing  and  mounting 
heights,  which  are  usually  found  already  fixed.  These  lamps 
must  be  carefully  selected  as  to  intensity  for  spacing  and  height 
and  used  with  proper  diffusing  globes  or  prismatic  reflectors  as 


IO76    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

may  be  needed  in  each  case.  In  these  grades  of  streets  and 
working  into  class  ia  streets,  luminous  flame  arc  lamps  are  avail- 
able and  even  more  effective  than  the  largest  sized  gas-filled  lamps. 
The  luminous  arc  lamps  are  particularly  desirable  when  their  full 
illuminating  efficiency  can  be  utilized.  These  more  powerful 
lamps  at  considerable  heights  would  also  be  used  for  the  lighting 
of  great  squares,  plazas  or  irregular  spaces  at  diagonal  inter- 
sections of  important  streets. 

With  this  great  range  of  light  sources,  admitting  of  many  and 
accurate  gradations  in  the  lighting  of  various  streets,  it  would 
seem  that  we  might  fairly  begin  to  give  an  average  and  minimum 
scale  of  the  illumination  required  on  streets  where  silhouette  or 
contrast  lighting  is  not  sufficient  but  where  direct  illumination, 
more  or  less  powerful,  becomes  necessary  as  on  ia  and  ib  streets, 
particularly,  and  in  some  cases  on  2a  and  3b  streets,  where  rapid 
and  frequent  motor  traffic  exists.  Such  a  standard  would  be 
of  great  value  for  safety,  as  a  gauge  of  responsibility  in  accident 
cases,  and  as  a  standard  to  which  engineers  may  work  safely. 
It  would  tend  to  so  standardize  the  lighting  of  streets  that  there 
need  be  less  changing  of  equipment  and  less  interference  with  a 
properly  designed  lighting  scheme  by  the  idiosyncrasies  of  chang- 
ing municipal  administrations.  A  standard  of  this  kind  was  de- 
scribed by  Dr.  Bell  in  his  Johns  Hopkins  lectures*  at  Baltimore, 
and  is  seen  abroad  in  the  high  minimum  standards  of  important 
streets  set  by  English  and  German  engineers. 

Mr.  Millar  in  his  paper  and  Mr.  Sweet  in  another,  have  given 
valuable  data  and  recommendations  as  to  the  avoidance  of  glare. 
These  must  be  carefully  borne  in  mind  with  the  newer  forms  of 
lamps.  In  my  experience,  lamps  of  100  scp.  or  under  do  not 
give  a  sufficient  quantity  of  light  to  avoid  glare  by  diffusing  globes 
in  commercial  street  lighting  installations.  In  other  words,  the 
amount  of  light  absorbed  is  too  great  in  comparison  with  the  whole 
to  be  economical.  This  is  borne  out  by  the  results  of  careful  tests 
in  New  York  city  with  both  series  and  multiple  lamps.  This 
should  be  borne  in  mind,  particularly,  with  the  gas-filled  lamp  with 
its  small  light  source  of  great  intensity,  and  glare  should  be  taken 
care  of  by  height,  good  sized  white  reflectors,  and  careful  ad- 

*  Lectures  on  Illuminating  Engineering,  (1910). 


THE   EFFECTIVE   ILLUMINATION   OF   STREETS  IO77 

justment  of  the  position  of  the  small  light  source  and  the  re- 
flector. The  general  practise  in  this  country  is  to  hang  the  lamps 
too  law,  and  Mr.  Millar's  observations  on  height  seem  to  bear 
this  out.  While  the  costs  of  higher  iron  ornamental  posts  for 
city  use  would  be  more  expensive,  such  an  installation  using  bare 
lamps  with  well  designed  good  sized  reflectors  would  be  more 
economical  in  watts  per  candle  output.  The  element  of  cost  in 
this  regard  does  not  exist  where  lamps  are  suspended  from  or  set 
on  the  poles  of  overhead  lines.  In  my  opinion,  improved  results 
would  follow  placing  the  newer  types  of  lamps  in  such  cases 
higher  than  formerly  and  dispensing  with  diffusing  globes.  The 
English  and  German  practise  follows  this  idea  in  both  large  and 
small  units  and  it  must  be  said  that  glare  is  not  offensive  in  those 
installations  which  use  bare  lamps  and  reflectors,  or  with  flame 
lamps  with  slightly  cloudy  globes  or  refractors,  placed  at  heights 
of  24  to  30  ft.  (7.31  to  9.14  m.).  They  thus  obtain  the  utmost 
effect  of  their  light  sources  and  direct  the  rays  downward  and 
along  the  street,  obtaining  a  high  over-all  efficiency.  The  same 
result  could  be  obtained  in  cities  in  this  country  where  there  may 
be  obtained  the  height  necessary  to  avoid  diffusing  globes  on 
lamps  of  high  power. 

The  kind  of  pavements  and  their  condition  as  Mr.  Millar  points 
out  have  a  marked  effect  on  the  general  appearance  of  a  street 
lighting  installation.  This  is  most  marked  between  a  wet  and 
dry  pavement  with  the  extreme  contrast  between  the  specular 
and  diffuse  reflection.  Motor  vehicle  traffic  has  affected  street 
lighting  in  many  ways  on  account  of  the  necessity  of  stronger 
lighting  due  to  increased  rapidity  of  movement  and  among  these, 
its  effect  on  pavements  is  very  marked.  It  calls  for  a  smooth 
surface  pavement  which  is  usually  dark  in  color  but  becomes 
highly  polished  by  traffic  giving  much  specular  reflection.  Under 
extreme  conditions  this  would  approach  the  effect  of  a  wet  as- 
phalt pavement.  Under  reasonably  dry  conditions  with  the  usual 
amount  of  light  colored  dust  always  present,  these  pavements  give 
a  mild  specular  reflection  of  almost  diffuse  irregularity  with  the 
agreeable  effect  noted  on  Seventh  Avenue,  in  New  York.  Under 
extreme  conditions,  though,  it  becomes  a  difficult  problem  to 
counteract  the  extreme  darkening  of  the  surface  of  a  street  or 
road.     An  instance  of  this  occurred  in   191 3  in  Central  Park 


IO78     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

where  the  former  dust  colored  macadam  roads  were  treated  with 
oil  and  greatly  darkened.  A  50  per  cent,  increase  in  the  candle- 
power  of  the  incandescent  lamps  hardly  offsets  this  effect.  These 
roads  were  of  course  without  any  added  illumination  from  private 
sources  or  from  reflection  from  buildings. 

Mr.  Millar's  emphasis  on  these  variables  in  street  lighting  is 
well  founded  and  shows  that  they  must  be  taken  into  account 
seriously  in  street  lighting  work.  The  best  way  to  study  these 
variables  is  by  trial  installations  on  the  streets  themselves. 

Mr.  C.  E.  Stephens  (By  letter)  :  The  application  of  electrical 
energy  in  the  production  of  street  illumination,  to  my  mind,  is 
one  of  the  most  important  subjects  for  consideration  by  scientific 
associations.  More  than  any  other  piece  of  electrical  apparatus, 
the  street  lamp  is  in  the  public  eye.  Its  importance  is  not  due  to 
the  value  of  this  character  of  load  as  a  market  for  electrical 
energy,  but  to  the  good  or  bad  indirect  effect  on  the  electrical 
industry,  resulting  from  whether  our  street  lighting  installations 
are  good  or  bad. 

Referring  to  possible  improvements  in  street  lighting,  it  seems 
to  me  that  greater  improvements  can  be  expected  in  the  immediate 
future,  from  a  more  scientific  application  of  available  light 
sources,  rather  than  from  radical  improvements  in  the  efficiency 
of  available  light  sources.  While  the  efficiency  of  light  produc- 
tion is  extremely  low,  the  energy  cost  is  also  relatively  low  when 
compared  with  the  capital  charges  for  interest  and  depreciation  on 
the  fixtures,  transmission,  etc.,  and  other  items  of  cost  that  must 
be  included.  A  further  improvement  in  efficiency  of  the  source 
of  light  would  have  to  be  very  great  in  order  to  materially  reduce 
the  present  cost  of  lighting.  It  is,  therefore,  a  fitting  time  to 
carefully  analyze  the  application  of  the  source  and  to  secure  the 
most  illumination  possible  from  a  given  flux  or  volume  of  light. 

Let  us  hope  that  such  investigations  as  are  at  present  being 
carried  on  by  the  electrical  industry  can  be  continued,  to  the  end 
that  a  standard  of  street  illumination  will  be  set  which  will 
secure  ample  visual  discrimination,  with  comfort,  and  a  mental 
activity,  necessary  for  safety ;  and  further  that  the  time  will  soon 
come  when  the  doctors  will  agree. 

Mr.  G.  N.  Chamberlain  (By  letter)  :  As  a  brief  resume 
of  the  general  conditions  and  limitations  of  street  lighting  and  of 


THE   EFFECTIVE   IEEUMINATION    OF   STREETS  IO79 

the  particular  problems  before  the  street  lighting  engineer,  this 
paper  is  the  best  that  has  come  to  my  attention.  The  author  has 
given  a  logical  division  of  the  subject;  he  has  clearly  outlined  the 
different  classes  of  street  lighting  and  called  attention  to  the 
various  desiderata. 

The  difference  in  the  nature  of  the  street  surfaces  within  the 
last  few  years  and  its  importance  upon  the  question  of  street 
lighting  is  very  opportunely  mentioned  by  Mr.  Millar.  The  ex- 
tensive adoption  of  such  surfaces  giving  almost  no  diffusion, 
but  a  high  degree  of  specular  reflection,  has  brought  about  very 
different  requirements  and  these  must  be  met  by  the  engineer  if 
satisfactory  results  are  to  be  obtained.  The  relative  importance 
and  effect  of  glare  in  street  lighting  is  another  most  important 
matter.  As  is  often  the  case  with  subjects  given  a  great  deal  of 
prominence,  it  is  possible  I  believe  to  over-estimate  the  effect  of 
glare.  A  street  so  lighted  that  no  light  source  is  visible  and  the 
brightest  visible  part  is  the  surface  of  the  street  near  the  lamp, 
certainly  brings  in  no  glare  troubles,  but  is  not  a  pleasing  ar- 
rangement to  the  passerby.  How  far  we  should  go  in  regard  to 
cutting  down  the  intensity  of  the  light  source  and  removing  it 
from  the  line  of  vision  is  one  of  the  problems  that  call  for  further 
investigation. 

The  question  of  large  versus  small  light  sources,  while  un- 
settled, is  not  as  prominent  as  it  was  a  few  years  ago,  the  gen- 
eral tendency  being,  as  Mr.  Millar  points  out,  decidedly  toward 
the  larger  units.  The  cluster  arrangement  of  smaller  units,  so 
much  in  evidence  a  few  years  ago,  is  being  almost  entirely  super- 
seded by  the  single  lamp  standard.  This  change  has  been  brought 
about  by  the  introduction  of  the  ornamental  arc  and  the  high 
candlepower  incandescent  unit. 

Under  the  heading  "Theoretical  Considerations  which  have 
not  been  Demonstrated,"  Mr.  Millar  considers  the  subject  of 
color  and  "animation"  of  the  light  source  as  one  of  individual 
taste  and  speculation.  The  engineers  who  have  made  the  claims 
referred  to  have  had  extensive  opportunities  for  tests  and  ob- 
servation and  have  given  expression  to  the  decided  advantages 
of  color  and  animation  of  light  sources.  To  the  writer's  knowl- 
edge, these  two  factors  have  determined  the  final  selection  of  the 
lighting  units  supplied  in  several  important  installations. 
16 


IOSO     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

GAS  STREET  LIGHTING.* 


BY  F.  R.  HUTCHINSON. 


Synopsis:  The  following  paper  outlines  the  progress  in  street  light- 
ing by  gas.  Various  steps  in  the  development  of  gas  lighting  are  described 
and  illustrated. 


It  shall  be  my  aim  in,  more  or  less  briefly,  covering  this  sub- 
ject by  illustration  and  description  a  few  of  the  many  styles  of 
gas  street  lighting  standards  and  lamps  that  have  been  designed 
and  put  in  rather  general  use  since  the  introduction  of  the  old 
flat  gas  lamp. 

Some  comparisons  in  candlepower  are  given  in  the  following 
paragraphs,  but  all  are  not  mentioned  as  complete  data  were  not 
available  at  the  time  of  preparing  the  paper. 

Fig.  i  pictures  the  flat  flame  gas  lamp.  On  a  consumption  of 
6y2  cu.  ft.  of  manufactured  gas  per  hour,  this  lamp  developed 
a  lower  hemispherical  candlepower  of  27. 

Fig.  2  shows  type  of  incandescent  mantle  street  lamp,  best 
known  as  the  "boulevard  lamp,"  most  commonly  used  following 
the  introduction  of  the  incandescent  gas  mantle.  This  style  of 
lamp  is  to-day  still  popular  and  there  are  more  gas  lamps  of  this 
design  now  in  use  than  any  other  kind  in  America.  The  boule- 
vard lamp  develops  a  lower  hemispherical  candlepower  of  64 
and  consumes  3^2  cu.  ft.  of  manufactured  gas  per  hour.  It  is 
a  well  known  fact  that  considerably  greater  efficiency  is  obtained 
with  the  mantle  lamp  than  with  the  old  flat  flame  burner.  With 
but  little  more  than  half  the  gas,  about  two  and  one-half  times  the 
light  is  secured. 

Unfortunately  American  municipalities,  usually  space  lamps  in 
accordance  with  their  appropriations,  which  are  generally  small, 

*  A  paper  read  at  a  meeting  of  the  section  of  the  Illuminating  Engineering  Society, 
May  7,  1915. 

The   Illuminating   Engineering   Society   is   not   responsible    for    the   statements    or 
opinions  advanced  by  contributors. 


HUTCHINSON  I     GAS   STREET   LIGHTING  I08l 

rather  than  as  they  should  to  get  the  best  results.  In  America 
gas  street  lamps  are  spaced  from  ioo  to  200  ft.  apart ;  in  Euro- 
pean cities  about  65  ft.  apart,  situated  usually  100  ft.  diagonally 
apart  measured  from  lamp  to  lamp. 

When  the  inverted  gas  burner  came  into  general  use  for  indoor 
illumination,  its  economy  was  so  pronounced  in  comparison  with 
the  upright  burner  that  both  manufacturers  and  municipalities 
began  looking  into  its  application  for  street  lighting. 

One  mantle  of  the  inverted  type  does  not  look  well  in  the  boule- 
vard lamp,  so  a  burner  was  designed  to  suspend  two  mantles  as 
shown  in  Fig.  3.  This  burner  consumes  about  5^4  cu.  ft.  of 
manufactured  gas  per  hour  and  develops  182  mean  lower  hemis- 
pherical candlepower. 

Following  the  introduction  of  the  inverted  gas  burner,  and  its 
application  in  the  "boulevard  type  lamp,"  experiments  were  made 
and  lamps  designed  of  various  mantle  units  and  of  somewhat 
ornamental  appearance.  One  of  the  first  of  such  types  is  that 
shown  in  Fig.  4. 

The  post  or  standard  was  known  as  the  "Boulevard,"  bearing 
the  same  name  as  the  lamp  illustrated  in  Figs.  2  and  3.  On  this 
post  was  suspended  a  three  mantle  gas  lamp  with  a  reflector 
shade.  This  lamp  developed  400  candlepower  (mean  lower 
hemispherical)  on  a  consumption  of  11  cu.  ft.  of  manufactured 
gas  per  hour. 

A  somewhat  more  ornamental  post  was  next  constructed  which 
suspended  two,  three-mantle  gas  lamps  equipped  with  elaborate 
globes  and  clear  outer  skirts  as  shown  on  Fig.  5. 

The  candlepower  of  these  lamps  was  considerably  lower  than 
that  of  the  lamp  shown  in  Fig.  4,  as  the  lamp  in  the  latter  case  was 
fitted  with  a  shade  and  equipped  with  a  clear  globe,  while  the 
lamps  shown  in  Fig.  5  were  fitted  with  clear  outer  skirts  and 
alabaster  globes.     The  gas  consumption  was  the  same. 

Another  style  of  standard  and  lamp  is  shown  in  Fig.  6.  This 
standard  may  be  equipped  with  three  or  five  lamps  each  con- 
taining one  or  two  mantles  as  desired.  With  all  lamps  lighted, 
this  standard  equipped  with  two  mantles  to  each  lamp  consumes 


I082     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

22  cu.  ft.  of  natural  gas  or  about  2,7  cu.  ft.  of  manufactured  gas 
per  hour.  The  candlepower  is  not  known  but  claimed  to  be  1,000 
with  all  mantles  lighted. 

Fig.  1 1  is  a  night  view  of  a  street  showing  the  lamps  and  stand- 
ards illustrated  in  Fig.  6  lighted. 

Fig.  7  illustrates  a  lamp  which  is  used  between  street  inter- 
sections and  Fig.  8  a  standard  for  street  intersections.  (See 
Figs.  12  and  13.) 

The  lighting  unit  in  these  lamps  consists  of  a  double  inverted 
fixture  containing  two  mantles.  On  a  manufactured  gas  con- 
sumption of  6  cu.  ft.  per  hour  each  lamp  produces  150  candle- 
power  (mean  lower  hemispherical).  With  natural  gas,  consider- 
ably higher  efficiencies  are  obtained. 

The  "Sixth  City,"  Cleveland,  O.,  not  wishing  to  be  outdone  by 
any  of  its  neighbors  has,  through  its  energetic  and  ingenious 
lighting  superintendent,  designed  and  is  now  using  for  its  east 
side  parks  and  boulevards  ornamental  lamps  of  the  type  shown  in 
Fig.  10. 

All  these  lamps  are  at  present  equipped  with  an  automatic 
clock  attachment  that  lights  and  extinguishes  the  main  burners 
from  a  pilot  light  that  is  constantly  burning.  Fig.  15  shows  a 
two-mantle  burner  equipped  with  a  clock  attachment  fitted  to 
the  supply  pipe. 

Each  lamp  consumes  4.7  cu.  ft.  of  natural  gas  per  hour  and 
develops  about  135  candlepower. 

Fig.  17  shows  the  construction  of  a  recently  designed  automatic 
pressure  valve — not  yet  tried  and  proven  in  actual  use — which 
is  intended  to  displace  the  automatic  clock  device  now  used  for 
lighting  and  extinguishing  lamps.  This  valve,  also  shown  fitted 
to  burner  in  Fig.  16,  operates  by  increasing  and  decreasing  the 
gas  pressure  in  mains  supplying  lamps  on  park  boulevards.  The 
details  of  operation  are  indicated  in  Fig.  17.  (Gas  supply  enters 
valve  through  12  at  pressure  of  five  ounces  pressure  and  raises 
diaphragm  which  in  turn  raises  valve  point  10  allowing  gas  to 
enter  passage  way  2  to  lamp.  At  this  pressure  pilot  is  supplied 
with  gas  through  3.  When  pressure  is  reduced  to  one  ounce, 
pressure  is  not  sufficient  to  raise  diaphragm  which  seats  valve 
point  10  in  seat  between  1  and  2.  Hinged  trip  5  which  might  be 
termed  "low  pilot  valve"  is  released  when  pressure  is  reduced 


tjmoi 


-* 


be   - 
O 


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Fig.  ii. — Night  view  of  an  installation  using  equipment  shown  in  Fig.  6. 


Fig.  12.— Showing  type  of  equipment  for  street  intersections. 


Fig.  13. — Gas  lighting  installation  on  Delaware  Avenue,  Buffalo,  N.  Y. 


Fig.  14. — Gas  lighting  at  Panama-Pacific  Exposition. 


I  al. 


Fig.  15.  Fig.  16. 

Automatic  clock  lighting  attachment  for  gas  lamps. 


TUBE  TO 
PILOT 


Fig.  17. — Diagram  of  automatic  clock  lighting  attachment. 


Fig.  18. — Gas  illumination  at  the  Panama -Pacific  Exposition. 


Fig.  19.— A  three-mantle,  high  pressure  gas  lamp. 


HUTCHINSON:     GAS   STREET   LIGHTING  I083 

from  five  to  one  ounce,  which  permits  gas  at  this  low  pressure  to 
flow  through  4  to  pilot,  maintaining  substantially  the  same  flame 
on  pilot  as  with  five  ounce  pressure,  without  permitting  any  gas  to 
flow  to  main  burner.  Description  of  parts  and  ports:  1 — area 
or  passageway  for  gas  to  main  burner  at  five  ounce  pressure  and 
pilot  burner  at  one  ounce  pressure ;  2 — continued  port  or  passage- 
way to  main  burner ;  3 — port  or  passageway  to  pilot  for  five  ounce 
pressure ;  4 — port  or  passageway  to  pilot  for  one  ounce  pressure ; 
5 — hinged  trip  or  low  pilot  valve;  6 — oiled  leather  diaphragm; 
7 — spring  attached  to  10  to  close  low  pressure  pilot  valve; 
8 — brass  stop  to  equalize  tension  of  spring  7;  9 — balance  weight 
to  close  valve  point  with  one  ounce  pressure;  10 — main  valve; 
11 — flash  governing  screw  to  release  air  from  chamber  above 
diaphragm;  12 — gas  passageway  for  service  entering  lamp  post.) 

GAS  LIGHTING  AT  PANAMA-PACIFIC  EXPOSITION. 

Fig.  14  shows  a  close  view  of  a  post  and  lantern  equipment 
used  at  the  Panama-Pacific  International  Exposition  for  the 
lighting  of  the  "Zone."  These  lamps  are  equipped  with  a  mer- 
cury valve  for  distant  control.  The  posts  are  located  75  ft.  (22.86 
m.)  apart.  All  gas  supplied  to  the  exposition  grounds  is  conveyed 
in  the  mains  at  30  pounds  pressure.  A  by-pass  cock  is  installed  in 
the  box  seen  at  base  of  the  post  where  there  is  also  a  governor  to 
reduce  the  pressure  to  that  of  a  5-in.  (12.7  cm.)  water  column. 
All  gas  lamps  are  screened  by  specially  designed  lanterns  of  vari- 
ous types.  These  lanterns  consist  of  a  wooden  frame  covered 
with  canvas  in  either  pink  or  orange  color  and  at  night  the  illum- 
inating effect  is  very  beautiful.  All  entrances  and  exits  to  the 
exposition  are  gas  lighted,  the  entrances  by  three  and  five-mantle 
gas  lamps,  the  exits  by  one-mantle  lamps. 

Fig.  18  shows  a  night  view  of  the  "Zone."  (Note  the  different 
shapes  and  designs  of  lanterns  surrounding  the  gas  lamps.) 

In  the  State  and  Foreign  Area  of  the  exposition  the  street 
lighting  is  done  with  high  pressure  gas  lamps.  Fig.  9  shows  a 
standard  and  lamp.  These  lamps  are  mounted  on  posts  18  ft. 
high.  Gas  is  delivered  to  lamp  at  3  pounds  pressure.  The  mean 
lower  hemispherical  candlepower  is  1,160;  the  consumption  is 
24.30  cu.  ft.  (0.68  cu.  m.)  manufactured  gas  per  hour. 

Before  leaving  the  subject  of  high  pressure, — Fig.  19  shows 


I084     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

a  foreign  three-mantle  high  pressure  gas  lamp  which  develops 
a  candlepower  of  4,000  on  a  natural  gas  consumption  of  35  cu.  ft. 
(0.96  cu.  m.)  per  hour.  On  a  short  life  test  made  on  this  lamp 
from  March  4  to  16,  1915,  during  a  burning  period  of  160 
hours,  but  one  mantle  was  replaced  through  breakage.  No 
globes  or  other  parts  were  replaced.  The  gas  (natural)  deliv- 
ered at  this  lamp  was  at  the  rate  of  35  cu.  ft.  per  hour  at  2-lb. 


Fig.  20.— Method  of  suspension  for  gas  lamps  on  streets  not  having 
overhead  trolley  wires. 


(1.36  kg.)  pressure.  In  street  illumination  abroad,  this  lamp  is 
located  in  the  center  of  the  street  about  30  ft.  (9.14  m.)  from 
the  ground.  Figs.  20  and  21  show  the  manner  of  suspending  gas 
lamps  over  the  center  of  street  and  the  lowering  gear.  The  con- 
struction shown  in  Fig.  20  is  used  where  there  are  no  overhead 
trolley  wires  on  streets  not  exceeding  80  ft.  (24.38  m.)  in  width. 
The  arrangement  shown  in  Fig.  21  is  for  street  crossings  having 
overhead  trolley  wires.    The  lamp  is  moved  to  the  side  and  then 


HUTCHINSON  :     GAS   STREET   LIGHTING 


I085 


lowered.     Flexible  metal  tubing  is  used  from  an  ell  at  the  top 
over  to  the  lamp. 

There  are  many  other  styles  of  standards  and  lamps  than  those 
illustrated  in  this  paper,  but  I  have  tried  to  select  examples  of 
most  kinds  in  somewhat  general  use. 


Fig.  21.— Method  of  suspending  gas  lamps  on  streets  having  overhead  trolley  wires. 

The  United  States  has  been  slow  to  adopt  high  pressure  gas 
street  lighting  and  it  will  probably  be  many  years  before  it  be- 
comes very  generally  used,  but  time  here,  as  well  as  abroad,  will 
see  it  in  much  more  common  use  than  now.  The  excellent  quality 
of  light,  high  candlepower  and  economy  of  operation  will  be 
recognized,  and  when  it  is,  our  fellow  electric  members  of  the 
Society  will  have  to  look  out  for  their  laurels. 


I086    TRANSACTIONS  OF  IEEUMINATING  ENGINEERING  SOCIETY 

SHEET  GLASS  IN  LIGHTING.* 


BY  EDGAR  H.  BOSTOCK. 


This  subject  can  best  be  treated  under  two  principal  divisions, 
namely:  (i)  factory  operations  in  the  production  of  sheet  glass; 
(2)  variations  that  can  be  made  in  the  glass. 

This  will  give  an  understanding  of  what  results  can  or  cannot 
be  readily  obtained,  and  perhaps  some  idea  of  the  advantages  and 
limitations  of  sheet  glass  as  applied  to  fixture  manufacture. 

FACTORY  OPERATIONS. 

The  factory  operations  herein  described  are  those  employed  in 
a  Kansas  factory,  where  the  low  price  of  gas  from  the  adjacent 
gas  fields  is  very  favorable  for  the  manufacturer.  The  gas  is 
supplied  through  a  10-in.  main,  this  particular  factory  consuming 
about  1,500,000  cu.  ft.  of  gas  per  day. 

Sheet  glass  is  made  in  a  tank  furnace  the  inside  dimensions  of 
which  are  usually  18  to  20  ft.  in  width,  by  45  to  60  ft.  in  length. 
Such  a  furnace  when  in  full  blast  contains  anywhere  from  300 
to  400  tons  of  molten  glass. 

The  furnace  contains  two  recesses — one  through  which  the  gas 
passes  and  the  other  admitting  the  air.  The  gas  and  air  come 
together  so  as  to  burn  across  the  furnace.  There  are  two  sets 
of  flues  filled  with  checker  work,  one  set  of  which  carries  off  the 
exhaust  gases  while  the  other  heats  the  entering  gas.  The  fur- 
nace is  arranged  so  that  the  fire  can  be  reversed,  and  the  heat 
accumulated  in  the  checkerwork  from  the  exhaust  gas,  utilized  in 
heating  the  entering  gas  and  air.  By  this  means  a  much  higher 
temperature  can  be  secured  than  if  the  fire  were  fed  with  cold 
air  and  gas. 

This  furnace  heats  the  glass  from  the  top  down,  rather  than 
from  the  bottom  up,  and  there  are  particular  reasons  for  so 
doing.  The  specific  gravity  of  clay  is  less  than  that  of  molten 
glass,  so  that  to  keep  the  bottom  in  the  tank,  it  is  necessary  to  heat 

*  A  condensed  statement  of  an  illustrated  talk  given  at  a  meeting  of  the  New  York 
Section  of  the  Illuminating  Engineering  Society,  May  25,  1915. 

The   Illuminating   Engineering   Society   is   not   responsible   for   the   statements    or 
opinions  advanced  by  contributors. 


BOSTOCK  :     SHEET   GLASS   IN    LIGHTING 


I087 


from  the  top.     The  bottom  of  the  tank  is  heated  hardly  to  red- 
ness, and  the  denser  glass  remains  at  the  bottom. 

The  molten  glass  flows  off  from  the  upper  surface  to  the  outlet 
from  which  it  is  worked.     A  ring  of  clay  floats  on  the  glass  in 


Fig.  1.— Steps  in  blowing  sheet  glass. 


front  of  the  working  holes,  and  serves  to  stop  the  flow  of  glass. 
The  glass  is  melted  from  a  mixture  of  sand,  limestone  and  ground 
carbon  with  a  certain  proportion  of  old  broken  glass.  The  mix- 
ture is  inserted  in  the  furnace  by  means  of  the  long  handled 


Io88     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

shovel.  To  protect  his  face  from  the  heat,  the  workman  wears 
what  is  called  a  face  board,  which  is  held  in  place  by  a  plug 
inserted  between  his  teeth. 

Fig.  i  shows  the  method  of  working  the  glass  in  blowing  and 
forming  a  sheet.  The  workman  employs  an  iron  pipe  about 
50  in.  long,  the  end  of  which  is  heated  to  a  slight  redness  so  that 
the  glass  will  adhere  to  it.  Glass  may  have  to  be  gathered  six 
or  seven  times,  depending  upon  the  size  of  the  article  to  be  made 
and  the  density  of  glass.  When  a  sufficient  quantity  is  gathered, 
the  workman  blows  down  the  pipe  forming  a  bubble  inside  the 
molten  glass.  This  is  formed  by  swinging  and  rotating,  the  pipe 
being  rested  part  of  the  time  on  an  iron  block  or  "lazy- jack." 
In  blowing,  the  workman  takes  advantage  of  the  expansion  of 
heated  air,  at  proper  intervals  holding  his  thumb  over  the  end  of 
the  pipe  instead  of  blowing.  As  part  of  the  glass  bubble  cools 
and  hardens  it  is  reheated  and  the  operation  continued.  Owing 
to  the  mass  of  glass,  the  lower  part  of  the  bubble  retains  its  heat 
longest.  The  cylinder  is  formed  by  rolling  the  bubbles  on  an 
iron  table.  When  the  proper  shape  is  secured,  the  further  end  is 
blown  open  the  cylinder  placed  on  an  iron  horse  and  the  cap 
removed. 

The  cylinder  is  then  carried  to  another  secondary  or  flattening 
oven,  cracked  open  lengthwise,  opened  and  flattened  out  on  a  sheet 
of  very  highly  polished  clay.  The  workmen  are  very  expert  and 
the  sheet  so  produced  is  usually  approximately  of  the  size  desired. 
In  fact  a  workman  gathering  16  lbs.  will  gather  all  day  without 
varying  more  than  2  or  3  oz.  They  will  make  sheets  to  cut  40 
by  60  in.  with  little  more  than  the  necessary  allowances,  and  the 
cylinders  will  not  vary  more  than  1  in.  in  circumference  from 
end  to  end.  Considerable  physical  endurance  is  necessary  for 
the  pipe  weighs  12  to  15  lbs.,  and  the  glass  bubble  out  at  the  end 
may  weigh  20  or  25  lbs. 

In  cracking  the  cylinder  for  removing  the  cap,  a  thread  of  hot 
glass  is  laid  on  the  cylinder  long  enough  for  local  heating  and 
then  the  proper  point  is  touched  with  cold  metal,  perhaps  an 
iron  strip  and  the  glass  cracks  along  the  heated  thread. 

In  splitting  open,  the  workman  will  take  a  rod  of  iron  heated 
at  one  end,  with  some  carbon  to  prevent  scratching,  and  work  the 
iron  up  and  down  the  cylinder.     With  the  cylinder  at  just  the 


bostock:   sheet  glass  in  lighting  1089 

right  heat,  one  extreme  edge  is  touched  with  his  wet  thumb,  which 
starts  a  crack  that  follows  the  iron  practically  the  full  length  of 
the  cylinder.  The  heat  in  the  flattening  furnace  is  just  sufficient 
to  render  the  glass  malleable,  say  about  5000  C.  The  flattened 
glass  passes  to  the  annealing  furnace,  through  which  it  is  carried 
on  rollers. 

Another  kind  of  sheet  glass  is ,  manufactured  by  the  casting 
and  rolling  process.     In  this  a  "pot  furnace"  is  used,  in  which 
pots  about  45  in.  in  diameter  are  filled  with  the  glass  mixture 
and  heated.     When  all  are  ready  the  workmen  lift  out  the  pots 
and  carry  them  to  a  casting  table,  pouring  out  the  molten  glass  on 
the  table  and  rolling  it  out  to  the  required  thickness  with  heavy 
rollers,  one,  two  or  three  pots  being  used,  depending  upon  the 
size  of  the  sheet  required.     This  method  is  used  for  making  large 
sheets  of  plate  glass.     Such  sheets  are  usually  cast  and  rolled  to 
a  thickness  of  Y\  in.,  and  later  ground  and  polished  down  to  Y  in. 
When  glass  is  manufactured  in  thick  plates  it  is  necessary  to 
anneal  it  very  carefully,  and  therefore  as  soon  as  the  plate  has 
been  rolled,  it  is  taken  to  an  annealing  oven.     These  ovens  are 
often  400  to  500  ft.  in  length,  and  a  large  plate  may  be  kept  in 
such  an  oven  from  7  to  10  days  before  it  is  thoroughly  annealed. 
When  the  sheet  is  annealed,  it  is  polished  by  electrical  machin- 
ery, first  with  rough  river  sand  and  then  successively  with  a  finer 
sand,  emery  and  rouge.     Curious  to  relate,  after  the  finest  me- 
chanical polishing,  it  is  necessary  to  re-polish  portions  of  the  plate 
by  hand. 

All  the  plate  glass  which  is  manufactured  is  ground  down  from 
YA  to  Ya  in.  in  thickness,  in  order  to  remove  any  inequalities  and 
warping  which  may  be  present. 

Figured  rolled  glass  is  made  by  a  slightly  different  process. 
In  this  a  printing  roller  is  used  instead  of  a  plain  one.  After  the 
glass  is  rolled  by  the  smooth  roller  into  a  sheet  the  printing  is 
put  on  by  rolling  a  figured  roller  over  the  plastic  glass. 

Another  process  which  will  be  of  interest,  although  not  a 
method  of  manufacturing  glass  plates,  is  the  pressing  of  glass 
into  various  shapes.  In  this  the  workman  gathers  a  certain 
amount  of  glass  upon  an  iron  rod  and  puts  it  into  a  mold;  a 
second  workman  watches  the  mold  and  when  it  is  filled  to  the 


IO9O     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

proper  height  he  cuts  the  thread  with  a  pair  of  sheers.  A  cap  is 
then  placed  on  the  mold  and  it  is  pushed  under  a  plunger  which 
is  forced  down  into  the  mold  forming  whatever  article  may  be 
necessary. 

A  new  process  which  has  recently  come  into  existence  is  that 
of  making  window  glass  by  machine.  It  is  more  or  less  success- 
ful depending  upon  whether  one  makes  hand-blown  glass  or 
machine-blown  glass.  In  any  event,  the  inventor  of  this  has  fol- 
lowed very  closely  the  hand-blown  process.  It  takes  an  expert  to 
tell  the  difference  between  the  machine  and  hand-blown  glass  to- 
day. 

These  are  some  general  processes  which  it  is  necessary  to  un- 
derstand in  order  to  comprehend  some  of  the  more  complicated 
methods  which  are  in  use  for  making  the  various  glasses  used  by 
illuminating  engineers. 

In  making  colored  glass,  or  glass  designed  to  shut  out  certain 
light  rays,  there  are  some  further  processes  which  have  to  be 
taken  into  consideration.  One  common  process  is  that  of  manu- 
facturing flashed  glass,  a  clear  glass  coated  with  a  film  of  colored 
glass  upon  one  side.  To  produce  this,  the  workman  when  he 
first  starts  to  "gather"  dips  his  pipe  in  a  small  pot  of  colored 
glass  of  the  color  desired,  for  the  first  and  possibly  for  the 
second  "gathering."  He  then  carries  his  pipe  to  a  pot  of  crystal 
glass  and  "gathers"  on  top  of  the  colored  glass  the  necessary 
amount  of  crystal  glass  to  form  the  sheet  or  the  article  that  he  is 
going  to  blow  out.  As  he  blows  and  forms  the  different  articles 
the  skin  of  the  colored  glass  remains  on  the  interior  of  the  cyl- 
inder, and  will  be  distended  to  whatever  thickness  of  film  he 
wants  according  to  the  quantity  of  colored  glass  that  he  has 
gathered.  By  this  process  blown  glass  of  various  color  densities 
can  be  manufactured  according  to  the  thickness  of  the  film  of 
color  that  is  used. 

Silver  reflector  glass  is  manufactured  in  the  same  way  as 
sheet  glass  up  to  the  point  where  the  workman  blows  the  ball  of 
glass.  The  workman  then  thrusts  the  ball  into  a  clam  shell  mold 
upon  which  has  been  machined  a  series  of  lines,  all  ending  in  a 
common  point  at  the  bottom  of  the  mold.  He  then  blows  his 
glass  into  the  ribs  of  the  mold.     Compressed  air  is  sometimes 


bostock:    sheet  glass  in  lighting  1091 

used  for  this  process.  The  ball  is  then  taken  back  to  the  furnace, 
reheated  and  swung  out  in  the  cylinder  where  the  marks  upon 
the  ball  are  followed  in  cutting  the  cylinder.  The  skill  of  the 
workman  is  brought  into  play  to  keep  the  line  in  exactly  a  hori- 
zontal direction. 

Crackled  glass  is  made  by  a  variation  of  this  process.  The 
workman  proceeds  as  before  until  he  has  the  ball  blown  when  he 
thrusts  the  bottom  of  it  into  a  receptacle  containing  water.  This 
must  be  done  very  carefully  for  if  the  glass  ball  is  immersed  too 
deep  it  will  crack.  After  reheating  it,  the  cracks  are  melted  to- 
gether except  just  upon  the  skin  where  they  have  broken  through. 
When  the  glass  is  swung  out  into  the  cylinder,  the  crackled  marks 
being  swung  out  with  the  cylinder,  the  plate  becomes  crackled 
glass. 

Muffled  glass  is  made  by  the  same  general  process  except  that 
the  blowing  process  is  continued  until  the  cylinder  is  formed 
when  it  is  dropped  in  a  two-piece  mold  which  closes  upon  the 
cylinder,  the  workman  blowing  the  glass  inside  the  mold.  He 
then  produces  upon  the  cylinder  whatever  marks  may  be  cut  in 
the  mold. 

The  necessity  for  annealing  glass  referred  to  before  will  be 
understood  when  it  is  realized  that  a  sheet  of  glass  of  any  thick- 
ness at  all  cools  much  faster  upon  the  outer  skin  than  it  does 
within.  Of  course,  in  very  thin  glass  it  is  of  very  little  importance 
but  in  glass  of  any  thickness  at  all,  even  of  one  millimeter,  a 
strain  is  caused  by  the  quick  cooling  of  the  outer  skin  which  is 
sometimes  very  uneven.  It  is  possible  to  have  a  glass  that  will 
not  stand  even  the  extremes  of  temperature  in  our  own  climate 
here  because  it  is  not  well  tempered,  and  this  problem  increases 
with  the  thickness  of  the  glass  because  of  the  internal  stress  set 
up  is  much  larger.  As  an  illustration  of  this  point,  glass  tears 
are  sometimes  made  by  dropping  extremely  hot  molten  glass  into 
a  bucket  of  cold  water,  the  skin  of  the  glass  being  chilled  im- 
mediately while  the  interior  is  clear  red.  These  tears  may  be 
laid  upon  the  floor  and  hit  with  a  sledge  hammer  without  effect  on 
account  of  the  extreme  hardness  of  the  outer  skin,  but  if  by 
any  chance  the  outside  skin  is  scratched  at  any  point  it  will  ef- 
fect the  internal  structure,  the  internal  strains  are  so  great  that 


IO92     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  "tear"  is  immediately  reduced  to  a  powder.  This  is  exactly 
what  happens  when  a  glass  ball  or  a  heavy  blown  globe  is  not 
properly  annealed.  It  may  stand  extremely  hard  usage,  but 
when  once  the  surface  is  scratched,  the  ball  is  broken  on  account 
of  the  unequal  stresses. 

*The  writer  became  interested  in  the  subject  of  sheet  glass 
through  the  influence  and  kindness  of  some  of  the  members  of 
this  Society.  At  that  time  there  was  very  little  known  about  the 
subject.  Illuminating  gas  was  first  used  extensively  in  the  Soho 
Works  of  Watt  and  Bolten  in  Birmingham,  England,  and  just 
three  miles  from  the  works  of  Watt  and  Bolten  stands  the 
large  glass  works  of  Chance  Brothers  &  Company.  It  is  very 
likely  that  the  first  sheet  glass  used  in  lighting  was  made  to  pro- 
tect the  gas  jet  burners  used  at  the  Watt  and  Bolten  Works. 

There  was  very  little  further  use  made  of  sheet  glass  in  lighting 
until  the  time  of  electric  lighting,  as  the  small  gas  flames  used  did 
not  require  very  much  protection. 

One  of  the  first  instances  that  the  writer  remembers  of  the  use 
of  sheet  glass  with  a  definite  view  of  improving  lighting  condi- 
tions occurred  in  the  equipment  of  the  United  Engineering  Build- 
ing. In  the  ceiling  lighting  of  the  auditorium  on  the  second  floor 
Mr.  C.  E.  Knox  devised  the  first  large  installation  of  ceiling  or 
dome  lighting.  He  did  not  know  what  glass  to  use,  as  those 
available  were  very  few,  so  the  glass  chosen  for  this  installation 
was  a  crystal  ripple,  sand  blasted.  It  was  the  only  thing  available 
of  any  diffusive  power  that  he  could  place  between  the  lamp  and 
the  line  of  the  ceiling.  He  desired  to  keep  the  lamp  out  of  view 
and  attained  it  by  grinding  one  surface  of  the  glass.  The  diffi- 
culty was  that  a  cleaning  problem  was  introduced  which  will 
probably  exist  as  long  as  the  installation  remains. 

The  next  large  installation  that  came  to  the  writer's  attention 
was  the  lighting  of  the  Soldiers'  Memorial  Building  at  Pitts- 
burgh, by  Mr.  Bassett  Jones.  Mr.  Jones  went  into  this  problem 
very  extensively  and  measured  the  absorption  and  refraction  of 
a  number  of  the  various  glasses.  It  was  the  intention  to  produce 
a  warm  glow  rather  than  a  cold  white  light  and  therefore  a  glass 

*  The  remainder  of  this  lecture  was  illustrated  by  means  of  a  number  of  sheets  of 
glass  illustrating  the  various  points  discussed  by  Mr.  Bostock.  As  no  illustrations  are 
available,  these  cannot  be  shown. 


BOSTOCK  :     SHEET   GLASS   IN    LIGHTING  IO93 

was  chosen  in  which  the  color  is  not  apparent,  such  a  slight  amount 
of  tint  was  included ;  so  that  while  the  absorption  is  only  10  per 
cent.,  the  effect  is  that  of  warmth  when  the  lamps  are  turned 
on.  Tungsten  lamps  were  just  coming  into  use  when  this  installa- 
tion was  planned.  Two  types  of  glassware  were  used  in  this 
installation  in  order  to  equalize  the  lighting.  Certain  conditions 
in  the  ceiling  made  necessary  a  slightly  deeper  tint  of  glass  to 
increase  the  amount  of  amber  light.  This  glass  was  molded  so 
skilfully  by  the  glass  manufacturer  that  there  is  an  appearance  of 
uniformity  over  the  whole  surface.  This  difference  is  mentioned 
in  order  to  emphasize  the  mobility  of  glass.  The  glass  mixer 
is  able  to  mix  colors  in  order  to  reproduce  any  given  intensity 
and  shade. 

Ten  or  fifteen  years  ago  there  sprang  up  an  era  of  mosaic  dome 
lighting  and  a  good  many  domes,  good,  bad  and  indifferent  were 
made  without  any  regard  to  the  illuminating  value  of  the  glass 
that  was  used  in  them.  The  glass  makers,  however,  in  making 
glass  for  these  domes  discovered  certain  facts  in  glass  making,  and 
when  the  demand  came  for  a  diffusing  glass  to  be  used  in  the 
new  indirect  lighting  they  were  able  by  making  a  mixture  of  opal 
and  flint  glass  to  turn  out  the  glass  which  is  now  known  as  the 
"alabaster"  type.  This  glass  is  made  by  mixing  a  given  amount 
of  opal  and  flint  glass  upon  the  casting  table  and  rolling  the 
mixture  in  the  same  way  that  plate  glass  is  rolled.  The  glass 
mixer  is  able  to  vary  the  absorption  of  this  glass  by  varying  the 
quantities  of  the  ingredients.  If,  for  instance,  a  certain  type  of 
indirect  dish  is  to  be  made  in  which  it  is  necessary  to  have  60 
per  cent,  absorption,  the  glass  manufacturer  simply  figures  out 
how  much  opal  glass  and  how  much  flint  glass  will  give  him  that 
60  per  cent,  combined  absorption  and  reflection.  It  is  possible  to 
do  almost  anything  with  this  type  of  glass ;  second  and  third 
colors  may  be  added,  the  opal  may  be  tinted,  and  the  flint  may 
be  tinted. 

Some  six  or  seven  years  ago  the  writer  became  interested  in 
trying  to  do  away  with  the  great  problem  caused  by  the  surface 
of  acid  etched  glass.  The  particular  installation  that  was 
brought  to  my  attention  at  that  time  was  the  installation  of 
lanterns  around  the  then  new  Pennsylvania  Terminal.      These 


1094     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

had  been  glazed  with  ground  glass  and  the  cleaner  was  apt  to  take 
a  greasy  rag  to  clean  the  glassware.  The  glass  of  course  was 
soon  streaked  with  all  shades  of  grey  and  black  and  it  would  be 
impossible  to  even  venture  a  guess  as  to  how  much  light  ab- 
sorption had  been  added  to  the  original  glass.  The  problem  at 
that  time  was  to  find  a  glass  in  which  the  same  effects  would  be 
obtained  as  with  ground  glass,  and  yet  a  glass  which  was  as 
readily  cleanable  as  window  glass. 

The  glass  which  was  finally  adopted  is  made  by  a  process 
which  produces  a  glass  plain  on  one  side  and  flashed  with  any 
required  color  on  the  other  side.  The  glass  in  this  installation  is 
flashed  with  opal  and  as  it  was  made  to  duplicate  ground  glass, 
it  has  about  30  per  cent,  absorption.  It  is  possible,  however,  for 
this  glass  to  be  produced  with  absorptions  of  from  20  to  60  per 
cent.  This  glass  can  be  cleaned  just  as  easily  and  as  readily  as 
window  glass. 

Some  four  years  ago  when  Mr.  D'Arcy  Ryan  was  planning  the 
lighting  of  the  Panama-Pacific  Exposition  Buildings,  he  was  con- 
fronted with  the  problem  of  illuminating  the  windows  of  build- 
ings which  were  lit  by  flood  lighting  so  as  to  eliminate  reflecting 
points  of  light.  One  of  the  first  troubles  he  discovered  was  that 
when  the  windows  are  set  rather  deep  in  the  facade,  the  windows 
appear  as  black  spots  due  to  the  fact  that  light  passes  through 
the  window  plate  at  900  and  therefore  is  not  reflected.  The 
problem  was  to  glaze  the  windows  with  a  glass  having  the 
same  luminosity  under  flood  lighting  as  the  rest  of  the  facade. 
A  new  type  of  glass  was  produced  through  research  work  by 
Mr.  Jones  called  "Deflex"  glass.  This,  he  found,  set  up  the 
maximum  amount  of  specular  reflection,  and  is  the  one  which 
was  adopted  by  Mr.  Ryan  for  the  exposition  buildings.  With 
the  modification  of  a  wire  content  this  was  used  for  the  dome  at 
Horticultural  Hall  where  Mr.  Ryan  obtained  such  wonderful 
effects. 

Last  year  Mr.  Edwards  of  the  National  Lamp  Works  pre- 
sented at  our  1914  convention  a  paper  on  the  lighting  of  rooms 
through  translucent  glass  ceilings,  in  which  he  gave  the  results 
of  his  tests  of  several  different  glasses.  It  is  interesting  to  know 
that  Mr.  Edwards  was  led  into  this  work  by  the  desire  of  the 


bostock:    sheet  glass  in  lighting  1095 

National  Lamp  Works  to  glaze  the  rooms  of  their  own  buildings 
at  Xela  Park  with  a  glass  which  would  give  a  maximum  diffusion 
so  that  the  points  of  light  from  lamps  within  the  room  could  not 
be  observed  from  the  outside.  Mr.  Edwards  picked  out  a  rolled 
glass  which  is  very  beautiful  in  design  and  workmanship,  and 
which  sets  up  very  good  diffusion,  and  is  at  the  same  time  an 
artistic  glass.  The  glass  has  abotot  54  per  cent,  transmission 
which,  considering  the  fact  that  it  is  of  such  a  definite  pattern, 
is  a  highly  efficient  glass.  It  became  evident  after  the  test  con- 
ducted by  Mr.  Edwards  had  been  undertaken  that  a  different 
theory  of  light  diffusion  in  sheet  glass  could  be  evolved.  Crystal 
glass  is,  of  course,  the  ideal  glass  in  use  for  such  installations 
because  of  its  small  absorption.  In  all  tests  which  were  made 
wherever  a  glass  whose  deflective  surfaces  were  cylindrical  in 
shape,  it  was  found  that  a  better  diffusion  was  secured.  As  long 
as  a  definite  sharp  angle  was  present  a  direct  reflection  was  notice- 
able from  the  angle  of  the  glass  without  transmission,  and  there- 
fore, maximum  diffusion  was  secured  by  making  all  reflective 
surfaces  cylindrical  in  shape.  A  new  glass  was,  therefore,  de- 
vised from  this  acquired  data  and  the  manufacturers  are  now 
making  a  rolled  glass  which  contains  a  series  of  small  semi- 
cylindrical  projections.  It  was  thought  at  first  that  it  was  not 
possible  to  roll  this  glass  making  these  semi-circular  projections 
touch  each  other,  and  a  small  flat  plane  was  left  between  each  pro- 
jection so  that  it  is  not  a  perfect  diffusive  glass.  It  is  the  writer's 
opinion,  however,  that  the  right  theory  is  being  applied  to  pro- 
duce a  perfect  diffusing  glass.  This  is  the  glass  that  was  used 
in  the  crow's  nest  in  the  "YVoolworth  Tower  and  it  is  being  glazed 
under  the  direction  of  Mr.  Madgsick.  This  is  the  last  word 
which  we  have  in  sheet  glass  for  diffusion  of  light  to-day. 

One  other  application  of  sheet  glass  to  illuminating  engineering 
has  been  evolved  quite  recently.  It  is  a  new  method  of  sign 
lighting  built  upon  multiple  reflection  of  light.  Fig.  2  illus- 
trates the  sign  made  up  and  the  principle  upon  which  it  depends. 
The  sign  is  lighted  by  means  of  a  line  lamp  and  the  theory  upon 
which  it  is  based  is  that  if  the  incident  angle  of  the  entering  light 
remains  within  the  reflective  angle  of  the  glass  it  has  been  thrown 
on,  the  light  will  be  reflected  back  and  forth  within  the  glass  and 
will  not  leave  it.  Now  if  this  were  a  plain  piece  of  glass  it  would 
17 


IO96     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

not  be  apparent  to  the  eye  that  there  was  any  light  there  at  all 
except  at  the  edges  where  the  light  escaped.  If  now  the  surface 
of  the  glass  is  abraded  by  any  means  at  all  there  is  set  up  a  dif- 
ferent angle  of  reflection  at  that  point  and  so  the  light  is  visible 


MJ1TI 


Fig.  2. — Diagram  of  sign.  A  and  D,  wire  of  straight-filament  lamp.  B  and  C,  path 
of  light  rays  confined  within  reflective  surface  of  glass.  E,  face  of  glass  in  double 
sign  so  metered  as  to  bring  path  of  light  within  refractive  angle  of  glass. 
F,  abraded  surface,  where  light  becomes  visible. 


at  the  particular  point  where  the  angle  changes.  In  the  first  ex- 
periments merely  the  surface  of  the  glass  was  abraded,  but  better 
results  are  attained  by  cutting  the  glass  deeply.  These  signs  have 
recently  been  put  on  the  market. 


FERREE   AND   RAND:     EXPERIMENTS   ON   THE   EYE  IO97 

SOME  EXPERIMENTS  ON  THE  EYE  WITH  INVERTED 
REFLECTORS  OF  DIFFERENT  DENSITIES  * 


BY  C.  E.  FERREE  AND  G.  RAND. 


Synopsis:  In  previous  papers  read  before  this  society  by  the  present 
writers,  the  gradation  of  surface  brightness  and  its  distribution  in  the 
field  of  vision  were  shown  to  be  important  factors  in  the  effect  of  lighting 
conditions  on  the  eye.  In  the  work  described  in  the  present  paper,  grada- 
tion of  surface  brightness  is  made  the  chief  variable.  Inverted  reflectors 
of  six  degrees  of  density  are  employed,  and  a  correlation  is  made  between 
the  illuminating  effects  obtained  and  the  tendency  to  cause  loss  of  power 
to  sustain  clear  seeing  and  to  produce  ocular  discomfort. 


INTRODUCTION. 
This  paper  is  the  fourth  in  a  series  in  which  the  effect  of  differ- 
ent conditions  of  lighting  on  the  eye  is  investigated.  In  the 
first  paper,  two  tests  were  described — one  designed  to  be  used  as 
a  general  test  for  detecting  the  comparative  tendencies  of  different 
lighting  conditions  to  cause  a  loss  in  the  eye's  power  to  sustain 
clear  seeing  for  a  period  of  work;  the  other  for  detecting  the 
tendency  to  produce  ocular  discomfort.  In  the  second  paper,  the 
application  of  the  first  of  these  tests  to  various  lighting  conditions 
was  begun.  Two  purposes  were  had  in  making  this  application : 
(1)  the  studying  and  perfecting  of  the  test  itself  for  use  in 
lighting  work,  which  it  is  obvious  could  not  be  done  effectively 
under  one  set  or  type  of  lighting  conditions;1  and  (2),  the  inves- 
tigation of  pertinent  lighting  effects,  the  results  of  which  could  be 
made  both  to  serve  as  a  guide  for  further  work,  and  to  provide 
cumulative  data  from  which  conclusions  may  be  drawn  as  the  con- 
ditions and  stage  of  advancement  of  the  work  may  warrant. 
This  paper  was  divided  into  two  sections.  In  the  first  the  test 
was  applied  to  the  determination  of  the  effect  on  the  eye  of  three 
lighting  installations,  direct,  semi-indirect  and  indirect,  so  se- 
lected as  to  give  wide  differences  in  illuminating  effects.  In  the 
second  section  the  effect  of  six  variations  in  intensity  for  the 
direct  and  semi-indirect  installations  was  determined.     In  both 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing  Society,  Washington,   D.   C,   September  20-23,    1915. 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


IO98     TRANSACTIONS  OF  IEEUMINATING  ENGINEERING  SOCIETY 

of  these  cases  the  tests  were  all  made  at  one  position  in  the  room, 
the  point  marked  as  the  position  of  the  observer  in  Fig.  1  of  the 
present  paper.  Obviously,  however,  the  effect  of  an  unfavorable 
installation  on  the  eye  will  vary  with  the  position  of  the  observer 
in  the  room.  In  the  third  paper,  therefore,  the  tests  were  re- 
peated for  these  installations  at  four  positions  in  the  room :  the 
first  with  six  reflectors  in  the  field  of  view ;  the  second  with  four ; 
the  third  with  two,  and  the  fourth  with  none.  The  following 
features  were  also  included :  the  work  of  the  intensity  series  was 
completed,  i.  e.,  six  intensities  of  light  were  used  with  the  indi- 
rect reflectors ;  a  test  was  described  for  determining  the  effect  on 
the  fixation  muscles  of  the  eye;  and  a  series  of  miscellaneous 
experiments  was  conducted  pertaining  to  the  hygienic  employment 
of  the  eye.  In  these  experiments  the  following  points  were  taken 
up :  the  effect  of  varying  the  area,  and  conversely  the  intrinsic 
brilliancy  of  the  ceiling  spots  above  the  reflectors  of  the  indirect 
system  of  lighting  used ;  the  effect  of  varying  the  angle  at  which 
the  light  falls  on  the  work  in  a  given  lighting  situation ;  the  effect 
of  using  an  opaque  eye-shade  with  dark  and  light  linings  with  a 
number  of  lighting  installations;  the  effect  on  the  efficiency  of 
the  fixation  muscles  of  three  hours  of  work  under  each  of  these 
installations ;  the  effect  of  motion  pictures  on  the  eye  for  different 
distances  of  the  observer  from  the  projection  screen;  and  a  deter- 
mination of  the  tendency  of  the  different  conditions  of  lighting 
used  in  these  experiments  to  produce  ocular  discomfort,  and  a 
comparison  of  the  tendency  to  produce  discomfort  and  to  cause 
loss  of  efficiency. 

Time  cannot  be  taken  here  even  for  a  brief  statement  of  the 
results  obtained  in  these  experiments.  For  the  purpose  of  this 
paper,  it  will  be  sufficient  to  say  that  gradation  of  surface  bright- 
ness and  its  distribution  in  the  field  of  vision  were  shown  to  be 
important  factors  in  the  effect  on  the  eye.  In  the  work  to  be 
described  in  the  present  paper,  gradation  of  surface  brightness 
has  been  made  the  chief  variable.  Inverted  opal  glass  reflectors 
of  six  degrees  of  density  have  been  employed  and  a  correlation 
has  been  obtained  between  the  illuminating  effects  produced  and 
their  tendency  to  cause  loss  of  efficiency  and  to  produce  ocular 
discomfort.     As  the  work  progresses,  an  attempt  will  be  made 


FERREE   AND   RAND:     EXPERIMENTS   ON   THE   EYE  IO99 

not  only  to  investigate  this  factor  further  in  some  of  its  more 
important  relations  to  lighting  practise,  but  to  take  up  in  turn,  so 
far  as  is  practicable,  each  of.  the  other  factors  mentioned  in  the 
former  papers.2 

CONDITIONS  TESTED. 

An  effort  has  been  made  to  get  a  series  of  reflectors  similar  in 
size  and  shape  and  differing  only  in  density.  It  is  our  ultimate 
purpose  to  use  these  reflectors  both  in  accord  with  the  principles 
of  direct  and  indirect  lighting,  and  by  employing  additional  trans- 
lucent and  opaque  reflectors,  differing  if  need  be  in  size  and 
shape,  to  vary  first  one  and  then  the  other  of  the  distribution 
factors  mentioned  in  the  former  papers.  So  far,  however,  we 
have  been  able  to  use  only  six  of  the  number  of  reflectors  needed 
to  carry  out  this  plan,  and  these  in  accord  with  the  principle  of 
indirect  lighting.  They  were  all  turned  towards  the  ceiling  and 
were  installed  the  same  distance  from  it.  So  installed,  as  the 
photometric  measurements  will  show,  the  chief  variables  have 
been  the  brightness  of  the  reflectors  and  the  ceiling  spots  above 
the  reflectors, — more  especially,  the  brightness  of  the  reflectors. 
The  reflectors  used  will  be  designated  here  by  the  numerals, 
I,  II,  III,  IV,  V  and  VI ;  and  will  be  described  in  greater  detail 
in  an  appendix  to  the  paper.  They  were  all  installed  30  in. 
(0.76  m.)  from  the  ceiling3  and  were  held  by  Plume  and  Atwood 
semi-indirect  holders  attached  to  cords  dropped  from  the  eight 
outlets  shown  in  Fig.  1. 

It  has  been  our  wish  to  conduct  this  investigation,  as  has  been 
the  case  in  all  our  work  on  the  distribution  factors,  with  the 
quality  and  intensity  of  the  light  made  approximately  the  same. 
Unfortunately,  with  the  material  available,  the  quality  of  the 
light  could  not  be  made  in  all  cases  uniformly  alike.  Clear  tung- 
sten lamps  were  used  as  light  sources  with  each  installation,  but 
two  of  the  reflectors,  I  and  II,  were  not  free  from  color.  The 
density  of  these  reflectors  had  been  secured  in  part,  by  giving 
them  a  brownish  tone.  Just  how  much  effect  this  would  have, 
if  any,  on  the  results  of  the  tests  we  are  not  prepared  at  this  time 
to  say.  The  fact  should  be  borne  in  mind,  however,  in  considering 
the  results  obtained.  It  was  decided  to  make  the  intensity  of 
light  as  nearly  equal  as  possible  at  the  test  object  and  to  give  a 


IIOO    TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

supplementary  specification  of  the  lighting  effects  in  the  remainder 
of  the  room. 

At  the  test  object  the  light  was  photometered  in  several  direc- 
tions. It  was  made  approximately  equal  in  the  plane  of  the  test 
object  and  as  nearly  as  possible  equal  in  the  other  directions. 
The  specification  of  the  lighting  effects  in  the  remainder  of  the 
room  was  accomplished  as  follows,  (i)  A  determination  was 
made  of  the  average  illumination  of  the  room  under  each  set  of 
reflectors.     The  room  was  laid  out  in  3  ft.  (0.90  m.)  squares  and 


Fig.  1.— Plan  of  test  room. 

illumination  measurements  were  made  at  66  of  the  intersections 
of  the  sides  of  these  squares.  Readings  were  taken  in  a  plane 
122  cm.  above  the  floor  with  the  receiving  test-plate  of  the  illum- 
inometer  in  the  horizontal,  the  45 °  and  900  positions,  measuring 
respectively,  the  vertical,  the  450  and  horizontal  components  of 
illumination.  The  122  cm.  plane  was  chosen  because  that  was  the 
height  of  the  test  object.  (2)  A  determination  was  made  of  the 
brightness  of  prominent  objects  in  the  room,  such  as  the  test 
card,  the  reflectors,  the  reading  page,  the  specular  reflection  from 


FERREE   AND   RAND:     EXPERIMENTS   ON   THE   EYE  HOT 

surfaces,  etc.  The  brightness  measurements  were  made  by  means 
of  a  Sharp-Millar  photometer  with  the  receiving  test-plate  re- 
moved. The  instrument  was  calibrated  against  a  magnesium 
oxide  surface  obtained  by  depositing  the  oxide  from  the  burning 
metal  on  a  white  card.  By  this  method  the  reflecting  surfaces 
were  used  as  detached  test-plates.  The  readings  were  converted 
into  candlepower  per  square  inch  by  the  following  formula: 
brightness  =  foot-candles/V  X  144.  (3)  Photographs  were  made 
of  the  room  for  each  set  of  reflectors  employed.  They  will  not  all 
be  included  in  this  paper,  however,  because  too  little  difference 
in  illuminating  effects  is  shown  for  the  different  reflectors  to 
warrant  so  extensive  a  use  of  the  photographic  method  of  speci- 
fication. 

The  tests  were  conducted  in  a  room  30.5  ft.  (9.29  m.)  long, 
22.3  ft.  (6.797  m.)  wide,  and  9.5  ft.  (2.895  m0  mgli.  In  Fig.  1, 
this  room  is  shown  drawn  to  scale :  plan  of  room,  north,  south, 
east  and  west  elevations.  In  the  plan  of  room  are  shown  the  66 
stations  at  which  the  illumination  measurements  were  made ;  and 
the  positions  of  the  outlets  for  the  lighting  fixtures,  A,  B,  C,  D, 
E,  F,  G  and  H.  In  the  drawing,  east  elevation,  the  position  of 
the  observer  at  which  the  tests  were  taken  is  represented.4  So 
far  in  the  work  with  these  reflectors  the  tests  have  been  made  at 
only  one  point  in  the  room. 

Table  I  gives  the  illumination  measurements  for  each  of  the 
66  stations  represented  in  Fig.  I.  These  measurements  were 
made  with  the  receiving  test-plate  of  the  illuminometer  in  the 
horizontal,  the  vertical  and  the  45  °  planes.  Tables  II  and  III 
have  been  compiled  to  supplement  Table  I  for  the  purpose  of 
making  a  comparative  showing  of  the  evenness  of  illumination  at 
the  122-cm.  level  given  by  the  six  sets  of  reflectors.  Two  cases 
may  be  made  of  this :  (1)  a  comparison  may  be  made  of  a  given 
component  from  station  to  station;  or  (2)  the  difference  between 
the  components  may  be  compared.  To  facilitate  these  compari- 
sons (a)  the  mean  variation  from  the  average  of  each  of  the 
components  has  been  computed;  and  (b)  the  difference  in  the 
average  of  the  three  components  has  been  determined.  Results 
for  the  first  of  these  points  are  shown  in  Table  II ;  and  for  the 
second  in  Table  III. 


II02     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


TABLE  I. 
Showing  the  illumination  measurements  in  foot-candles  for  each  of  the 
66  stations  represented  in  Fig.  i  for  the  six  types  of  reflectors  used. 

Division  A. 

Vertical,  reflector  type  450,  reflector  type 


Station 
I 
2 
3 
4 
5 
6 

7 
8 

9 
10 
11 

12 

13 
14 
15 
16 

17 
18 

19 
20 
21 
22 

23 
24 

25 
26 

27 
28 
29 
30 
3i 
32 
33 
34 
35 
36 
37 
38 

39 
40 

4i 


Horizontal,  reflector  type 
III 


I 

I.40 
I.50 
I.49 
I.S5 
2.40 
2.20 
2.6o 
2.90 
2.70 

i-54 
2.10 

3-90 
4- 5o 
3.20 
3.10 
4-5o 
3.80 
2.60 

3-3° 

4.10 

5.20 

4.0 

4.0 

4.90 

3-90 

2.50 

2.80 

4.80 

5-8o 

4-5o 

4-50 

5.60 

5.o 

4.70 
5.20 
4-5o 
4.60 
4.90 
4.10 
2.60 
2.0 


11 
1-35 
1.2S 
i-52 
1.46 
2.20 
2.40 
2.50 
3.10 
2.60 
1.41 
1.88 

4-3° 

4.90 

34o 

3.10 

4.40 

3.10 

1.86 

2.40 

3- 7o 

4.60 

3-50 

3-7° 

4.90 

4. 10 

2.10 

2.80 

5-85 

6.0 

3.80 

3-9° 

5-30 

3.60 

3.80 

4.90 

4.10 

4.0 

5-4o 

4.10 

2.40 

1.67 


hi 


1.30 
1.20 
1.27 

1.47 

2.0 

2.10 

2.30 

2.90 

2.50 

1.32 

1.78 

3-7o 

4-5o 

3-50 
3.20 

43o 
3.10 
1.90 
2.50 
3-7o 
4- 50 
3-So 

3  7o 
4.70 
4.20 
1.78 
2.40 
4.70 
6.20 
4-5o 
4.60 
5.60 

4-25 

3.80 

5-o 

4-50 

4.60 

54o 
4.0 
2.0 
1.62 


o.55 

0.58 

0.50 

0.52 

0.50 

o-54 

o.57 

1-25 

1. 17 

1.30 

1. 16 

1. 10 

1.1 

1.03 


I.I5 

i-34 

1.42 

1.42 

1.42 

1-52 

1.86 

2.10 

1.80 

1.99 

2.0 

1.72 


o-53 

o.55 

0.46 

0.40 

0.41 

0.40 

0.46 

0.87 

1.0 

1.30 

1.0 

1.06 

1.20 

0.91 


05 

35 
11 

15 
33 
10 

54 
64 
61 

54 
90 
68 


0.50 
0.49 
0.48 
0.42 
0.50 
043 
045 
o.93 
0.94 
1.22 
0.94 
1.20 
0.97 
o.95 


1.20 
1.25 
i-37 
1. 14 
1.32 

i-i5 
1.42 
1.60 
1.48 
1.66 
1.80 
1.50 


2.10 

2.30 

1.65 

1.62 

2.50 

2.20 

1.50 

2.40 

2.70 

3.10 

2.50 

2.60 

3-o 

2.40 


34o 
3.80 

34o 

3-30 
4.0 

3-3° 
3-7o 
4.40 
3.60 

3-7o 

4.0 

3.20 


2.0 

2.70 

1.70 

1.70 

2.20 

1.48 

1. 10 

1.60 

2.20 

2.90 

2.20 

2.30 

2.70 

2.30 


3-o 

4.0 

2.70 

2.50 

3-7o 

2.60 

2.90 

3-5o 

2.80 

3-o 

3-8o 

3.10 


1.72 
2.40 
1.90 
1.69 
2.10 
1.62 
0.97 
1.90 
2.20 
2.70 
2.30 
2.10 
2.80 
3-3o 


3.20 

4.0 

3.10 

3-o 

34o 

2.80 

2.80 

3.80 

3-3o 

3-5o 

4.20 

3.20 


FERREE  AND   RAND:     EXPERIMENTS   ON   THE   EYE 


1 103 


TABLE  L— | 

Continued.) 

Horizontal,  reflector  type 

Vertical 
I 

,  reflector  type 
II            III 

45°, 

reflector  type 

Station 

I 

II 

hi 

I 

II 

in 

42 

3-9° 

4.40 

4.40 

I.80 

I.60 

I.64 

3-4° 

3.20 

34o 

43 

5-40 

5-40 

5.60 

2.20 

1.86 

I.84 

4.70 

4.0 

4.40 

44 

4.40 

4.IO 

3-7o 

2.IO 

1.76 

I.50 

4.0 

3-40 

3.20 

45 

4.IO 

4-3° 

4.20 

2.IO 

1. 71 

1.68 

3-8o 

340 

3-3o 

46 

5.20 

5.60 

5-7o 

2.IO 

1.60 

1.68 

4.60 

4.IO 

440 

47 

4-50 

4.20 

4-5o 

I.76 

H58 

1.52 

3.60 

3-30 

3-30 

48 

3-9° 

3-70 

3.80 

2.0 

1.94 

1.76 

3.60 

3- 30 

3-3o 

49 

4.90 

4.80 

5.10 

2.30 

2.10 

2.0 

3-90 

4.20 

3.80 

50 

4.10 

3.60 

4.0 

2.30 

2.0 

2.10 

3.80 

3-5o 

34o 

5i 

3-90 

3-7° 

3-9° 

2.30 

1.90 

1.98 

3- 70 

3-30 

3-5o 

52 

4.40 

4-5o 

4.60 

2.30 

i-95 

2.0 

4.10 

3-70 

3-9° 

53 

3.60 

3-7o 

3.80 

2.0 

1.58 

1.80 

3-3o 

3.20 

3.20 

54 

3.10 

3-5o 

3-4o 

I.70 

1.48 

1.46 

3.20 

2.90 

3.10 

55 

4.10 

4-3° 

4.10 

2.30 

1.70 

1.80 

4.20 

3-8o 

3-7o 

56 

3.60 

3-o 

3-30 

2.IO 

1.80 

1.86 

3-50 

3.10 

3.60 

57 

3.60 

3-o 

3.80 

2.30 

1.82 

2.0 

3-5o 

3-o 

3-7° 

58 

4.40 

4.40 

5 -40 

2.IO 

2.10 

2.10 

4.20 

4.10 

4.40 

59 

3-3o 

3.60 

3.60 

I.63 

1.85 

1.66 

3° 

3.20 

3.20 

60 

3-o 

2.60 

2.90 

2.0 

1.90 

1.66 

3-5o 

3.10 

3.20 

61 

3.10 

2.90 

3.20 

2.50 

2.0 

2.0 

3-9° 

3.60 

3-9° 

62 

2.60 

2.60 

2.50 

2.20 

2.10 

1.92 

3-5o 

34o 

3.20 

63 

2.50 

2.50 

2.10 

2.20 

2.15 

2.60 

3-40 

34o 

3.10 

64 

3.10 

2.30 

3° 

2.40 

2.0 

2.10 

4.0 

3-3° 

3.60 

65 

2.40 

2.40 

2.30 

I.98 

1.65 

i-59 

3.10 

2.70 

2.80 

66 

1.23 

1.25 

1.20 

Averaj 

re  3.61 

3-45 

3-49 

I.65 

1.44 

i-43 

3-3i 

2.98 

3-o5 

Division  B. 

Horizontal,  reflector  type 

Vertical 
IV 

,  reflector  type 
V             VI 

45°  1 

reflector  type 

Station 

rv 

V 

VI 

IV 

V 

VI 

I 

I.50 

i-45 

1-37 

2 

I.32 

1.36 

1.30 

3 

I.42 

1.40 

i-35 

4 

I.50 

i-53 

1.58 

5 

2.30 

2.50 

2.40 

6 

2.70 

2.30 

2.40 

7 

2.6o 

2.60 

2.50 

8 

3-40 

3.60 

3-30 

9 

2.80 

2.80 

2.80 

10 

1-55 

1.48 

1.56 

11 

2.00 

1.94 

2.00 

12 

4.20 

4-30 

4.10 

O.65 

0.51 

o.53 

2.6o 

2.40 

2.10 

13 

4.70 

54o 

4.90 

0.59 

O.58 

0.60 

2.90 

3.IO 

2.90 

14 

3.60 

3-4° 

3.60 

O.56 

0.49 

0.50 

1.88 

1.88 

1.92 

II04     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


TABLE  I.— {Continued.) 

Horizontal,  reflector  type       Vertical,  reflector  type 


45°,  reflector  type 


Station 

IV 

V 

VI 

IV 

V 

VI 

IV 

V 

VI 

15 

3.10 

3-4o 

3-3o 

0.58 

0.49 

0.43 

1.72 

1.80 

1.80 

16 

4.40 

4.70 

4.80 

o.55 

0.40 

0.56 

2.30 

2.70 

2.60 

17 

3.10 

3.60 

3-7o 

0.44 

0.43 

0.50 

1.64 

1.85 

2.0 

18 

1.88 

1.96 

2.0 

0.49 

0.51 

o-57 

1. 14 

I.I5 

I.I5 

19 

2-75 

2.60 

2.80 

1.25 

1. 10 

I-I3 

2.10 

1.88 

1.84 

20 

4.20 

3.80 

4-30 

1.20 

1.20 

1. 18 

2.70 

2.30 

2.60 

21 

4.60 

5-o 

5.o 

1.22 

1.48 

1.36 

2.80 

2.50 

3.20 

22 

3-7° 

3.80 

4.10 

1. 18 

1.05 

1.04 

2.50 

2.40 

2.50 

23 

3.80 

4.40 

4.20 

I.I5 

1.26 

1.06 

2.30 

2.70 

2.50 

24 

5.20 

5-9o 

5-7o 

1.47 

1-52 

1.27 

3.20 

3-3° 

3-o 

25 

4.90 

4-50 

4-30 

1-25 

1.31 

1.07 

2.90 

2.80 

2.40 

26 

2.40 

2.50 

2.20 

27 

2.70 

2.80 

2-75 

28 

5-io 

4.90 

5.20 

i-45 

1.24 

1. 14 

3.80 

34o 

3.60 

29 

5.60 

6.10 

6.40 

i-54 

i-34 

i-35 

4-3° 

4.40 

4.60 

30 

4-3o 

4-3° 

4-5o 

i-37 

1.27 

1.36 

3.20 

3-o 

3-5° 

31 

4.20 

4.0 

4.40 

1.30 

1.26 

1.30 

3-o 

2.90 

3-3o 

32 

5.60 

5-8o 

6.20 

1.38 

1.40 

i-53 

3-7o 

4-25 

4-5 

33 

4.10 

4-50 

4.80 

1.42 

1.28 

1.38 

3.10 

34o 

3.80 

34 

4.0 

4.0 

4.20 

1.80 

2.0 

1.88 

3-o 

3-30 

3-5° 

35 

5-4o 

5.60 

5-8o 

2.10 

2.20 

2.40 

4.0 

4.0 

4.40 

36 

4.40 

4-30 

4-5o 

1.70 

2.0 

1.98 

3-4o 

3-5o 

3.60 

37 

4-3o 

4.40 

4-30 

1.88 

1.96 

1.92 

3-4o 

3-30 

3-5° 

38 

5.20 

5.o 

5-5o 

2.30 

2.30 

2.20 

4.60 

4.10 

4.40 

39 

4-3° 

4.20 

4-5o 

2.20 

1.68 

1.90 

3-8o 

3-3o 

3-7o 

40 

2.60 

2.40 

2.60 

4i 

1.80 

1. 81 

1.92 

42 

4-50 

4.20 

4.40 

1.82 

1.90 

1.85 

3-5o 

3-6o 

3.80 

43 

5-4o 

5-5o 

5-8o 

2.10 

2.10 

2.10 

4-5o 

4-3o 

4.80 

44 

3.80 

3-7o 

4-5o 

1.90 

2.10 

2.0 

3-3° 

2.70 

3-9° 

45 

4.20 

4.40 

4.60 

1.90 

1.90 

1.98 

3.60 

3-9o 

3-9° 

46 

5-4° 

5-8o 

6.20 

1.90 

1.85 

1.88 

4-30 

4.70 

4.60 

47 

3-90 

4.0 

4-50 

1.80 

1.78 

1.72 

3.60 

3-3o 

3- 80 

48 

3.60 

3- 7o 

4-5o 

1.91 

1.94 

2.30 

3.20 

3-3o 

4.0 

49 

5.o 

4.90 

5-30 

2.20 

2.60 

2.60 

4-5o 

4.60 

4.80 

50 

3-9° 

4.0 

4.20 

2.40 

2.20 

2.80 

3-7o 

3-7o 

4.20 

5i 

3-90 

3-8o 

4.20 

2.40 

2.20 

2.60 

3-7o 

3.60 

4.10 

52 

4-65 

4.70 

5-o 

2.50 

2.50 

2.50 

4.10 

4.20 

4.20 

53 

4.0 

3-5° 

4.0 

2.10 

2.10 

2.10 

3-5o 

3.20 

3.60 

54 

3-7o 

3-5o 

3.80 

1.74 

1.70 

1.82 

3.20 

3-3o 

3.60 

55 

4.20 

4.70 

5.o 

2.40 

2.0 

2.20 

4.0 

4-3° 

4.90 

56 

3.20 

3-3° 

3.60 

2.20 

2.20 

2.10 

3-5° 

3.60 

3-9o 

57 

3-4o 

3-5o 

3.60 

2.20 

2.30 

2.20 

3.60 

3- 80 

3-7° 

58 

4.60 

5-io 

5- 20 

2.20 

2.30 

2.40 

4.20 

4.90 

4.60 

FERREE   AND   RAND:     EXPERIMENTS   ON   THE   EYE  1 105 


TABLE  I.— (Continued.) 
Horizontal,  reflector  type       Vertical,  reflector  type 


45°,  reflector  type 


Station 

59 
60 
61 
62 

63 
64 
65 
66 


IV 

3-9° 
2.50 
3.20 
2.30 
2.50 
3.10 
2.30 
1. 14 


v 

3-9° 
2.50 
3.20 
2.60 
2.40 
2.90 
2.40 
1. 16 


VI 

4-3° 

3-o 

3.80 

2.50 

2.60 

3-o 

2.40 

1.42 


IV 

1.78 
2.0 
2.30 
2.10 

2.60 
2.30 
2.0 


V 

1.81 

2.20 
2.60 

2.30 
2f8o 
2.40 
2.0 


VI 

2.40 
2.40 
2.40 
2.40 
2.IO 
2.40 
2.IO 


IV 

3.20 

3-30 

4.40 

3.20 

3.60 

4.0 

3.10 


V 

3-50 
3-70 

4.20 

3-o 

3-8P 

4.0 

3.00 


VI 

4.0 

3.80 

4.6 

3-4o 

3-4o 

4.0 

3.10 


Average  3.80      3.70      4.20 


1.71 


3-3°      3-3i       3-49 


1.675     1.68 

TABLE  II. 
Compiled  from  Table  I  to  show  a  comparison  of  the  evenness  of  the  illu- 


mination at  the  122-cm.  level  given  by  the  six  types  of  reflector  used 
Mean  variation  of  components 


Percentage  of 
mean  variation  of  components 


Type  of 
reflector 

Vertical 

Horizontal 

45° 

I 

O.976 

O.516 

O.582 

II 

O.999 

O.487 

O.576 

III 

I.066 

O.430 

O.562 

IV 

1. 21 

O.498 

O.60I 

V 

I. IO 

0.539 

O.628 

VI 

1.47 

0.574 

O.677 

Vertical 

Horizontal 

45° 

27.O 

31-3 

17.6 

29.O 

33-8 

19-3 

3°-5 

30.1 

18.4 

31.8 

29.7 

18.2 

29.8 

32.1 

I9.0 

35-o 

31.2 

19.4 

TABLE  III. 
Compiled  from  Table  I  to  show  the  difference  in  the  average  values  of  the 
three  components  of  illumination  for  the  six  types  of  reflector  used. 


Difference  between  components 


Percentage  of 
difference  between  components 


Type  of  Vertical  and  Vertical 

reflector  horizontal  and  450 

I  I.96  O.3O 

II  2.0I  O.47 

III  2.06  O.44 

IV  2.125  0.50 
V  2.02  0.39 

VI  2.49  0.71 


450  and 
horizontal 

1.66 

i-54 

1.62 

1.625 

1.63 

1.78 


Vertical  and 
horizontal 

54-3 
58.3 
59o 
55-9 
54-6 

59-3 


Vertical 
and  450 

8-3 
13.6 
12.6 

13.2 
10.5 

16.9 


450  and 
horizontal 

50.2 
51-7 
53-1 
49.2 
49.2 
51.0 


Figs.  2-5  are  taken  from  the  series  of  photographs  showing  the 
illumination  effects  produced  by  the  six  types  of  reflector  used.5 
As  was  stated  earlier  in  the  paper,  not  so  much  use  has  been 
made  of  the  photographic  method  of  specification  in  this  as  in 
the  former  papers.  In  the  former  papers  three  photographs  were 
given  for  each  set  of  reflectors.  One  of  these  was  taken  from 
the  south  end  of  the  room  at  a  point  4  ft.  (1.22  m.)  from  the 


II06     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

west  wall.  This  photograph  was  taken  so  as  to  comprehend  as 
much  of  the  room  as  was  possible  in  one  view.  It  included  the 
greater  part  of  the  ceiling,  floor,  and  north  wall,  six  of  the  fixtures 
and  about  one-half  of  the  east  wall.  Another  was  taken  to  show 
the  illumination  effects  in  the  west  half  of  the  room.  This  photo- 
graph represents  the  distribution  of  light  and  shade  on  the  greater 
part  of  the  west  wall  and  adjacent  ceiling  and  includes  two  of  the 
fixtures.  A  third  was  taken  primarily  for  showing  the  brightness 
measurements  of  all  surfaces  having  a  very  high  or  very  low 
brilliancy  in  the  field  of  view  of  the  observer.  To  have  carried 
out  this  program  in  full  in  the  present  work  would  have  required 
the  insertion  here  of  eighteen  photographs.  The  amount  of 
difference  in  the  distribution  of  light  and  shade  for  the  different 
reflectors  was  much  too  small  to  warrant  this.  It  has  in  fact  been 
deemed  sufficient  to  include  in  this  paper  photographs  for  only  the 
second  and  third  of  these  positions  and  for  only  two  of  the  sets 
of  reflectors  used, — the  most  opaque  and  the  least  opaque.  The 
photographs  for  the  second  position  are  shown  in  Figs.  2  and  3 ; 
for  the  third,  in  4  and  5.  In  representing  the  brightness  measure- 
ments in  Figs.  4  and  5,  the  spot  measured  is  marked  by  a  letter 
and  the  numerical  value  of  the  brightness  measurement  in  candle- 
power  per  square  inch  is  printed  near  by.  The  spots  are  lettered 
for  convenience  of  reference  in  the  tables  of  brightness  measure- 
ments. The  photographs  were  taken  from  a  point  directly  be- 
hind the  position  of  the  observer  as  near  to  the  south  wall  of  the 
room  as  was  possible ;  and  although  not  all  of  the  observer's  field 
of  view  is  covered  by  the  brightness  measurements  made,  owing 
to  the  narrow  field  of  the  camera  as  compared  with  the  binocular 
field,  still  the  order  of  magnitude  of  brightness  differences  present 
in  the  field  of  view  is  well  represented  by  these  measurements. 

In  Tables  IV  and  V  are  given  the  brightness  measurements  of 
the  room  for  the  six  sets  of  reflectors.  These  tables  also  include 
the  letters  identifying  the  measurements  with  the  spots  measured 
as  shown  in  Figs.  4  and  5.  The  distribution  of  light  and  shade 
in  the  room  was  so  similar  for  the  different  sets  of  reflectors  that 
the  spots  measured  have  approximately  the  same  location  for 
each  set  of  reflectors.  Two  sets  of  measurements  were  made 
of  the  brightness  of  the  reflectors, — one  with  the  opening  of  the 


i\  bio 


Fig.  2.— Showing  the  illumination  of  the  west  wall  of  the  room,  Reflector  I. 


Fig.  3.-Showing  the  illumination  of  the  west  wall  of  the  room,  Reflector  VI. 


Fig.  4- — Showing  the  illumination  effects  in  the  north  end  of  the  room,  Reflector  I; 
and  the  brightness  measurements  of  all  surfaces  having  a  very  high  or  a  very  low- 
brilliancy.  This  photograph  was  taken  from  a  point  directly  behind  the  observer 
as  near  to  the  south  wall  of  the  room  as  was  possible,  and  comprehends  as  much 
of  the  observer's  field  of  view  as  could  be  included  in  the  field  of  the  camera. 


■ona 

T 

■       ■""'"        -0,0 

c         s> 

.0107    '°'*~>.      ""« 

a' 

£ 

■  *zu 

A 
-JO 

F 

■aoi 

A    a  1 

r? 

1 

-,-d 

-r 

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LjJu 

rirj- 

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Jnfcii 

wmm 

mm\ 

mmmmilH£^^^f 

ri         l 

mmm,\ 

"•*'"  *         11^3^    % 

W.  gmtti 

Fig.  5. — .Showing  the  illumination  effects  in  the  north  end  of  the  room,  Reflector  VI; 
and  the  brightness  measurements  of  all  surfaces  having  a  very  high  or  a  very  low 
brilliancy.  This  photograph  was  taken  from  a  point  directly  behind  the  observer 
as  near  to  the  south  wall  of  the  room  as  was  possible,  and  comprehends  as  much 
of  the  observer's  field  of  view  as  could  be  included  in  the  field  of  the  camera. 


FERREE   AND   RAND:     EXPERIMENTS   ON   THE   EYE  1 107 

illuminometer  close  to  the  reflector  and  the  other  with  the  opening 
as  nearly  as  possible  in  the  position  of  the  observer  when  making 
the  test.  In  the  former  case  the  receiving  arm  was  turned  normal 
to  the  surface  measured  and  the  instrument  was  supported  in 
such  a  position  that  the  opening  was  about  4  in.  (10.16  cm.)  from 
this  surface.  The  surfaces  of  some  of  the  reflectors  presented  so 
much  unevenness  of  brightness  that  overlapping  measurements 
were  made  and  an  average  taken.  These  average  values  are  given 
in  Table  IV.  In  Table  V  is  given  the  brightness  of  the  reflectors 
as  measured  from  the  position  of  the  observer.  These  measure- 
ments were  taken  of  the  reflectors  at  outlets  A,  B  and  C  (Fig.  i) 
for  each  of  the  six  installations.  A  comparison  of  these  measure- 
ments will  show  that  reflector  B  has  in  each  case  a  higher  value 
than  reflector  A,  and  C  a  higher  value  than  B.  Whether  or  not 
this  can  be  wholly  accounted  for  because  the  reflectors  were  not 
perfect  diffusers  we  are  not  prepared  to  say.  That  is,  the  angle 
subtended  by  reflector  A  at  the  point  of  observation  was  less  than 
that  subtended  by  B,  and  by  B  less  than  that  subtended  by  C; 
so  that  at  the  distance  at  which  these  reflectors  was  viewed  ap- 
proximately all  of  A  occupied  the  field  of  the  illuminometer  in 
making  the  brightness  match,  while  only  the  brighter  central 
portions  of  B  and  C  were  comprehended  in  this  field,  still  less  of 
the  duller  periphery  being  included  for  C  than  for  B. 

In  Tables  VI  and  VII,  are  shown  some  prominent  ratios  of 
surface  brightness  for  the  six  sets  of  reflectors.  In  compiling 
these  ratios  it  has  been  considered  important  to  make  a  compara- 
tive showing  for  the  different  types  of  reflectors  (a)  of  the 
extremes  of  surface  brightness  and  (b)  of  the  relation  of  the 
brilliancy  of  objects  in  the  surrounding  field  to  the  surface  bright- 
ness at  the  point  of  work.  Extremes  of  surface  brightness  are 
shown  by  giving  the  ratios  between  surfaces  of  the  first,  second, 
third,  etc.,  order  of  brilliancy  and  the  lowest  order  of  brilliancy; 
and  the  comparison  of  the  brilliancy  of  objects  in  the  surrounding 
field  to  the  brightness  at  the  point  of  work  by  giving  the  ratios 
of  the  surfaces  of  the  first,  second,  and  third  order  of  brilliancy 
to  the  brightness  of  the  test  card  and  the  reading  page  in  the 
working  position. 


II08     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 


TABLE  IV. 
Showing  the  brightness  measurements  in  candlepower  per  square  inch  for 
the  surfaces  A,  B,  C,  D,    etc.    (Figs.  4  and  5),  the  test  card  and  reading 
page.     These  measurements  were  taken  with  the  illuminometer  close  to  the 
surface  measured  and  with  its  receiving  arm  normal  to  this  surface. 

Surface  Reflector  Reflector  Reflector  Reflector  Reflector  Reflector 

measured  type  I.  type  II  type  III  type  IV  type  V  type  VI 

A O.264  O.361  O.392  0.614  0.848  0.920 

B O.030  0.01985  0.024  0.0IOI  0.0137  0.0193 

C 0.029  0.021  0.021  0.0123  0.0166  0.0156 

D 0.0193  0.0106  0.0075  0.0070  0.00767  0.0107 

F 0.00238  0.00246  0.00229  0.00282  0.00255  0.0026 

F 0.0034  0.00394  0.0034  0.00396  0.00396  0.00396 

G 0.0040  0.00392  0.0042  0.00497  0.00418  0.00458 

H 0.00414  0.00396  0.0044  0.00506  0.0043  0.00466 

I  0.0044  0.00402  0.00453  0.00528  0.0042  0.00484 

J 0.00163  o.ocii  0.00128  0.00141  0.00123  0.00163 

K 0.0036  0.00387  0.00414  0.0044  0.00425  0.00414 

L 0.0023  0.00224  0.00282  0.00299  0.00273  0.00299 

M 0.00458  0.00405  0.00484  0.0052  0.00427  0.00506 

N 0.00277  0.00216  0.00216  0.00334  0.00268  0.00268 

0 0.00348  0.00299  0.00462  0.00361  0.00361  0.00365 

p   0.0037  0.00312  0.00506  0.00409  0.0037  0.00397 

Q 0.00097  0.00083  0.00106  0.00099  0.000924  0.00106 

R 0.00199  0.0029  0.00207  0.00220  0.00246  0.00238 

Test  card.  0.00312  0.00308  0.00308  0.00317  0.00312  0.00317 
Reading 
page 
hori- 
zontal-- 0.00528  0.00497  0.00506  0.0052  0.00484  0.00484 
Reading 
page 

45°  po- 
sition.. 0.00352         0.00348         0.00352         0.00348         0.00334         0.00339 

TABLE  V. 
Showing  the  brightness  measurements  in  candlepower  per  square  inch  of 
the  reflectors  used  when  the  measurements  are  made  from  the  position  oc- 
cupied by  the  observer  during  the  test.  In  these  measurements  the  receiving 
arm  of  the  illuminometer  was  placed  as  nearly  as  possible  in  the  position  of 
the  observer's  eye  during  the  test,  and  was  pointed  at  the  reflector.  The 
position  of  the  reflector  in  each  case  is  shown  by  the  letters  A,  B  and  C  in 
Fig.  1. 

Position  of    Reflector        Reflector         Reflector         Reflector         Reflector         Reflector 
reflector        type  I  type  II  type  III  type  IV  type  V  type  VI 

A 0.II9  O.156  O.180  O.2325  O.327  O.382 

B 0.1755  0.1913  0.2025  0.2535  0.338  0.405 

C 0.2025  0.338  0.397  0.544  0.722  0.830 


FERREE  AND  RAND:    EXPERIMENTS  ON  THE  EYE  IIO9 

Supplementary  to  Tables  IV,  VI  and  VII  we  have  computed 
for  the  six  types  of  reflector  the  mean  variation  of  the  several 
brightness  values  from  their  average  values.  While  important 
from  the  standpoint  of  showing  the  variations  from  the  mean  for 
the  different  types  of  reflector,  such  a  comparison  is,  however, 
probably  not  so  important  from  the  standpoint  of  the  eye  as  are 
the  comparisons  given  in  Tables  IV  to  VII.  That  is,  from  the 
standpoint  of  the  effect  on  the  eye  it  is  probably  more  important 
to  give  a  representation  of  the  brightness  of  individual  surfaces, 
more  especially  of  surfaces  showing  extremes  of  brightness,  than 
it  is  to  give  the  mean  variation  from  the  average  brightness  of  all 
the  surfaces.  In  order  to  make  possible  the  comparison  with  and 
without  the  reflector  and  the  spot  above  the  reflector,  the  table  is 
made  to  show  separately  the  mean  variation  of  the  following 
measurements:  (a)  for  all:  (&)  for  all  but  the  reflector;  and 
(c)  for  all  but  the  reflector  and  the  spot  above  the  reflector. 
Results  are  given  in  Table  VIII. 

As  was  stated  earlier  in  the  paper  the  effect  of  a  harmful  in- 
stallation on  the  ability  of  the  eye  to  maintain  its  efficiency  for  a 
period  of  work  varies  with  the  position  of  the  observer  in  the 
room.  In  the  former  work  the  tests  were  made  at  four  positions, 
one  in  which  six  fixtures  were  in  the  field  of  view ;  one  in  which 
four  were  in  the  field  of  view ;  one  in  which  two  were  in  the  field 
of  view;  and  one  in  which  none  was  in  the  field  of  view.  This 
variation  of  the  position  in  which  the  observation  is  made  accom- 
plishes two  purposes  :  ( 1 )  it  gives  us  a  more  representative  idea 
of  the  difference  of  the  effect  on  the  eye  of  the  six  types  of  light- 
ing used;  and  (2)  it  shows  the  effect  of  varying  the  number  of 
surfaces  in  the  field  of  view  showing  brightness  differences,  par- 
ticularly the  number  of  primary  sources.  So  far  we  have  been 
able  to  conduct  the  tests  for  the  reflectors  used  in  this  work  at 
only  one  of  these  positions,  namely,  the  one  with  six  reflectors 
in  the  field  of  view.6  Later  we  expect  to  repeat  the  tests  for 
at  least  a  part  of  these  reflectors  at  the  other  three  positions. 

The  results  for  the  effect  on  the  eye  are  given  in  Table  IX.7 
The  values  given  in  this  table  are  averaged  in  each  case  from 
the  results  of  6  three-hour  tests  and  are  typical  of  the  results 
obtained  for  all  of  our  observers.     In  order  to  show  the  repro- 


I IIO     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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FERREE   AND   RAND:     EXPERIMENTS   ON    THE   EYE 


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1 1 12     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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FERREE   AND   RAND:     EXPERIMENTS   ON   THE   EYE  1 1 13 

ducibility  of  the  results  obtained  and  that  the  variations  produced 
by  the  changes  in  lighting  effects  are  much  greater  than  the  vari- 
ations in  the  test  itself,  subject  to  all  the  variable  factors  which 
may  influence  it,  the  mean  variation  from  the  average  result  has 
been  computed  in  each  case.  The  value  of  this  in  per  cent,  is 
given  in  column  15.8 

TABLE  VIII. 
Compiled  from  Table  IV  to  show  the  mean  variations  in  surface  bright- 
ness for  the  six  types  of  reflector  used. 

Division  A. 

Percentage 
Mean  variation  of  mean  variation 

for  the  three  reflectors  for  the  three  reflectors 

Reflector  type  Reflector  type 

Measurements  considered                I                     II  III  I  II  HI 

All 0.02885  0.0373  0.0405        134.8     148.0  148.4 

All  but  the  reflector 0.00667  0.00412  0.00411       93.2       75.3  70.3 

All  but  the  reflector  and 
the  spots  above  the  re- 
flector   0.000917  0.000884  0.0012         29.5       29.7  35.8 

Division  B. 

Percentage 
Mean  variation  of  mean  variation 

for  the  three  reflectors  for  the  three  reflectors 

Reflector  type  Reflector  type 

Measurements  considered               IV                  V  VI  IV  V  VI 

All 0.06494  0.08852  O.09597      168.O      170.8  170.5 

All  but  the  reflector 0.0020  0.00274  0.00342      42.4      56.0  62.0 

All  but  the  reflector  and 
the  spots  above  the  re- 
flector     0.00111  0.000964  0.00104      30.9      30.0  30.2 

In  Chart  i  a  graphic  representation  is  made  of  the  results  of 
this  table.  In  constructing  this  chart,  the  total  length  of  the  test 
period  is  plotted  along  the  abscissa,  and  the  ratio  of  the  time  the 
test  object  is  seen  clear  to  the  time  it  is  seen  blurred  in  the  three- 
minute  records  before  and  after  work  is  plotted  along  the  ordin- 
ate. Each  one  of  the  large  squares  along  the  abscissa  represents 
one  hour  of  the  test  period,  and  along  the  ordinate  an  integer  of 
the  ratio. 

So  far  in  all  our  work  we  have  shown  for  the  sake  of  complete- 
ness of  representation  the  gradation  of  surface  brightness  in 
three  ways. — (i)  Brightness  measurements  of  prominent  sur- 
faces have  been  made.  (2)  Ratios  have  been  given  between 
surfaces  of  the  first,  second,  third,  etc.,  order  of  brilliancy  and 
surfaces  of  the  lowest  order  of  brilliancy;  and  between  sur- 


1 1 14     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


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FERREE   AND    RAND:     EXPERIMENTS   ON    THE   EYE  1 1 15 


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IIl6     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

faces  of  the  first,  second  and  third  order  of  brilliancy  and  the 
brightness  at  the  point  of  work.  And  (3)  the  mean  variation 
from  the  average  and  the  percentage  of  mean  variation  have  been 
shown.     In  the  consideration  of  these  specifications,  a  number  of 

CHART  I. 
Showing  the  tendency  of  the  six  types  of  reflectors  to  cause  loss  of 
visual  efficiency,  or  power  to  sustain  clear  seeing.     Ratio  time  clear  to 
time  blurred  is  plotted  against  length  of  test  period. 

Foot-candles 


Reflector 
Type  I  . . 
Type  II  . 
Type  III 
Type  IV 
Type  V  . 
Type  VI 


Volts 

III 

IIO 

107.5 
105.5 
105.5 
107.5 


Horizontal 

Vertical 

45° 

4-1 

I.I4 

2.7 

3-7 

I.I3 

2.6 

4.2 

I.I6 

2.6 

3-8 

LIS 

2-5 

3-7 

LIS 

2.6 

4.2 

I.I6 

2.7 

1 

n 

in 
r? 

single  items  might  be  selected  as  of  possible  significance  in  rela- 
tion to  the  effect  on  the  eye.  Among  these  may  be  mentioned  the 
order  of  magnitude  of  the  highest  brilliancies ;  the  average  bril- 
liancy; the  ratio  of  the  highest  to  the  lowest  order  of  brilliancy; 
the  ratio  of  the  highest  order  of  brilliancy  to  the  average  bril- 


FERREE   AND   RAND:     EXPERIMENTS   ON   THE   EYE 


II 17 


liancy ;  the  ratio  of  the  average  to  the  lowest  order  of  brilliancy ; 
the  ratio  of  the  highest  order  of  brilliancy  to  the  brilliancy 
at  the  point  of  work,  (brightness  of  test  card  and  reading  page)  ; 
etc.  In  order  to  see  which  of  these  correlate  most  closely  with 
the  results  of  the  test  for  tendency  to  cause  loss  of  efficiency, 

CHART  II. 
Showing  the  tendency  of  the  six  types  of  reflectors  to  cause  loss  of 
visual  efficiency  or  power  to  sustain  clear  seeing.    Percentage  drop  in  ratio 
time  clear  to  time  blurred  is  plotted  against  brightness  of   reflector  in 
candlepower  per  square  inch. 

Foot-candles 
Reflector  Volts 

Type  I   in 

Type  II    no 

Type  III    107.5 

Type  IV    105.5 

Type  V    105.5 

Type  VI    107.5 

80 


Horizontal 

Vertical 

45° 

Cp.  per 
sq.  in. 

4.1 

1. 14 

2.7 

O.264 

3-7 

I-I3 

2.6 

0.36l 

4.2 

1. 16 

2.6 

0.392 

3.8 

LIS 

2-5 

O.614 

37 

LIS 

2.6 

O.848 

4.2 

I.I6 

2.7 

0.920 

curves  are  constructed  in  which  some  of  these  features  are  plotted 
against  the  results  of  the  test.  These  curves  are  given  in  Charts 
II  to  IV.  In  Chart  II  per  cent,  loss  of  efficiency  is  plotted  against 
the  highest  order  of  brilliancy,  namely,  the  brightness  of  the  re- 
flectors. In  Chart  III  and  IV  are  grouped  the  remainder  of  the 
curves. 

Another  method  of  evaluating  the  results  of  our  test  was  briefly 


IIl8     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 


treated  of  in  a  discussion  of  Mr.  Cravath's  paper  by  one  of  the 
writers.  (The  Transactions,  1914,  IX,  pp.  1051-1053.)  In 
this  method  the  ratio  of  the  time  seen  clear  to  the  total  time  of 
the  observation  is  taken  as  the  measure  of  the  ability  of  the  eye 

CHART  III. 

Showing  the  tendency  of  the  six  types  of  reflectors  to  cause  loss  of 
visual  efficiency  or  power  to  sustain  clear  seeing.  In  curve  A  percentage 
drop  in  ratio  time  clear  to  time  blurred  is  plotted  against  ratio  of  average 
brightness  to  brightness  at  point  of  work ;  in  B,  against  ratio  of  lightest 
surface  to  brightness  at  point  of  work ;  and  in  C,  against  average 
brightness. 


30 


40 


I5 -"" 

Y 

i\ 

m 


60 


40 


B 


in - 

V 

/i 

71 


'5 


'70 


170 


270 


80 


40 


Y^e 

h 

002  0.04  0.06 

to  sustain  clear  seeing  at  the  time  the  test  is  taken.  For  the  sake 
of  comparing  this  method  of  evaluation  with  the  one  we  have  used 
in  the  rest  of  the  paper,  Charts  V  and  VI  have  been  constructed. 
In  Chart  V  length  of  test  period  is  plotted  along  the  abscissa,  and 
the  ratio  of  time  clear  to  total  time  of  observation  is  plotted  along 
the  ordinate.     In  plotting  these  lines,  one  of  the  larger  squares 


FERREE   AND   RAND:     EXPERIMENTS   ON    THE   EYE 


III9 


along  the  abscissa  represents  one  hour  of  the  test  period,  and 
along  the  ordinate,  0.1  ratio,  time  seen  clear  to  the  total  time  of 
the  observation.  That  is,  in  this  method  of  treating  the  results, 
since  the  ratios,  or  the  quantities  to  be  plotted  along  the  abscissa, 
are  much  smaller  than  they  are  in  the  former  method,  the  scale 

CHART  IV. 

1 
Showing  the  tendency  of  the  six  types  of  reflector  to  cause  loss  of 

visual  efficiency  or  power  to  sustain  clear  seeing.     In  curve  D  percentage 

drop  in  ratio  time  clear  to  time  blurred  is  plotted  against  ratio  of  lightest 

surface  to  average  brightness ;  in  E,  against  ratio  of  lightest  surface  to 

darkest  surface;  and  in  F,  against  ratio  of  average  brightness  to  darkest 

surface. 

D  E 

80 1 


00 1 

m  « 

Sn 

i^ 

YI  < 

^ 

40 
n 

1/ 

200 


600 


000 


80 


40 


m • 

711 

YJ»> 

•  1 

20 


4-0 


B0 


has  been  multiplied  by  10  for  convenience  of  representation.  In 
order  that  the  lines  may  all  start  at  a  common  point,  the  initial 
ratios  are  reduced  to  1  as  a  common  standard.  In  Chart  VI,  per 
cent,  loss  of  efficiency  as  evaluated  by  this  method  is  plotted 
against  intrinsic  brilliancy  of  reflector.  As  before,  intrinsic 
brilliancy  of  reflector  is  plotted  along  the  abscissa,  and  per  cent. 


II20     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

loss  of  efficiency  along  the  ordinate.  A  comparison  of  these  re- 
sults with  the  former  will  show  the  same  order  of  rating  of  the 
reflectors  but  a  slight  change  in  the  position  in  the  scale  given  to 
some  of  the  reflectors.     For  the  purpose  of  discovering  what  is 

CHART  V. 
Showing  the  tendency  of  the  six  types  of  reflectors  to  cause  loss  of 
visual  efficiency  or  power  to  sustain  clear  seeing.     Ratio  of  time  clear  to 
total  time  of  observation  is  plotted  against  length  of  test  period. 

Foot-candles 

Reflector 

Type  I    

Type  II   

Type  III   

Type  IV   

Type  V  

Type  VI   


Volts 

Horizontal 

Vertical 

45° 

III 

4-1 

I.I4 

2.7 

110 

3-7 

I.I3 

2.6 

107-5 

4.2 

I.I6 

2.6 

105-5 

3-8 

I.I5 

2.5 

105.5 

3-7 

LIS 

2.6 

107-5 

4.2 

I.l6 

2.7 

the  best  way  of  treating  the  results  of  the  tests,  several  methods 
have  been  employed.  Up  to  and  including  the  present  paper, 
however,  only  three  of  them  have  been  given  in  print :  ratio  of 
time  clear  to  time  blurred,  ratio  of  time  clear  to  total  time  of 


N 


FERREE   AND   RAND:     EXPERIMENTS   ON    THE   EYE 


II2I 


observation,  and  the  per  cent,  of  drop  in  the  ratio  time  clear  to 
time  blurred.    An  ultimate  decision  with  regard  to  what  is  the 
best  method  of  treatment  of  the  results  can  come,  we  believe,  only 
with  the  consideration  of  a  larger  number  of  cases. 
The  work  was  concluded  by  determining  for  the  six  types  of 

CHART  VI. 
i 
Showing  the  tendency  of  the  six  types  of  reflectors  to  cause  loss  of 

visual  efficiency  or  power  to  sustain  clear  seeing.    Percentage  drop  in  ratio 

time  clear  to  total  time  of  observation  is  plotted  against  brightness  of 

reflector  in  candlepower  per  square  inch. 

Foot-candles 


Reflector 


Type 
Type 
Type 
Type 
Type 
Type 


I   . 

II 

III 

IV 

V 

VI 


Volts 

Horizontal 

Vertical 

45° 

Cp.  per 
sq.  in. 

III 

4.1 

I.I4 

2.7 

O.264 

110 

3-7 

I.I3 

2.6 

O.361 

107-5 

4.2 

I.I6 

2.6 

0.392 

105-5 

3-8 

LIS 

2.5 

O.614 

105.5 

3-7 

1. 15 

2.6 

O.848 

107.5 

4.2 

I.l6 

2.7 

0.920 

installations  the  relative  tendencies  to  produce  ocular  discomfort. 
As  before,  two  cases  were  made  of  this  determination, — one  when 
the  eye  was  at  rest,  the  other  when  it  was  at  work.  For  a  de- 
scription of  how  the  determination  is  made,  and  a  discussion  of 
the  method  that  is  used,  see  the  Transactions  of  the  I.  E  .S., 
1913,  VIII,  pp.  54-58;  and  1915,  X,  pp.  496-501.  Space  will  be 
taken  here  only  for  presentation  of  the  results.     These  are  given 


1 122     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

in  Table  X.  In  this  table  are  given  also,  for  the  sake  of  com- 
parison, results  expressing  the  tendency  of  the  six  types  of  re- 
flectors to  cause  loss  of  ability  to  sustain  clear  seeing. 

APPENDIX. 
The  reflectors  used  in  this  work  were  supplied  by  the  Holo- 
phane  Works  of  the  General  Electric  Co.,  and  are  opal  glass  of 
light,  medium,  and  heavy  densities.  They  are  all  of  the  bowl 
type  and  of  the  same  size,  8  in.  Reflector  I  is  a  pressed  Sudan 
toned  brown;  reflector  II,  a  blown  white  glass,  toned  brown 
(experimental);  reflector  III,  a  pressed  Sudan;  reflector  IV,  a 
pressed  Druid;  reflector  V,  a  blown  Veluria;  and  reflector  VI,  a 
blown  white  glass  (experimental).  Reflectors  I,  III,  IV  and  V 
are  commercial  products,  but  II  and  VI  are  special,  inserted  in 
the  series  to  give  gradations  in  density.  As  was  stated  in  the 
text  these  reflectors  presented  considerable  unevenness  of  surface 
brightness.  This  was  especially  true  of  the  pressed  reflectors, 
which  are  smooth  on  the  inside  and  grooved  on  the  outside.  The 
glass  in  these  grooves  being  thinner  than  in  the  spaces  between, 
a  very  uneven  surface  brilliancy  is  given  to  the  reflector.  Further, 
reflector  IV,  because  of  its  imperfect  diffusion,  was  quite  a  little 
brighter  in  the  center,  at  the  location  of  the  filament,  than  at  the 
top  and  bottom.  In  determining  the  brightness  of  these  reflectors, 
overlapping  readings  were  taken  and  an  average  obtained. 

NOTES. 

1  The  truth  of  this  should  be  obvious  to  any  methodological  critic.  It  is  in 
fact  the  logical  corollary  of  the  application  of  a  new  test  to  a  new  field.  Until  a 
range  of  application  is  made  which  is  reasonably  representative  of  the  work  for 
which  the  test  is  designed  to  be  used,  a  comp'ete  description  of  the  test  itself,  in- 
cluding a  statement  of  the  factors  which  may  influence  its  results  and  full  directions 
how  to  use  it,  cannot  possibly  be  given  without  more  presumption  than  we  care  to 
exercise.  While  an  attempt  to  do  this  might  afford  a  certain  amount  of  specious  satis- 
faction to  the  practicing  engineer,  it  would  be  superficial  and  incomplete  and  calculated 
to  produce  trouble  in  the  work  of  others.  When  in  the  opinion  of  the  authors  a 
sufficient  range  of  work  has  been  covered,  a  separate  paper  will  again  be  devoted  to 
the  test  method  itself  in  which  data  collected  from  all  the  work  will  be  submitted, 
and  the  adaptability  and  application  of  the  method  to  different  kinds  of  work  will  be 
discussed.  It  is  clear,  we  think,  to  anyone  who  has  had  experience  in  developing  and 
applying  a  new  test  that  this  can  be  done  more  safely  and  effectively  at  the  close 
of  a  section  of  the  work  which  is  sufficiently  comprehensive  to  be  representative  of 
the  accomplishment  of  the  test,  than  at  its  beginning  or  while  the  work  is  yet  in 
progress.  In  this  later  paper  data  will  be  submitted  also  on  four  types  of  test  devised 
by  us  to  detect  changes  in  the  functional  condition  of  the  retina  as  the  result  of 
working   under    different    conditions    of    lighting. 

Two   points   keep  coming  up,   however,    with   a   degree   of   persistence    which   may 


FERREE   AND   RAND:     EXPERIMENTS   ON    THE    EYE  II23 

justify  a  somewhat  detailed  discussion  at  this  time.  The  first  pertains  to  the  sensi- 
tivity of  the  test  to  factors  extraneous  to  the  conditions  that  are  being  tested.  The 
point  was  briefly  discussed  in  the  original  paper  on  the  test  and  again  in  the  two  suc- 
ceeding papers.  It  was  brought  out  more  especially  in  Mr.  Cravath's  paper  and  in 
the  discussions  following  it.  Among  .other  things  it  was  shown  in  this  paper  that  by 
purposely  varying  these  factors  in  some  extreme  way  they  could  be  made  to  influence 
the  results  of  the  test.  The  more  crucial  point  was  not  shown  however;  namely, 
that  they  operate  against  the  usefulness  of  the  test  when  the  work  is  done  under  the 
conditions  that  ordinarily  obtain  in  a  well  conducted  experiment;  nor  does  the  paper 
contain  any  evidence  that  Mr.  Cravath  thinks  1  this  is  the  case.  In  our  own  work  a 
different  plan  has  been  pursued  with  regard  to  this  point.  Instead  of  trying  to  find 
out  what  effects  could  be  produced  by  means  of  procedures  that  would  not  be  per- 
mitted in  making  a  test,  every  care  has  been  taken  from  the  beginning  to  eliminate  or 
hold  as  constant  as  possible  all  extraneous  factors  which  might  influence  the  general 
and  muscular  efficiency  of  the  eye,  and  to  check  'up  the  effectiveness  of  this  control 
by  carefully  determining  the  mean  variation  in  the  results  for  each  set  of  lighting 
conditions.  This  we  have  considered  to  be  the  most  direct  and  feasible  plan  of  con- 
ducting the  work.  In  any  event,  it  is  obvious  that  there  is  no  need  of  futile  spec- 
ulation concerning  the  possibilities  of  influence  of  these  factors,  nor  of  any  in- 
definiteness  either  in  the  discussion  or  investigation  of  the  point,  so  long  as  the 
actual  value  of  the  influence  can  be  measured  by  determining  the  mean  variation  and 
its  relative  value  be  estimated  by  comparing  the  mean  variation  with  the  variations 
produced  by  changing  the  conditions  to  be  tested.  That  is,  a  measure  of  the  absolute 
and  relative  value  of  these  factors  is  readily  available  and  this  measure  has  been 
carefully  used  at  every  step  in  the  work.  We  need  scarcely  to  point  out  that  it  is  a 
well  recognized  principle  of  experimentation  in  comparative  work  such  as  we  are 
doing  that  as  long  as  the  mean  variation  is  safely  within  the  experimental  variation, 
the  method  is  considered  satisfactory  for  the  purpose  for  which  it  is  being  used. 

In  this  connection  it  may  not  be  out  of  place  to  give  here  a  more  detailed  account 
than  has  yet  been  given  of  the  method  that  has  been  used  in  selecting  and  training 
observers.  Care  is  exercised  in  the  first  place  to  choose  one  who  has  shown  a  satis- 
factory degree  of  precision  in  threshold  and  equality  judgments  in  other  optical  work 
in  the  laboratory,  and  whose  clinical  record  shows  no  uncorrected  defects  of  conse- 
quence The  observer  is  then  practised  on  the  three  minute  record  under  a  lighting 
condition  selected  and  maintained  for  the  purpose,  until  a  satisfactory  degree  of 
reproducibility  is  shown.  These  records  are  usually  run  in  series  of  five  with  a  twenty 
minute  rest  interval  between  each  record.  So  far  we  have  not  published  the  results 
of  an  observer  who  has  not  been  able  to  attain  a  reproducibility  in  the  time  seen 
clear  of  1  per  cent,  for  a  series  of  five  records  in  these  preliminary  experiments,  al- 
though this  degree  of  precision  is  unnecessary  unless  the  observer  is  being  trained  for 
work  in  which  there  are  very  small  differences  in  the  conditions  to  be  tested.  Since 
these  records  are  run  with  no  change  in  the  lighting  conditions  and  with  rest  intervals 
to  prevent  general  or  optical  fatigue,  they  serve  primarily  as  a  training  in  making  the 
judgment  and  as  a  check  on  the  precision  of  the  judgment.  In  the  second  stage  of 
preparation  the  observer  makes  a  number  of  three  hour  tests  with  records  before  and 
after  work  for  two  or  more  lighting  installations,  and  the  mean  variation  of  the 
results  from  the  average  is  determined.  Again,  if  a  sufficiently  small  mean  variation 
is  not  shown  where  there  has  been  no  change  in  the  lighting  conditions,  the  observer 
is  not  allowed  to  take  part  in  the  actual  work  of  testing.  This  last  mean  variation  is 
the  final  preliminary  check  upon  all  the  factors  that  may  vary  under  the  control  im- 
posed,— lack  of  reproducibility  in  the  judgment,  variable  physical  and  mental  fatigue, 
etc.  The  final  check  is  had  in  the  course  of  the  work  itself.  That  is,  a  number  of 
tests  are  made  for  each  lighting  condition  of  the  series  to  be  investigated,  and  the 
mean  variation  is  determined  for  each  and  compared  with  the  variations  that  are 
produced  by  the  changes  in  the  conditions  to  be  tested,  to  find  out  to  what  extent 
these  variations  may  be  ascribed  to  the  changes  made  and  to  what  extent  to  the 
normal  variation  of  the  test.  How  much  larger  is  the  variation  which  is  produced  by 
changing  the  lighting  conditions  than  is  the  normal  variation  for  each  condition  may 


1 124     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

be  seen  by  comparing  Columns  14  and  15  of  Table  IX.  In  the  work  of  the  preceding 
papers  the  excess  of  the  experimental  variation  over  the  mean  variation  was  much 
greater  still  as  might  be  expected  from  the  greater  differences  that  were  present  in 
the  lighting  conditions  tested.  For  example,  in  five  three  hour  tests  for  the  indirect 
system  for  Position  I  (see  this  Transactions  1915,  X,  pp.  413-426)  the  mean  variation 
in  per  cent  was  1.1;  for  the  semi-indirect  system  it  was  1.4;  and  for  the  direct  system, 
1.2;  while  the  percentage  drop  in  the  ratio  from  beginning  to  close  of  work  for  these 
systems  was  respectively,  8.5,  72.3,  and  80.9.  Similar  citations  may  be  made  for  the 
other  conditions  tested.  When  one  compares  in  these  cases  the  mean  variation  with 
the  magnitude  of  change  of  ratio  produced  by  changing  the  lighting  system,  it  be- 
comes obvious  how  unnecessary  has  been  the  concern  about  the  influence  of  extraneous 
factors  in  case  of  the  work  that  has  as  yet  been  done.  In  fact,  the  mean  variation 
has  been  so  safely  within  the  experimental  variation  that  the  writers  have  not  felt 
it  necessaiy  heretofore  to  make  the  numerical  comparison  in  print.  It  is  so  well 
recognized  as  an  experimental  principle  that  the  experimental  variation  shall  safely 
exceed  the  mean  variation  that  it  has  been  their  custom  to  give  the  comparison  only 
when  there  exists  some  grounds  for  doubt.  Heretofore,  we  have,  as  a  general  case, 
been   working   with   conditions   that  produced   a   large   difference  in   results. 

As  bearing  on  another  phase  of  the  question  of  reproducibility,  namely,  where 
a  long  interval  has  elapsed  between  two  series  of  tests,  we  may  cite  one  example 
where  two  series  were  taken  under  the  same  lighting  conditions  a  year  apart,  and 
the  variation  in  the  average  per  cent,  loss  of  efficiency  was  only  0.3.  In  this  case  a 
favorable  ligliting  system  was  used,  the  initial  ratios  were  closely  the  same,  and  the 
control  in  general  good,  although  no  especial  care  was  taken  to  make  it  so  more  than 
what  is  ordinarily  exercised.  It  is  not  presented,  however,  as  a  typical  instance.  It 
happens  to  be  the  only  case  of  which  we  have  a  record,  where  a  long  interval  has 
elapsed  between  two  tests. 

Moreover,  there  is  nothing  in  the  nature  of  the  test  other  than  its  superior  sen- 
sitivity that  should  make  it  more  susceptible  to  the  influence  of  extraneous  factors 
than  any  other  test  of  acuity.  The  principle  of  the  test  will  be  remembered  from  the 
earlier  papers.  It  is  merely  the  conventional  acuity  test  subjected  to  certain  features 
of  standardization  for  the  sake  of  greater  reproducibility,  and  made  into  an  endurance 
test  to  give  it  additional  sensitivity.  The  older  test  had  not  been  found  to  be  suf- 
ficiently sensitive  to  fatigue  conditions  to  warrant  adoption  in  our  work.  This  test 
is  in  fact  not  meant  to  be  a  fatigue  test.  It  was  designed  to  test  the  dioptric  condition 
of  the  eye,  and  may  be  used  with  more  or  less  success  as  a  test  of  how  far  a  given 
lighting  condition  is  conducive  to  clear  seeing  with  a  maximum  of  momentary  effort; 
but  it  has  not  the  essentials  of  a  fatigue  test  nor  of  its  converse,  the  ease  with  which 
clearness  of  seeing  is  attained, — which  is  what  is  needed  primarily  for  the  selection 
of  lighting  conditions  for  the  greater  part  of  the  work  that  we  are  ordinarily  called 
upon  o  do.  Almost  if  not  quite  as  good  results,  for  example,  may  be  gotten  with  it 
after  work  as  before,  when  there  is  every  other  reason  to  believe  the  eye  has  suf- 
fered considerable  depression  in  functional  power.  The  reason  for  this  is  obvious. 
Although  greatly  fatigued,  the  eye  can,  under  the  spur  of  the  test,  be  whipped  up  to 
give  almost  if  not  quite  as  good  results  as  the  non-fatigued  organ  when  only  a 
momentary  effort  is  required.  (See  Column  8,  Table  IX,  and  former  papers.)  If 
fatigued,  however,  it  can  not  be  expected  to  sustain  this  extra  effort  for  a  period  of 
time.  The  demonstration  of  this  fact  led  early  in  our  work  to  the  introduction  of 
the  time  element  into  the  test.  The  principle  involved  is  not  a  new  one.  It  is 
merely  the  application  of  a  very  old  and  well  known  one  to  the  work  of  testing  for 
optical  fatigue.  If,  for  example,  a  sensitive  test  is  wanted  for  the  detection  of 
fatigue  in  a  muscle,  as  good  results  can  not  be  expected  if  the  test  requires  only  a 
momentary  effort  on  the  part  of  the  muscle  as  would  be  attained  if  the  endurance  of 
the  muscle  were  taken  into  account.  For  our  purpose,  therefore,  the  old  acuity  test 
has  been  made  into  an  endurance  test,  in  which  the  fatigue  or  loss  of  functional 
efficiency  of  the  eye  is  measured  by  its  power  to  sustain  clear  seeing  for  a  period 
of  time.  As  such  it  should  and  does  show  a  sensitivity  for  detecting  fatigue  far  be- 
yond  what  can   be  attained   by  the  older   and   more   established   test   when   it  is   used 


FERREE  AND   RAND:     EXPERIMENTS   ON   THE   EYE  H25 

for  that  purpose.  And  being  a  test  which  is  more  sensitive  to  functional  changes  in 
the  eye,  it  doubtless  does  show  in  some  proportion  to  its  greater  sensitivity  more 
effect  of  the  indirect  as  well  as  of  the  direct  factors  that  influence  acuity;  but  since 
the  indirect  factors  can  be  subjected  to  control,  while  the  direct  factors  are  varied, 
there  is  in  proportion  to  the  sensitivity  .of  the  test  and  the  control  exercised  a  gain  for 
the  purpose  for  which  the  test  is  used.  That  this  gain  is  great  is  shown  in  all  our 
work  by  a  comparison  of  the  size  of  the  mean  variation  with  that  of  the  variation 
produced  by  the  change  in  the  conditions  to  be  tested. 

The  second  point  we   wish   to   discuss  here   refers  to  the  part  played  in  our  ex- 
periments by  a  factor  known  among  psychophysicists  as  the  error  of  expectation.     The 
belief  that  there  is   a  need   to   take   account   of  this   error   in   sense  judgments   arises 
from  the  difficulty  in  keeping  the  observer  in   ignorance  of   the  test  material  and  of 
a  certain  amount  of  the  experimental   procedure.      In  our  experiments  there  are  just 
two   points   on   which    the    observer   has   knowledge:    namely,   the   test   object   and   the 
lighting  conditions   or   system   under   which   the   work   is   done.      All   the   rest   is  kept 
concealed  from  him  unless  the  experimenter  should  in  turn  serve  as  observer  in  which 
case  his  results  are  checKcd  up  by  tnose  of  observers  who  have  not  served  as  experi- 
menter.     We   will   consider   this   factor   first   in   relation   to  the  test  object.      The   ob- 
server knows  what  the  test  object  is    (the  letters  li   in  8  point  type)    and   is  told  to 
record,    for    example,    when    the    dot   is    seen    separate    from    the   vertical    line    in    the 
letter  i.      The  question   at  issue  then   is  whether  proper   account  is  taken   in   our  ex- 
perimental procedure  of  the  influence  of  expectation  on  this  judgment.     The  question 
can  be  discussed  the  most  comprehensively  perhaps  by  first  considering  rather  broadly 
the  status   and   development  of   experimental   method  with   regard   to  this    factor.     As 
we  have  already  intimated,  the  probable  influence  of  expectation  is  an  inherent  diffi- 
culty in  all  sense  judgments,— photometric,  acuity,  threshold,  etc.     That  it  can  not  be 
entirely   eliminated   is,    we   think,    generally  conceded   as    axiomatic.      Psychophysicists 
have,  therefore,  turned  their  attention  to  attempts  to  compensate  for  it,  and  a  need  has 
been  felt  to  do  this  in  most  cases  only  when  the  work  requires  that  the  determination 
be  made  with  a  great  deal  of  precision.     Different  methods  may  be  employed  for  this 
purpose  all   of   which   are  more   or   less  open   to   question.      The   one  most   frequently 
used  perhaps,  is  the  method  of  ascending  and  descending  series.     From  a  consideration 
of  this  method  an  idea  may  be  had  in  a  general  way  of  all  the  methods  of  its  class. 
Rather  than  to  eliminate  or  even  to  lessen  the  operation  of  the  factor,  the  purpose  of 
this  method  is  to  control  its  direction  and  to  plan  the  experiment  in  opposing  series,  so 
as  to  compensate  for  its  influence  in  the  final  result.     That  is,  in  making  a  threshold 
determination,  for  example,   the  series  in  one    case   is    begun    below    the  threshold, 
and   the   observer   is   told   that   the   stimulus   will   be   increased   until   the   threshold   is 
reached;  in  the  other  case  the  procedure  is  reversed.     For  the  final  result  an  average 
is  taken   of  the  values  so   determined  on  the  assumption  that  expectation  in  the  two 
cases  will  influence  the  determination  by  equal  amounts  in  opposite  directions.     Much 
has  been  said  in  the  literature  of  psychophysics  with  regard  to  whether  this  method 
accomplishes   what   it   is   intended   to   accomplish,   and   more  might   be  said;    but   it  is 
immaterial   for   our   purpose  whether   it   does   or  not,    for   it  is   obvious   that   it  could 
not  be  applied  to  our  3  minute  records,  for  here  the  image  to  be  judged  rises  to  the 
threshold  of  discrimination  independently  of  the  control  of    either  the  observer  or  the 
experimenter.      The    individual    judgments,    therefore,    could    not   be    arranged   m    op- 
posing series  for  the  purpose  of  compensation.     An  entirely  different  type  of  method 
is  to  use  an  objective  check  on  the  judgment  of  the  observer,  and  by  this  means  en- 
deavor  to   weed  out   from   the   results  the   influence   of   subjective   factors.     We  tried 
for  several  months  to   devise  a  means  of  changing  the  stimulus  in   such   a  way  that 
an    objective   check    could    be   had   on    the    registration    of   the    observer    without    sac- 
rificing  the   principle   of   the   test.      Such   a  change,    however,    could  not   be    made   in 
the  test  object  which  did  not  at  the  same  time  permit  the  eye  to   relax  its  strain   at 
the  instant  of  change,  which  it  is  obvious  destroys  the  very  feature  which   gives  the 
test   its    superior   sensitivity.      The   attempt   to    get   an   objective   check,    however,    was 
made  more   for  the  sake   of  offsetting  possible  criticism   than   it  was   because   of   any 
belief  that  it  was  necessary  for  the  purpose  for  which  the  test  has  so  far  been  used; 


1 126     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

for,  as  we  have  already  stated,  a  determination  of  the  mean  variation  for  the  3  minute 
record,  each  one  of  which  consists  of  a  number  of  separate  judgments,  had  shown  us 
that  the  influence  of  expectation  as  a  source  of  variable  error  is  of  negligible  con- 
sequence. That  is,  the  mean  variation  is  the  measure  of  the  aggregate  effect  of  all 
the  variable  factors  including  expectation,  if  indeed  it  be  a  source  of  error  in  the 
case  under  consideration,  and  it  was  found  to  be  too  small  as  compared  with  the 
variations  produced  by  the  changes  in  the  conditions  tested  to  be  the  cause  for  any 
concern  for  the  purpose  of  the  work.  Moreover,  it  will  be  remembered  that  a  knowl- 
edge of  the  test  object  is  given  to  the  observer  as  one  of  three  changes  that  were 
made  in  the  conventional  acuity  test  to  minimize  very  obvious  sources  of  variable 
error,  among  w.iich  were  memory  and  expectation,  and  to  give  a  greater  reproduci- 
bility to  the  judgment.  We  can  do  no  better  probably  than  quote  from  the  original 
discussion.  "Visual  acuity  tests  of  the  Snellen  type,  especially  when  used  in  work 
in  which  it  is  required  to  make  successive  tests  on  the  same  person,  are  open  to  the 
following  objections,  (a)  The  judgment  is  in  terms  of  recognition.  A  letter  may  be 
recognized  when  it  is  not  seen  clearly.  In  any  judgment  based  on  the  recognition  of 
even  a  single  letter,  memory  plays  an  important  role.  It  is,  so  far  as  the  writer 
knows,  impossible  to  standardize  this  memory  factor  and  to  obtain  results  strictly  in 
terms  of  acuteness  of  vision,  (b)  The  test  card  is  made  up  of  quite  a  long  series 
of  letters.  As  the  test  progresses  the  letters  are  memorized  more  and  more  completely. 
It  is  practically  impossible  to  eliminate  this  progressive  error  when  a  number  of 
successive  judgments  have  to  be  made  as  is  the  case  before  a  final  result  is  reached 
in  any  single  visual  acuity  test  and  as  is  especially  the  case  when  a  number  of  suc- 
cessive  tests   have   to   be   given   to   the   same   person,    which   happens   in   much   of   the 

work  involved  in  the  solution  of  the  problem  here  proposed   (c)    The 

Snellen  series  contains  quite  a  large  number  of  letters.  The  eye  is  found  to  fatigue 
and  vision  to  blur  before  the  series  is  completed.  This  introduces  an  error  which  it 
is  practically  impossible  to  render  constant."  All  of  the  above  errors  were  elimin- 
ated, or  at  least  minimized,  in  the  tests  finally  adopted  by  us  by  changing  the  type 
of  judgment  and  by  adopting  a  simple  test  object,  made  up  of  only  two  characters, 
the  letters  li  in  8  pt.  type.  In  this  test  the  observer's  acuity  of  vision  is  determined 
by  the  distance  at  which  he  can  just  clearly  distinguish  the  two  test  objects.  In 
practise  it  has  come  to  be  a  matter  of  distinguishing  whether  or  not  the  dot  is 
separated  from  the  vertical  line  in  the  image  of  the  letter  i.  The  results  are  thus 
rendered  directly  in  terms  of  acuity  of  vision  and  the  progressive  errors  due  to 
memory  and  expectation  are  minimized.  In  this  regard  the  significance  of  the  change 
in  the  type  of  judgment  from  recognition  to  the  judgment  of  the  separateness  of  two 
simple  objects,  e.  g.,  the  dot  and  the  line  in  the  letter  i,  should  not  be  overlooked. 
When  the  criterion  is  recognition  and  the  task  set  for  the  observer  is  merely  to 
identify  the  test  object  with  its  name  or  some  memory  of  it  from  past  experience,  as 
is  the  case  in  the  old  form  of  the  test,  memory  and  expectation  play  their  maximum 
role.  Any  extraneous  clue  or  a  partial  discrimination  of  the  object  may  in  fact  serve 
as  a  basis  for  all  that  is  required  in  the  judgment.  When,  however,  the  task  set 
for  the  observer  is  a  different  one  and  he  is  required  to  judge  the  presence  or  ab- 
sence of  a  space  between  the  dot  and  line  in  the  letter  i,  the  role  of  these  factors 
is  reduced  to  a  minimum,  and  the  task  is  narrowed  down  to  the  judgment  of  a  space 
threshold,  one  of  the  simplest  and  most  reproducible  types  of  sense  judgment.  In 
short  then,  a  knowledge  of  the  test  object  is  given  to  the  observer  as  a  part  of  the 
modification  of  the  conventional  acuity  test  to  minimize  the  effect  of  variable  factors, 
among  which  memory  and  expectation  play  the  chief  role.  And  that  it  has  accom- 
plished its  purpose  is  abundantly  attested  by  a  comparison  of  the  size  of  the  mean 
variation  given  by  the  test  so  revised  as  compared  with  that  given  by  the  older  form. 
We  may  add  that  the  letter  1  is  used  in  connection  with  the  letter  i  for  two  reasons. 
(1)  A  steadier  fixation  is  given  than  can  be  attained  by  so  small  an  object  as  the 
letter  i;  and  (2)  a  standard  is  afforded  (an  unbroken  vertical  line)  in  terms  of  which 
to  judge  the  separateness  of  the  dot  from  the  vertical  line  in  the  letter  i. 

The  only  other  way  in  which  expectation  can  come  into  the  experiment  through 
knowledge   on    the   part   of    the    observer   is,    as    we   have   already   stated,    through    an 


FERREE    AND    RAND:     EXPERIMENTS    UN    THE    EVE  112/ 

awareness  of  the  conditions  or  lighting  system  tested.  The  observer  can  not  work 
for  three  hours  under  a  given  lighting  installation  without  being  more  or  less  aware 
that  the  same  installation  is  being  used  as  was  used  before,  or  a  different  one.  More- 
over, we  do  not  see  how  this  unfortunate  factor  can  be  completely  eliminated  unless 
imbeciles  be  used  for  observers.  We  wish  to  point  out,  however,  that  there  is  no 
greater  liability  to  harmful  influences  from  this  factor  in  our  test  than  in  the  older 
acuity  test  or  any  other  that  could  be  applied  to  the  same  type  of  work.  We  grant 
that,  in  any  test  that  could  be  used,  if  observers  of  strong  commercial  or  other  bias 
should  in  two  isolated  trials  get  better  results  for  one  type  of  lighting  than  another, 
there  might  be  grounds  for  suspecting  that  prejudiced  observations  were  made:  but 
if  each  condition  were  tested  a  number  of  times,  as  has  been  the  case  in  all  of  our 
work,  and  a  small  mean  variation  were  obtained  for  each  series  of  tests,  the  result 
would  look  much  more  like  the  response  of  an  organism  to  a  constant  set  of  condi- 
tions in  obedience  to  physiological  law  than  it  would  like  a  voluntary  reproduction 
guided  by  prejudice,  however  strong  and  constant  that  prejudice  might  be.  Here 
again  the  size  of  the  mean  variation  is  the  check  upon  the  validity  of  the  results, 
for  it  is  obvious,  we  think,  even  to  a  novice,  that  records  taken  at  intervals  of  from 
one  to  five  days  could  not  show  a  close  reproduction  if  the  fidelity  of  the  registration 
were  in  any  way  interfered  with  by  the  wishes  or  prejudice  of  the  observer.  Further- 
more, it  is  only  fair  to  say  that  it  would  be  difficult  to  find  a  group  of  observers 
freer  from  a  direct  interest  in  lighting  conditions  or  a  knowledge  of  their  significance 
than  is  the  group  from  which  the  greater  number  of  our  observers  are  selected. 

2  These  factors  are  the  evenness  of  illumination,  the  evenness  of  surface  bright- 
ness, the  diffuseness  of  light,  the  angle  at  which  the  light  falls  on  the  work,  intensity, 
and  quality. 

3  The  problem  of  installing  is  probably  not  the  same  for  the  inverted  translucent 
as  for  the  inverted  opaque  reflectors.  In  the  latter  case  the  height  should  be  so  ad- 
justed as  to  give  as  nearly  as  possible  an  even  distribution  of  surface  brightness  on  the 
ceiling,  and  evenness  of  illumination  on  the  working  plane.  In  case  the  inverted 
translucent  reflectors,  however,  if  the  distance  from  the  ceiling  is  made  great  enough 
in  all  cases  to  produce  these  effects,  it  may  throw  the  bright  reflectors  too  low  in 
the  field  of  vision  for  the  highest  efficiency  and  the  greatest  comfort  to  the  eye.  In 
this  regard  the  opaque  reflectors  have  the  advantage  that  it  is  always  easier  with 
them  to  get  the  brightest  surface  in  the  room  out  of  the  zone  of  most  harmful  in- 
fluence in  the  field  of  vision.  In  later  work  we  expect  to  conduct  a  series  of  ex- 
periments with  the  above  reflectors  in  which  the  height  from  the  ceiling  is  the 
factor   varied. 

4  The  track  along  which  the  test  card  was  moved  was  parallel  to  the  east  and 
west  walls  of  the  room.  When  taking  the  test  the  observer  faced  the  north  wall  in 
such  a  position  that  when  the  eyes  were  in  the  primary  position  the  lines  of  regard 
were  parallel  with  the  east  and  west  walls  of  the  room,  and  approximately  normal 
to  the  north  and  south  walls.  That  is,  the  head  was  erect  and  held  in  such  a  position 
that  the  objects  in  the  room,  reflectors,  etc.,  fell  as  symmetrically  as  was  possible 
within  the  field  of  view.  During  the  three  hours  of  reading  which  intervened  be- 
tween the  two  three  minute  records,  the  observer  moved  just  far  enough  back  from 
the  upright  supporting  the  mouth  board  to  give  room  for  the  book  to  be  held,  and 
to  permit  of  a  comfortable  reading  position.  Care  was  taken  to  have  the  eyes  sustain 
as  nearly  as  was  possible  the  same  general  relations  to  the  objects  of  the  room 
as  were  sustained  when  the  three  minute  records  were  •  taken.  This  could  be 
done  either  by  holding  the  head  erect,  etc.,  or  by  tilting  slightly  backward  in  the 
swivel  chair  used  by  the  observer  and  allowing  the  head  to  relax  a  compensating 
amount.  So  far  as  the  direct  optical  effects  are  concerned,  it  would  seem  to  be 
immaterial  which  of  these  positions  is  chosen,  so  long  as  approximately  the  same  field 
of  vision  is  obtained.  The  latter  is  usually  preferred  by  the  observer  as  causing  less 
general    fatigue.      When    taking   this   position,    the    book    is    elevated    and   held   at   ap- 

19 


1 128     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

proximately  an  angle  of  45°  (a  little  nearer  to  the  vertical  than  this  perhaps).  The 
brightness  measurements  of  the  book  at  this  angle  and  in  the  horizontal  are  not 
taken,  however,  so  much  because  of  this  as  to  give  the  brightness  of  the  book  in 
two  fixed  representative  positions  at  the  point  of  work.  Care  is  taken  to  have  print 
of  uniform  size  and  distinctness  for  use  with  the  three  systems  and  to  have  a  page 
which  gives  a  comparatively  small  amount  of  specular  reflection.  Uniformity  in  these 
regards  can  usually  be  secured  by  using  numbers  of  the  same  journal. 

5  It  should  not  be  needful  to  mention  that  the  recording  apparatus  is  screened 
from  the  observer's  view  while  the  test  is  being  made.  Before  photographing,  the 
screen  was  removed  and  the  apparatus  regrouped. 

6  This  is  the  test  station  shown  in  Fig.  1,  and  of  the  four  used  in  the  former 
work  is  the  one  nearest  to  the  south  wall  of  the  room. 

7  As  has  been  stated  in  our  former  papers,  in  the  consideration  of  the  effect  of 
a  given  lighting  situation  on  the  ability  of  the  eye  to  hold  its  efficiency  for  a  period 
of  work,  the  age  of  the  observer  and  the  condition  of  his  eyes  should  be  taken  into 
account.  All  of  the  observers  who  have  been  employed  by  us  in  this  work  have  been 
under  28  years  of  age.  Following  is  the  clinic  report  of  the  eyes  of  the  observer 
whose  results  are  given  in  Tables  IX  and  X,  made  by  Dr.  Wm.  Campbell  Posey  of 
Philadelphia. 

Observer  R. 
With  glasses.— Vision  of  right  eye  =  20/25.    Far  muscle  test  =  O  y2  esophoria. 
Vision  of  left  eye  =  20/20.  Near  muscle  test  =  orthophoria. 

Ophthalmoscopic  examination.— Right  eye  =  mixed  astigmatism,  y2  diopter. 
Left  eye  =  hyperopic  astigmatism,  il/2  diopters. 

External  condition. — Adduction  good;  eyes  slightly  divergent  under  cover; 
cornea  clear;  pupils,  2^  mm.;  irides  respond  equally  and  freely 
to    light,    accommodation,    and   convergence   stimuli. 

Glasses  worn  during  test. — Right  eye  =  — S.,  0.50  D. ;  — C,  0.37D.,  x  1600 
Left  eye  =  — C,  0.50  D.,  x  1800 
Early  in  our  work  the  problem  arose  whether  the  three  minute  records  before  and 
after  work  should  be  taken  in  the  same  room  in  which  the  work  was  done  or  in 
a  separate  room  reserved  solely  for  that  purpose.  To  test  this  point,  work  was 
done  in  both  ways.  It  was  found  that  the  effects  of  smaller  differences  in  lighting 
conditions  could  be  detected  when  both  the  three  minute  records  and  the  work  were 
done  under  the  lighting  conditions  to  be  tested.  That  is,  the  total  test  procedure, 
which  includes  both  the  three  minute  records  and  the  reading,  is  more  sensitive  when 
it  is  all  done  under  the  conditions  to  be  tested,  than  when  a  part  of  it  is  done  under 
these  conditions  and  a  part  in  a  separate  room.  Since  the  method  is  more  sensi- 
tive when  the  whole  procedure  is  conducted  under  the  lighting  conditions  to  be 
tested,  we  can  see  no  reason  why  even  the  purist  should  demand  that  a  part  of  it  be 
done  under  the  conditions  to  be  tested  and  a  part  somewhere  else,  so  long  as  the 
results  are  recognized  to  be  the  consequence  both  of  the  three  minute  records  and  of 
the  reading.  Our  purpose,  it  will  be  remembered,  has  been  to  get  a  sensitive  means 
of  detecting  the  relative  tendencies  of  different  lighting  conditions  to  cause  a  loss 
in  the  power  of  the  eye  to  sustain  its  ability  to  see  clearly;  and  the  method  is  more 
sensitive  when  the  three  minute  records,  also,  are  made  under  the  conditions  to  be 
tested.  This,  we  may  say,  is  our  chief  reason  for  the  practice.  A  justification,  we 
believe,  is  not  logically  needed.  Moreover,  the  method  so  conducted  is  just  as 
amenable  to  control  and  to  checks  upon  its  reproducibility,  as  if  it  were  used  in  the 
less  sensitive  form.  It  is,  in  fact,  considerably  more  amenable  to  control,  for  if  a 
separate  room  were  used  for  the  three  minute  records,  very  great  care  would  have 
to  be  exercised  to  see  that  it  was  always  illuminated  with  exactly  the  same  intensity 
of  light  that  was  used  in  the  room  in  which  the  reading  was  done.  If  the  illumina- 
tion were  not  accurately  the  same,  a  period  of  adaptation  would  have  to  be  allowed 
before  the  three  minute  record  could  be  made,  which,  in  case  of  the  record  taken 
after  work,   would  give  the   eye  opportunity  to   recover   from   the   fatigue  induced  by 


FERREE  AND   RAND:     EXPERIMENTS   ON   THE   EYE  H20, 

the  work.  It  is  obvious  that  a  great  deal  of  difficulty  would  be  encountered  in  ac- 
curately maintaining  this  control;  and,  if  it  were  not  so  maintained,  an  error  of 
considerable  consequence  would  be  introduced  into  the  work.  In  getting  control  not 
only  the  illumination  of  the  test  object  must  be  taken  into  account,  but  the  bright- 
ness of  the  whole  field  of  vision  with  its  complex  distribution  of  light  and  shade,  for 
this  conditions  the  state  of  adaptation  of  the  paracentral  and  peripheral  portions  of 
the  retina  which  in  turn  exerts  an  influence  on  the  part  of  the  retina  that  receives 
the  image  of  the  test  object.  It  may  be  added  also  that  adaptation  effects  in  the 
paracentral  and  peripheral  portions  of  the  retina  are  stronger  and  more  rapid  than  in 
the  central  portions.  . 

In  connection  with  the  fact  that  the  three  minute  records  add  sensitivity  to  the 
method  when  they  are  also  taken  under  the  conditions  to  be  tested,  we  may  say 
that  we  are  now  working  on  a  short  method  in  which  three  minute  records  with 
proper  .rest  intervals  are  used.  This  test  is  rougher  and  less  sensitive  than  the 
longer  method,  but  if  it  can  be  made  satisfactory,  it  might  be  more  adaptable  to 
practical    work. 

8  It  will  be  noted  in  this  table  that  there  is  very  little  variation  in  the  value  of 
the  initial  ratios.  We  noted  in  each  of  our  preceding  papers  and  again  in  our  dis- 
cussion of  Mr.  Cravath's  paper  that  the  sensitivity  of  the  test  varies  with  the  ratio  of 
the  working  distance  of  the  test  object  from  the  observer  to  the  acuity  distance. 
After  considerable  investigation  of  the  point,  we  adopted,  as  a  standard  to  be  at- 
tained  approximately,  a  ratio  of  distances  that  would  give  for  the  initial  record  a 
ratio  of  time  clear  to  time  blurred  of  3-5-  As  might  be  expected,  it  is  impossible  to 
get  this  ratio  of  3.5  exactly  from  any  single  ratio  of  working  distance  to  acuity 
distance  that  can  be  determined  in  advance  of  the  actual  record.  But  with  care  a 
close  approximation  may  be  attained,  and  since  the  loss  of  efficiency  is  judged  from 
the  amount  this  ratio  is  changed  from  the  beginning  to  the  close  of  work,  and  not 
from  the  ratio  itself,  the  failure  to  obtain  it  does  not  affect  a  comparison  of  the 
favorableness  of  different  lighting  conditions  for  the  eye,  any  more  than  is  represented 
by  its  effect  on  the  sensitivity  of  the  test.  In  short,  the  variations  in  this  ratio  from 
test  to  test  form  merely  one  of  the  group  of  variable  factors,  the  check  upon  the  effect 
of  which  on  the  results  of  the  test,  is  the  size  of  the  mean  variation;  and,  so  long 
as  this  mean  variation  is  safely  within  the  amount  of  variation  produced  by  changing 
the  conditions  to  be  tested,  the  control  may  be  considered  as  satisfactory  for  the 
purpose  of  the  work  that  is  being  done.  That  is,  when  this  check  is  properly  exer- 
cised, the  influence  of  a  variation  in  this  ratio  can  not  possibly  be  mistaken  for  the 
effect  of  the  condition  which  is  being  tested.  However,  in  the  course  of  the  deter- 
mination of  what  value  of  initial  ratio  should  be  used,  considerable  study  was  made 
of  the  effect  of  varying  the  ratio.  While  space  will  not  permit  us  to  quote  largely 
from  these  results  here,  still  an  idea  may  be  given  in  the  space  at  our  command  of 
the  order  of  magnitude  of  the  effect  that  is  produced.  That  is,  we  will  take  three 
cases  including  a  range  of  differences  amply  great  to  cover  what  is  ever  apt  to  occu, 
in  actual  work.  In  the  first,  the  initial  ratios  were  2.  and  3.  (difference,  1) ;  in  th* 
second,  2.67  and  5  (difference,  2.33);  and  in  the  third,  1.93  and  7-57  (d.fference, 
S64).  Tne  difference  in  the  percentage  loss  of  efficiency  for  the  first  case  was  1.4; 
in  the  second,  2;  and  in  the  third,  1.7.  The  effect  shown  in  these  cases,  it  will  be 
observed,   is  about  of  the  same  order  as  the  normal  mean  variation  of  the  test. 

•  In  order  to  make  a  fair  comparison  between  the  drop  in  ratio  time  clear  to  time 
blurred  caused  by  working  under  a  given  lighting  condition  and  the  mean  variation 
of  the  drop,  the  percentage  drop  and  the  percentage  mean  variation  are  both  esti- 
mated in  the  above  table,  also  in  the  citation  made  in  Note  8,  p.  1129,  on  the  same 
base  3  5  If  this  comparison  had  not  been  wanted  especially  to  show  that  the  mean 
variation  produced  by  changing  the  type  of  reflector,  it  would  have  been  more  in 
accord  with  custom  perhaps  to  have  expressed  the  mean  variation  as  a  percent,  of 
the  mean  value  of  the  drop.  Computed  in  this  way  the  value  of  the  mean  variation 
for  Reflectors  I-VI  would  have  been  in  order  5-6  per  cent.,  1.6  per  cent.,  1.3  per 
cent     33  per  cent.,   1.2  per  cent.,   1.4  per  cent.;  and  for  the  citation  in  Note  8,  they 


1 130    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

would  have  been  for  the  indirect  system  4.5  per  cent.,  for  the  semi-indirect  system 
0.7  per  cent.,  and  for  the  direct  system  0.5  per  cent.  This  method  of  estimating 
the  mean  variation  gives,  it  will  be  noted,  the  largest  per  cent,  variation  for  the  most 
favorable  lighting  condition  because  the  drop  in  ratio,  the  base  on  which  the  per- 
centage is  estimated,  is  the  smallest  for  this  condition.  The  actual  variation  we  have 
found  as  a  rule  is,  as  might  be  expected,   the  least  for  the  most  favorable  condition. 

DISCUSSION. 

Mr.  J.  R.  Cravath  :  Dr.  Ferree  calls  his  test  a  test  "loss  of 
efficiency  of  the  eye."  I  think  the  term  "eye- fatigue"  is  much 
briefer  and  more  expressive.  The  work  reported  in  a  previous 
paper  of  Dr.  Ferree  covered  conditions  rather  widely  varied. 
The  paper  we  have  before  us  now  covers  conditions  which 
come  within  fairly  narrow  limits  of  visible  source  brightness. 
The  results  have  been  especially  interesting  to  me  as  a  member 
of  the  Committee  on  Glare  because  we  have,  during  the  past  year, 
attempted  to  formulate  or  to  express  certain  limits  of  good  prac- 
tise which  are  least  conducive  to  glare.  In  ordinary  interior 
illumination,  we  state  in  our  report,  which  is  soon  to  be  published, 
that  contrasts  of  brightness  of  adjacent  surfaces  (I  mean  by 
adjacent  surfaces,  those  which  are  adjacent  within  the  visual 
field)  should  not  be  over  a  ratio  of  one  to  two  hundred,  and 
preferably  not  over  one  to  one  hundred.  That  ratio  was  taken 
as  the  result  of  an  examination  of  a  good  deal  of  data,  some  of 


80 

60 
u 
< 

20 
n 

100  200  300 

BRIGHTNESS  0FA-N 

Fig.  1. 


400 


them  in  previous  papers  of  Dr.  Ferree.    It  was  therefore  of  con- 
siderable interest  to  me  to  see  how  the  results  in  the  present  paper 


EXPERIMENTS  ON   THE  EYE  1 131 

conform  with  these  limits  and  in  order  to  do  that,  I  have  taken 
the  ratio  between  the  brightest  spot,  which  of  course,  is  the  re- 
flector, and  the  point  N  on  the  room  photograph  a  little  to  the 
right  of  the  reflector,  and  plotted  a  curve,  Fig.  1,  corresponding  to 
Chart  II  but,  instead  of  using  the  brightness  of  the  reflector,  I 
have  used  the  ratio  of  the  brightness  of  the  reflector  to  the  darkest 
point  along  side  of  it ;  that  is  the  point  N.  The  ratios  of  A  to  N 
under  200  seem  to  give  notably  less  fatigue  than  those  above 
1  to  200,  which  would  confirm  the  judgment  of  our  committee 
as  well  as  the  previous  results  obtained  from  various  sources. 

Dr.  J.  W.  ScherESChewsky:  I  want  to  congratulate  Dr. 
Ferree  on  the  extreme  care  which  is  evident  in  all  these  series  of 
tests  to  obtain  small  mean  deviations  and  secure  reproducibility  of 
results.  I  wish  to  call  attention,  however,  to  one  factor,  which 
in  all  probability,  will  have  considerable  effect  on  all  tests  which 
involve  muscular  action  and  that  is  the  question  of  weather  con- 
ditions. It  is  plain  to  all  who  have  read  this  paper  that  tests  of 
this  kind  such  as  Dr.  Ferree  has  here  published  are  labors  requir- 
ing a  great  deal  of  care  in  arranging  and  carrying  out,  and  it 
seems  to  me  that  we  ought,  by  all  means,  in  working  tests  of  this 
character,  to  insure,  as  much  as  possible  that  the  work  shall  not 
be  thrown  away  because  of  great  variations  in  the  results  due  to 
extraneous  factors.  Now  it  seems  to  me  that  tests  of  this  kind 
ought  never  to  be  conducted  in  very  hot  weather.  The  effect  of 
high  degrees  of  heat  and  humidity  is  to  reduce  the  endurance  of 
muscle.  That  seems  to  be  plain  from  Prof.  F.  Lee's  experiments 
which  were  done  in  the  investigations  of  the  New  York  Ventila- 
tion Commission,  in  which  it  was  found  that  sections  of  muscles 
removed  from  animals  which  had  been  subjected  to  high  degrees 
of  temperature  and  humidity  furnished  on  the  average  40  to  50 
per  cent,  less  contractions  than  muscles  of  animals  which  had 
not  been  so  exposed.  Therefore,  it  seems  to  me  that  persons  who 
conduct  tests  of  this  kind  in  very  hot  weather  would  find  a  great 
loss  of  efficiency  of  the  eye  simply  from  exposure  to  weather  con- 
ditions ;  so  in  the  future,  when  we  are  endeavoring  to  corroborate 
the  results  of  these  tests  by  similar  tests,  we  must  take  the  pre- 
caution never  to  undertake  such  tests  except  when  the  atmos- 
pheric conditions  are  distinctly  comfortable. 


1 132     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Mr.  T.  W.  Rolph  :  The  data  given  in  this  paper  are  very 
valuable  to  us  who  have  lighting  systems  to  design. 

I  should  like  to  call  attention  to  the  ratio  between  the  brilliancy 
of  the  ceiling  and  brilliancy  of  the  reflectors  as  obtained  in  these 
measurements.  Reflectors  4  and  5  are  typical  reflectors  of  the 
class  which  is  most  commonly  used  to-day  for  semi-indirect  light- 
ing, and  in  this  particular  installation,  which  does  not  represent 
all  installations,  but  is  possibly  a  typical  installation,  the  ratio 
between  the  brilliancy  of  the  reflector  and  the  brilliancy  of  the 
ceiling  is  one  to  fifty,  and  with  reflector  5,  one  to  sixty-one, 
taking  the  brightest  point  on  the  ceiling.  Those  are  the  re- 
flectors which  show  the  greatest  eye  fatigue,  and  this  shows 
us  how  far  we  will  still  have  to  go  in  reducing  intrinsic  brilliancy 
in  order  to  get  semi-indirect  lighting  systems  which  are  correct 
from  the  engineering  standpoint.  Now,  reflector  No.  3  is  a 
commercial  reflector  which  is  being  used  to  a  certain  extent  for 
semi-indirect  lighting.  It  is  denser  glass  and  it  is  harder  to  sell 
than  reflectors  4  and  5,  so  that  we  who  are  working  for  better 
lighting  in  the  commercial  field  have  that  to  contend  with.  Re- 
flector 3  shows  a  ratio  between  the  brilliancy  of  the  ceiling  and 
the  brilliancy  of  the  reflector  of  one  to  sixteen.  The  densest  re- 
flector tested  has  a  ratio  of  one  to  nine.  Three  years  ago,  in  a 
paper  on  the  "Engineering  Principles  of  Semi-Indirect  Lighting," 
I  argued  that,  from  the  engineering  standpoint,  the  brilliancy  of 
the  reflector  in  an  installation  should  be  approximately  the  same 
as  the  brilliancy  of  the  ceiling.  That  was  not  particularly  from 
the  standpoint  of  eye  protection,  but  from  the  standpoint  of  ob- 
taining the  maximum  diffusion  of  illumination,  arguing  that  if 
we  are  going  to  sacrifice  the  efficiency  of  direct  lighting  by  in- 
stalling semi-indirect  systems,  we  should  try  to  get  the  maximum 
engineering  value  of  the  semi-indirect  systems,  by  obtaining  max- 
imum diffusion,  and  that  this  would  be  obtained  when  the 
brilliancy  of  the  bowl  is  approximately  the  same  as  the  brilliancy 
of  the  ceiling.  This  paper  indicates  that  to  obtain  good  eye- 
protection  in  semi-indirect  lighting,  we  should  work  to  very  much 
denser  glassware  or  very  much  lower  brilliancy  of  reflector  bowl 
than  is  generally  practised  to-day.  Even  a  ratio  of  one  to  nine, 
where  the  reflector  is  nine  times  as  bright  as  the  ceiling,  shows  a 
considerable  degree  of  eye  fatigue. 


EXPERIMENTS  ON   THE  EYE  1133 

There  is  one  point  I  should  like  to  bring  out  in  connection  with 
the  measurement  of  the  intrinsic  brilliancy  of  these  reflectors, 
and  that  is  merely  a  suggestion  that  possibly  a  good  way  to  obtain 
the  intrinsic  brilliance  of  a  reflector  of  this  character  would  be  to 
take  the  candlepower  as  determined  on  the  photometer,  and  the 
area  of  the  reflector  as  determined  on  a  drawing  board,  and  thus 
find  the  candlepower  per  square  inch,  rather  than  to  take  lumin- 
osity measurements  of  the  reflector  at  various  points  and  average 
them.  I  believe  it  would  be  more  accurate  to  take  the  candle- 
power  of  the  reflector  and  simply  divide  it  by  the  projected  area 
in  the  direction  of  view. 

Mr.  J.  R.  Cravath  :  This  question  of  what  shall  be  taken  as 
the  criterion  of  brightness  is  something  that  Dr.  Ferree  evidently 
is  not  sure  of,  and  I  don't  think  any  of  the  rest  of  us  are — I  mean, 
what  particular  contrast  shall  be  taken.  Mr.  Rolph  has  just 
mentioned  the  contrast  of  the  brightness  of  the  reflector  with  the 
brightness  of  the  ceiling  above.  Dr.  Ferree  has  given  us  results 
showing  the  highest  brilliancy,  that  is,  the  brilliancy  of  the  re- 
flector, and  the  average  brilliancy,  and  the  ratio  of  the  highest  to 
the  lowest  and  the  ratio  of  the  highest  to  the  average,  the  ratio  of 
the  average  to  the  lowest  and  the  ratio  of  the  highest  to  the  bril- 
liancy of  the  point  of  work.  There  is  such  a  great  deal  to  be  said 
in  favor  of  his  objection  that,  possibly,  in  a  case  where  the  subject 
is  working  continuously  on  desk  work  or  reading  that  the  ratio  of 
the  brightest  object  in  view  to  the  work,  that  is,  to  the  paper  on 
which  the  eye  is  working,  should  be  the  criterion ;  because  in  that 
case,  the  brightest  objects  in  view  appear  simply  on  the  edge  of 
the  retina  most  of  the  time,  while  the  paper  is  on  the  center ;  but 
for  most  practical  purposes,  I  think  perhaps  the  criterion  adopted 
by  the  Committee  on  Glare  of  the  ratio  between  the  nearest  adja- 
cent surfaces  would  answer  all  practical  purposes  for  the  present. 
I  also  want  to  express  the  debt  that  I  feel  the  practical  men  of  the 
society  owe  to  the  investigators  who  bring  out  this  kind  of  data  ; 
it  is  exactly  what  we  need  to  make  progress  in  our  work. 

Dr.  C.  E.  FerrEE  (In  reply)  :  I  suggested  in  a  former  paper 
that,  theoretically  considered,  better  results  should  be  gotten  with 
the  semi-indirect  reflector  of  such  a  density  as  to  give  a  surface 
brilliancy  equal  to  that  of  the  ceiling  spot  than  are  obtained  with 


1 134     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  totally  indirect  reflector.  That  is,  if  the  reflector  is  made  of 
the  same  brightness  as  the  ceiling  spot,  the  same  light  flux  can  be 
obtained  with  a  lower  intrinsic  brilliancy  of  the  brightest  surface 
than  if  the  light  all  comes  from  the  ceiling  spot  because  of  the 
increase  of  luminous  area.  This  is  in  agreement,  I  believe,  with 
the  general  tenor  of  Mr.  Rolph's  discussion.  Unfortunately, 
however,  I  have  not  yet  been  able  to  obtain  reflectors  of  sufficient 
density  to  test  the  point  directly.  However,  in  the  work  that  we 
have  done,  an  increase  in  the  density  of  the  reflector,  so  far  as 
we  have  been  able  to  carry  the  increase  with  the  reflectors  sup- 
plied us  for  the  purpose,  has  been  accompanied  by  a  consistent 
improvement  in  the  effect  on  the  eye.  There  is  one  thing  to  be 
claimed,  however,  in  favor  of  the  indirect  reflector  when  all  is 
said  and  done.  It  is  easier  with  it  to  remove  the  brightest  spot  in 
the  field  of  vision  from  the  zone  of  harmful  influence  to  the  eye, 
especially  in  rooms  of  the  height  ordinarily  found  in  dwelling 
houses,  because  with  this  type  of  reflector  the  brightest  spot  is 
always  on  the  ceiling.  With  reference  to  the  effect  of  position  or 
rather  height  of  the  brightest  spot  in  the  field  of  vision,  it  may  not 
be  out  of  place  to  anticipate  here  in  slight  measure  the  content  of 
a  future  paper.  In  the  work  of  the  present  paper  the  reflectors 
were  installed  30  inches  from  the  ceiling.  This  is  in  accord  with 
general  practise  for  the  installation  of  totally  indirect  reflectors 
in  rooms  of  the  height  of  our  test  room  and  is  considered  to  give 
a  favorable  distribution  of  light  and  shade  on  the  ceiling  and  a 
comparatively  even  distribution  of  light  on  the  working  plane. 
So  installed,  however,  the  brightest  spot  (the  reflector)  is  dropped 
well  into  the  field  of  view,  especially  at  the  outlets  most  removed 
from  the  observer.  The  question  arises,  therefore,  whether  semi- 
indirect  reflectors  should  be  installed  according  to  the  principles 
of  indirect  lighting,  direct  lighting,  or  whether  some  compromise 
should  be  made  between  the  two.  We  have  begun,  therefore, 
a  series  of  tests  in  which  the  distance  of  the  reflector  from  the 
ceiling  is  varied.  So  far  we  have  been  able  to  finish  the  compari- 
son for  the  reflectors  of  least  and  greatest  density  at  distances  of 
30  in.  and  15  in.  from  the  ceiling.  The  15-in.  distance  gave 
quite  considerable  improvement  in  the  effect  on  the  eye  for  the 
reflector  of  least  density,  but  not  nearly  so  much  for  the  reflector 
of  greatest  density.     This  result  suggests  that  a  more  careful 


EXPERIMENTS   ON    THE   EYE  1 1 35 

study  should  be  made  of  the  method  of  installing  semi-indirect  re- 
flectors differing  in  density.  It  would  seem  that  the  denser  they 
are  the  more  nearly  they  can  afford  to  be  installed  as  indirect  re- 
flectors and  the  less  dense  they  are  the  more  nearly  they  should  be 
installed  as  direct  reflectors  so  far  as  eye  effects  of  the  kind  re- 
vealed by  our  tests  are  concerned. 

I  have  no  doubt  that  Dr.  Schereschewsky  is  right  about  the 
probable  effect  of  excessive  temperature  on  the  results  of  tests 
such  as  ours.  I  am  very  frank  to  confess,  however,  that  I  never 
do  anything  on  a  hot  day  if  I  can  help  it ;  and  I  certainly  would 
not  conduct  a  test  when  the  temperature  is  excessively  high. 
Through  the  greater  part  of  the  year  the  temperature  of  our  test 
room  is  kept  within  a  small  variation  by  thermostat  control.  If 
it  is  necessary  to  work  on  warm  days  electric  fans  are  used ;  but 
on  no  account  are  tests  ever  made  on  hot,  humid  days.  In  fact 
nearly  as  much  care  has  been  taken,  I  should  say,  to  secure  uni- 
formity in  temperature  control  in  our  work  as  has  been  taken  to 
secure  a  uniform  control  of  illumination  and  brightness  effects. 
I  am  confident,  therefore,  that  our  results  so  far  have  not  suf- 
fered from  temperature  as  a  variable  factor.  If  I  may  digress 
here  for  a  moment,  I  should  like  to  say,  with  no  reference  what- 
ever to  Dr.  Schereschewsky,  whose  discussions  I  have  always 
found  to  be  most  considerate  and  intelligently  liberal  in  tone,  that 
I  am  becoming  somewhat  tired  of  the  subject  of  extraneous 
factors.  To  speculate  about  their  probable  influence  may  be  of 
considerable  cultural  value  to  those  who  have  heretofore  thought 
little  about  the  subject,  but  there  is  no  need  to  worry  about  their 
influence  or  to  stand  in  the  way  of  reasonable  progress  when  a 
gauge  on  the  amount  of  their  influence  may  be  and  has  been  had 
at  every  step  in  the  work.  In  this  latter  connection  I  refer  to  a  care- 
ful determination  of  the  mean  or  average  variation.  If  this  is  done 
as  it  has  been  done  at  every  step  in  the  training  of  the  observer ; 
if  moreover  it  is  done  for  each  condition  tested  and  a  comparison 
made  of  its  amount  with  the  amount  of  variation  produced  by 
changing  the  condition  tested;  exact  knowledge  is  had  in  every 
case  whether  or  not  the  results  obtained  are  significant.  The 
subject  of  gauging  the  influence  of  variable  factors  is  too  old  and 
has  been  too  carefully  worked  out  to  justify  the  raising  in  any 


1 136     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

scientific  body  of  as  much  elementary  discussion  as  has  been 
raised  with  regard  to  it  in  this  Society.  The  procedure  in  general 
is  very  simple  and  straightforward.  Train  the  observer  on  every 
feature  of  the  test  method  with  careful  attention  to  the  size  of 
the  mean  variation.  In  the  actual  work  determine  the  mean  varia- 
tion for  each  set  of  conditions  tested  and  compare  it  with  the 
variation  produced  by  changing  the  conditions  to  be  tested.  If 
its  sum  for  any  two  sets  of  conditions  is  not  less  than  the  dif- 
ference between  the  average  results  obtained  for  the  two  con- 
ditions these  results,  it  is  usually  considered,  can  not  be  claimed 
as  significant.  I  have  spent  months,  for  example,  in  the  training 
of  an  observer  on  the  different  features  of  the  test  method,  only 
to  discard  him  at  the  end  of  that  time  because  a  sufficient  degree 
of  precision  of  record  could  not  be  obtained  under  a  constant  set 
of  lighting  conditions.  Those  who  have  shown  in  such  a  course 
of  training  an  unsatisfactory  degree  of  precision  usually  reveal  on 
examination,  I  may  say,  some  uncorrected  optical  defect.  Muscle 
imbalance  more  often  than  any  other  seems  to  have  been  the 
defect  in  the  cases  which  have  so  far  given  us  trouble.  This 
may  mean  that  the  extrinsic  more  often  than  the  intrinsic  muscles 
are  the  cause  of  a  variable  performance  on  the  part  of  the  eye 
in  tasks  such  as  we  have  set  for  it  in  our  tests,  but  it  is  also 
probable  that  the  occurrence  is  due  to  a  considerable  extent  to  the 
fact  that  in  ophthalmological  practise  small  defects  in  muscle 
balance  are  more  often  left  uncorrected  than  are,  for  example, 
refraction  defects. 

In  concluding  my  comments  on  this  point  I  think  I  may  be 
justified  in  mentioning  that  I  have  spent  a  greater  number  of 
years  than  I  like  to  recall  in  trying  to  get  control  of  the  variable 
factors  that  influence  the  response  of  the  eye;  and  that  I  have 
added  considerably  to  the  precision  of  its  performance  under 
experimental  conditions,  I  can  only  call  upon  my  published  work 
to  testify.  It  is  not  likely,  therefore,  that  in  the  course  of  de- 
veloping a  new  test  I  would  show  such  a  degree  of  incaution  with 
regard  to  the  most  elementary  and  well-known  principles  of  ex- 
perimentation as  was  made  the  subject  of  serious  and  somewhat 
pretentious  inquiry  in  the  discussions  of  the  paper  preceding  the 
present  one,  and  in  the  discussions  aroused  by  Mr.  Cravath's 
paper. 


EXPERIMENTS  ON   THE  EYE  IX37 

I  am  glad  Mr.  Cravath  has  given  us  still  another  way  of  plotting 
the  results  of  the  tests  against  brightness  effects.     It  has  not 
occurred  to  me,  however,  to  attach  any  especial  importance  as  a 
separate  factor  to  the  ratio  of  the  brilliancy  of  the  brightest  area 
to  that  of  its  immediately  contiguous  surroundings.     There  are, 
for  example,  only  two  possible  effects  that  I  could  conceive  to  be 
due  to  this  relation,  neither  one  of  which  would  seem  to  me  to 
warrant  making  of  it  a  separate  factor,     (i)  It  would  enhance 
by  physiological  induction  in  some  proportion  to  the  difference 
in  physical  brightness,  the  brightness  of  the  sensation  aroused  by 
the  reflector  and  thus  increase  its  power  to  set  up  muscular  strain 
by  distracting  the  eye  from  the  adjustment  needed  for  the  work 
in  hand.     So  considered,  however,  its  action  would  merely  be 
that  of  an  auxiliary  factor,  supplementary  to  the  actual  bright- 
ness of  the  reflector.    As  such  it  is  of  course  of  a  great  deal  of 
importance,  greater  perhaps,  for  example,  that  the  relation  of 
lightest  to  darkest  surface,  as  brightnesses  are  graded  in  a  room 
ordinarily  well  illuminated.    In  short  it  would  seem  to  me  that  the 
point  of  reference  in  determining  the  relations  that  are  of  im- 
portance to  the  eye  is  the  brightness  at  the  point  of  work.    Any 
extreme    deviation    above    or   below   this   brightness,    especially 
above,  or  anything  that  would  make  these  deviations  conspicuous 
to  vision  would  seem  to  me  to  be  of  prime  importance.    I  would, 
therefore,    consider    it    an    important    addition    to    our    present 
method  of   specifying  brightness  effects  to  give  more  detailed 
measurements,  so  far  as  is  practicable,  of  the  surroundings  im- 
mediately contiguous  to  the  brightest  spot,  because  the  effect  of 
that  spot  upon  sensation  is  to  an  important  degree  dependent 
upon  the  immediate  surroundings;  but  I  would  by  no  means  be 
willing  to  make  these  measurements  and  that  of  the  brightest  spot 
the  sole  specification  of  brightness  effects,  as  Mr.  Cravath  sug- 
gests might  be  sufficient  for  our  present  needs.    Moreover,  it  must 
not  be  overlooked  in  this  connection  that  a  curve  plotted  on  a 
basis  of  the  ratio  of  A,  brightness  of  the  reflector,  to  N  for  the 
different  conditions  tested  must  give  a  curve  very  similar  to  that 
plotted  on  the  basis  of  the  brightness  of  the  reflectors  alone,  for 
N  does  not  vary  greatly  from  a  constant  value  for  the  six  sets  of 
reflectors  we  have  used.    Obviously,  therefore,  cognizance  should 
be  taken  of  this  fact  before  too  much  general  importance  is  attn- 


1 138     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

buted  to  this  ratio  as  a  separate  factor  from  the  shape  of  the 
curve  plotted  by  Mr.  Cravath  for  this  particular  set  of  conditions. 
(2)  There  might,  it  is  conceivable,  be  some  unknown  effect  on 
the  retina  which  directly  depresses  its  functional  power  or  in- 
directly disturbs  the  adjustment  of  the  eye.  I  have,  however, 
already  tested  quite  extensively  the  tendency  of  different  lighting 
conditions  to  depress  the  functional  power  of  the  retina  for  as 
much  as  ten  hours  of  continuous  work  and  have  found  reason  to 
believe  that  very  little  indeed  of  our  results  for  the  tests  for  loss 
of  efficiency  could  be  ascribed  to  a  depression  of  retinal  function. 
There  are  four  ways,  I  may  say,  in  which  a  change  in  the  func- 
tional activity  of  the  retina  may  be  manifested:  (a)  a  change  in 
sensitivity  to  color  and  brightness;  (b)  a  change  in  lag  or  the 
time  required  for  the  sensation  to  reach  its  maximum;  (c)  a 
change  in  the  susceptibility  to  fatigue  or  exhaustion,  measured  by 
rate  of  exhaustion;  and  (d)  a  change  in  the  power  of  recovery, 
measured  by  rate  of  recovery.  All  of  these  points  were  covered 
in  the  tests  mentioned  above.  Short  of  such  an  investigation  a 
complete  record  can  not  be  given  of  the  functional  state  of  the 
retina  at  any  time  or  as  the  result  of  any  condition  or  set  of 
conditions  to  which  it  may  be  subjected.  But  when  such  tests 
have  been  conducted  for  a  period  of  exposure  of  the  eye  to  the 
conditions  tested  more  than  three  times  as  long  as  was  used  in  the 
tests  for  loss  of  efficiency,  it  would  seem  reasonable  to  conclude 
that  the  results  of  this  latter  test  could  not  be  ascribed  to  any 
considerable  extent  to  a  depression  of  retinal  activity. 

Mr.  Cravath  has  always  quarreled  with  me  over  what  the  test 
should  be  called  and  perhaps  on  good  grounds.  If  "fatigue"  is  a 
more  palatable  term  to  the  engineer  than  "loss  of  efficiency,"  I  am 
quite  willing  that  the  test  shall  be  called  a  fatigue  test.  I  have 
in  fact  called  it  that  part  of  the  time  myself.  My  reason  for  calling 
it  something  else  in  the  beginning  was  primarily  one  of  pro- 
fession. Among  men  in  physiological  and  psychological  optics 
the  term  fatigue  as  applied  to  the  eye  has  been,  since  the  days  of 
Fechner  and  Helmholtz,  a  technical  term  connotating  a  retinal 
condition.  It  was  chiefly  to  avoid  the  chance  of  confusion  with 
the  narrower  usage  of  fatigue  that  I  chose  the  broader  term  loss 
of  efficiency  as  a  brief  designation  of  what  is  really  tested,  namely, 
the  loss  in  the  power  of  the  eye  to  sustain  clear  seeing. 


EXPERIMENTS   ON    THE   EYE  1139 

DISCUSSION.* 

Mr.  J.  R.  Cravath  (Communicated)  :  To  my  mind  this  work 
of  Dr.  Ferree's  as  reported  in  his  paper  and  at  previous  conven- 
tions of  the  Society  is  of  great  and  far  reaching  importance. 
Before  we  can  deal  intelligently  with  problems  of  illumination  we 
must  have  methods  of  measuring  the  effect  of  different  kinds  of 
illumination  upon  the  eye.  Methods  devised  previous  to  the 
Ferree  test  were  generally  admitted  to  be  unsatisfactory  in  that 
they  took  no  account  of  the  fatiguing  effect  of  continuous  work 
under  given  conditions.  It  will  be  noted  that  Prof.  Ferree  refers 
to  his  test  as  one  to  determine  the  "efficiency  of  the  eye"  while 
I  have  usedf  the  term  "eye  fatigue"  instead  of  "eye  efficiency." 
It  is  of  course  the  privilege  of  the  originator  of  a  method  to 
apply  whatever  descriptive  terms  he  wishes  to  the  method,  but  it 
appears  to  me  that  "eye  fatigue"  expresses  more  nearly  what  is 
really  brought  out  by  the  Ferree  test  and  conveys  a  more  definite 
meaning  to  the  majority  of  those  not  intimately  in  touch  with  this 
kind  of  work.  In  connection  with  Dr.  Ferree's  results  on  mov- 
ing pictures,  it  has  been  my  observation  that  some  moving  picture 
shows  are  so  well  equipped  and  operated  that  the  pictures  are 
free  from  flicker  and  vibration  and  there  is  very  little  conscious 
eyestrain,  while  others  using  worn  out  films  and  making  no  effort 
to  get  steady  light  or  to  prevent  vibration  of  the  machine  produce 
pictures  which  are  very  trying  to  the  eyes.  I  should  suppose 
that  a  picture  show  in  a  suburb  like  Bryn  Mawr  would  be 
obliged  to  maintain  a  high  standard  of  service  as  compared  with 
many  others  throughout  the  country  and  that  probably  Dr.  Fer- 
ree's results  on  moving  picture  shows  might  show  fatigue  rather 
less  than  the  average. 

Dr.  Nelson  M.  Black  (Communicated)  :  The  Illuminating 
Engineering  Society  is  to  be  congratulated  that  the  carrying  out 
of  a  series  of  investigations  of  such  magnitude  has  been  under 
the  direction  of  such  scientific  and  painstaking  observers  as  the 

*  The  following  discussion  while  it  applies  somewhat  to  the  foregoing  paper  refers 
more  particularly  to  a  paper  entitled  "Further  Experiments  on  the  Efficiency  of  the 
Eye  LTnder  Different  Conditions  of  Lighting"  by  C.  E.  Ferree  and  G.  Rand,  which 
appears  on  pp.  448-501,  vol.  X,  of  the  Transactions  of  the  I.  E.  S. 

t  Cravath,  J.  R.,  Some  Experiments  with  the  Ferree  Test  for  Eye  Fatigue  ;  Trans. 
I.  E.  S.,  vol.  IX,  p.  1033. 


1 140     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

authors.  The  mass  of  data  is  almost  appalling  but  the  deductions 
made  are  clear,  concise  and  very  important. 

The  comparison  of  the  loss  in  efficiency  of  the  eye  when  the 
observer  is  in  the  different  positions  in  the  room  and  the  eyes 
are  subjected  to  the  varying  degrees  of  surface  brightness  of 
objects  within  the  field  of  view  with  the  three  different  sources 
of  illumination  is  most  interesting  and  instructive.  The  deduc- 
tions from  the  series  of  experiments,  that  the  scale  of  brightness 
magnitude  and  the  illumination  effects  for  the  indirect  system  is 
very  close  to  what  the  eye  is  adapted  to  stand  without  loss  of 
efficiency,  is  most  important  and  could  be  taken  as  a  standard 
in  determining  the  amount  of  surface  brightness  of  objects  allow- 
able in  lighting  installations  of  any  character. 

Another  important  point  is  that  the  position  of  the  observer  in 
the  room  does  not  seem  to  materially  affect  ocular  efficiency  under 
the  indirect  system,  especially  when  one  considers  that  the  illumi- 
nation of  the  working  surface  remains  approximately  the  same 
with  all  systems. 

The  result  of  the  experiments  conducted  with  the  eye  shades 
with  dark  and  light  lining  are  in  accord  with  those  obtained  by 
Ives  and  Luckiesh  in  their  investigations  of  the  influence  of  the 
direction  of  light  on  ocular  comfort,  i.  e.,  that  the  most  pleasant 
landscape  to  view  seemed  to  be  one  in  which  there  was  a  prepon- 
derance of  brightness  in  the  sky,  with  a  foreground  showing 
various  degrees  of  light  and  shade. 

The  authors  state  "it  is  a  question  whether  any  practical  good 
can  accrue  to  the  practise  of  lighting  from  a  knowledge  of  just 
what  part  of  the  visual  apparatus  it  is  that  falls  off  in  function 
as  the  result  of  an  unfavorable  condition  of  lighting."  It  would 
seem  that  this  is  of  prime  importance. 

The  result  of  the  investigation  of  the  effect  of  the  three  systems 
of  lighting  upon  the  factors  mentioned  as  involved  in  clear  see- 
ing, i.  e.t  the  sensitivity  of  the  eye  to  colored  and  white  light  and 
the  ability  to  make  fine  discriminations  and  accommodation,  will 
be  awaited  with  interest. 

Dr.  Walter  B.  Lancaster  (Communicated)  :  Is  it  not 
increasingly  clear  as  each  successive  paper  in  this  series  appears 
that   Prof.   Ferree  and   Dr.   Rand  are  more   successfully  solv- 


EXPERIMENTS    ON    THE    EYE  II4I 

ing  these  problems  they  have  undertaken  than  any  investi- 
gators so  far  in  the  field  ?  It  is  not  to  be  expected  that  we  should 
agree  with  all  their  interpretations  of  their  results.  The  import- 
ant thing  is  that  their  methods  seem  to  give  consistent  and  repro- 
ducible results  in  their  hands. 

I  am  glad  to  see  that  they  have  apparently  abandoned  their 
view  that  the  first  of  the  three  tests,  is  a  test  of  the  efficiency  of 
the  accommodation  and  now  speak  of  it  as  "a  test  of  the  ability 
of  the  eye  to  hold  its  efficiency  for  a  period  of  work,"  and  as 
"a  test  for  loss  of  efficiency  for  clear  seeing;"  that  is  they  do  not 
commit  themselves  to  any  theory  of  how  the  test  works.  As  a 
result  of  the  few  trials  I  have  made  of  the  test  on  myself  and 
half  a  dozen  other  observers,  I  am  convinced  that  the  accommo- 
dation has  nothing  to  do  with  the  blurring  but  that  it  is  a  retinal 
affair  and  depends  chiefly  on  steadiness  of  fixation — immobility 
of  the  eye,  and  that  in  turn  on  attention,  to  a  by-no-means-negli- 
gible degree.  However,  this  is  a  minor  matter,  the  important 
question  being,  does  it  give  results  when  applied  to  problems  of 
the  hygiene  of  the  eye. 

Their  observation  on  eye-shades  with  light  and  dark  linings 
are  very  convincing  and  important  (Table  XXV,  page  500),  since 
they  agree  so  well  with  what  was  to  be  expected  theoretically  but 
contradict  the  popular  view.  This  popular  view  will  die  hard 
like  the  popular  view  of  the  importance  of  shielding  the  eyes  by 
wearing  glasses  impervious  to  ultra-violet  light. 

The  results  of  tests  on  moving  pictures  are  also  important 
since,  while  every  one  knew  that  bad  moving  pictures  are  very 
fatiguing,  few  suspected  that  good  moving  pictures  were  so 
harmless  as  shown  by  chart  VIII. 

The  results  of  specular  versus  diffuse  reflection  (Chart  V, 
page  485),  do  not  show  as  great  a  falling  off  in  efficiency  under 
specular  reflection  as  might  have  been  expected.  Doubtless  this 
is  due  to  the  fact  that  so  small  a  percentage  of  the  total  illumina- 
tion of  the  test  object  was  specular  under  the  conditions  of  this 
particular  experiment.  The  angle  at  which  the  light  falls  on  the 
work  is  more  important  than  these  figures  would  imply.  This 
is  strikingly  shown  by  some  facts  to  be  found  in  Table  XX,  viz., 
even  after  three  hours  work  under  diffuse  illumination  the  ratio 


1 142     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

time  clear  to  time  blurred  (3.18)  is  the  same  as  the  ratio  at  the 
very  beginning  of  work  under  specular  reflection.  This  may  not 
be  a  legitimate  inference  to  be  drawn  from  the  table.  I  should 
be  glad  to  have  this  matter  made  clear.  For  example,  Table 
XIII,  p.  473,  gives  a  column  of  these  ratios  for  different  inten- 
sities and  at  the  beginning  of  work  these  are  3,  5,  3.5,  4,  2.1,  4.8 
for  the  six  different  intensities  tried.  Why  should  there  be  such 
an  enormous  difference  at  the  beginning  of  the  work  at  9  a.  m? 
Compare  footnote  on  p.  461,  which  speaks  of  a  variation  of 
1  per  cent,  or  less.  What  factors  are  responsible  for  these  wide 
differences  in  the  initial  values  granting  that  the  ratios  between 
the  initial  and  terminal  values  are  not  so  variable?  It  is  the 
ratios  that  are  most  important  but  the  other  figures  are  not  with- 
out significance. 

The  new  test  for  fixation  is  of  interest  to  ophthalmologists  but 
will  probably  not  meet  with  universal  acceptance  by  them.  It 
appears  to  be  a  test  for  maintaining  binocular  fusion  under  forced 
convergence.  What  a  variable  thing  this  is  with  different  sub- 
jects, all  ophthalmologists  know.  With  selected  and  trained  ob- 
servers it  might  none  the  less  prove  a  useful  test.  My  present 
feeling  is  that  the  first  test  is  a  better  test  of  fixation  (monocular 
of  course).  Additional  data  as  to  the  conditions  of  this  new  test 
would  be  very  acceptable.  Convergence  with  this  stereoscope  at 
18  is  equal  to  that  convergence  as  ordinarily  tested  say  in  meter 
angles  or  by  Duane's  method  or  even  by  measuring  simply  the 
distance  from  the  eyes  to  the  nearest  point  at  which  an  object 
can  be  seen  single.  The  data  quoted  from  Dr.  Posey  are  ob- 
viously contradictory  and  therefore  probably  misprints.  The 
nearer  the  eye  the  object  is  placed  the  lower  the  ratio  should  be, 
yet  Table  XXI,  page  489,  shows  the  ratio  at  the  beginning  of  work 
when  the  object  was  at  20  to  have  been  5.66,  though  the  illumina- 
tion was  less  favorable,  while  the  ratio  at  22  was  3.7  in  one  case 
and  3.6  in  the  other.  On  its  surface  this  indicates  inconsistency 
in  the  test  of  the  same  description  as  the  inconsistency  in  Table 
XIII  mentioned  above. 

The  authors  call  attention  to  the  significant  fact  that  Chart  I 
shows  for  position  IV  "still  a  considerable  loss  of  efficiency  pro- 
duced by  the  three  systems  of  lighting."     They  rightly  conclude 


EXPERIMENTS   ON    THE   EYE  ll43 

that  "evenness  of  surface  brightness  is  not  the  only  factor  in  a 
lighting  situation  which  may  influence  the  amount  of  loss  of 
efficiency  sustained  by  the  eye  as  a  result  of  a  period  of  work." 
So  also  Table  XXIII  shows  that  the  tendency  to  produce  discom- 
fort is  still  marked  if  the  direct  system  is  used  even  in  position 
IV  (with  all  the  sources  behind  the  observer  and  no  glaring  sur- 
faces in  front).     The  time  limen  is  ,57  for  direct  but  101  for  in- 
direct, i.  e.,  it  takes  75  per  cent,  longer  to  produce  discomfort 
with  indirect  than  with  direct  illumination  when  the  observer 
is  reading.     I  think  they  do  not  call  attention  to  the  important 
fact  that  when  not  reading  the  time  limen  is  not  nearly  so  much 
longer  for  indirect  than  direct,  viz.,  235  direct,  265  indirect,  is 
only  13  per  cent,  longer  than  direct.     It  pleased  me  very  much 
to  find  this  feature  so  well  brought  out  by  these  tests.    As  there 
is  no  reason  to  believe  the  observers  were  on  the  watch  for  it, 
it  cannot  be  attributed  to  expectant  attention,  as  it  might  have 
been  if  I  had  reported  it,  for  it  is  what  I  should  have  expected 
from  my  personal  experiences  and  sensations  with  different  ways, 
of  lighting,  though  high  authorities  in  illumination  do  not  agree 
with  me.    I  believe  that  even  if  the  sources  are  all  out  of  sight 
and  the  brightness  of  the  surface  of  the  book  is  the  same  in  both 
cases  the  eyes  will  feel  more  discomfort  and  loss  of  efficiency  when 
the  light  is  not  diffuse  but  comes  from  a  relatively  small  source 
and  therefore  one  of  high  brilliancy.     In  other  words  while  it  is 
an  enormous  advance  toward  comfort  to  put  the  direct  source 
behind  and  so  out  of  sight  of  the  reader  it  still  leaves  much  to  be 
desired  if  the  source  is  one  of  high  intrinsic  brilliancy  and  there- 
fore small  and  relatively  concentrated.     For  many  years  I  have 
given  my  patients  a  rough  and  ready  test  to  determine  whether 
their  lighting  was  bad.    If  a  pencil  is  held  a  few  inches  from  the 
book  the  shadow,  if  the  lighting  is  good,  should  be  blurred  and 
indistinct  as  from  a  north  window.    In  proportion  as  it  is  sharp 
and  defined,  the  source  is  small  and  of  high  brilliancy  and  the 
illumination  is  harsh.     In  the  experiment  above,  in  position  IV, 
the  shadows  cast  on  the  page  when  reading  under  the  direct  sys- 
tem would  be  markedly  different  from  the  shadows  cast  in  the 
same  position  under  the  indirect  system.    With  the  observer  not 
reading  but  looking  at  the  wall  in  front  of  him  this  factor  would 
become  subordinate. 
20 


1 144     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

Dr.  Percy  W.  Cobb  :  We  have  presented  to  us  in  this  paper1 
descriptions  of  various  lighting  installations  with  detailed  photo- 
metric data,  as  well  as  descriptions  of  other  sets  of  conditions 
under  which  the  eye  is  called  upon  to  work;  and  alongside  of 
these  the  results  of  a  test  from  which  conclusions  are  drawn  as 
to  the  loss  efficiency  of  the  eye  resulting  from  a  period  of  work 
under  each  of  these  several  conditions.  This  seems  to  me  to  sum 
up  the  tendency  of  the  paper  in  spite  of  the  disclaimer  which 
appears  in  the  last  paragraph  to  the  effect  that  "the  purpose  has 
been  primarily  to  procure  methods  of  working  and  to  find  out,  as 
broadly  as  one  may,  the  applicability  of  these  methods  to  the 
problems  surrounding  the  hygiene  of  the  eye." 

The  quotation  suggests  to  me  an  important  omission  on  the 
part  of  the  authors,  all  the  more  likely  to  be  overlooked  because 
of  the  completeness  of  description  in  other  respects;  and  I  wish 
here  to  raise  the  question :  How  far  may  the  results  of  the  test 
as  applied  be  trusted  as  a  true  measure  of  the  loss  of  efficiency  of 
the  eye? 

It  is  to  be  remembered  that  the  test  is  original  with  one  of  the 
authors  and  has  not,  with  one  exception,  been  used  by  any  one 
else.  The  work  done  with  it  has  almost  entirely  been  confined  to 
its  application,  as  in  the  present  paper,  to  the  eye  before  and 
after  a  period  of  work  under  specified  conditions.  The  mode  of 
procedure  has  been  described  but  nowhere  have  we  had  any  full 
and  detailed  account  as  to  its  susceptibility  to  influences  other 
than  the  state  of  efficiency  or  of  fatigue  of  the  eye.  Such  in- 
formation as  we  have  on  this  latter  question  is  limited  to  a  few 
general  statements  which  have  appeared  from  time  to  time  in  the 
course  of  the  papers  of  one  of  the  authors  and  since  the  bulk  of 
the  work  under  discussion  is  taken  up  with  the  reporting  of  the 
results  of  the  test  under  the  diverse  conditions  of  the  experiments, 
it  seems  to  me  that  we  have  the  right  to  ask  for  much  more 
convincing  proof  than  we  have  as  yet  had  that  the  results  truly 
indicate  loss  of  efficiency  of  the  eye. 

Photometrists  will  no  doubt  agree  that  in  the  photometry  of 
lights  of  identical  spectral  character  (or  identical  color)  one  may 
reproduce  his  own  results  to  within  a  fraction  of  one  per  cent. 
The  eye  can  equate  to  within  about  that  limit  of  accuracy.  If, 
however,  we  wish  to  know  what  are  the  fluctuations  in  the  sensi- 


EXPERIMENTS   ON    THE   EYE  1 145 

tivity  of  the  observer's  eye  while  the  measurements  are  in  pro- 
gress, we  see  at  once  that  they  are  included  in  that  fraction  of 
one  per  cent.,  and  the  mean  deviation  of  the  results  from  their 
mean  or  the  probable  error  may  either  of  them  be  taken,  for 
purposes  of  comparison,  as  the  index  of  such  fluctuations. 

Now  the  method  that  we  are  at  present  considering  measures 
fluctuations  of  the  sensitivity  of  the  eye.  In  footnote  14,  page  461 
it  is  stated  that  five  separate  tests  of  three  minutes  duration 
on  the  same  observer  taken  with  twenty  minute  rest-intervals, 
and  taken  under  identical  conditions,  gave  results  whose  varia- 
tions always  fell  within  the  limit  of  one  per  cent.2  It  is  to  be 
remembered  that  the  analogy  to  this  is  not  the  accuracy  with 
which  the  photometrist  may  reproduce  his  measurement,  but  the 
accuracy  with  which  he  may  reproduce  his  probable  error  or  his 
mean  variation. 

It  may  be  that  this  analogy  is  not  permissible  in  the  present 
case.  The  test  method  is,  as  far  as  I  know,  different  from  any 
procedure  heretofore  recognized  and  its  limitations  may  be  much 
less  than  those  of  the  methods  recognized  by  psychologists  and 
sense-physiologists  generally.  It  is  nevertheless  a  matter  of 
general  opinion,  I  find,  among  those  who  have  up  to  the  present 
conducted  investigations  of  this  character  on  the  performance  of 
sense-organs,  that  quantitative  results  are  not  to  be  relied  on  for 
reproducibility  to  within  one  per  cent,  when  obtained  in  a  few 
minutes,  and  they  have  been  driven  to  much  more  time-consuming 
and  laborious  methods  to  arrive  at  results  which  they  consider 
admissible. 

Such  methods  are  of  course  prohibitive  for  the  purpose  of  the 
authors.  They  might  however  be  applied  once  for  all  to  settle 
the  points  on  which  the  method  is  open  to  presumptive  criticism. 
It  seems  to  me  that  a  thorough-going  investigation  of  the  method 
on  this  plan,  not  only  as  to  reproducibility  but  in  other  respects, 
is  not  only  possible  but  much  to  be  desired  by  those  to  whom  the 
paper  is  addressed. 

There  is  another  point  on  which  there  seems  to  me  to  be  room 
for  more  than  one  opinion.  That  is,  that  in  the  application  of 
the  test  as  used  by  the  authors  of  the  paper  the  observer  is  in  full 
knowledge  of  all  its  details.  He  knows  exactly  what  the  test- 
object  is  that  he  is  looking  at,  and  that  it  is  identically  the  same 


1 146     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

and  at  the  same  distance  before  and  after  the  work-period. 
Without  any  question  as  to  the  honesty  of  the  observer  in  wishing 
to  report  exactly  as  he  sees,  I  think  it  will  be  found,  and  even 
stated  by  the  observer  himself  in  many  cases,  that  he  has  the 
utmost  difficulty  in  keeping  his  preconceptions  separate  from  his 
judgments.  I  mean  this  remark  to  apply  not  specifically  to  the 
work  under  discussion  but  to  such  work  as  I  have  been  concerned 
with,  and  in  general  to  quantitative  work  on  the  sense-organs. 
The  newness  of  the  method  and  the  importance  of  the  con- 
clusions to  be  drawn  from  its  results  would  seem  to  warrant  ex- 
perimental justification  of  this  feature  of  the  test  for  the  exact 
situation  in  which  the  test  is  used,  especially  in  view  of  the  fact 
that  the  opinion  will  be  found  to  be  fairly  general  that  there 
should  be  one  or  more  factors  in  the  experimental  procedure, 
unknown  to  the  observer  except  as,  through  the  particular  sense- 
channel  under  investigation,  he  may  get  knowledge  of  them  that 
shall  determine  the  result  of  the  experiment.3 

In  making  reference  to  the  possibility  of  the  test  being  subject 
to  influences  other  than  the  state  of  efficiency  or  fatigue  of  the 
eye,  the  fact  in  mind  was  that  in  the  greater  part  of  the  work 
reported  in  this  paper  the  tests  were  conducted  with  the  observer 
at  the  same  point  and  under  the  same  lighting  conditions  as  during 
the  work-period.  That  is  to  say,  in  this  portion  of  the  work 
the  test  was  not  conducted  under  the  same  conditions  in  any  two 
different  experiments  whose  results  are  compared.  More  than 
this,  from  the  information  at  hand  I  cannot  see  that  the  inten- 
tion of  the  authors  to  conduct  the  test  under  eye-conditions  iden- 
tical with  those  of  the  work-period  was  fulfilled.  In  footnote  8, 
page  453,4  it  is  stated  that  during  the  work-period  the  book  was 
held  at  an  angle  of  45 °  and  it  is  there  also  implied  that  the  ob- 
server was  permitted  to  assume  a  comfortable  reading  position. 
From  what  is  said  further  in  this  note,  and  from  inspection  of 
Figs.  2,  3,  and  4  it  seems  clear  that  the  track  carrying  the  test- 
card  was  horizontal.  The  natural  inferences  are  that  the  eyes 
were  directed  downward  at  an  angle  of  about  45 °  during  the 
work-period,  that  being  probably  the  most  comfortable  reading 
position  under  the  circumstances  as  stated,  and  that  for  the  test 
they  were  raised  to  a  horizontal  direction.  The  book — a  large 
white  area  in  the  visual  field — is  at  the  same  time  removed,  and 


EXPERIMENTS  ON   THE  EYE  IJ47 

by  the  shift  of  the  line  of  vision  the  light-source  and  bright  areas 
in  the  upper  part  of  the  room  are  thrown  by  the  amount  of  that 
shift  nearer  to  the  center  of  the  visual  field.  This  gives  in  effect 
neither  uniform  conditions  for  the  test  in  different  experiments ; 
nor  does  it  give  in  any  particular  experiment  like  conditions,  as 
far  as  the  eye  is  concerned,  for  the  reading  period  on  the  one 
hand  and  for  the  tests  conducted  befbre  and  after  it  on  the  other. 
Now  the  test,  involving  as  it  does  continuous  fixation  of  the 
small  mark  on  the  test-card,  does  not  call  for  the  same  perform- 
ance on  the  part  of  the  eye  as  does  reading  where  fixation  is 
momentary  and  continually  shifting;  and  it  is  by  no  means  cer- 
tain that  the  two  processes  are  equally  affected  by  the  conditions. 
In  other  words  the  difference  in  the  results  of  the  test  in  any  two 
of  these  experiments  may  be  due,  in  part  at  least,  to  the  difference 
in  sensitivity  of  the  test  conducted  as  it  is  under  different  con- 
ditions.5 It  may  be  said,  at  any  rate,  that  a  reasonable  doubt 
exists  on  this  point  and  that  nothing  has  so  far  been  done  to  es- 
tablish the  fact  in  question. 

What  has  been  said  in  the  foregoing  may  be  summed  up  in  a 
few  words.  The  fact  that  there  is  in  the  test  method  as  used  by 
the  authors  no  check  by  which  bias  on  the  part  of  the  observers 
may  be  ruled  out,  and  the  fact  that  it  has  not  been  shown  whether 
or  not  the  test  is  influenced  by  the  variations  in  the  conditions 
surrounding  its  application,  throw  a  reasonable  doubt  on  the 
question  whether  its  results  truly  reflect  the  loss  of  efficiency  of 
the  eye. 

Such  doubt  may  be  due  to  misapprehension  of  the  facts  or  to 
erroneous  premises.  I  think,  however,  that  the  doubt  will  be 
found  fairly  general  among  those  presumably  qualified  to  under- 
stand, and  might  be  cleared  away  by  a  thorough-going  investiga- 
tion of  the  test-method,  based  on  experimental  procedures  which 
are  beyond  dispute. 

The  illuminating  engineer  can  make  application  of  such  a  test, 
provided  he  has  unqualified  assurance  of  its  validity,  and  proper 
instruction.  For  these  he  must  look  to  the  psychologist  or  the 
sense-physiologist.  The  authors  will  add  immensely  to  the  value 
of  their  work  by  supplying  them. 


1 148    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

FOOTNOTES. 

1  This  discussion  applies  to  the  paper  of  Drs.  Ferree  and  Rand  presented  at  the 
Convention  of  1914  (these  Transactions,  Vol.  X,  pp.  448-501).  As  for  some  reason 
it  could  not  be  published  in  its  proper  place  it  is  given  here,  with  such  additions  in 
the  form  of  footnotes  as  have  been  found  necessary  in  view  of  the  contents  of  the 
present  paper. 

-  Although  the  mean  variation  of  the  ratio,  time  clear:  time  blurred,  is  men- 
tioned in  the  footnote  cited  it  is  to  be  remarked  that  this  1  per  cent,  variation  applies 
strictly  to  the  time  seen  clear.  The  corresponding  variation  in  the  ratio  will  be 
found  to  be  4.5  per  cent.,  assuming  140  seconds  in  180  as  the  average  time  seen  clear. 
It  is  not  plain  why  the  results  are  stated  in  terms  of  the  ratio,  while  the  mean  varia- 
tions are  given  as  applying  to  the  time  seen  clear.  This  fact  throws  doubt  on  the 
mode   of  derivation   of  the   mean  variations  given   in  Table   IX   of  the  present  paper. 

3  It  is  by  no  means  impossible  to  introduce  a  variable  factor  in  the  test,  un- 
known to  the  observer.  Such  a  factor  would  be  furnished  by  the  use,  in  different 
experiments,  of  slightly  different  test-cards.  These  might  be  made  from  cards  origi- 
nally identical  by  obliterating  the  space  between  the  i  and  its  dot  in  varying  degrees 
with  a  fine  pen.  For  the  individual  cards  of  such  a  set  the  reading  distances  should 
be  slightly  different.  They  could  be  so  selected  as  to  be  used  at  the  same  distance 
and  the  difference  could  reasonably  be  expected  to  appear  in  the  results  without 
being"  evident  to  the  observer  during  the  progress  of  the  test.  This  would  give  an 
answer  to  the  question  as  to  the  importance  of  the  factor  of  expectation  in  the 
observer. 

4  See  also  Note  4  following  the  present  paper.  It  is  difficult  to  imagine  a  com- 
fortable reading  position  with  the  book  held  at  an  angle  with  the  vertical  unless 
the  eyes  are  directed  downward  from  the  horizontal  to  almost  the  same  degree. 

5  This  contention  is  frankly  admitted  in  Note  7  at  the  end  of  the  present  paper: 
"It  was  found  that  the  effects  of  smaller  differences  in  lighting  conditions  could  be 
detected  when  both  the  three  minute  records  and  the  work  were  done  under  the 
lighting  conditions  to  be  tested." 

It  is  argued  therefrom  that  the  method  is  thus  more  sensitive  and  not  open 
to  objection  since  the  result  is  a  consequence  of  the  tests  and  the  work  combined, 
done  under  the  lighting  conditions  to  be  tested.  But  how  in  such  a  case,  to  illus- 
trate, as  is  implied  in  the  quotation?  If  no  result  is  observed  when  the  illumination 
conditions  for  the  test  are  standardized,  and  a  positive  result  when  they  are  con- 
ducted under  the  conditions  to  be  investigated,  it  would  appear  that  the  result  is 
logically  to  be  ascribed  to  the  conditions  surrounding  the  tests.  There  would  be  no 
objection  to  the  inclusion  of  this  effect  in  the  result  if  there  were  in  practical  life 
any  work  that  the  eyes  are  called  upon  to  do  at  all  comparable  with  the  effort  that 
such  a  test  demands;  and  if  the  eye  conditions  were  actually,  as  well  as  nominally, 
identical  for  the  tests  and  the  intervening  work-period. 

The  objection  to  the  standardization  of  the  test-conditions  raised  by  the  authors 
further  on,  namely  that  slight  differences  in  the  level  of  adaptation  will  materially 
affect  the  results,  applies  with  equal  force  to  the  procedure  of  the  authors  as  in- 
dicated by  what  I  have  just  said.  The  necessity  emphasized  for  the  control  of  the 
"whole  field  of  vision  with  its  complex  distribution  of  light  and  shade"  applies 
equally  well  as  an  objection  to  the  change  in  the  distribution  of  light  on  the  retina 
brought  about  by  shifting  the  eyes  from  the  oblique  reading  position  to  the  horizontal 
position  demanded  by  the  test.  The  statement  (Note  4)  that  "Care  was  taken  to 
have  the  eyes  sustain  as  nearly  as  was  possible  the  same  general  relations  to  the  ob- 
jects of  the  room "  contains  nothing  to  imply  that  such  a  shift  was  avoided. 


EXPERIMENTS   ON    THE   EYE  1 149 

Dr.  C.  E.  Ferree  (In  reply)  :  I  agree  with  Mr.  Cravath  that 
our  results  for  the  moving  pictures  selected  probably  show  less 
fatigue  than  would  be  shown  in  the  average  by  a  wide  testing  of 
moving  picture  houses.  For  example  it  is  stated  in  the  text: 
"The  tests  were  conducted  in  a  local  theater,  selected  primarily 
because  of  the  favorable  conditions  that  prevailed.  The  definition 
at  the  screen  was  good  and  the  pictures  were  unusually  steady 
and  free  from  flicker.  The  conditions  were,  we  think,  fairly 
representative  of  what  is  found  in  the  better  class  of  motion 
picture  houses."  I  should  like  very  much  for  comparative  pur- 
poses to  test  the  effect  produced  in  some  of  our  lower  grade 
houses,  especially  on  a  Saturday  night  when  frequently  the  rate 
at  which  the  pictures  are  given  to  the  eye  is  very  much  increased. 
We  hope  later  to  make  a  more  extensive  investigation  of  motion 
picture  effects.  This  investigation  was  made  primarily  to  find 
out  whether  our  test  would  show  an  effect  of  motion  pictures  on 
the  eye. 

Dr.  Black  says :  "The  authors  state  'It  is  a  question  whether 
any  practical  good  can  accrue  to  the  practise  of  lighting  from  a 
knowledge  of  just  what  part  of  the  visual  apparatus  it  is  that  falls 
off  in  function  as  the  result  of  an  unfavorable  condition  of  light- 
ing.' It  would  seem  that  this  is  of  prime  importance."  I  should 
have  appreciated  it  very  much  if  Dr.  Black  had  elaborated  on  this 
statement.  I  should  be  glad  to  know  the  opinion  of  the  opthal- 
mologists  with  regard  to  the  importance  of  pursuing  the  analy- 
tical study. 

I  am  very  glad  indeed  for  many  reasons  to  take  into  account 
anything  that  Dr.  Lancaster  may  have  to  say  about  the  work  we 
are  doing.  I  shall  mention  only  one  of  these  reasons  here.  Real- 
izing from  his  intimate  knowledge  of  eye  testing  something  of  the 
difficulties  one  may  expect  to  find  in  applying  an  unfamiliar  test, 
he  made  a  trip  to  our  laboratory  before  attempting  any  work  at 
all  with  the  test,  to  find  out  just  how  we  made  the  application 
ourselves. 

Dr.  Lancaster  says  in  the  first  paragraph  of  his  discussion: 
"...  their  methods  seem  to  give  consistent  and  repro- 
ducible results  in  their  hands."  Apropos  of  this  statement  by 
Dr.  Lancaster  a  word  of  comment  and  explanation  may  not  be 


1 150     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

out  of  place  here.1  So  far  as  the  test  has  been  applied  by  us,  the 
mean  variation  from  test  to  test  has  been  very  much  less  than 
any  experimental  variation,  from  which  we  have  drawn  differen- 
tial conclusions  with  regard  to  the  relative  merits  of  lighting  con- 
ditions, and  no  results  have  been  or  will  be  published  as  signifi- 
cant in  a  variation  of  lighting  conditions  in  which  the  change  in 
result  produced  is  not  safely  in  excess  of  the  mean  variation  of 
the  test.  In  fact,  because  of  the  amount  of  this  excess  of  the 
experimental  variation  over  the  mean  variation,  we  have  not  as 
yet  felt  urged  to  compile  and  publish  full  data  on  the  reproduci- 
bility of  the  test. 

Dr.  Lancaster  says  in  the  second  paragraph  of  his  discussion : 
"I  am  glad  to  see  that  they  (the  authors)  have  apparently 
abandoned  their  view  that  the  first  of  the  three  tests  is  a  test  of 
the  efficiency  of  the  accommodation  and  now  speak  of  it  as  'a  test 
of  the  ability  of  the  eye  to  hold  its  efficiency  for  a  period  of  work' 
and  as  'a  test  for  loss  of  efficiency  for  clear  seeing' ;  that  is  they 
do  not  commit  themselves  to  any  theory  of  how  the  test  works." 
I  am  somewhat  puzzled  to  understand  how  Dr.  Lancaster  has 
gotten  the  impression  from  anything  we  have  published  that  we 
considered  the  test  referred  to  be  of  itself  anything  but  a  test  of 
the  aggregate  loss  of  functioning  of  the  eye.  The  test  was  not 
designed  to  be  analytical  in  nature,  but  merely  to  show  changes  in 
the  eye's  ability  to  see  clearly  for  the  three-minute  interval  con- 
sumed by  the  test  before  and  after  work.  This  is  shown  by  the 
title  of  the  first  paper  "Tests  for  the  Efficiency  of  the  Eye,  etc.," 
and  in  the  discussions  of  the  test  in  the  same  paper  pp.  45-50  in 
which  it  it  always  referred  to  as  a  test  for  the  efficiency  of  the 
eye  not  as  a  test  for  the  efficiency  of  the  accommodation  or  any 
other  single  function.  Indeed  on  p.  50  of  that  paper  the  statement 
is  made  very  explicitly.  "This  ratio  as  stated  earlier  in  the  paper 
expresses  the  efficiency  of  the  eye  for  clear  seeing  for  an  interval 
of  three  minutes  at  the  time  at  which  the  test  was  taken."  In 
connection  with  the  test  for  aggregate  effect,  however,  tests  de- 
signed to  be  analytical  in  nature  were  made,  namely,  tests  for 
changes  (a)  in  the  response  of  the  retina  to  colored  and  colorless 
light;  (b)  in  the  rate  of  exhaustion;  and  (c)  for  the  rate  of 
recovery  of  the  retina;  and  (d)  for  the  rate  of  lag  of  sensation; 

6  See  also  discussion  of  Mr.   Cravath's  paper,  Trans.   I.   E.  S.,   1914.  vol.   IX. 


EXPERIMENTS  ON   THE  EYE  II51 

also  tests  for  loss  of  efficiency  of  the  fixation  muscles.  It  was 
only  because  these  tests  showed  very  little  if  any  significant  effect 
that  we  suggested  very  tentatively,  subject  to  the  results  of  a 
further  test  bearing  more  directly  upon  the  accommodation 
muscles,  that  the  results  gotten  in  the  general  test  were  due 
largely  to  loss  in  efficiency  of  the  accommodation  muscles.  The 
first  test  was  not  designed  to  test  for  losses  in  power  to  accom- 
modate alone,  nor  was  it  used  for  that  purpose.  So  far  as  its 
relation  to  the  eye  is  concerned,  it  was  used  merely  as  an  explor- 
ative test  to  separate  out  good  from  bad  hygienic  conditions  rated 
according  to  an  aggregate  effect  on  clear  seeing. 

Dr.  Lancaster  further  says:  "I  am  convinced  that  the  accom- 
modation has  nothing  to  do  with  the  blurring  but  that  it  is  a 
retinal  affair  and  depends  chiefly  on  steadiness  of  fixation — im- 
mobility of  the  eye,  and  that  in  turn  on  attention  to  a  by-no- 
means-negligible  degree."  It  may  perhaps  be  inferred  from  this 
statement  that,  since  the  greater  amount  of  blurring  takes  place 
under  the  conditions  which  would  distract  the  fixation  most  and 
therefore  lead  to  the  greatest  unsteadiness  of  fixation,  Dr.  Lan- 
caster considers  that  the  blurring  comes  as  an  effect  of  unsteady 
fixation  on  the  functioning  of  the  retina.  This  point  of  view 
carries  the  writer  back  to  a  group  of  problems  in  the  study  of 
which  he  spent  four  years.7  Space  cannot  be  taken  here  to  go  into 
that  work.  It  is  sufficient  to  say  that  since  the  time  of  Fechner,8 
it  has  been  held  that  involuntary  eye-movements,  or  unsteadi- 
ness of  fixation,  are  of  prime  importance  in  keeping  the  retina 
from  becoming  exhausted  during  the  course  of  a  working  day. 
That  is,  so  far  as  the  functioning  of  the  retina  alone  is  concerned, 
unsteadinesss  of  fixation  or  movements  of  the  eye  both  voluntary 
and  involuntary  work  for  clear  seeing,  not  blurring;  and  the 
lighting  system  which  by  the  strain  it  puts  on  the  muscles  causes 
the  greatest  unsteadiness  of  fixation,  should  be  the  system  which 
causes  the  least  and  not  the  greatest  blurring  in  the  test  following 

7  See  C.  E.  Ferree,  An  Experimental  Examination  of  the  Phenomena  Usually 
Attributed  to  Fluctuation  of  Attention,  Amer.  Jdur.  of  Psych.,  1906,  XVII,  pp.  79- 
121;  The  Intermittence  of  Minimal  Visual  Sensation,  ibid,  1908,  XIX,  pp.  57-130; 
The  Streaming  Phenomnoa,  ibid,  1908,  XIX,  pp.  483-504;  The  Fluctuation  of  lumi- 
nal Visual   Stimuli  of  Point  Area,  ibid,    1913,  XXIV,  pp.   377-410. 

'See  Fechner,  Pogg.  Ann.,  1838,  XUV,  p.  525;  Helmholtz,  Physiol.  Optik., 
1896,  p.  510;  Fick  and  Gurber,  Archiv  fur  Opthal.,  1890,  XXXVI,  (2),  p.  246;  Hess, 
ibid,  1894,  XL,  (1),  p.  274;  MacDougall,  Mind,  1902,  XL,  p.  316;  1903,  XIJ,  p.  289; 
and  the  present  writer,  loc.  cit. 


1 152     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

the  period  of  work.  And  so  it  would,  as  is  abundantly  shown  in 
the  references  cited  on  the  effect  of  eye-movement  on  the 
functioning  of  the  retina,  if  the  unsteadiness  of  fixation  and  ac- 
commodation caused  by  such  a  lighting  system  did  not  also 
interfere  with  the  clear  imaging  of  light  on  the  retina  that  is 
needed  for  clear  seeing.9 

In  paragraph  five  Dr.  Lancaster  expresses  the  belief  that  while 
the  major  significance  should  be  attached  to  the  change  of  ratio 
of  time  seen  clear  to  time  seen  blurred  before  and  after  work, 
considerable  significance  should  be  attached  also  to  the  difference 
in  the  value  of  this  ratio  before  work  for  the  different  lighting 
conditions.  One  of  the  reasons  he  gives  for  this  is  that  in  Table 
XIII,  which  shows  the  results  for  six  tests  on  the  effect  of 
variation  of  the  intensity  of  light  with  the  indirect  system,  and  of 
variation  of  intrinsic  brightness  of  the  ceiling  spots  above  the 
reflector  produced  by  using  socket  extenders  with  some  of  the 
shorter  lamps,  these  initial  ratios  seem  to  vary  as  much  if  not 
more  than  the  final  ratios,  or  as  the  change  in  ratio  before  and 
after  work.  These  initial  ratios  were  respectively  3,  5,  3.5,  4,  2.1, 
4.8.  If,  however,  Dr.  Lancaster  will  observe  the  table  closely, 
he  will  see  that  the  ratio  of  the  working  distance  to  the  acuity 
distance  is  not  the  same  in  all  of  these  cases.  The  same  ratio  of 
time  clear  to  time  blurred  should,  therefore,  not  be  expected  even 
were  the  lighting  conditions  the  same.  Whenever,  for  example, 
the  working  distance  has  been  chosen  closer  to  the  eye,  propor- 
tionate to  the  acuity  distance,  a  higher  ratio  of  time  clear  to  time 
blurred  should  be  expected.  This,  it  will  be  seen,  happened  in 
all  but  one  of  the  above  cases  in  spite  of  differences  in  lighting 
conditions.  However,  everything  else  being  equal,  it  is  perhaps  true 
that  the  more  unfavorable  lighting  condition  will  cause  greater 
proportionate  blurring  in  the  initial  record  observation,10  and  if 
so,  the  results  of  this  initial  observation  may  have  some  diagnostic 
value.    We  have,  however,  never  felt  it  safe  to  use  the  results  of 

9  That  is,  unsteadiness  of  accommodation  interferes  with  the  clear  imaging  of 
the  light  on  each  retina,  and  unsteadiness  of  fixation  with  the  imaging  on  function- 
ally corresponding  areas  of  the  two  retinae.  Functionally  corresponding  is  used 
here  in  the  usual  sense,  namely,  areas  of  the  two  retina  which  in  binocular  seeing 
combine  their  images  into  one.  If  the  images  do  not  fall  fairly  accurately  on  these 
areas,  doubling  and  consequent  blurring  result. 

10  The  above  statement  is  made  with  reservation.  The  pornt  will  be  discussed 
more  fully  later. 


EXPERIMENTS  ON   THE  EYE  1 1 53 

the  initial  observation  in  this  way  because  they  are,  when  com- 
pared from  day  to  day  as  they  would  have  to  be  in  this  case,  the 
least  reproducible  feature  of  our  test.  In  the  way  in  which  we 
are  accustomed  to  evaluate  our  results,  the  deviation  from  close 
reproducibility  of  this  feature  of  the  test  enters  into  the  evaluation 
of  the  favorableness  of  lighting  conditions  for  the  eye  no  more 
than  is  represented  by  its  comparatively  slight  effect  on  the  sen- 
sitivity of  the  test.  That  is,  we  so  conduct  our  test  and  evaluate 
its  results  as  to  give  negligible  weight  to  this  item,  the  successful 
accomplishment  of  which  is  shown  in  the  small  mean  variation 
gotten  in  the  actual  work  of  testing.  Dr.  Lancaster  thinks  the 
variation  of  the  ratios  for  the  initial  test  quoted  above  has  all  the 
more  significance  when  compared  with  the  estimation  of  the 
degree  of  reproducibility  of  the  3-minute  record  given  in  foot- 
note 14,  p.  461.  Here  it  is  stated  that  with  the  practised  ob- 
servers we  used  the  maximum  variation  of  time  clear  in  five 
consecutive  records  for  the  fresh  eye  with  a  rest  interval  of 
20  minutes  between  each  record  has  always  fallen  within  1 
per  cent,  for  all  the  observers  whose  results  have  been  pub- 
lished. The  following  points  will  show  that  little  stress  should 
be  laid  on  this  comparison.  (1)  The  reproducibility  tests  (for 
which  the  1  per  cent,  reproducibility  was  quoted)  on  the  fresh 
eye  were  made  with  exactly  the  same  ratio  of  working  distance 
to  acuity  distance.  In  the  tests  of  which  Dr.  Lancaster  quotes 
results  this  ratio  was  different.  (2)  The  reproducibility  tests 
were  also  made  always  on  the  same  morning  with  a  20-minute 
rest  interval  under  very  favorable  and  always  identical  rest  con- 
ditions. The  tests  referred  to  by  Dr.  Lancaster  were  taken  on 
different  days.  And  (3)  the  1  per  cent,  deviation  in  the  repro- 
ducibility tests  were  from  the  average  of  the  time  seen  clear;  the 
deviations  quoted  by  Dr.  Lancaster  were  in  the  ratio  time  clear  to 
time  blurred. 

In  the  sixth  paragraph  Dr.  Lancaster  says :  "The  new  test  for 
fixation  is  of  interest  to  ophthalmologists  but  will  probably  not 
meet  with  universal  acceptance  by  them.  It  appears  to  be  a  test 
for  maintaining  binocular  fusion  under  forced  convergence. 
What  a  variable  thing  this  is  with  different  subjects  all  ophthal- 
mologists know.     With  selected  and  trained  observers  it  might 


1 154    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

none  the  less  prove  a  useful  test."  We  do  not  quite  see  how  its 
variability  from  observer  to  observer  affects  the  purpose  for 
which  we  have  used  the  test.  Our  purpose  is  to  select  practised 
observers  and  see  how  much  the  power  of  each  to  maintain  bin- 
ocular combination  of  images  is  affected  by  both  the  work  and  the 
test  under  a  given  lighting  condition.  The  point  of  comparison 
is  not  at  all  one  of  individual  differences,  but  how  much  for  a 
given  individual  the  power  to  maintain  the  binocular  combination 
is  affected  by  work  under  the  lighting  conditions  which  are 
being  tested.  I  do  not  think,  therefore,  that  Dr.  Lancaster's 
point  is  relevant  to  the  purpose  for  which  the  test  has  been  used, 
nor  can  I  see  that  it  constitutes  any  objection  to  the  use  of  the 
test  to  supplement  the  tests  now  used  by  the  ophthalmologist  for 
the  fixation  muscles.  I  have  already  pointed  out  in  the  text  that 
it  may  be  more  important,  even  in  the  work  of  the  clinic,  to  de- 
termine the  eye's  power  to  sustain  co-ordinated  muscular  action 
than  it  is  to  determine  the  maximum  pulling  power  of  the  indi- 
vidual muscles  by  a  momentary  effort,  for  it  is  obviously  the 
power  to  sustain  co-ordinated  muscular  action  that  is  of  prime 
importance  in  determining  whether  the  eye,  so  far  as  the  fixation 
muscles  are  concerned,  is  able  to  carry  on  sustained  work.  In 
fact  sustained  co-ordination  is  just  what  is  demanded  of  the  eye  in 
continuous  work.  It  seemed  to  me,  therefore,  that  this  type  of 
test  more  nearly  measures  what  is  demanded  of  the  working 
eye  than  do,  for  example,  the  ordinary  abduction  and  adduction 
tests. 

Later  in  this  paragraph,  Dr.  Lancaster's  discussion  shows  that 
he  has  misunderstood  our  data.  He  has  apparently  understood 
the  table  reading  "Distance  at  which  test  object  is  normally 
seen  single"  to  mean  that  nearest  point  at  which  it  can  be  seen 
single  by  a  maximum  effort  of  convergence.  This  is  given  in  the 
table  as  1 8  cm.  for  the  observer  used.  This  distance  was  not 
the  nearest  point  at  which  the  test  objects  could  be  seen  single 
with  maximum  effort,  but  the  distance  at  which,  as  the  wording 
of  the  heading  indicates,  they  were  most  easily  held  combined. 
Therefore,  when  the  test  objects  are  set  either  nearer  to  the 
eyes  or  further  away,  they  will  be  held  combined  with  effort. 
The  observer  whose  results  are  given  in  Table  XXI,  in  order 


EXPERIMENTS   ON    THE   EYE  1 1 55 

to  put  the  eyes  under  strain  to  combine  these  images,  preferred 
to  set  the  objects  at  a  greater  rather  than  a  less  distance  than 
18  cm.  from  the  eye.  The  22  cm.  distance,  therefore,  should 
and  did  give  for  the  fresh  eye  a  smaller  ratio  of  total  time 
single  to  total  time  double  for  this  observer  than  the  20  cm.  We 
should  have  made  it  clear  in  discussing  the  test  that  a  point  either 
nearer  or  further  than  the  most  favorable  could  be  used  and  that 
the  latter  was  used  in  case  of  the  observer  whose  results  were 
given  in  Table  XXI.  My  explanation  of  the  oversight  is  that  I 
had  always  used  the  other  condition  myself  and  had  become  ac- 
customed to  think  of  the  test  in  that  way.  In  explaining  this 
point  we  have  doubtless  also  explained  the  contradiction  which 
Dr.  Lancaster  thought  to  exist  between  Dr.  Posey's  clinic  data 
and  the  results  of  Table  XXI.  We  are  deeply  indebted  to  Dr. 
Lancaster  for  calling  our  attention  to  the  point.  Either  an  ex- 
planatory footnote  should  have  been  appended  to  the  table  or 
the  results  of  another  observer  should  have  been  selected. 

Dr.  C.  E.  FerrEE  (In  reply  to  Dr.  Cobb)  :  In  replying  to  Dr. 
Cobb's  discussion  I  am  somewhat  in  doubt  whether  to  consider 
it  merely  a  discussion  of  the  paper  immediately  preceding  the 
present  one  or  as  being  intended  to  apply  also  to  the  present 
paper.  Since  it  has  been  revised  by  appending  footnotes  which 
take  into  account  the  contents  of  the  present  paper,  the  natural 
presumption  is  that  in  as  far  as  the  body  of  the  paper  is  not 
modified  by  these  footnotes,  what  is  said  is  meant  to  apply  to 
the  present  as  well  as  the  preceding  paper. 

In  a  brief  review  of  the  beginning  of  the  discussion  I  may  be 
pardoned  perhaps  for  calling  attention  to  the  fact  that  in  the 
quotation  made  from  our  paper  in  his  opening  paragraph  he 
has  abstracted  from  its  context  just  what  was  favorable  for  the 
point  he  wished  to  make  and  ignored  the  rest.  The  quotation 
should  continue:  "While  in  many  places  attention  has  been 
called  to  results  that  have  seemed  to  have  general  significance, 
the  intention  has  been,  in  general,  to  limit  all  comments  and  con- 
clusions strictly  to  the  conditions  under  which  the  work  was 
done."  This  in  connection  with  the  quotation  made  seemed  to 
me  at  the  time  to  be  a  fair  statement  of  the  case  and  it  seems  to 


1 156     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

be  so  to  me  yet.  The  conditions  under  which  the  work  has  been 
done  have  been  made  clear  at  every  point  and  not  the  slightest 
attempt  has  been  made  to  draw  conclusions  beyond  these  condi- 
tions. Moreover,  to  do  this  is  not  in  the  least  degree  contradic- 
tory to  the  purpose  expressed  in  the  sentence  quoted,  namely, 
"primarily  to  find  out,  as  broadly  as  one  may,  the  applicability  of 
our  test  method  to  the  problems  surrounding  the  hygiene  of  the 
eye."  It  was  well  known,  for  example,  that  the  work  was  being 
done  by  methods  the  precision  and  applicability  of  which  were 
under  investigation  for  each  new  set  of  conditions  employed. 
This  investigation,  however,  I  need  scarcely  to  state,  was  not  a 
part  of  the  actual  work  of  testing.  It  was  completed  and  the 
observer  trained  to  a  satisfactory  degree  of  precision  before  that 
work  was  begun.  That  is,  not  until  an  observer  selected  on  the 
basis  of  both  his  freedom  from  optical  defects  and  a  precision 
already  shown  in  other  work  in  physiological  optics,  had  also 
attained  to  a  satisfactory  degree  of  precision  in  the  3-minute 
record  under  a  given  lighting  condition  and  in  the  3-hour  test 
under  several  conditions,  and  a  careful  comparison  of  results  in 
the  actual  work  of  testing  had  shown  that  the  variations  produced 
by  changing  the  conditions  to  be  tested  was  by  a  large  margin 
safely  in  excess  of  the  mean  variation  from  the  average  for 
each  of  the  conditions  tested,  were  his  results  accepted  as  sig- 
nificant. Then  and  not  until  then  were  data  incorporated  into 
tables  and  curves  purporting  to  represent  the  effect  of  the  con- 
ditions tested  upon  the  ability  of  the  eye  to  sustain  clear  seeing. 
It  is  clear  then,  I  think,  that  both  of  these  procedures,  the  pre- 
liminary investigation  of  the  precision  and  applicability  of  the 
test  to  each  new  set  of  conditions  and  the  actual  work  of  testing 
these  conditions  have  been  features  of  our  work  just  as  was 
stated  in  the  concluding  paragraph  referred  to,  and  not  the  latter 
alone  or  predominantly,  as  was  gratuitously  inferred  by  Dr. 
Cobb.  Furthermore,  until  a  wider  range  of  work  is  covered  we 
intend  that  our  purpose  shall  remain  primarily  that  of  finding 
out  as  broadly  as  we  may  the  applicability  of  our  method  to  new 
conditions ;  but  that  purpose,  it  is  obvious,  when  satisfied  should 
not  and  will  not  in  the  least  prevent  us  from  doing  the  actual 
testing  for  these  conditions ;  and  the  result  for  this  testing,  it  is 
scarcely  needful  to  say,  may  reasonably  be  expected  to  make  up 


EXPERIMENTS   ON    THE   EYE  1 157 

the  larger  part  of  future  papers  as  they  have  of  the  papers  al- 
ready presented,  without  the  liability  of  anyone's  misunderstand- 
ing either  what  has  been  intended  or  what  has  been  done. 

In  his  third  paragraph  Dr.  Cobb  charges  that  we  have  not 
published  enough  data  in  our  papers  to  insure  the  reader  of  the 
reliability  of  the  methods  employed,  and  leaves  it  rather  pointedly 
to  be  inferred  both  here  and  elsewhere  in  the  discussion  that  to 
the  best  of  his  belief  sufficient  precautions  have  not  been  taken 
to  guard  the  results  against  the  influence  of  extraneous  factors. 
We  regret  that  this  charge  is  not  more  specific,  for  then  it  not 
only  would  have  more  meaning  but  it  could  be  answered  in 
briefer  space.  However,  let  us  recall  (i)  just  what  precautions 
have  been  taken  that  the  influence  of  variable  factors  extraneous 
to  the  effect  of  the  conditions  tested  should  not  enter  into  the 
conditions  of  the  experiment  to  an  extent  that  would  be  harmful 
for  the  purpose  for  which  the  experiment  was  used,  and  that  no 
variations  produced  by  such  factors  should  be  confused  with  the 
variations  produced  by  changing  the  conditions  to  be  tested;  and 
(2)  just  how  much  data  has  been  published  with  regard  to  these 
precautions  up  to  the  present  time.  Before  beginning  and  pre- 
liminary to  the  work  the  results  of  which  have  been  published 
in  our  last  three  papers,  a  study  was  made  for  the  express  pur- 
pose of  finding  out  just  what  factors  would  be  likely  to  influence 
the  results  of  the  work,  and  methods  were  devised  for  controlling 
these  factors.  Obviously  a  study  of  the  influence  of  a  factor 
can  be  made  by  varying  that  factor  when  all  other  conditions  are 
held  constant  and  noting  the  effect  on  the  results.  Such  a  study 
could  have  gone  on  endlessly  and  the  presentation  of  its  results 
would  have  consumed  endless  space.  Moreover,  such  work  leads 
to  nothing  once  the  factors  are  known  and  methods  have  been 
devised  to  control  them.  That  type  of  investigation  of  the  test 
was  pursued  to  some  extent,  however,  by  Mr.  Cravath,  and  the 
results  of  his  work  were  published.  In  our  own  work  instead 
of  trying  to  find  out  at  needless  length  what  effects  could  be  pro- 
duced by  means  of  a  procedure  that  never  would  be  permitted 
in  making  a  test,  every  care  has  been  taken  to  control  the  factors 
the  possibility  of  the  influence  of  which  had  been  revealed  in 
the  preliminary  experiments ;  and  the  effectiveness  of  the  control 


1 1 58     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

was  checked  up  by  carefully  determining  the  mean  variation  of 
the  results  for  each  set  of  lighting  conditions.  The  size  of  this 
mean  variation  is,  it  is  well  known,  the  measure  of  the  net  in- 
fluence of  the  factors  extraneous  to  the  conditions  which  are 
being  tested.  When,  for  example,  two  lighting  systems  are  being 
tested  and  it  is  found  that  the  difference  in  the  average  result 
obtained  for  the  two  systems  is  not  greater  than  the  sum  of  the 
mean  variations  for  both,  the  conclusion  can  not  be  certainly 
drawn  that  a  significant  difference  in  effect  is  produced  by  the 
two  systems.  This  method  of  treating  results  has  been  devised 
as  a  gauge  on  the  influence  of  variable  extraneous  factors  and 
should  be  too  well  known  to  need  further  discussion  here.  Let 
it  be  sufficient  to  state  that  this  check  upon  the  absolute  and  rel- 
ative value  of  the  influence  of  such  factors  has  been  carefully 
applied  at  every  step  in  the  work.  This  we  have  already  stated. 
We  have  also  given  a  statement  of  the  care  that  was  exercised 
in  the  selection  of  observers  based  both  upon  their  optical  con- 
dition and  the  precision  they  had  already  shown  in  other  work  in 
physiological  optics;  and  a  very  detailed  description  of  the  care- 
ful method  that  was  used  in  training  the  observer  separately  on 
each  feature  of  the  test  with  careful  attention  to  the  size  of  the 
mean  variation  throughout.  Short  of  a  paper  devoted  to  the 
test,  the  data  that  has  been  published  on  the  above  points  can 
scarcely  be  considered  insufficient.  Statements  of  the  precau- 
tions that  have  been  taken  in  the  control  of  the  extraneous  fac- 
tors and  in  the  selection  and  training  of  observers  have  been 
published  as  the  need  arose  in  all  four  papers  and  amplified  both 
in  the  public  and  written  discussions  both  of  our  own  papers 
and  Mr.  Cravath's.  A  statement  of  the  standard  of  precision 
to  which  each  observer  must  attain  in  the  3-minute  records 
before  he  was  allowed  even  to  participate  in  the  practise  series 
of  the  3-hour  tests  was  made  in  connection  with  the  publica- 
tion of  the  second  and  third  papers11  and  again  in  the  fourth 
paper.  A  comparison  of  the  mean  variation  for  each  lighting 
condition  with  the  variation  produced  by  changing  the  condition 
to  be  tested  was  given  as  a  regular  feature  of  the  presentation 
of  the  results  for  the  work  of  the  fourth  paper.     Here  we  are 

11  The  second  and  third  papers,   it  will  be    remembered,    were    published    simul- 
taneously. 


EXPERIMENTS    OX    THE    EYE  1 159 

working  with  smaller  variations  in  lighting  effects  and  there  was 
need  to  show  the  comparison.  In  the  presentation  of  the  data 
of  the  second  and  third  papers,  however,  the  comparison  was 
not  considered  necessary.  The  changes  made  in  the  conditions 
tested  in  that  work  were  so  large  and  the  variations  produced  by 
changing  the  conditions  tested  so  absurdly  much  greater  than  the 
normal  variation  for  each  of  the  conditions  tested  that  the  com- 
parison seemed,  as  I  have  already  said,  not  only  needless  but  dis- 
tinctly ostentatious.  A  representative  numerical  statement  of  the 
comparison,  however,  is  given  in  the  fourth  paper.  Moreover,  a 
detailed  statement  will  be  given  in  a  final  paper  devoted  to  the 
test.  We  have  taken  considerable  care  to  describe  the  exact  con- 
ditions under  which  the  work  was  done,  or  to  give  precautions  that 
were  taken  to  guard  against  the  influence  of  variable  factors. 

In  the  fourth  and  fifth  paragraphs  Dr.  Cobb  compares  our  work 
with  photometry  in  a  way  that  needs  not  only  elucidation  but  some 
correction.  There  is,  for  example,  absolutely  no  difference 
between  the  two  kinds  of  work  that  would  make  one  capable  and 
the  other  incapable  of  precise  performance.  In  photometry  a 
judgment  of  brightness  equality  is  employed  which  may  range  or 
vary  through  a  difference  threshold  on  either  side  of  equality.  In 
our  work  a  visual  acuity  judgment  is  employed  which  is  nothing 
more  nor  less  than  the  judgment  of  a  space  threshold.  Of  the 
two  the  latter  is  the  more  precise  even  when  the  judgment  of 
equality  is  made  between  two  lights  of  the  same  composition.  A 
different  use  is  also  made  of  the  judgment.  In  photometry  the 
judgment  is  used  to  equate  the  power  of  two  lights  to  arouse 
equal  sensations  with  the  eye  at  a  given  standard  of  performance. 
In  our  work  the  judgment  is  used  to  measure  the  ability  of  the 
eye  to  hold  itself  up  to  a  given  standard  of  performance  from 
beginning  to  end  of  a  period  of  work  under  this  or  that  lighting 
condition.  In  careful  work  when  the  photometric  judgment  is 
used  to  equate  the  power  of  two  lights  to  arouse  sensations  of 
equal  intensity  the  observer  is  first  trained  to  a  satisfactory  de- 
gree of  precision  in  making  the  judgment  before  the  work  of 
photometering  is  done,  and  this  photometering  itself  is  checked 
by  the  degree  of  reproducibility  of  the  results  obtained,  or  the 
size  of  the  mean  variation.     If,  however,  the  photometric  judg- 


Il6o     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ment  were  used  to  measure  the  power  of  the  eye  to  hold  itself  up 
to  a  certain  standard  of  performance  from  the  beginning  to  the 
end  of  a  period  of  work  under  a  given  lighting  condition,  and 
we  have  used  it  in  that  way  in  our  work  on  determining  the 
ability  of  the  retina  to  maintain  its  power  to  discriminate  bright- 
ness differences  through  a  period  of  work  under  different  lighting 
conditions,  the  method  of  training  the  observer  and  the  check  on 
the  precision  of  the  work  should  be  carried  out  just  as  we  have 
carried  it  out  in  our  work  on  the  power  of  the  eye  to  hold  itself 
up  to  a  certain  standard  of  acuity.  That  is,  precision  is  first  at- 
tained in  making  the  photometric  judgment.  The  observer  is  then 
given  a  period  of  training  and  practise  in  which  the  precision  is 
compared  before  and  after  work  under  a  given  lighting  condition. 
As  a  third  step  the  observer  is  allowed  a  period  of  practise  under 
different  lighting  conditions  until  a  satisfactory  degree  of  repro- 
ducibility is  attained  in  the  figure  or  ratio  expressing  a  com- 
parison either  of  the  sensitivity  or  the  size  of  the  difference  thres- 
hold before  and  after  work.  And  lastly  in  the  actual  work  of 
testing,  the  final  results  are  compiled  from  a  large  number  of 
determinations,  and  the  precision  is  checked  up  by  the  size  of  the 
mean  variation.  It  is,  for  example,  very  misleading  for  Dr. 
Cobb  to  state  in  reference  to  our  work  as  he  has  in  the  sixth 
paragraph : 

It  is  nevertheless  a  matter  of  general  opinion,  I  find,  among  those 
who  have  up  to  this  present  time  conducted  investigations  of  this  char- 
acter on  the  performance  of  the  sense  organs,  that  quantitative  results 
are  not  to  be  relied  on  for  reproducibility  to  within  i  per  cent.,  when 
obtained  in  a  few  minutes,  and  they  have  been  driven  to  much  more  time 
consuming,  laborious  methods  to  arrive  at  results  which  they  consider 
admissible. 

Dr.  Cobb  points  out  that  the  test  is  original  with  the  authors 
and  should,  because  it  is  so  very  new,  be  subjected  to  probation 
and  searching  criticism  before  it  be  given  a  place  in  the  sun 
along  with  methods  hoary  and  worn  with  service.  Since  the 
question  is  raised  it  might  be  well  to  find  out  just  how  new  in 
its  essential  principles  the  method  really  is.  Just  two  features  are 
involved  in  the  test  method, — one  is  that  visual  acuity  or  clear- 
ness of  seeing  may  be  measured  by  the  smallest  visual  angle  the 
eye  is  able  to  discriminate;  the  other,  a  principle  equally  old,  is 
that  a  loss  of  efficiency  or  depression  of  function  in  a  machine, 


EXPERIMENTS   ON    THE   EYE 


Il6l 


apparatus,  or  living  organ  or  organism  will  show  out  more  plainly 
when  a  prolonged  rather  than  a  momentary  performance  is  re- 
quired. Our  intention  has  been  to  combine  these  principles  in 
their  simplest  terms  into  a  test  of  the  comparative  power  of  the 
eye  to  sustain  its  power  of  clear  seeing  or  aggregate  functional 
activity  under  different  conditions  of  lighting  and  with  different 
kinds  and  conditions  of  use.  Allow  me  to  quote  from  a  state- 
ment of  the  principle  of  the  test. 

The  principle  of  the  test  will  be  remembered  from  the  earlier  papers. 
It  is  merely  the  conventional  acuity  test  subjected  to  certain  features  of 
standardization  for  the  sake  of  greater  reproducibility  and  made  into  an 
endurance  test  to  give  it  additional  sensitivity.     The  older  test  had  not 
been  found  to  be  sufficiently  sensitive  to   fatigue  conditions  to  warrant 
adoption  in  our  work.    This  test  is  not  in  fact  meant  to  be  a  fatigue  test. 
It  was  designed  to  test  the  dioptric  condition  of  the  eye  and  may  be  used 
with  more  or  less  success  perhaps  as  Dr.  Cobb  used  it  "as  a  test  of  how 
far  a  given  lighting  condition  is  conducive  to  clear  seeing  with  a  maxi- 
mum of  momentary  effort"   (provided,  however,  it  is  used  with  a  degree 
of  precision  and  in  connection  with  a  plan  of  experimentation  that  will 
warrant  the  drawing  of  conclusions)  ;  "but  it  has  not  the  essentials  of  a 
fatigue  test  nor  of  its  converse,  the  ease  with  which  clearness  of  seeing 
is  attained,  which  is  what  is  needed  primarily  for  the  selection  of  lighting 
conditions  for  the  greater  part  of  the  work  that  we  are  ordinarily  called 
upon  to  do.     Almost  if  not  quite  as  good  results  may  be  gotten  with  it, 
for  example,  after  work  as  before,  when  there  is  every  other  reason  to 
believe  the  eye  has  suffered  considerable  depression  in  functional  power. 
The  reason  for  this  is  obvious.     Although  greatly  fatigued  the  eye  can, 
under  the  spur  of  the  test,  be  whipped  up  to  give  almost  if  not  quite  as 
good  results  as  the  non-fatigued  organ  when  only  a  momentary  effort  is 
required.     If    fatigued,  however,   it   cannot   be   expected   to   sustain   this 
extra  effort  for  a  period  of  time.    The  demonstration  of  this  fact  had  led 
early  in  our  work  to  the  introduction  of  the  time  element  into  the  test. 
The  principle  involved  is  not  a  new  one.    It  is  merely  the  application  of 
a  very  old  and  well  known  one  to  the  work  of  testing  for  optical  fatigue. 
If,  for  example,  a  sensitive  test  is  wanted  for  the  detection  of  fatigue  in 
a  muscle,  as  good  results  cannot  be  expected  if  the  test  requires  only 
momentary  effort  on  the  part  of  the  muscle  as  would  be  attained  if  the 
endurance   of   the   muscle  were  taken   into   account.     For   our  purpose, 
therefore,  the  old  acuity  test  has  been  made  into  an  endurance  test,  in 
which  the  fatigue  or  loss  of  functional  efficiency  of  the  eye  is  measured 
by  its  power  to  sustain  clear  seeing  for  a  period  of  time.     As  such  it 
should  and  does  show  a  sensitivity  for  detecting  fatigue  far  beyond  what 
can  be  attained  by  the  older  and  more  established  test  when  it  is  used 
for  that  purpose." 


Il62     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

The  discussion  in  the  eighth  paragraph  of  the  influence  of  ex- 
pectation or  pre-knowledge  on  the  part  of  the  observer  is  also 
absurdly  misleading.  The  discussion  is  introduced  by  the  sen- 
tence "That  is,  in  the  application  of  the  test  as  used  by  the  authors 
of  the  paper  the  observer  is  in  full  knowledge  of  all  its  details." 
Obviously  the  reader  is  meant  to  infer  from  this  statement  that 
the  observer  is  put  under  some  exaggerated  or  special  condition 
of  pre-knowledge  not  proper  to  a  well  conducted  experiment. 
Later  when  pinned  down  to  cases  it  develops  that  the  critic  is  able 
to  name  only  two  items  of  which  the  observer  has  knowledge, 
namely,  the  test  object  and  the  fact  that  in  the  3-minute  records 
it  is  always  kept  at  the  same  distance  after  work  as  before.  Why 
it  is  necessary  in  order  to  have  a  properly  standardized  acuity 
experiment  to  give  the  observer  a  knowledge  of  the  test  object 
and  to  change  the  type  of  judgment  from  recognition  to  that  of 
a  space  threshold,  the  surest  and  most  reproducible  of  the  sense 
judgments,  has  been  discussed  at  length  in  our  first  and  fourth 
papers.  The  second  point,  it  is  obvious,  can  not  be  of  the  slightest 
consequence.  As  a  matter  of  fact  the  observer  does  not  know 
unless  he  is  told  that  the  distance  of  the  test  object  is  the  same 
after  work  as  before.  The  experimenter  knows  this,  but  there  is 
absolutely  nothing  in  the  conduct  of  the  experiment  to  tell  the 
observer  that  the  distance  of  the  test  object  has  not  been  changed 
in  the  3  hours  that  have  elapsed  since  the  first  record  has  been 
taken.  But  even  if  he  did  know  it  had  not  been  changed,  the 
knowledge  could  not  have  the  slightest  influence  on  his  judgment 
of  when  the  space  between  the  dot  and  the  vertical  line  in  the 
letter  i  sinks  below  the  threshold  of  discrimination,  how  often  it 
goes  below  the  threshold,  or  how  long  it  stays  there ;  for  it  drops 
below  the  threshold  not  because  of  any  change  in  the  distance  or 
size  of  the  test  object  or  its  parts,  but  because  the  eye  is  not  able 
to  hold  its  adjustment  for  clear  seeing.  For  a  somewhat  full  dis- 
cussion of  the  importance  of  the  factor  pre-knowledge  in  experi- 
ments in  physiological  optics,  of  how  it  may  be  eliminated  and 
compensated  for  in  accord  with  the  best  principles  of  experi- 
mentation at  the  present  time,  the  reader  is  referred  to  Note  1,  of 
the  paper  "Some  Experiments  on  the  Eye  with  Inverted  Reflec- 
tors, etc.,"  which  appears  on  previous  pages  of  this  number  of 
the  Transactions. 


EXPERIMENTS   ON    THE   EYE  H63 

Up  to  this  time  in  Dr.  Cobb's  discussion  I  had  understood  that 
his  doubts  as  to  whether  the  results  of  our  test  have  really  meas- 
ured the  loss  of  efficiency,  rested  on  several  contentions :  the  fact 
that  only  one  other  investigator  had  published  results  on  the  tests 
besides  ourselves ;  his  claim  that  no  data  has  been  published  that 
could  be  considered  as  showing  a  safeguarding  of  the  results 
against  the  influence  of  extraneous,  factors;  the  charge  that  the 
observer  knows  what  the  test  object  is  and  that  it  is  the  same 
distance  from  the  eye  in  the  records  taken  before  and  after  work ; 
the  recrimination  that  such  precision  as  was  attained  by  our 
observers  in  the  course  of  several  months  of  training  in  one 
feature  of  the  experiment  could  not  in  the  opinion  of  the  ex- 
perts of  his  acquaintance  be  obtained  in  a  few  minutes ;  etc.,  etc. 
In  the  ninth  paragraph,  however,  it  develops  that : 

In  making  reference  to  the  possibility  of  the  test  being  subject  to 
influences  other  than  the  state  of  efficiency  or  fatigue  of  the  eye,  the  fact 
in  mind  was  that  in  the  greater  part  of  the  work  reported,  the  tests  were 
conducted  with  the  observer  at  the  same  point  and  under  the  same  light- 
ing conditions  as  during  the  work  period.  That  is  to  say,  that  in  this 
portion  of  the  work  the  test  was  not  conducted  under  the  same  conditions 
in  any  two  different  experiments  whose  results  are  compared. 

Dr.  Cobb's  contention  here  is  that  the  3-minute  record  before 
and  after  the  reading  period  should  have  been  taken  in  a  sepa- 
rate test  room  having  always  the  same  intensity  and  distribution 
of  light  regardless  of  what  distribution  and  intensity  of  light 
the  eye  was  exposed  to  during  the  3  hours  of  reading  which 
intervened.    That  is,  immediately  at  the  close  of  this  period  the 
observer  would  have  been  brought  into  a  room  for  the  3-minute 
record  in  which  for  a  part  of  the  work  the  distribution  effects 
would  have  had  to  be  widely  different  from  the  previous  3- 
hours  exposure   (the  distribution  series),  and  for  another  part 
of  the  work  both  the  distribution  and  intensity  would  have  been 
widely  different  (the  intensity  series).     Thus  the  eye  in  every 
test  would  have  taken  the  record  at  the  close  of  work  in  a  dif- 
ferent state  of  adaptation  or  sensitivity  than  at  the  beginning. 
How  very  futile  and  inadvisable  this  would  have  been  more  es- 
pecially  for  the  work  in  the  intensity   series   I   scarcely  need 
once  more  to  point  out.     Even  in  the  work  in  the  distribution 
series,  the  only  part  of  the  work  for  which  Dr.  Cobb's  proposal 


1 164    TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

could  have  at  all  been  considered,  very  great  care  would  have 
had  to  be  exercised  to  see  that  the  separate  room  was  always 
illuminated  with  exactly  the  same  intensity  of  light  that  was 
used  in  the  room  in  which  the  reading  was  done.  If  the  illumi- 
nation of  the  two  rooms  were  not  accurately  the  same,  a  period 
of  adaptation  would  have  had  to  be  allowed  before  the  3-minute 
record  could  have  been  made,  which  in  case  of  the  record  taken 
after  work,  would  have  given  the  eye  opportunity  to  recover 
from  the  fatigue  induced  by  the  work.  It  is  obvious  that  a  great 
deal  of  difficulty  would  be  encountered  in  accurately  maintaining 
this  control;  and  if  it  were  not  so  maintained  an  error  of  con- 
siderable consequence  would  be  introduced  into  the  work.  More- 
over, in  getting  this  control,  not  only  the  illumination  of  the  test 
card  must  be  taken  into  account,  but  the  brightness  of  the  whole 
field  of  vision  with  its  complex  distribution  of  light  and  shade, 
for  this  conditions  the  state  of  adaptation  of  the  paracentral 
and  peripheral  portions  of  the  retina,  which  in  turn  exerts  an 
influence  on  the  part  of  the  retina  that  receives  the  image  of  the 
test  object.  It  is  obvious  further  that  this  duplication  of  light 
and  shade  could  not  be  made  in  a  separate  test  room  without 
copying  the  work  room  and  the  lighting  system  employed  in  each 
case,  which  would  of  course  no  longer  make  of  it  a  separate 
room.  Furthermore,  it  was  found  early  in  the  work  that  the 
effects  of  smaller  differences  in  lighting  could  be  detected  when 
both  the  3-minute  records  and  the  work  were  done  under  the 
lighting  conditions  to  be  tested.  That  is,  the  total  test  procedure, 
which  includes  both  the  3-minute  records  and  the  reading,  is 
more  sensitive  when  it  is  all  done  under  the  conditions  to  be 
tested,  than  when  a  part  of  it  is  done  under  these  conditions  and 
a  part  of  it  in  a  separate  room.  Since  the  method  is  more  sensi- 
tive when  the  whole  procedure  is  conducted  under  the  lighting 
conditions  to  be  tested,  we  can  see  no  reason  why  even  the  purist 
should  demand  that  a  part  of  it  should  be  done  under  the  condi- 
tions to  be  tested  and  a  part  of  it  elsewhere  so  long  as  the  results 
are  recognized  to  be  the  consequence  of  the  3-minute  records 
and  of  the  reading.  There  are,  it  is  obvious,  two  reasons  why 
the  method  should  be  more  sensitive  when  the  3-minute  records 
are  taken  in  the  work  room.  ( 1 )  The  method  is  more  amenable 
to  control  when  the  eye  is  subjected  to  no  change  in  lighting 


EXPERIMENTS   ON    THE   EYE  1 165 

effects  in  the  3  hours  intervening  between  the  two  records 
that  have  to  be  compared.  And  (2)  the  3-minute  record  itself 
is  a  task  for  the  eye  as  well  as  the  reading.  The  difference  be- 
tween the  fatigue  it  induces  in  case  of  the  first  and  second  records 
may  be  greater  under  a  bad  lighting  system  than  under  a  good. 
If  so,  this  adds  on  to  the  effect  of  the  reading  to  make  up  the 
total  effect  determined  by  comparing  the  two  records.  Whether 
it  does  or  not,  however,  seems  to  me  of  little  consequence  for 
it  is  differential  of  conditions  just  as  well  as  the  reading.  That 
is,  if  the  effect  does  add  on  to  the  effect  of  reading,  the  total 
result  is  only  as  if  a  longer  reading  period  were  used.  Here, 
however,  Dr.  Cobb  files  his  final  demurrer  (footnote  5)  :  "There 
would  be  no  objection  to  the  inclusion  of  this  effect  in  the  result 
if  there  were  in  practical  life  any  work  that  the  eyes  are  called 
upon  to  do  at  all  comparable  with  the  effect  that  such  a  test  de- 
mands." Our  reply  to  this  would  be  ( 1 )  that  there  are  no  tests 
for  acuity,  momentary  or  sustained,  comparable  in  effect  with  the 
ordinary  use  of  the  eyes  for  the  same  length  of  time.  If  there 
were  they  would  not  be  tests;  (2)  the  effect  added  is  not  the 
total  of  the  strain  of  the  3-minute  record,  merely  the  difference 
in  effect  of  two,  one  taken  before  and  one  after  work;  and  (3) 
if  an  effect  is  added,  the  net  result  is  only  the  same  as  would  be 
attained  if  a  longer  reading  period  were  used. 

Dr.  Cobb  goes  on  to  say  that  "More  than  this  from  the  infor- 
mation at  hand  I  can  not  see  that  the  intention  of  the  authors 
to  conduct  the  test  under  conditions  identical  with  those  of  the 
work  period  was  fulfilled."  He  bears  this  out  with  a  descrip- 
tion of  the  observer's  position  during  the  3-minute  records  and 
the  reading  period,  as  he  interprets  it.  In  the  treatment  of  this 
point  Dr.  Cobb's  discussion  indicates  his  viewpoint.  Apparently 
it  was  supposed  that  the  observer  sat  primly  erect  with  eyes 
modestly  lowered  ("at  an  angle  of  about  450")  away  from  the 
garish  effects  of  the  selected  products  of  modern  lighting,  tak- 
ing great  care  to  face  these  products  to  which  it  was  the  sole  pur- 
pose of  the  experiment  to  expose  the  eyes  only  so  long  as  was 
necessary  to  view  the  test  object  for  the  3-minute  records.  Such, 
he  contends,  is  the  natural  inference  from  an  inspection  of  Figs. 
2,  3  and  4  (which  show  nothing  but  the  test  object,  the  track 
on  which  it  was  carried  and  the  observer's  empty  chair),  and 


Il66     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

"from  what  is  said  further  in  this  note"  describing  the  observer's 
position,  the  details  of  which  he  fails  to  give  or  to  reconcile  in 
the  slightest  regard  with  his  interpretation.  I  may  be  pardoned 
perhaps  for  pointing  out  that  Dr.  Cobb's  inference  is  the  natural 
one  on  only  two  assumptions:  (a)  that  he  has  not  carefully  read 
the  description  of  conditions  given  in  the  note  in  question;  and 
(b)  that  he  has  taken  for  granted  that  the  authors  have  not  a 
sufficient  comprehension  of  what  they  are  trying  to  accomplish 
in  these  tests  and  of  the  chief  point  of  significance  of  the  some- 
what extensive  results  they  have  obtained.  Allow  me  to  quote 
from  the  description  given  in  the  present  paper. 

Care  was  taken  to  have  the  eyes  sustain  as  nearly  as  was  possible  the 
same  general  relations  to  the  objects  of  the  room  as  were  sustained  when 
the  3-minute  records  were  taken.  This  could  be  done  either  by  hold- 
ing the  head  erect,  etc.,  or  by  tilting  slightly  backward  in  the  swivel  chair 
used  by  the  observer  and  allowing  the  head  to  relax  a  compensating 
amount.  So  far  as  the  direct  optical  effects  are  concerned  it  would  seem 
to  be  immaterial  which  of  these  positions  is  chosen,  so  long  as  approxi- 
mately the  same  field  of  vision  is  obtained.  The  latter  is  usually  pre- 
ferred by  the  observer  as  causing  less  general  fatigue.  When  taking  this 
position,  the  book  is  elevated  and  held  at  approximately  an  angle  of  450 
(a  little  nearer  to*  the  vertical  than  this  perhaps). 

Moreover,  the  description  given  in  the  third  paper,  while  not 
quite  so  full  as  this,  differed  from  it  in  no  way  that  could  lead  to 
Dr.  Cobb's  interpretation,  either  as  a  necessary  or  a  probable 
criticism.  But  Dr.  Cobb  protests  finally  (footnote  4)  :  "This 
position  can  not  be  comfortable."  It  is  not  so  comfortable  for 
the  eyes  as  the  one  we  were  naturally  inferred  by  him  to  take, 
but  otherwise  it  is  very  comfortable  indeed.  For  further  proof 
we  can  only  recommend  that  he  try  it.  The  above  description  of 
the  reading  position  of  the  observer  should  also  render  pointless 
the  contention  made  in  the  latter  part  of  footnote  5.  This  con- 
tention is : 

The  objection  to  the  standardization  of  the  test  conditions  raised 
by  the  authors  further  on,  namely,  that  slight  differences  in  the  level  of 
adaptation  will  materially  affect  the  results,  applies  with  equal  force  to 
the  procedure  of  the  authors  as  indicated  by  what  I  have  just  said.  The 
necessity  emphasized  for  the  control  of  the  whole  field  of  vision  with  its 
complex  distribution  of  light  and  shade  applies  equally  well  as  an  objec- 
tion to  the  change  in  the  distribution  of  light  on  the  retina  brought  about 
by  shifting  the  eyes  from  the  oblique  reading  position  to  the  horizontal 


EXPERIMENTS  ON   THE  EYE  1167 

position  demanded  by  the  test.  The  statement  (note  4)  that  "Care  was 
taken  to  have  the  eyes  sustain  as  nearly  as  possible  the  same  general  rela- 
tions to  the  objects  of  the  room  ..."  contains  nothing  to  imply  that 
such  a  shift  was  avoided. 

As  we  have  already  clearly  shown  by  quoting  from  the  original 
description  of  conditions,  the  reading  position  was  not  oblique, 
hence  no  shift  from  such  a  position  to  the  horizontal  is  demanded 
in  passing  from  reading  to  the  3-minute  record.  Moreover,  that 
there  shall  be  no  abrupt  transition  from  reading  page  to  test  card 
a  fixed  interval  of  pre-exposure  to  a  surface  of  the  same  bright- 
ness and  size  of  the  test  card  is  allowed  before  the  3-minute 
record  is  begun. 

The  footnotes  appended  to  Dr.  Cobb's  discussion  are,  I  under- 
stand, meant  to  apply  specifically  to  our  present  paper.  All  of 
them  have  already  been  covered  in  connection  with  the  above 
rejoinder  but  2  and  3.  Footnote  2  is  based  on  a  confusion  arising 
from  Dr.  Cobb  not  reading  correctly  our  statement  of  the 
standard  of  precision  that  must  be  attained  in  the  practise  on  the 
3-minute  records  before  the  observer  was  allowed  to  enter  on  the 
next  stage  of  the  preliminary  work.  The  1  per  cent,  is  not  a 
mean  or  average  variation.  It  is  an  outside  limit  beyond  which 
no  individual  variation  ever  went  for  the  observers  whose  results 
were  published  in  the  paper.  It  is  somewhat  difficult  to  under- 
stand how  he  could  have  misread  the  original  statement.  This 
statement  is :  "For  a  single  series  of  five  tests  these  variations 
in  the  time  seen  clear  in  the  3-minute  periods  have  always  fallen 
within  1  per  cent,  for  all  of  the  observers  we  have  used  and  for 
all  systems  of  lighting"  (Trans.  Aug.  30,  1915,  p.  461).  A  typ- 
ical mean  variation  in  the  time  seen  clear  in  one  of  these  practise 
series  of  five  tests  is  for  Observer  R  approximately  0.37  per  cent. ; 
for  Observer  G  it  was  slightly  smaller.  Corresponding  to  the 
mean  variation  in  the  time  seen  clear  of  0.37  per  cent,  for  Ob- 
server R,  the  mean  variation  of  the  ratio  time  clear  to  time 
blurred  is  1.4  per  cent.  We  hope  this  additional  explanation  will 
clear  up  the  doubt  in  Dr.  Cobb's  mind  with  regard  to  how  the 
mean  variation  was  obtained  for  Table  IX  of  the  present  paper. 
In  Table  IX  the  mean  variation  was  of  the  drop  in  ratio  time 
clear  to  time  blurred  produced  by  making  a  change  in  the  con- 
dition to  be  tested.    This  mean  variation  was  taken  of  the  drop 


Il68     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

so  that  the  average  value  of  the  drop  could  be  compared  with  its 
average  variation  to  see  whether  the  change  produced  by  chang- 
ing the  system  could  be  considered  as  significant.  The  citation 
given  by  Dr.  Cobb  should  not  have  caused  confusion  because  it 
was  not  only  clear  but  obvious  from  the  text  just  what  was  done 
in  both  cases. 

In  the  brief  first  statement  made  of  our  standard  of  precision 
in  the  practise  work  on  the  3-minute  record,  it  was,  we  may  say, 
considered  more  significant  for  the  purpose  for  which  the  3- 
minute  record  was  to  be  used  in  the  actual  work  of  testing  to 
show  that  all  of  the  individual  variations  fell  within  a  given  small 
limit  than  to  indicate  what  the  average  variations  were,  leaving 
the  reader  in  doubt  as  to  how  wide  a  range  of  throw  the  in- 
dividual variations  might  have.  As  to  whether  the  result  was 
expressed  in  terms  of  the  time  seen  clear  or  the  ratio  time  clear 
to  time  blurred  seems  to  me  quite  immaterial.  Both  expressions 
are  significant,  and  one  is  readily  derivable  from  the  other  when 
the  time  seen  clear  and  the  total  time  of  observation  are  known. 

In  footnote  3  Dr.  Cobb  raises  again  the  question  already  much 
discussed  of  the  possibility  of  introducing  an  objective  check  on 
the  influence  of  subjective  factors.  We  have  patiently  explained 
several  times  before  that  there  are  two  ways  of  checking  up  the 
influence  of  subjective  factors, — the  objective  check  and  a  care- 
ful determination  of  the  mean  variation,  and  that  neither  one  of 
these  possibilities  has  been  overlooked  in  our  work.  We  tried 
for  several  months  to  devise  a  means  of  changing  the  test  ob- 
ject in  such  a  way  that  an  objective  check  could  be  had  on  the 
registration  of  the  observer  without  sacrificing  the  principle  of 
the  test.  Such  a  change  of  sufficient  magnitude  to  be  of  any 
definite  service  could  not,  we  found,  be  made  in  the  test  object 
which  did  not  at  the  same  time  permit  the  eye  to  relax  its  strain 
at  the  instant  of  change,  which,  it  is  obvious,  destroys  the  very 
feature  which  gives  the  test  its  superior  sensitivity.  The  attempt 
to  get  an  objective  check  was  made,  I  may  say,  to  offset  possible 
criticism  rather  than  because  of  any  belief  that  it  was  necessary 
for  the  purpose  for  which  the  test  has  so  far  been  used ;  for,  as 
we  have  already  stated,  a  determination  of  both  the  maximum 
and  mean  variations  for  the  3-minute  records,  each  one  of  which 


EXPERIMENTS   ON    THE   EYE  I169 

consists  of  a  number  of  separate  judgments,  had  shown  us  that 
the  influence  of  expectation  and  other  subjective  factors  has 
been,  under  the  conditions  for  which  the  work  has  been  done, 
of  negligible  consequence.  Dr.  Cobb  suggests  as  an  objective 
check  that  different  cards  be  used  in  some  of  which  the  space 
between  the  dot  and  the  vertical  line  of  the  letter  i  be  obliterated 
in  different  amounts  by  a  fine  pen.  '  We  have  found  the  change 
he  suggests  not  to  be  of  any  additional  service  for  the  following 
reasons:  (i)  A  change  that  would  be  large  enough  to  affect 
appreciably  the  amount  of  time  that  the  angle  of  separation  be- 
tween dot  and  line  is  below  the  threshold  of  discrimination  is 
too  large  to  escape  the  observation  of  the  observer.  When  the 
eye  goes  out  of  adjustment,  the  lapse  is  apparently  too  abrupt 
and  too  great  to  permit  of  a  change  that  would  not  be  detectable 
to  the  observer  with  a  well  adjusted  eye  to  influence  significantly 
the  course  of  the  record.  That  is,  a  diminution  by  so  small  an 
amount  would  not  put  it  below  the  threshold  when  the  eye  was 
well  adjusted,  nor  would  an  increase  by  the  same  amount  put 
it  above  the  threshold  in  one  of  the  lapses  of  adjustment.  The 
additional  strain,  moreover,  does  not  seem  to  be  significantly 
great.  It  might  be  perhaps  if  the  angle  of  separation  which  it  is 
necessary  to  employ  were  at  or  very  near  the  threshold  of  dis- 
crimination, but  it  is  not  at  or  very  near  the  threshold  of  dis- 
crimination, as  we  have  explained  many  times.  (2)  The  check 
proposed  is  not  directly  objective,  it  could  serve  only  indirectly 
as  a  check  and  very  indirectly  at  that.  A  test  object  like  the 
letter  E,  for  example,  which  could  be  turned  in  different  direc- 
tions and  the  observer  be  required  to  tell  which  way  it  points  is 
used  in  acuity  tests  as  an  objective  check.  Here  the  judgment  of 
the  observer  is  checked  up  directly  by  the  knowledge  of  the  ex- 
perimenter. Dr.  Cobb,  however,  proposes  to  vary  the  results 
of  the  observer  by  varying  one  of  the  factors  which  is  supposed 
to  influence  these  results,  and  from  the  working  of  this  variation 
to  detect  whether  the  observer  is  judging  his  experiences  hon- 
estly. This  in  experimental  procedure  is  known  as  the  method 
of  concomitant  variations,  and  by  common  acceptance  must  itself 
be  very  carefully  checked  up  before  its  results  are  considered  of 
any  significance.  The  only  way  it  could  be  checked  up  would  be 
carefully  to  determine  the  mean  variation  for  each  change  and 


I  I/O     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

compare  this  variation  with  the  variation  produced  by  changing 
the  angle  of  separation.  This  would  have  to  be  done  before  it 
could  be  told  whether  the  change  was  operative  and  thus  even 
the  slightest  check  be  had  on  the  verity  of  the  observer's  judg- 
ments. That  is,  in  this  roundabout  procedure  one  would  have 
to  rely  fundamentally  at  every  step  on  the  check  we  have  used 
from  the  beginning,  namely,  a  careful  determination  of  the  mean 
variation,  and  the  procedure  itself  invites  cumulation  of  error 
and  uncertainty.  Dr.  Cobb's  proposal  is,  in  methodological  pro- 
cedure, not  unlike  setting  a  thief  to  catch  a  thief,  and  is  to  say 
the  least  distinctly  meretricious. 


burrows:    small  incandescent  lamps  1171 

SMALL  INCANDESCENT  LAMPS  AND  SPECIAL 
ILLUMINATION  PROBLEMS.* 


BY  ROBERT  P.  BURROWS. 


Synopsis:  The  paper  presents  certain  improvements  in  miniature 
lamps  resulting  in  their  increased  use  in  commercial,  professional,  and 
industrial  fields;  a  brief  study  of  dry  cells  and  their  relation  to  small 
incandescent  lamps  in  the  various  fields  together  with  a  suggested  method 
of  testing  dry  cells  in  order  to  obtain  such  data  as  will  enable  the  proper 
application  of  small  lamps;  and  a  few  interesting  examples  of  how  the 
application  of  engineering  knowledge  to  comparatively  simple  devices  will 
increase  their  usefulness.  A  few  of  the  many  uses  of  small  lamps  are 
also  mentioned. 


The  purpose  of  this  paper  is  to  call  attention  to  the  fact  that  the 
small  incandescent  lamps  commonly  classed  as  miniature  lamps 
are  coming  to  be  recognized  as  contributing  a  great  deal  to  certain 
special  fields  of  lighting.  Not  long  ago  small  lamps  were  looked 
upon  as  playthings  and  had  little  or  no  commercial  application. 
This  was  due,  partly,  to  the  limitations  of  the  carbon  filament  in 
applications  where  the  cost  of  supplying  energy  is  necessarily 
high.  With  the  introduction  of  tungsten  as  a  filament  material, 
a  considerably  higher  efficiency  for  these  lamps  was  possible. 
However,  it  was  not  until  the  introduction  of  the  drawn-wire, 
tungsten  filament  that  the  lamps  became  recognized  as  having 
many  commercial  possibilities.  This  filament  improvement,  with 
its  increased  efficiency  and  strength,  did  more  than  anything  else 
to  place  miniature  lamps  in  the  position  they  now  hold.  High 
efficiency  made  possible  the  use  of  dry  cells  as  a  source  of  energy. 

With  the  discovery  that  drawn-wire  tungsten  could  be  coiled 
into  concentrated  filaments,  further  fields  for  miniature  lamps 
were  opened.  Certain  problems  in  the  projection  of  light  were 
materially  simplified  by  the  concentrated  filament  and  because  it 
was  possible  to  get  a  greater  length  of  wire  in  a  small  space,  the 
high  voltage,  small  bulb  lamps  of  very  much  increased  efficiency 

*  A  paper  presented  at  the  ninth  annual  convention  of  the  Illuminating  Engineer- 
ing Society,  Washington,  D.   C,   September  20-23,    I01 5- 

The  Illuminating  Engineering  Society  is  not  responsible  for  the  statements  or 
opinions  advanced  by  contributors. 


1 172     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

found  their  use  in  decorative  fields.  The  introduction  of  an  inert 
gas  into  certain  types  of  these  small  lamps  greatly  increased  their 
efficiency. 

Following  the  increased  demand  came  a  study  of  the  manufac- 
ture of  these  miniature  lamps,  a  study  which  is  constantly  going 
on,  and  which  is  gradually  taking  them  out  of  the  class  of  hand 
made  products.  The  difficulties  encountered  in  cutting  and 
mounting  by  hand  a  little  piece  of  wire  one  third  the  diameter  of 
a  human  hair  and,  say,  10  mm.  in  length  can  be  more  readily 
appreciated  when  it  is  known  that  0.5  mm.  in  the  length  of  fila- 
ment in  certain  types  of  these  lamps  means  about  5  per  cent, 
difference  in  voltage.  Thus  it  can  be  seen  how  a  higher  quality 
and  comparatively  low  cost  is  obtainable  with  machine  manu- 
facture. A  number  of  these  miniature  lamps  now  have  their 
filaments  coiled  and  cut  by  very  accurate  machines  and  a  few  have 
semi-automatically  mounted  filaments. 

With  the  growing  interest  in  miniature  lamps  came  greater 
demands  for  their  correct  application  to  the  fields  involved. 
Where  a  few  years  ago  almost  any  lamp  which  would  give  light 
would  suffice,  it  is  now  demanded  that  light  not  only  shall  be 
produced  economically,  but  that  every  detail  of  the  lamp  must 
be  specially  designed  for  the  purpose.  For  instance,  the  dry 
cell  hand-lantern  first  came  on  to  the  market  with  demands  that 
all  the  light  possible  should  be  obtained  from  a  single  dry  cell 
without  regard  for  the  life  of  lamp  or  battery.  These  lanterns 
have  now  settled  down  to  replace  the  old  oil  lantern,  and  the 
manufacturers  are  requiring  that  the  life  of  battery  and  lamp 
shall  receive  fully  as  much  consideration  as  the  light  produced. 
In  order  to  obtain  a  maximum  amount  of  light  throughout  the 
life  of  a  dry  cell  it  became  necessary  to  study  their  limitations. 
This  involved  study  of  current  limitations,  recuperation,  the  effect 
of  heat,  cold  and  dampness,  and  the  ageing  of  cells  while  not  in 
actual  use. 

Inasmuch  as  dry  cells  are  coming  to  be  used  as  the  source  of 
energy  for  small  lamps  in  a  great  many  fields,  it  will  undoubtedly 
be  of  interest  to  study  some  of  their  characteristics. 

One  of  the  first  questions  that  presented  itself  in  this  study  was 
how  to  obtain  data  which  would  place  all  of  the  limiting  char- 


burrows:    small  incandescent  lamps  i  173 

acteristics  of  dry  cell  operation  on  such  a  basis  that  the  results 
would  be  comparable  at  all  times.  The  Electro-chemical  Society 
had  at  one  time  published  a  few  suggestions  on  the  subject,  but 
as  far  as  could  be  determined,  nothing  standard  had  been  decided 
upon.  After  a  number  of  tests  under  various  conditions  the 
following  procedure  was  drafted  and  sent  to  the  various  large 
battery  manufacturers  with  a  request  for  their  suggestions  and 
criticisms  and  received  their  approval. 

METHOD  OF  TESTING  DRY  CELLS  WHEN  DISCHARGING 
THROUGH  MINIATURE  TUNGSTEN  LAMPS. 

Class  No.  1 — Flashlight  Batteries. 

Class  No.  2 — Standard  No.  6  Dry  Cell  Batteries. 

General  Instructions. 

1 — All  tests  are  to  be  conducted  at  a  temperature  of  not  lower  than  700  F. 
and  as  near  thereto  as  possible.    Actual  temperature  to  be  noted. 

2 — The  current  at  rated  volts  is  to  be  obtained  on  each  lamp  before  start 
of  test. 

3 — All  lamps  and  tests  are  to  be  numbered. 

4 — At  the  completion  of  each  test  potential-time  curves  are  to  be  plotted 
for  all  the  data  obtained.  Besides  the  four  curves  obtained  from 
the  data  taken  on  tests  of  standard  No.  6  dry  cell  batteries,  a  curve 
is  to  be  plotted  which  will  be  the  average  of  the  above  four  curves. 
In  comparison  tests  the  same  scale  is  to  be  used  for  all  curves. 

5 — The  open  circuit  or  recuperating  periods  are  to  be  not  less  than  two 
hours  and  shall  be  a  fixed  period  of  time  for  each  test.  The  last 
period  each  day  as  well  as  the  last  period  each  week-end  is  to  be 
noted. 

6 — Enough  extra  lamps  of  the  same  rating  are  to  be  on  hand  for  each 
test  in  order  to  replace  lamps  immediately,  should  any  burn  out. 

7 — The  voltmeter  used  is  to  have  an  electrical  resistance  of  approximately 
100  ohms  per  volt  and  to  be  in  circuit  only  when  readings  are  taken. 

8 — The  electrical  resistance  of  the  wires  between  lamps  and  batteries  must 
not  exceed  0.0025  ohm  per  cell.  (This  is  approximately  the  resist- 
ance of  1  foot  of  No.  14  B-S  gauge  copper  wire.) 

Class  No.  1 — Flashlight  Batteries. 
The  battery  cells  shall  be  soldered  together  by  means  of  copper  wires 

in  order  to  insure  good  connections  between  cells. 
The  following  data  should  be  obtained : 
1 — Initial  open  circuit  voltage  at  start  of  test  only. 
2 — Initial  closed  circuit  voltage  at  start  of  test  only. 


1 174     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

3 — The  voltage  at  the  end  of  the  ist,  3rd  and  7th  periods  of  burning.  The 
voltage  at  the  end  of  every  7th  period  thereafter. 

Each  period  is  to  be  of  five  minutes  duration,  with  four  periods  per 
day. 

The  life  of  the  battery  is  to  be  considered  ended  when  the  potential 
drops  to  0.5  volt  per  cell. 

In  plotting  curves,  time  shall  be  stated  in  minutes. 

Class  No.  2 — Standard  No  6  Dry  Cell  Batteries. 
The  following  data  should  be  obtained : 
1 — Initial  open  circuit  voltage  at  start  of  test  only. 

2 — Voltage  readings  during  the  ist,  3rd  and  5th  periods  of  burning  and 
during  every  5th  period  thereafter. 
There  shall  be  four  periods  per  day. 
The  duration  of  each  period  shall  be  as  follows : 

Duration  of  period 

Less  than  0.3  watt  per  cell 1  hour 

0.3  to  0.5  watt  (inclusive)  per  cell 30  minutes 

0.5  to  1.3  watts  (inclusive)  per  cell 15  minutes 

1.3  watts  or  more  per  cell 5  minutes 

The  following  voltage  readings  are  to  be  taken: 

Duration  of  period  Readings 

I   hour    initial  closed  circuit 

End  of  20  minutes 
End  of  40  minutes 
End  of  period 

30  minutes  initial  closed  circuit 

End  of  10  minutes 
End  of  20  minutes 
End  of  period 

15  minutes  initial  closed  circuit 

End  of  5  minutes 
End  of  10  minutes 
End  of  period 

5  minutes  initial  closed  circuit 

End  of  1  minute 
End  of  3  minutes 
End  of  period 
The  life  of  the  battery  is  to  be  considered  ended  when  the  potential 

of  each  cell  drops  to  0.7  volt. 
In  plotting  curves  time  shall  be  stated  in  hours. 

A  typical  discharge  curve  of  two  dry  cells  in  series  plotted  from 
data  taken  in  accordance  with  the  above  outline  is  shown  in  Fig.  1 . 
The  average  curve  is  plotted  as  the  average  of  the  points  on  the 

1  This  reading  to  be  taken  after  needle  has  come  to  apparent  rest. 


burrows:    small  incandescent  lamps 


1 175 


other  three  curves  and  is  the  curve  for  which  lamps  must  be  de- 
signed to  operate  most  efficiently.  It  must  be  understood  that  this 
curve  is  actually  a  series  of  cycles  of  discharges  and  recuperations. 
The  start  and  completion  of  such  a  cyclic  curve  is  shown  in  Fig.  2 
and  was  obtained  by  means  of  a  recording  voltmeter  with  a  special 
scale.  It  is  interesting  to  note  the  difference  between  these  cycles 
as  shown  in  Fig.  3.  These  particular  curves  show  the  difference 
between  the  first  and  fourth  cycle  and  bring  out  the  point  that 
initial  closed  circuit  readings  are  of  little  value.     Fig.  4  shows  a 


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Fig.  1.— Typical  voltage  discharge  curve  of  dry  cells. 
(Three  batteries  ;  two  dry  cells  in  series.) 


Fig.  2. — Chart  of  voltage  variation  of  dry  cells  at 
start  and  completion  of  discharge. 


cycle  at  the  end  of  the  life  of  the  two  cells  shown  in  Fig.  1  and 
shows  why  it  is  not  economical  to  use  these  cells  after  their 
potential  has  dropped  to  0.7  volt  per  cell.  It  will  be  noted  that 
the  voltage  starts  at  2.2  volts  and  drops  in  one  minute  to  1.4  volts 
which  is  only  50  per  cent,  voltage  of  the  battery  and  would  con- 
sequently give  little  light.  The  curve  continues  on  down  to  0.2 
volt,  and  this  cycle  will  be  repeated  for  several  hours,  but  the 
abscissa  in  hours  would  continually  decrease,  thereby  shortening 
the  period  of  efficient  light  production  to  a  matter  of  seconds.     It 


1 176     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

has  been  shown  by  numerous  tests  that  after  two  hours  recuper- 
ation of  the  cell  there  is  no  appreciable  increase  in  power.  Fig.  12 
curve  A,  shows  the  marked  effect  of  low  temperature.  This 
curve  was  obtained  from  a  test  of  five  cells  in  series  operating  at  a 
temperature  of  about  22 °  F.  After  twenty  hours  the  battery  was 
placed  in  a  temperature  of  about  700  F.  and,  as  curve  B  shows,  it 
increased  in  voltage  while  discharging  until  it  nearly  reached  the 
normal  operating  voltage  for  that  period  in  its  life.  It  has  been 
stated  that  a  drop  of  50  in  temperature  below  700  decreases  the 


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Fig.  3. — Voltage  variation  between  first  and  fourth  periods  of  discharge. 
A,  variation  in  first  period  ;  B,  variation  in  fourth  period. 


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Fig.  4. — Cyclic  variation  of  voltage  for  one  period  of  discharge  and  recuperation. 
Two  dry  cells  in  series  ;  variation  during  one  complete  period. 


current  by  one  ampere.  However,  this  does  not  reduce  the 
capacity  of  the  battery  if  the  latter  is  brought  back  to  a  tempera- 
ture of  700  F.,  as  shown  by  the  previous  curve.  It  will  be  seen 
that  the  two  curves  in  Fig.  12  do  not  quite  come  together  after  the 
cold  battery  had  been  brought  up  to  the  temperature  of  the  one 
operating  under  normal  conditions.  This  may  be  explained  by 
the  fact  that  this  battery  was  subjected  to  a  certain  amount  of 
moisture.     Moisture  permanently  reduces  the  capacity  of  a  cell. 


burrows:    small  incandescent  lamps  i  177 

There  are  a  great  many  uses  for  small  lamps  using  dry  cells  as 
a  source  of  energy,  chief  among  which  is  the  dry  cell  hand 
lantern.  A  number  of  different  types  of  these  lanterns  are  shown 
in  Fig.  5.  Lamps  of  this  type  are  used  by  watchmen,  campers, 
firemen  and  farmers. 

The  reflector  design  for  hand  lanterns  has  become  quite  im- 
portant. At  first  the  manufacturers  wanted  all  the  light  possible 
in  one  direction  and  consequently  used  a  polished  parabolic  re- 
flector which  was  practically  useless  for  any  other  purpose  than 
to  see  comparatively  great  distances  ahead.  This  did  very  well 
for  watchmen,  or  hunters  and  campers,  but  was  almost  useless 
around  the  home  or  on  the  farm.  Reflectors  are  now  being  scien- 
tifically designed  to  meet  the  demand  for  a  more  distributed  light. 

Another  use  for  dry  cell  lighting  coming  into  prominence  is  the 
lighting  of  summer  cottages  or  permanent  camps  where  a  great 
deal  of  light  is  not  needed.  The  convenience  of  having  a  little 
light  is  considered  well  worth  the  small  expense  of  such  an  in- 
stallation. 

An  interesting  example  of  what  can  be  accomplished  by  apply- 
ing a  little  engineering  knowledge  to  a  comparatively  simple,  but 
nevertheless  ingenious  device,  is  that  of  an  egg  tester  recently 
equipped  with  miniature  lamps  and  proper  reflectors.  The  orig- 
inal model  of  this  device  was  equipped  with  one  6- volt,  0.84 
ampere  miniature  lamp,  using  four  No.  6  dry  cells  as  a  source  of 
energy  and  having  a  piece  of  tin  as  a  reflector  (Figs.  9  and  9a). 
Two  small  parabolic  reflectors  were  designed  and  recommended 
to  be  placed  one  behind  each  opening  and  to  contain  6-volt,  0.35 
ampere  lamps.  These  reflectors  and  the  distribution  obtained  are 
shown  in  Figs.  8  and  8a.  It  will  be  seen  that  the  maximum  light 
is  directed  through  the  egg  and  not  to  one  side.  As  a  direct  result 
of  these  recommendations,  the  battery  life  was  increased  400  per 
cent.,  the  effective  light  flux  was  increased  300  per  cent.,  and  the 
number  of  eggs  candled  per  battery  increased  400  per  cent. 

Among  other  novelties  using  flashlight  lamps  are  a  fishing 
bobber,  shown  in  Fig.  6;  luminous  fish  bait,  where  a  small  lamp 
with  a  dry  cell  as  a  source  of  energy  is  placed  in  the  "tail"  of  the 
bait,  for  night  or  early  morning  fishing.  In  the  industrial  field  a 
good  example  of  the  use  of  these  small  lamps  is  an  office  signal 


1 178     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

system  (Fig.  10),  not  in  wide  use,  but  of  great  convenience. 
This  system  is  so  arranged  with  small  lamps  that  the  executive 
may  place  a  call  for  any  of  his  assistants  and  know  by  the  signal 
on  his  desk  whether  or  not  his  call  is  receiving  attention. 

In  the  professional  field  there  are  a  great  many  uses  for  these 
small  lamps.  The  retinascope,  a  small  instrument  for  throwing 
an  intense  beam  of  light  into  the  pupil  of  the  eye,  using  a  dry  cell 
as  a  source  of  energy,  is  coming  into  use  among  doctors  for  eye 
examination.  There  are  numerous  other  small  devices  on  this 
same  principle,  such  as  a  cycstoscope  for  internal  diagnosis, 
dentists'  mouth  mirrors  with  a  lamp  and  battery  attached  to  the 
handle,  and  various  devices  for  eye,  ear  and  nose  examination 
where,  under  usual  conditions,  proper  seeing  is  difficult. 

The  class  of  lamps  commonly  known  as  automobile  lamps  and 
their  application  to  automobile  lighting  is  so  well-known  that  it 
is  hardly  necessary  to  discuss  them  here.  These  same  lamps, 
however,  are  being  used  for  motor  boat  lighting  and  in  some  cases 
utilize  the  same  sources  of  power  as  are  used  on  automobiles.  A 
very  simple  and  effective  method  of  lighting  motor  boats  is  with 
dry  cells.  A  battery  of  twelve  dry  cells  connected  in  series-multi- 
ple to  obtain  an  average  voltage  of  3.5  volts,  is  used  as  a  source 
of  energy  and  has  such  a  capacity  that  it  is  possible  with  care, 
to  use  the  port  and  starboard  lights,  two  riding  lights  and  thirteen 
cabin,  galley  and  stateroom  lamps  with  one  set  of  batteries  per 
season.  For  this  purpose  3.5-volt,  0.42-ampere  lamps  operating 
at  an  efficiency  of  1.25  w.  p.  c.  are  used.  A  complete  outfit  is 
shown  in  Fig.  7. 

Probably  the  best  example  of  exacting  conditions  imposed  upon 
these  small  lamps  now  as  compared  to  the  consideration  given 
them  a  few  years  ago  is  that  of  the  miner's  lamp.  This  subject 
has  previously  been  discussed  before  this  society  so  that  great 
detail  is  not  necessary.  The  conditions  imposed  upon  the  lamp 
were  that  they  should  have  a  uniform  life  of  200  or  300  hours 
depending  upon  the  source  of  energy,  not  more  than  5  per  cent, 
giving  a  life  less  than  250  or  170  hours,  respectively.  The  second 
condition  imposed  was  that  at  no  time  during  the  life  of  the  lamp 
and  a  twelve-hour  discharge  of  the  battery  should  the  amount  of 


)\-}& 


Fig.  5.— Typical  dry  cell  hand  lanterns. 


Fig.  6.— Fishing  bobber.  Fig.  7.— Motor  boat  lighting  equipment. 


85°      75°     65°       55°  45"  35° 


Fig.  S. — Suggested  reflectors 
for  egg  tester. 


Fig.  Sa. 


90°  75°G5°55"45°    35°      2S 


Fig.  9. 


Fig.  9a. 


Fig.  io.- — An  office  signal  system. 


burrows:    small  incandescent  lamps 


1 179 


light  fall  below  1.5  lumens.  The  third  condition  imposed  was 
that  the  uniformity  of  current  and  candlepower  should  meet 
fairly  close  conditions.  To  meet  these  meant  careful  reflector 
design  and  study  of  the  battery  discharge  curves  so  that  the  most 
efficient  lamp  would  be  designed  for  this  service. 

The  first  step  in  this  design  was  to  obtain  an  average  potential- 
time-discharge  curve  for  a  number  of  batteries  discharging 
through  lamps  of  such  current  rating  that  they  would  discharge 
the  battery  to  its  most  economical  voltage  in  the  allotted  time. 
Such  a  typical  curve  (A)  is  shown  in  Fig.  n.  By  means  of  an 
exponential  equation  involving  lamp  life  with  applied  voltage, 
curve  C,  Fig.  11,  was  plotted.  From  this  curve  it  is  possible  to 
ascertain  the  life  of  a  lamp  when  burned  at  any  voltage  on 


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Fig.  11. — Typical  voltage  discharge  of 
miner's  lamp  battery. 


Fig.  12. — Effect  of  low  temperature  on  voltage 
discharge  of  dry  cells. 


curve  A.  For  example,  if  a  lamp  is  designed  for  300  hours  life 
at  2  volts,  in  order  to  determine  its  life  at  1.9  volts,  it  is  only 
necessary  to  find  1.9  volts  on  curve  A  and  the  corresponding  point 
on  curve  C.  This  gives  a  correction  factor  which  when  multiplied 
by  300  will  give  the  life  at  1.9  volts.  The  average  ordinate  D  of 
this  curve  gives  the  voltage  V  for  which  a  lamp  may  be  designed 
to  have  the  same  life  as  when  burned  on  the  potential-time  curve 
A.  The  obtaining  of  this  voltage  is  most  important  since  the  life 
of  incandescent  lamps  is  an  inverse  function  of  voltage. 

Inasmuch  as  the  requirements  were  so  drawn  up  as  to  combine 
the  reflector  with  the  lamp,  it  was  necessary  to  take  up  the  ques- 
tion of  reflector  design.  The  reflector  engineers  were  held  to  the 
angle  of  the  beam  of  light,  and  also  the  distribution  across  the 


Il80     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

beam.  Fig.  14  shows  the  theoretical  minimum  allowable  distri- 
bution of  illumination  on  a  plain  surface  20  in.  (0.58  m.)  from  a 
reflector  as  required  by  the  Bureau  of  Mines.  From  this  distri- 
bution, it  was  a  comparatively  simple  matter  to  plot  a  curve  show- 
ing the  distribution  of  light  from  a  reflector  which  would  give 
this  distribution  of  illumination.  This  curve  is  shown  in  Fig.  13. 
From  this  curve  it  was  necessary  to  obtain  the  shape  of  the  re- 
flector which  would  give  the  required  distribution  of  illumination 


kM^^aH^^^^- 

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Fig.  13. — Distribution  curve  of  mine  lamp  reflector  to  meet 
Bureau  of  Mines  specifications. 


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[ 

s 

4 

Fig.  14. — Minimum  distribution  of  illumination  to  meet  Bureau 
of  Mines  specifications  for  miner's  lamps.  (Theoretical  dis- 
tribution across  a  7-ft.  circle.) 


over  the  circle  specified.  In  Fig.  15  is  shown  one  shape  of  re- 
flector which  will  give  a  distribution  closely  approximating  that 
required.  The  finish  of  the  reflector  must  give  an  illuminated 
area  which  will  answer  the  requirements  that  when  "observed2 
with  the  eye  there  shall  be  no  black  spots  within  the  7-foot  circle 
or  any  sharply  contrasting  areas  of  bright  and  faint  illumination 

2  Procedure  for  establishing  a  list  of  permissible   Portable  Electric  Mine  Lamps. 
Schedule  6A,  Dept.  of  Interior,  Bureau  of  Mines. 


burrows:    small  incandescent  lamps 


1181 


anywhere."  Two  finishes  have  been  used,  porcelain  enamel  and 
aluminum.  With  a  knowledge  of  the  efficiency  of  these  finishes 
and  the  volume  of  light  required  from  a  reflector,  the  amount  of 
light  the  lamp  would  have  to  give  was  determined,  including 
factors  of  safety,  since  the  foregoing  are  minimum  values.  After 
determining  this  amount  of  light,  and  transferring  it  into  a  value 
of  candlepower,  the  final  step  was  to  combine  this  candlepower 
with  the  voltage  and  current  before  determined  and  to  obtain  the 
efficiency  of  the  lamp.  This  efficiency  had  to  be  such  as  to  give 
the  required  life.  With  the  above  data,  it  was  possible  to  design 
lamps  to  give  the  maximum  amount  of  light  under  the  conditions 
laid  down. 

All  the  foregoing  details  are  mentioned  to  show  that  in  small 
lamps  a  careful  study  of  voltage  conditions,  reflector  design,  and 


+m 


I  HOLE 


2$"D.  0VERFL*N6Et*| 


Fig.  15. — Experimental  mine  lamp  reflector. 


the  requirements  of  the  device  using  these  small  lamps  is  becoming 
more  necessary  as  the  uses  of  these  lamps  increase.  Opposed  to 
the  old  idea  that  small  lamps  were  mere  playthings  is  the  growing 
tendency  to  expect  them  to  do  even  more  than  should  be  expected 
from  them.  Uniformity  of  performance,  as  judged  from  ex- 
perience with  large  lamps,  is  very  difficult  to  obtain,  for  small 
lamps  are  generally  of  low  voltage  and  high  current.  The  ac- 
curacy of  manufacture  nesessarily  is  not  as  good  and  the  diffi- 
culty in  supplying  the  proper  voltage  at  the  lamp  terminals  is 
great.  The  regulation  of  the  sources  of  energy  used  is  not  the 
best  and  each  small  voltage  drop  in  wires  or  contacts  is  a  con- 
siderable percentage  of  the  total.  Also,  for  the  same  efficiency, 
the  life  is  only  one  tenth  to  one  third  of  that  of  the  large  lamps, 


Il82     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

and  on  account  of  the  types  of  bases  used  the  allowable  current 
is  limited.  A  careful  consideration  of  these  small  lamps  will 
show  that  they  should  receive  at  least  as  much  attention  as  the 
large  lamps  where  they  are  to  be  applied  to  important  fields  of 
illumination. 

DISCUSSION 

Mr.  L.  C.  Porter:  The  number  of  uses  to  which  min- 
iature lamps  are  being  put  is  almost  infinite  and  almost  every  day 
sees  new  devices  and  new  ways  of  using  them.  It  is  a  very  wide 
field  and  one  which  is  rapidly  increasing.  The  lamps  are  used 
for  all  sorts  of  spectacular  efforts,  in  theatrical  work  especially, 
and  since  the  beginning  of  the  European  War  there  has  been 
a  great  demand  for  miniature  lamps  for  hand  lanterns  used 
in  the  trenches.  A  number  of  interesting  applications  have  been 
brought  about  by  this  war.  Small  lamps  are  used  for  signaling 
and  a  large  number  of  these  signal  outfits  are  being  sold.  The 
lamps  and  reflectors  are  held  in  hand  and  used  for  signal  purposes 
both  at  night  and  day. 

Stereopticon  and  small  moving  picture  machines  for  home  use 
is  another  field  for  the  lamps.  The  railroads  are  using  a  consid- 
erable number  for  position  light  signals;  the  medical  and  dental 
professions  use  large  quantities.  In  fact,  the  miniature  lamp 
business  is  growing  more  rapidly  than  that  of  regular  lamps. 


CODE   OF   LIGHTING  H&3 

CODE  OF  LIGHTING. 


Below  is  a  prefatory  note  which  was  omitted  from  the  Code  of 
Lighting  that  appeared  in  the  November  20,  191 5,  Vol.  X,  No.  8, 
issue  of  the  Transactions,  beginning  on  page  605. 

The  Code,  which  was  prepared  jointly  by  the  Committee  on 
Factory  Lighting  and  the  Committee  on  Lighting  Legislation, 
was  presented  at  the  Ninth  Annual  Convention  held  in  Wash- 
ington, D.  C,  Sept.  20-23,  1915.  The  Code  has  been  accepted 
by  the  Council  and  is  issued  in  separate  pamphlet  form  by  the 
Society. 

PREFACE. 

The  following  Code  of  Lighting  for  Factories,  Mills  and  other 
Work  Places,  has  been  prepared  by  committees  of  the  Illumin- 
ating Engineering  Society  in  order  to  make  available  authoritative 
information  for  legislative  bodies,  factory  boards,  public  service 
commissions  and  others  who  are  interested  in  enactments,  rules 
and  regulations  for  better  lighting. 

While  the  code  is  intended  as  an  aid  to  industrial  commissions 
and  other  similar  bodies  in  those  states  and  municipalities  which 
shall  actively  take  up  the  questions  of  legislation  as  related  to 
factory  and  mill  lighting,  it  is  intended  in  equal  measure  for  the 
industries  themselves  as  a  practical  working  guide  in  individual 
efforts  to  improve  lighting  conditions.  The  language  of  the  code 
has  not  been  drafted  according  to  legal  phraseology  but  is  simple 
and  pointed  throughout,  thus  being  readily  available  for  trans- 
forming into  legal  orders,  and  at  the  same  time  as  a  working 
guide  in  practical  design  and  installation  work. 


1 184     TRANSACTIONS  OE  ILLUMINATING  ENGINEERING  SOCIETY 

REPORT  OF  THE  CHAIRMAN  OF  THE  COMMITTEE 
ON  LIGHTING  LEGISLATION.* 


During  the  early  part  of  the  past  year  the  Committee  on 
Lighting  Legislation  made  a  general  survey  of  the  state  laws 
relating  to  lighting  in  the  United  States  and  prepared  a  trans- 
cript (taken  from  the  statute  books)  of  the  laws  relating  to 
lighting  in  the  states  of  New  York,  Pennsylvania,  Connecticut, 
Illinois  and  Wisconsin. 

The  study  of  these  laws  led  to  the  conclusion  that  with  few 
exceptions  existing  state  lighting  legislation  is  crude,  fragmen- 
tary and  often  meaningless. 

It  was  suggested  that  this  committee  frame  a  model  lighting 
law  to  serve  as  a  guide  to  legislators  contemplating  the  enact- 
ment or  amendement  of  laws  pertaining  to  lighting.  The  diffi- 
culties in  the  way  of  framing  a  model  law  applicable  to  all  classes 
of  lighting  are  apparent  and  the  committee  decided  to  confine  its 
work  for  the  present  to  formulating  a  code  of  lighting  for  fac- 
tories, mills  and  other  places  and  a  code  of  lighting  for  school 
houses. 

Accordingly  a  special  committee  on  factory  lighting  and  a 
special  committee  on  school  lighting  submitted  to  the  Committee 
on  Lighting  Legislation  technical  data  and  rules  upon  which  to 
base  a  lighting  code. 

A  large  part  of  the  attention  of  the  Committee  on  Lighting 
Legislation  has  been  devoted  for  the  past  six  months  to  the  con- 
sideration of  a  comprehensive  report  of  the  Factory  Lighting 
Committee,  of  which  Prof.  C.  E.  Clewell  is  chairman,  containing 
material  upon  which  was  based  the  Code  of  Lighting  now  placed 
before  you. 

The  purpose  of  the  code  is  primarily  to  provide  legislators 
with  material  upon  which  to  base  laws,  rules  and  regulations  re- 
lating to  the  lighting  of  factories,  mills  and  other  work  places, 
but  the  Code  is  intended  also  to  serve  as  a  guide  to  factory  man- 
agers and  others  in  remodeling  the  lighting  of  existing  buildings 
and  in  planning  the  lighting  of  new  buildings. 

Although  much  of  the  material  offered  is  concrete  and  directly 
serviceable  in  the  design  of  lighting  installations,  the  Articles  are 

*  Read  at  the  convention  of  the  Society  at  Washington,  D.  C,  Sept.  20,  1915. 


COMMITTEE   ON   LIGHTING   LEGISLATION  I185 

necessarily  more  or  less  general  depending  upon  the  limitations 
imposed  by  the  present  state  of  the  art  of  lighting. 

The  committees  have  had  the  advantage  not  only  of  construc- 
tive criticism  from  their  own  combined  membership  of  fifteen, 
including  a  legal  representative  skilled  in  legislatve  work,  but 
also  from  a  considerable  number  of  industrialists  and  factory 
managers  connected  with  some  of  the  leading  manufacturing 
companies  and  institutions  in  the  country. 

The  Code  is  to  be  published  in  separate  pamphlet  form  with 
cover  and  is  to  have  an  index  which  is  now  being  prepared. 

Committee  on  Lighting  Legislation. 

L.  B.  Marks,  Chairman, 

O.  H.  Basquin, 

C.  O.  Bond, 

C.  E.  Clewell, 

O.  H.  Fogg, 

C.  L.  Law, 

M.  Luckiesh, 

F.  J.  Miller, 

G.  H.  Stickney, 
L.  A.  Tanzer, 
W.  H.  Tolman. 

Committee  on  Factory  Lighting. 

C.  E.  ClEwell,  Chairman, 
W.  A.  D.  Evans, 

T.  J.  Litle,  Jr., 

D.  M.  Petty, 
R.  E.  Simpson. 


Il86     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ERRATUM. 


The  accompanying  table  of  data  was  inadvertently  omitted 
from  the  paper  entitled  "Present  Practise  in  the  Lighting  of 
Armories  and  Gymnasiums  with  Tungsten  Filament  Lamps,"  by 
A.  L.  Powell  and  A.  B.  Oday,  which  appeared  in  the  November 
20,  1915,  issue  (vol.,  No.  8,  pp.  746-759)  of  the  Transactions. 


(Note.— This  table  is  to  aament  Lamps,"  by  A.  L.   Powell  and  A.  B. 

ONS.) 
EQUIPMENT. 


Regiment 


Infantry— 

7th  X.  G.  X.  V 


ist  X.G.  X.  V 


Location 


New  York 
Citv 


New  York 
City 


Di^.rrange- 

siment  of 

in    lamps 


taggered 

5  rows 


Legularly 
n  3  rows 


Height  of 

lamps  in 

feet 


Side 
rows  40 
Centre 


Balcony 


19  ft.  -wide.    25-w.,  round  bulb.  Fig.  1 
all  frosted  lamps.     In  white 
bowl   refls.     Set   flush   with 
ceiling.     10-ft.  centers. 

On  side  walls  under  and  above  Fig.  2 
balcony.  Bracket  fixtures  on 
16'   centers.      Prismatic  en- 
closing elobes.    Two  25-watt 


n«t 


Il86     TRANSACTIONS  OF  ILLUMINATING  ENGINEERING  SOCIETY 

ERRATUM. 


The  accompanying  table  of  data  was  inadvertently  omitted 
from  the  paper  entitled  "Present  Practise  in  the  Lighting  of 
Armories  and  Gymnasiums  with  Tungsten  Filament  Lamps,"  by 
A.  L.  Powell  and  A.  B.  Oday,  which  appeared  in  the  November 
20,  1915,  issue  (vol.,  No.  8,  pp.  746-759)  of  the  Transactions. 


ERRATA. 


Page  1 151. — Text;  third  line  from  bottom,  omit  word  "observa- 
tion." 

Page  1 1 58. — Seventh  line  from  top;  substitute  the  words  "the 
comparison"  for  "it." 

Page  1 1 58. — Delete  late  sentence  of  the  first  paragraph. 

Page  1 158. — Second  paragraph,  ninth  line;  words,  'is  nothing 
more  or  less  than  a  space  threshold'  should  be  'is  nothing 
more  or  less  than  the  judgment  of  a  space  threshold.' 

Page  1 165. — Delete  the  second  sentence  reading,  'In  the  treat- 
ment of  this  point  Dr.  Cobb's  discussion  indicates  his  view- 
point.' 

Page  1 165. — Line  21,  words  'have  not  a  sufficient  comprehen- 
sion,' should  be  'have  only  a  minimum  comprehension.' 

Page  1 1 68. — Fourteenth  line  from  bottom  word  'observation' 
should  be  'notice.' 

[The  sentences  deleted  above  were  not  the  author's.] 


(Note.— This  table  is  to  aament  Lamps,"  by  A.  L.  Powell  and  A.  B. 

ONS.) 
EQUIPMENT. 


Regiment 


Infantry — 

7th  N.  G.  X.  V. 


71st  X.  G.  X.  V. 

•SahX.G.X.Y. 

i2thX.  G.  X.Y. 
ist  X.  G.  X.  J. 


47th  X.  G.X.  Y. 
small  shed  . 


23rd  X.G.  X.Y. 

State  Armory 
State  Armory 


Coast  Defence— 
X.  G.  X.  Y. 


Location 


DiA-rrange- 

siknent  of 

in  [  lamps 


[86 


155 


New  York 
Citv 


New  York 

City 


New  York 
City 


New  York     200 
City 

Xewark.       25? 
X.  J. 


taggered 
5  rows 


egularly 
n  3  rows 


taggered 
5  rows 


Regularly 

3  rows 

Legularly 

4  rows 


Height  of 

lamps  in 

feet 


Side 
rows  40 
Centre 
row  45 


Balcony 


19  ft.  wide.    25-w.,  round  bulb.  Fig.  1 
all  frosted  lamps.     In  white 
bowl   refls.     Set   flush    with 
ceiling.     10-ft.  centers. 

On  side  walls  under  and  above  Fig.  2 
balcony.  Bracket  fixtures  on 
16'   centers.      Prismatic  en- 
closing globes.    Two  25-watt 
each  globe. 

:i  ft.  wide.  Below  200-watt 
lamps.  Prismatic  bowl  re 
flectors  on  34-ft.  centers. 


Gas  below  and  above  balcony 
for  emergency. 

Balcony  narrow. 


Brooklyn       130  daggered  ] 
3  rows 


Brooklyn 


Schenectady 
X.  Y. 


Legularly  j 
3  rows     ] 

130  Regularly 
3  rows 


Albanv,        ix^ 

x.  y. 


Xew  York 
City 


180 


taggered  .  Outside  20 
5  rows        Center  25 

egularly 
2  rows 


Xo  balconv. 


rius  ini)U- 1 


to  .ceo,,,,,  am  .  ,,,,,,,  e„ti,l,,l  •■  !•„,,„,  Practise  i„  the  ■,.,„!„«  of  Armorle.  and  Gymnasiums  with  Tungrten  HI, ,,t  Ump.  ■■  bv  A     I,    Powell  aid  A    B 

<M»y,wM<* ■•'•  ■'•"'PP.  746-759  of  vol.  X,  No.  8  (November  ao,  19.5)  toue  of  the  Transactions.)  P  * 


API 

SNDIX   1 

lira 

NATIC 

n  Dai 

'A   ON 

Armories  Lighted  with  Various  Types  01 

Modern 

Equipment. 

lafcJt 

«i,  ft 

Heigli 

1  oloi 
ol 

Color 
of 

Color 
of 

!:I';!s 

Size  <>| 

Total 

Watt* 

Type  of  R<  Bei  toi 

Type 
Fixture 

w 

Height  of 
feet 

Balcony 

Aetna 

Com 



ti  ■; 

G.N.  V. 

|B6  x  17I 

51.000 

90 

(,reen 

Gr  en 

Ught 

28 

as 

28.000 

0.55 

0.<j2 

Prl  maU.    i  nclofltnc   mm      i  i,„ 

l'"wl  rrll.vtur  witli   n.  I...I    |.m 
iii.ilimli-.li  „va  mouth.    17"  (tin 

m    "  high  1 

Steel 

Bide 

rows  40 
Centre 

all  frosted  lamps     in  whifa 

bowl    refls,     Set    flu-.h    will 

row  45 

ceiling.      io-fl 

■ 

> 

SO 

Brick 

Gray 

«gj 

24 

500  b.  f 

12,000 

o.5o 

0.73 

Pn    ltd    in  ismatic    bowl    red*. 
1  1'  i"  dia     ■ 

6-  spread 

■~° 

On  side  walls  under  and 

■ 

j-.i 

closing  globes.    Two 

each  globe. 

Brick. 
- .  ,t  1 1»  v- 

Gray 

Med. 

48 

loo  b.  f 

19,200 

0.50 

0.72 

■'  ■'     i"  i  unati     bowl   refls. 
difl 

2  light  ring 
fixtures 

■  ' 
■ 

25 

It   ft.  wide.      Below   2cowat 
lamps.     Prismatic  tiowl  re 
flectorson  34-ft.  a  a 

Utfc  N 

City 

JOOX.So 

36.00° 

50 

Dark 

Dark 

Dark 

36 

300  b.  f 

10,800 

0.30 

o-43 

Pn  ■—• .]    prismatic    bowl     refls 
n'-"di.i..  7  W"  high.' 

fixtures 

1 

:° 

Gas  below  and  above  1 
for  emergency. 

60 

Buir 

Buff 

32 

cSr 

12.800 

o,37 

o.4l 

la"  Sat  white  gloss  reflector. 

1  ombina- 

: 

20 

Balcony  narrow. 

47th  N 

1  -bed 

Brooklyn 

26.000 

40 

Blue 

lurk 

1,0am* 

8 

75o 

6,000 

0.23 

0.36 

1  nt'1'i-.ing  globes.     12 
dia.  witb  ventilated  holder.1 

Stcel 

■ 

32 

cable 

-    G.N.Y 

Brooklyn 

2OOX30O 

60,000 

7S 

Cream 

Oak 

Med. 

■5 

b'.T 

15,000 

0.25 

0.42 

opal  red.     16 

dia.,    .,"  .Ii  1  p.  nmmil  Mjeki  t   am 

Sir.   1 

1 

35 

State  Armory 

Schenectady, 

N    V 

130  I  85 

11,000 

- 

" 

- 

•8 

icob.  f 

,,*» 

0.44 

0.40 

Pn  ssed  prismatic  bowl  refl.,  s,\ 
deep.o 

firtu™ 

I  1  ■_'iil:irly 

- 

-.rmory 

X.  V. 

MO*  175 

42,000 

15 

Cream 

Pine 

Dark 

26 

,  i-  :;, 

.9,500 

0.46 

0.7. 

10"  enameled  stei  '■  1 

it  inclosing  globe.1 

fi££ 

- 

Outside  20 
Center  25 

City 

1S0  x  170 

30.500 

70 

White 

MgW 

8 

K 

8,000 

0.36 

0.44 

enti  ocloaing  globe 
■  :.i  [at    1  copper  1  isiii] 
around  socket.     30"  over  all.« 

Steel 
cable 

35 

No  balcony. 

vth  X.  G.  N.  V 

Xew  York 
City 

40,000 

..,, 

I  Mil 

!. 

14 

270o°bdf. 

14,500 

0,28 

0-43 

Deep    bowl    porcelain  enamele< 
eflectors  17"  dia." 

Steel 

fci  mil.irly 

40 

200-watt  under   balcony   will 
prismatic  reflectors. 

ij,thN.f,.  NY. 

Brooklyn 

s„ 



;;:;:; 

16 
16 

750  b.  f. 
b.  f. 

28,000 

0-43 

0.69 

Deep   bowl  dense   opal    red.,    if>' 
il  socket  am 
skeleton  holder.6 

Steel 

1 

Side 
rows  a 

■;'fW  i  - 

work 

rows  60 

-  --  N.  V    . 

45 

Dark 

dark' 

':         ■    . 

24 

0.30 

0.43 

16"  enameled  steel  refl.,  ventilat 

Steel 

' 

City 

ed    bolder    and     8" 

2nd  Batterv. 

globe  around  lamp.10 

-    S.  Y .  . 

Xew  York 
City 

50 

Dark 

Dark 

27 

clear 

13.500 

0.2S 

0.40 

-    enameled  steel  red.,  ventilat 
ed    bi  'i  li  t    and          opali  a  en 

Stei : 

■     ■' 

3* 

3rd  Battery, 

globe  around  lamp.1" 

N.  Y. 

Brooklyn 

,,,,,. 

Nat. 

lllack 

">-5S 

1  pal  refl.,  iff 

Steel 

: . 

tan 

b   1 

.    ep,  mogul  socket  and 

Cavalry— 

bark 

' 

Squadron  A    . 

New  York 
Cily 

50 

Buff 

Tan 

l..irk 

8 

cS 

' 

0.27 

0.39 

S"  enameled  steel  refl.,  ventilat- 
ed    holder    and    B"    opalescent 
globe  around  lamp.1" 

Steel 

I-:,  -ularly 

30 

Brooklyn 

54.0OO 

70 

White 

30 

0.42 

0.6s 

1   dense  opal  refl.,   16" 

.;.  .  |>    mogul  socket  ami 
skeleton  1 

Steel 

35 

1    J    ! 

Engines* 

loam 

■ 

Cily 

70 

Brick 

tight 

Rrct-ii 

Pin. 

2, 

b.  f. 

21,000 

0.31 

Deep    bowl    porcelain    enameled 
sleel  red.,  r    difl 

Steel 

legularly 

43 

Ha  Icon  v    14    ft.    wide,    [■:■'      ft 
high. 

aulcor,* . 

Brooklyn 

var- 

,1..! 

5 

0.36 

Deep  bowl  dense  opal   refl..    16' 

Stei  1 

"5 

Pig.  4 

.rowii 

oak 

wood 

.  1 1  _  1  .  ■   '  <l>  L-p,  inogul  socket  am! 
skeleton  bolder.5 

cable 

rical 

2nd  N- 

Clak, 

Pine 

50  b,  f. 

0.45 

Deep   bowl   dense  opal    refl.,    16' 

,lj,i   .  ..,     .I.  i']i.  miimil    siiil.i.  1    ;mh 
skeleton  holder.'' 

■ 

work 

I 

.ex** 

40,000 

70 

Brick 

Dark 

wood 

18 

e-icTr 

.S,ooo 

o.45 

o.75 

■,"  enameled  Bteel  refl    and    1  1 
split  rical  enclosing  globe.11 

Steel 

staggered 
.-,  rows 

45 

Fig.  5 

■  d 

Toffiv 

tll'il     Of 

the-   ol 

ler  pra 

:tise  th 

following  data  are  appended.) 

200  x  300 

6O.OO0 

85 

Tan 

Wood 

Wood 

730 

40 

28,800 

0.48 

0.46 

1  Corona  combination  gna  and 

■  1 :     :  1  j 

tllll-iih      '. 

electric  fixtures:  15  K'<s  ■""'    ■■' 

center  30 

electric  each. 

■ 

Brooklyn 

51.OOO 

85 

CreAtn 

Blue 

Wood 

900 

clfar 

36,000 

0.70 

0.67 

1  Corona  combination  .gas  and 

electric  fixtures:  15  gas  and  30 
electric  each. 

_ 

Regularly 

3  rows 

1 


TRANSACTIONS 

OF  THE 

Illuminating 
Engineering  Society 

NO.   I,  1915 
PART  II 

Miscellaneous  Notes 


TRANSACTIONS   I.    E.    S.  -    PART    II 


Council  Notes. 

A  meeting  of  the  Council  was  held 
January  14  in  the  general  offices  of  the 
Society,  29  West  39th  Street,  New  York, 
N.  Y.  Those  present  were:  A.  S. 
McAllister,  president;  E.  M.  Alger. 
C.  O.  Bond,  H.  Calvert,  Ward  Harrison. 
George  A.  Hoadley,  C.  A.  Littlefield, 
general  secretary;  L.  B.  Marks,  Preston 
S.  Millar,  A.  S.  Miller,  J.  Arnold  Nor- 
cross,  A.  L.  Powell,  representing  G.  H. 
Stickney,  vice-president  and  chairman 
of  the  Committee  on  papers.  Upon  invi- 
tation: M.  Luckiesh,  chairman  of  the 
School  Lighting  Committee;  A.  Hertz, 
chairman  of  the  Finance  Committee ; 
and  Norman  Macbeth,  chairman  of  the 
New  York  Section. 

The  Finance  Committee  submitted  an 
oral  report  on  the  total  expenses  and 
receipts  for  the  first  three  months  of 
the  present  fiscal  year  compared  with 
the  corresponding  period  of  the  last 
year.  Upon  recommendation  of  the 
committee  the  Council  authorized  the 
payment  of  vouchers  No.  1943  to  No. 
1976  inclusive,  aggregating  $1,919.91. 

A  written  progress  report  was  re- 
ceived from  the  Time  and  Place  Com- 
mittee (1915  Convention).  The  report 
indicated  that  of  the  places  under  con- 
sideration, Washington,  D.  C.  was  the 
one  most  favored. 

An  oral  report  was  given  by  Ward 
Harrison  on  behalf  of  Mr.  W.  M.  Skiff, 
chairman  of  the  1914  Convention  Com- 
mittee. 

Reports  on  section  activities  were  re- 
ceived from  F.  A.  Vaughn,  vice-presi- 
dent of  the  Chicago  Section;  A.  L. 
Powell  for  G.  H.  Stickney,  vice-presi- 
dent of  the  New  York  Section;  Ward 
Harrison,  vice-president  of  the  Pitts- 
burgh Section;  and  George  A.  Hoadley. 


vice-president  of  the  Philadelphia  Sec- 
tion. 

Mr.  C.  O.  Bond  reported  orally  on 
a  proposal  that  the  Philadelphia  Section 
become  affiliated,  along  with  the  local 
sections  of  other  engineering  societies, 
with  the  Engineers'  Society  of  Phila- 
delphia. It  was  resolved  that,  if  the 
Philadelphia  Section  desires  to  join  the 
movement,  the  Council  will  be  disposed 
to  consider  the  proposal  favorably,  pro- 
vided the  expense  is  not  too  great. 

Mr.  M.  Luckiesh  gave  an  oral  report 
on  behalf  of  the  Committee  on  School 
Lighting  and  submitted  the  manuscript 
of  a  lecture  entitled,  "Safe-Guarding 
the  Eyesight  of  Children."  It  was  re- 
solved that,  after  the  manuscript  had 
passed  through  the  usual  publication 
channels,  the  lecture  be  published;  and 
that  the  committee  announce  the  fact 
that  the  lecture  is  to  be  available  for 
those  interested  in  the  subject  of  school 
lighting. 

A  written  report  was  received  from 
the  Committee  on  Glare  from  Reflecting 
Surfaces,  giving  data  on  the  results  of 
tests  made  on  the  so-called  "window" 
envelopes.  It  was  voted  that  the  report 
be  returned  to  the  committee  with  a 
request  that  the  last  paragraph  be  re- 
vised as  indicated,  and  that  the  title  be 
so  worded  as  to  indicate  that  these  en- 
velopes had  passed  through  the  mails 
and  were  submitted  for  test  by  a  letter 
carriers'  association. 

The  appointment  of  the  following 
Committee  on  Remodeling  the  Lighting 
of  the  General  Offices  was  confirmed : 
H.  E.  Ives,  chairman;  Clarence  L.  Law. 
Thos.  W.  Scofield;  L.  B.  Marks  and 
George  W.  Cassidy,  advisory  members. 

A  written  report  was  received  from 
the  Committee  on  Remodeling  the  Light- 
ing   of    the    General    Offices.      It    was 


TRANSACTIONS    I.    E.    S.— PART    II 


voted  that  the  Committee  be  requested 
to  proceed  with  a  temporary  installation, 
as  outlined  in  the  committee"s  report,,  in 
order  that  it  may  be  tried  out  by  the 
Council  at  its  meetings. 

The  following  additional  committee 
appointments    were   confirmed : 

Committee  on  Factory  Lighting  :  C.  E. 
Clewell,  chairman ;  W.  A.  D.  Evans, 
T.  J.  Litle,  Jr.,  R.  E.  Simpson  and  G. 
H.  Stickney. 

Committee  on  Popular  Lectures:  C.  F. 
Scott. 

Committee  on  Constitutional  Revision  : 
W.  D.  Weaver,  chairman ;  Louis  Bell, 
L.  B.  Marks,  and  C.  H.  Sharp. 

The  resignation  of  the  following 
committee  members  were  accepted  with 
regret : 

Dr.  H.  E.  Ives  from  the  Committees 
on  Research,  Popular  Lectures,  and 
Lighting  Legislation.  Dr.  Alexander 
Duane  from  the  Committee  on  Papers. 

An  invitation  from  the  trustees  and 
faculty  of  the  University  of  North 
Carolina  to  appoint  a  representative  to 
attend  the  inauguration  of  Mr.  William 
Kidder  Graham  as  president  of  the 
university  was  received.  President 
McAllister  was  empowered  to  appoint 
a  representative. 

A  proposal  to  create  a  class  of  mem- 
bers to  be  known  as  fellows  was  tabled 
for  the  next  meeting  of  the  Council. 
It  was  understood  that  copies  of  this 
proposal  would  be  mailed  to  the  mem- 
bers of  Council  for  consideration  in  the 
meantime. 

The  following  communication  was  re- 
ceived from  Dr.  C.  H.  Sharp,  secre- 
tary of  the  United  States  National  Com- 
mittee of  the  International  Commission 
on  Illumination. 

In  the  normal  course  of  events  this  com- 
mittee would  be  obliged  at  this  time  of  the  year 
to  request  from  the  Illuminating  Engineering 
Society  the  regular  annual  contribution   of  $100 


toward  the  expenses  of  the  committee  and  toward 
the  payment  required  by  the  International  Com- 
mission on  Illumination.  Last  year  the  com- 
mission was  supported  by  the  contributions  of 
five  countries,  namely  England,  France,  Ger- 
many, Italy  and  United  States.  The  expenses 
of  the  commission  were  very  small  so  that  the 
honorary  secretary  has  a  substantial  fund  in  the 
treasury,  which  on  account  of  the  temporary 
suspension  of  the  activities  of  the  commission  is 
likely  to  be  but  little  encroached  upon.  This 
committee,  therefore,  makes  no  call  on  you  at 
this  time  for  any  further  funds.  The  expecta- 
tion is,  however,  that  at  the  close  of  the  war  the 
International  Commission  on  Illumination  will 
again  become  active  and  the  regular  contribu- 
tion will  be  required. 

The  following  resolution  submitted 
by  the  Committee  on  Editing  and  Pub- 
lication was  adopted : 

The  Committee  on  Editing  and  Publication 
recommends  that  technical  and  trade  journals 
be  advised  that  the  papers  of  the  Society 
may  be  reprinted  in  whole  or  in  part,  subse- 
quent to  the  dates  of  presentation,  by  any 
member  of  the  technical  or  trade  press,  pro- 
vided  proper  credit  is   given. 

It  was  suggested  by  several  members 
of  the  Council  that  all  matters  of  routine 
business  might  be  transacted  by  the 
Council  Executive  Committee  previous 
to  each  council  meeting. 

Consideration  of  the  outlines  of  work 
for  the  present  year,  submitted  by  com- 
mittees, was  deferred  until  the  next 
meeting. 


Section  Activities. 

CHICAGO    SECTION 

Prof.  Morgan  Brooks  of  the  Univer- 
sity of  Illinois  delivered  a  lecture  on 
"Vision  and  Illumination"  at  a  meeting 
of  the  Chicago  Section  in  the  rooms  of 
the  Western  Society  of  Engineers, 
December  18,  1914.  During  his  lecture 
Prof.  Brooks  described  an  instrument 
which  he  called  a  rapid  illuminometer. 

At   a   meeting   held    January   29,    Dr. 
Clayton    H.    Sharp    presented    a    paper 


TRANSACTIONS    I.    E.    S. — PART    II 


entitled  "The  Knowns  and  Unknowns  of 
Physical  Light." 

The  tentative  program  of  papers  for 
the  Chicago  Section  for  the  season  1914- 
1915  is  as  follows : 

February — Other  Light  Sources  (Gas 
and  Electric). 

March — Decoration  :  Color  Schemes  ; 
Fixture  Forms  ;  Use  of  Colored  Sources. 

April — Lighting  of  Small  Interiors  : 
Homes ;  Small  Offices ;  Show  Windows. 

May — Lighting  of  Large  Interiors : 
Churches ;  Halls  ;  Large  Offices. 

June — Lighting  of  Open  Air  Spaces : 
Streets ;  Building  Exteriors  :  Signs. 

NEW  ENGLAND  SECTION 
A  meeting  of  the  New  England  Sec- 
tion was  held  in  the  Engineers'  Club  on 
Friday,  February  5.  Mr.  Munroe 
Rhodes  Pevear  of  Boston  gave  a  paper 
on  "Three  Color  Illumination"  which 
was  illustrated  by  practical  demonstra- 
tions. Mr.  Pevear  has  made  an  exhaus- 
tive study  of  commercial  methods  for 
procuring  light  of  any  degree,  intensity 
or  color.  The  paper  was  accompanied 
by  a  number  of  demonstrations. 

The  programs  of  coming  meetings 
will  be  announced  later. 

PHILADELPHIA   SECTION 

A  meeting  of  the  Philadelphia  Section 
was  held  January  15  at  the  Engineers' 
Club,  1317  Spruce  Street.  Two  papers 
were  presented,  one  by  Harry  Markle 
on  "The  Lighting  of  Willow  Grove 
Park,"  and  the  other  on  "Piping  Houses 
for  Gas  Lighting"  by  Mr.  H.  R.  Sterrett. 
Seventy-five  members  and  guests  were 
present. 

The  following  program  has  been  an- 
nounced for  the  rest  of  the  season : 

February  8 — Joint  meeting  with  Amer- 
ican Institute  of  Electrical  Engineers. 
"A  Year's  Progiess  in  Illumination"  by 
Prof.  Geo.  A.  Hoadley;  "Recent  Devel- 


opments and  Applications  of  Incandes- 
cent Lamps"  by  Geo.  H.  Stickney.  Elec- 
tric lamps  will  be  exhibited. 

February  19 — "Scientific  Management" 
by  Frederick  W.  Taylor.  A  demonstra- 
tion of  the  pathescope,  a  new  moving 
picture  device,  will  be  given. 

March  19 — "A  Method  of  Securini: 
Uniformity  of  Reading  of  the  Flicker 
Photometer  with  Different  Observers" 
by  Herbert  E.  Ives  and  E.  F.  Kingsbury. 
Photometric  apparatus  will  be  exhibited. 

April  16 — "The  Problem  of  Lighting 
Design,"  by  Prof.  Arthur  J.  Rowland. 
This  paper  will  include  a  discussion  of  the 
following  items :  Methods  used  for  de- 
signing: (a)  direct  lighting  (b)  indirect 
lighting ;  difficulties  and  faults  in  the  use 
of  such  methods ;  accuracy  to  be  ex- 
pected in  the  results  accomplished ;  what 
constitutes  good  design.  Exhibition  of 
new  types  of  lighting  fixtures. 

May  21 — "Store  Lighting"  by  W.  R. 
Moulton.  This  meeting  will  be  held  in 
Baltimore.  Md.  The  place  will  be 
announced  later. 


NEW    YORK    SKCTION 

The  New  York  Section  held  a  joint 
meeting  with  the  Metropolitan  Section 
of  the  Professional  Photographers' 
Society  of  New  York  in  the  Engineer- 
ing Societies  Building,  January  14.  Two 
papers  were  presented :  one  "The  Appli- 
cation of  the  Tungsten  Lamp  to  Pho- 
tography" by  Mr.  M.  Luckiesh,  physicist 
of  Nela  Research  Laboratory,  Cleve- 
land, O. ;  the  other  "Gas  Lamps  for 
Photography"  by  Mr.  R.  F.  Pierce  of 
the  Welsbach  Company.  Gloucester, 
N.  J.  The  papers  were  discussed  by 
representatives  of  both  societies.  Mr. 
J.  E.  Williamson  gave  a  short  talk  on 
"Submarine  Photography,"  which  was 
accompanied  by  lantern  slides. 

The  tentative  program    for   the    New 


TRANSACTIONS    I.    E.   S. — PART    II 


York  Section  for  the  rest  of  the  season 
is  as  follows : 

February — "The  Type  C  Lamp  for 
Street  Lighting"  by  Mr.  W.  H.  Rolin- 
son;  "The  Magnetite  Lamp  for  Street 
Lighting"  by  Mr.  C.  A.  B.  Halvorson,  Jr. 

March — This  meeting  is  to  be  ar- 
ranged by  the  Fine  Arts  Committee  of 
the  Section.  There  will  be  a  symposium 
on  light  by  various  artists,  decorators 
and  architects ;  each  speaker  is  to  have 
about  ten  minutes  to  explain  the  light- 
ing needs  of  his  profession. 

April — Joint  meeting  of  the  New  York 
sections  of  the  Illuminating  Engineering 
Society,  the  National  Commercial  Gas 
Association  and  the  National  Electric 
Light  Association  to  discuss  the  com- 
mercial side  of  the  good  lighting  propa- 
ganda. Addresses  will  be  given  by  rep- 
resentatives of  the  three  organizations. 

May — To  be  announced  later. 

June — Dr.  Hollis  Godfrey  of  Phila- 
delphia, Pa.,  has  been  invited  to  present 
a  paper  on  "Good  Lighting  as  an  Aid  to 
Welfare  Work"  to  include  a  description 
of  the  work  which  he  has  done  in  the 
Metropolitan  Life  Insurance  Building  in 
New  York. 

PITTSBURGH    SECTION 

The  Pittsburgh  Section  held  a  joint 
meeting  with  several  engineering  socie- 
ties in  Cleveland,  O.,  January  29.  A 
popular  lecture  entitled  "Safeguarding 
the  Eyes  of  School  Children,"  accom- 
panied by  a  series  of  lantern  slides,  was 
given  by  Mr.  M.  Luckiesh. 

The  program,  as  far  as  known,  for 
the  rest  of  the  season  is  given  below. 

February  19 — A  popular  lecture  on 
"Home  Lighting." 

March  19 — Joint  meeting  with  the 
American  Institute  of  Electrical  Engi- 
neers. Paper:  "Projector  Lanterns  and 
Searchlights"  or  "Incandescent  Lamp 
Manufacture." 


New  Members 

The  following  twenty-four  applicants 
were  elected  members  of  the  Society  at 
a  Council  meeting  held  January  14 : 

Adam,  John  Neil 

New  Business  Assistant  to  Division 
Agent,  Public  Service  Electric  Co., 
271  North  Broad  St..  Elizabeth, 
N.J. 

Andrews,  William  S. 

Consulting  Engineering  Department, 
General  Electric  Co.,  Schenectady. 
N.  Y. 

Butler,  Henry  E. 

Assistant  to  Illuminating  Engineer, 
General  Electric  Co.,  Illuminating 
Engineering  Laboratory,  Schenec- 
tady, N.  Y. 

Billau,  Lewis  S. 

Assistant  Electrical  Engineer,  Bal- 
timore &  Ohio  Railway  Co.,  Balti- 
more, Md. 

Rmkrson,  Harrington 

Counseling  Engineer  on  Efficiency, 
The  Emerson  Co.,  30  Church  St., 
New  York,  N.  Y. 

Emerson  Guy  C. 

Consulting  Engineer  for  Municipal 
Works.  Boston  Finance  Commis- 
sion, 73  Bemont  St.,  Boston,  Mass. 

Faught,  Ray  C. 

Local  Supply  Department  (Mana- 
ger) General  Electric  Co.,  121 7 
Munsey  Building,  Baltimore,  Md. 

Huilman,  D.  B. 

Electrical  and  Mechanical  Engineer, 
Philadelphia  &  Reading  Railway 
Co.,  Reading,  Pa. 

Hoover,  John  Walter. 

Supt.  Lighting  and  Merchandise 
Sales,  Gas  Division,  Consolidated 
Gas,  Electric  Light  &  Power  Co. 
of  Baltimore,  Baltimore,  Md. 


TRANSACTIONS    I.    E.    S.  — PART    II 


Hess,  Wm.  L. 

Doctor,  eye,  ear,  nose  and  throat, 
400  California  Building.  Denver. 
Colo. 

Hewitt.  Conrad 

Supt.  of  the  Building,  Metropolitan 
Museum  of  Art,  Fifth  Avenue  and 
82nd  St..  New  York.   N.  Y. 

Jones,  W.  R. 

Engineer  of  Construction.  Univer- 
sity of  Penna.  (Light  &  Heat  Sta- 
tion). 3401  Spruce  St..  Philadelphia. 
Pa. 

Kingsbury,  Edwin  F. 

Laboratory  Assistant.  Physical  Lab- 
oratory, United  Gas  Improvement 
Co.,  3101  Passyunk  Avenue,  Phila- 
delphia. Pa. 

Mohr,  William 

Supt.  of  Lamps  and  Lighting.  Muni- 
cipal Department,  Room  8.  City 
Hall,  Baltimore,  Md. 

McLaughlin.  John  C. 

Chief  Clerk.  Potomac  Elec.  Power 
Co.,  231  Fourteenth  N.  W..  Wash- 
ington.  D.   C. 

Marsh,  George  Everett 

Assistant  Professor  of  Electrical 
Engineering,  Armour  Institute  of 
Technology,  Chicago,  111. 

Muncy,  Victor  Emanuel 

Professor  of  Mechanics  and  Applied 
Electricity,  Ohio  Mechanics'  Insti- 
tute. Cincinnati.  Ohio. 

Orner,  Aleert 

Designer  and  Salesman  of  Lighting 
Fixtures,  Consolidated  Chandelier 
Co.,  132  West  14th  St..  New  York. 
N.  Y. 


Pillsbury,  Charles  L. 

Consulting  Engineer  895  Metropoli- 
tan Life  Building.  Minneapolis. 
Minn. 

Pfeiffer,  Bernard  V. 

Engineer,  Nashville  Gas  &  Heating 
Co..  611  Church  St..  Nashville. 
Tenn. 

Platt,  Charles  J..  Jr. 

General  Foreman,  United  Electric 
Light  &  Power  Co.,  130  East  15th 
St.,  New  York.  N.  Y. 

Rosenfeld,  Eugene  I. 

President  &  General  Manager,  Eu- 
gene I.  Rosenfeld  &  Co.,  Inc.,  8  S. 
Howard    St.,    Baltimore,    Md. 

Simonson,  G.  Metcalfe 

Assistant  Electrical  Engineer,  State 
Department  of  Engineering,  Forum 
Building,  Sacramento,  Cal. 

Wilder,  Stuart 

Engineer,  Electrical  Dept,  West- 
chester Lighting  Co..  1st  Avenue 
and  1st  St..  Mt.  Vernon,  N.  Y. 


Index  for  Volume  IX. 

The    index     for    Volume     IX     (1914 
Transactions)  is  mailed  with  this  issue. 


NOTICE. 


The  Committee  on  Editing  and  Pub- 
lication will  be  glad  to  publish  in  the 
Transactions  personals,  obituaries,  and 
such  news  items  as  are  of  interest  to 
the  members  of  the  Society.  All  items 
of  this  sort  should  be  addressed  to  the 
Illuminating  Engineering  Society,  29 
West  39th  Street,  New  York.  N.  Y. 


TRANSACTIONS 


OF  THE 


Illuminating 
Engineering  Society 

NO.  2,  1915 
PART  II 

Miscellaneous  Notes 


TRANSACTIONS    I.    E.    S. — PART   II 


Council  Notes. 

A  meeting  of  the  Council  was  held 
February  n  in  the  general  offices  of 
the  Society,  29  West  39th  Street,  New 
York,  N.  Y.  Those  present  were : 
A.  S.  McAllister,  president;  E.  M. 
Alger,  C.  O.  Bond,  H.  Calvert,  P.  W. 
Cobb,  Ward  Harrison,  C.  A.  Littlefield. 
general  secretary ;  L.  B.  Marks,  treas- 
urer; Preston  S.  Millar,  Alten  S.  Miller, 
W.  Cullen  Morris,  J.  Arnold  Norcross, 
G.  H.  Stickney.  Upon  invitation  Mr. 
V.  R.  Lansingh. 

Written  reports  on  section  activities 
were  submitted  by  the  following  vice- 
presidents:  Ward  Harrison  (Pittsburgh 
Section)  ;  George  A.  Hoadley  (Phila- 
delphia Section)  ;  G.  H.  Stickney  (New 
York  Section)  ;  and  F.  A.  Vaughn 
(Chicago  Section). 

After  a  discussion  of  whether  the 
Philadelphia  Section  of  the  I.  E.  S. 
should  become  an  affiliated  member  of 
the  Engineers'  Society  of  Philadelphia, 
it  was  voted  that  the  matter  be  laid 
upon  the  table. 

Upon  recommendation  of  the  Finance 
Committee,  the  Council  authorized  the 
payment  of  vouchers  Nos.  1977  to  2006 
inclusive  and  Nos.  2008  to  201 1  inclusive 
aggregating  $1,050.01. 

It  was  voted  that  the  report  of  the 
Committee  on  Glare  on  window  en- 
velopes be  published  in  the  Transac- 
tions subject  to  the  usual  publication 
procedure  of  the  proper  committees. 

Mr.  Preston  S.  Millar,  chairman, 
reported  orally  for  the  Sustaining  Mem- 
bership Committee. 

A  written  report  of  the  Committee  on 
Time  and  Place  was  read  by  Mr.  G.  H. 
Stickney,  chairman.  The  committee 
recommended  that  the  1915  Convention 
be  held  in  Washington,  D.  C,  during 
the  third  or  fourth  week  in  September. 


Committee  appointments  and  changes: 

The  resignation  of  Mr.  Preston  S. 
Millar  from  the  Committee  on  Consti- 
tutional Revision  was  accepted. 

The  resignation  of  Mr.  G.  H.  Stick- 
ney from  the  Committee  on  Factory 
Lighting  was  accepted. 

The  resignation  of  Dr.  H.  E.  Ives  as 
chairman  of  the  Committee  on  Remod- 
eling the  Lighting  of  the  General  Offices 
was  accepted  with  a  vote  of  thanks 
from  the  Council. 

Dr.  C.  H.  Sharp  was  appointed  sec- 
retary of  the  Committee  on  Constitu- 
tional Revision. 

Prof.  W.  S.  Franklin  was  appointed  a 
member  of  the  Committee  on  Popular 
Lectures. 

Mr.  H.  Calvert  submitted  blue  prints 
showing  by  curves  the  expenses  and 
income  of  the  Society  from  1907  to  1914. 

It  was  voted  that  the  Committee  on 
Constitutional  Revision  be  requested  to 
recommend  (1)  changes  in  the  Consti- 
tution which  would  increase  the  dues 
of  members  to  $10.00  and  create  an 
additional  grade  of  members  having 
dues  of  $5.00;  (2)  qualifications  for 
membership  in  these  two  grades. 


Section  Activities. 

CHICAGO    SECTION 

Nelson  M.  Blank.  M.  D.,  of  Milwau- 
kee, Wis.,  delivered  a  lecture  on  "A 
Resume  of  the  Physical,  Physiological 
and  Psychical  Phases  of  Vision,"  at  a 
meeting  of  the  Chicago  Section  in  the 
rooms  of  the  Western  Society  of  Engi- 
neers, February  25,   1915- 

The  tentative  program  of  papers  for 
the  Chicago  Section  for  the  season  1914- 
191 5  is  as  follows: 

March — Decoration  :  Color  Schemes  ; 
Fixture  Forms ;  Use  of  Colored  Sources. 

April — Lighting  of  Small  Interiors: 
Homes;  Small  Offices;  Show  Windows. 


TRANSACTIONS   I.    E.    S. — PART   II 


May — Lighting  of  Large  Interiors  : 
Churches  ;  Halls ;  Large  Offices. 

June — Lighting  of  Open  Air  Spaces : 
Streets;  Building  Exteriors;  Signs. 

NEW  ENGLAND  SECTION 

A  meeting  of  the  New  England  Sec- 
tion was  held  in  the  Engineers'  Club, 
Boston,  February  26.  Three  papers 
were  presented :  "Effects  of  Radiation 
on  the  Eye"  by  Dr.  Louis  Bell,  "The 
Axial  Chromatic  Aberration  of  the 
Human  Eye"  by  Dr.  P.  G.  Nutting,  and 
"How  Faulty  Illumination  Injures  the 
Eye"  by  Dr.  Walter  B.  Lancaster. 

The  programs  of  coming  meetings  will 
be  announced  later. 

NEW   YORK  SECTION 

A  meeting  of  the  New  York  Section 
was  held  in  the  Engineering  Societies 
Building,  February  11.  Mr.  C.  A.  B. 
Halvorson  presented  a  paper  on  "The 
Arc — Its  Status  as  a  Street  Illuminant," 
which  was  accompanied  by  a  demonstra- 
tion of  the  effect  of  varying  current  and 
voltage  at  the  arc,  and  a  description  of 
the  possibilities  of  the  various  types  of 
metallic  flame  arcs. 

The  tentative  program  for  the  New 
York  Section  for  the  rest  of  the  season 
is  as  follows : 

March — A  paper  by  L.  C.  Porter  and 
W.  G.  Gove  on  the  lighting  of  the  new 
cars  of  the  New  York  Municipal  Rail- 
way Corporation. 

April — Joint  meeting  of  the  New 
York  Section  of  the  Illuminating  Engi- 
neering Society,  the  National  Commer- 
cial Gas  Association,  and  the  National 
Electric  Light  Association  to  discuss  the 
commercial  side  of  the  good  lighting 
propaganda. 

May — To  be  announced  later. 

June — To  be  announced  later. 


PHILADELPHIA    SECTION 

The  Philadelphia  Section  held  a  joint 
meeting  with  the  American  Institute  of 
Electrical  Engineers  at  the  Engineers' 
Club,  on  February  8.  Two  papers  were 
presented,  one  by  George  A.  Hoadley 
on  "A  Year's  Progress  in  Illumination," 
and  the  other  on  "Recent  Develop- 
ments and  Applications  of  Incandescent 
Lamps"  by  George  H.  Stickney. 

A  meeting  of  the  Philadelphia  Section 
was  held  February  19  at  the  Engineers' 
Club,  1317  Spruce  Street.'  Mr.  Fred- 
erick W.  Taylor  presented  a  paper  on 
"Scientific  Management."  A  demon- 
stration of  the  pathescope,  a  new  mov- 
ing picture  device,  was  given. 

The  following  program  has  been 
announced  for  the  rest  of  the  season : 

March  19 — "A  Method  of  Securing 
Uniformity  of  Reading  of  the  Flicker 
Photometer  with  Different  Observers" 
by  Herbert  E.  Ives  and  E.  F.  Kingsbury. 
Photometric  apparatus  will  be  exhibited. 

April  16 — "The  Problem  of  Lighting 
Design,"  by  Prof.  Arthur  J.  Rowland. 
This  paper  will  include  a  discussion  of 
the  following  items :  Methods  used  for 
designing:  (a)  direct  lighting,  (b)  indi- 
rect lighting;  difficulties  and  faults  in 
the  use  of  such  methods ;  accuracy  to  be 
expected  in  the  results  accomplished; 
what  constitutes  good  design.  Exhibi- 
tion of  new  types  of  lighting  fixtures. 

May  21 — "Store  Lighting"  by  W.  R. 
Moulton.  This  meeting  will  be  held  in 
Baltimore,  Md.  The  place  will  be 
announced  later. 

PITTSBURGH    SECTION 

The  Pittsburgh  Section  held  a  meet- 
ing in  Cleveland  on  January  29  at  the 
Addison  School,  79th  and  Hough 
Streets.  Preceding  the  meeting  an 
informal  dinner  was  held  at  the  Univer- 
sity   Club,    following    which    there    was 


TRANSACTIONS   I.    E.    S. — PART   II 


an  inspection  of  several  rooms  in  the 
Addison  School,  each  of  which  was 
equipped  with  a  different  system  of 
lighting  fixtures.  Two  papers  were 
presented,  one,  "Safeguarding  the  Eye- 
sight of  School  Children,"  accompanied 
by  a  number  of  slides,  was  presented 
by  Mr.  Magdsick  in  the  absence  of  the 
author,  Mr.  M.  Luckiesh;  and  the  other, 
"A  Discussion  of  Present  Practise  in 
School  Lighting"  by  Mr.  E.  B.  Rowe. 
Interesting  examples  of  school  room 
lighting  were  shown  by  slides.  Sixty 
members  and  guests,  including  members 
of  the  Board  of  Public  Education  and 
teachers,  were  present.  This  meeting 
indicates  a  broadening  of  the  activities 
of  the  Society  and  represents  an  attempt 
to  popularize  good  lighting  through 
public  education.  The  Section's  efforts 
are  directed  toward  the  saving  of  eye- 
sight, and  no  better  place  for  this  work 
is  apparent  than  in  the  schools.  Par- 
ticular credit  is  due  the  authors  of  the 
papers  for  preparing  good  material,  for 
their  time  and  expense  in  preparing 
slides  and  illustrations,  and  for  arrang- 
ing the  several  different  displays  in  the 
school  rooms.  The  co-operation  of  the 
local  Board  of  Education  and  the  school 
authorities  was  given  freely  and  appre- 
ciated. 

The  regular  monthly  meeting  of  the 
Pittsburgh  Section,  held  February  19 
at  the  Engineers'  Society  Auditorium, 
was  preceded  by  a  dinner  at  the  Fort 
Pitt  Hotel.  Before  the  meeting  the 
members  and  guests  inspected  several 
exhibition  booths  showing  various  light- 
ing features.  In  a  preliminary  talk, 
Dr.  Edward  Stieren  described  by  means 
of  colored  charts  the  structure  of  the 
human  eye  and  its  usual  optical  defects. 
Prof.  Francis  C.  Caldwell  of  the  Ohio 
State  University  presented  a  paper 
entitled  "Illumination  and  Eye  Fatigue." 


His  subject  included  a  general  resume 
of  the  methods  used  in  measuring  visual 
acuity,  and  a  discussion  of  the  results 
of  the  various  investigators. 

March  19 — Joint  meeting  with  the 
American  Institute  of  Electrical  Engi- 
neers. Paper:  "Projector  Lanterns  and 
Searchlights"  or  "Incandescent  Lamp 
Manufacture." 


New  Members. 

The  following  twenty-three  applicants 
were  elected  members  of  the  Society  at 
a  Council  meeting  held  February  11: 

Ache  son,  Albert  R. 

Professor  of  Mechanical  Engineer- 
ing, Syracuse  University;  Consult- 
ing Engineer,  Bureau  of  Gas  and 
Electricity,  City  of  Syracuse;  Syra- 
cuse, N.  Y. 

Ball,  Wm.  J. 

Secretary,  Tri-City  Electric  Com- 
pany,  1529  Third  Ave.,  Moline,  111. 

Blakeslee,  Doraf  Wilmot 

Assistant  Professor  of  Electrical 
Engineering,  University  of  Arkan- 
sas, Fayetteville,  Ark. 

Carpenter,  C.  A. 

Electrical  Engineer,  Graham,  Burn- 
ham  &  Co.,  1417  Railway  Exchange, 
Chicago,  111. 

Fleming,  John  P. 

New  Business  Representative,  The 
United  Gas  Improvement  Co.,  1035 
Market  St.,  Philadelphia,  Pa. 

Goldsmith,  Lester  M. 

Testing  and  Designing  Engineer, 
Perpetual  Fuse  Company,  1606  S. 
Fourth  St.,  Philadelphia,  Pa. 

Gleason,  Marshall  T. 

Gleason,  Tiebout  Glass  Co.,  99  Com- 
mercial St.,  Brooklyn,  N.  Y. 

Gross,  J.  Harry 

Park  Engineer,  Park  Board,  Druid 
Hill  Park,  Baltimore,  Md. 


TRANSACTIONS    I.   E.  S. — PART    II 


Howe,  Lucien 

Ophthalmologist,  520  Delaware  Ave., 
Buffalo,  N.  Y. 

Hirsch,  H.  H. 

President,  Hirsch  Electric  Mine 
Lamp  Company,  314  N.  12th  St., 
Philadelphia,  Pa. 

Kelley.  J.  B. 

Salesman,  Frank  H.  Stewart  Elec- 
tric Co.,  37  N.  7th  St.,  Philadelphia, 
Pa. 

KOLLMORGEN,   FREDERICK   L.   G. 

Optical  Expert,  Keuffel  &  Esser  Co., 
Adams  St.,  Hoboken,  N.  J. 
Lienesch,  Walter  H. 

General  Manager,  Chicago  Concrete 
Post     Co.,     608     S.     Dearborn     St., 
Chicago,  111. 
Lee,  Stanton  P. 

Architect,  53  Third  St.,  Troy,  N.  Y. 
Norris,  B.  H. 

Assistant  to  W.  D'A.  Ryan.  General 
Electric  Co.,  Illuminating  Engineer- 
ing Laboratory,  Schenectady,  N.  Y. 
Porter,  Geoffrey 

Assistant    Chief     Engineer,     B.     C. 
Electric   Railway    Co.,    Ltd.,    Canall 
St.,  Vancouver,  B.  C. 
Pindell,  Wm.  H..  Jr. 

Incandescent  Lamp  Salesman,  Ster- 
ling Electric  Lamp  Division  of  Gen- 
eral Electric  Co.,  313  Union  Trust 
Bldg.,  Baltimore,  Md. 
Ramirez,  Charles  E. 

Representative,  Bayley  &  Sons,  Inc., 
101  Park  Ave.,  New  York,  N.  Y. 

Seiler,  Alvix 

Agent  for  Westinghouse  Lamp  Co., 
Greensburg,  Pa. 

Sinclair,  H.  A. 

Secretary  and  Treasurer,  The 
Tucker  Elec.  Construction  Co.,  114 
W.  30th  St.,  New  York,  N.  Y. 

Thompsox.  Robt.  J. 

Manager.  Welsbach  Co..  863  Mis- 
sion St.,  San  Francisco,  Cal. 


Tomlixsox,  L.  C. 

Electrical    Engineer,    32    Greenleaf 

St.,  Maiden,  Mass. 
Wynne,  V.  C. 

Consulting   Engineer,   90    State    St., 

Albany,  N.  Y. 


Sustaining  Membership. 

The  George  Cutter  Company  of  South 
Bend.  Ind.,  and  the  New  Haven  Gas 
Light  Company  were  elected  sustaining 
members  of  the  Society  at  a  Council 
meeting  held  February  11. 


Personals. 


L.  B.  Marks  and  J.  E.  Woodwell,  con- 
sulting engineers,  103  Park  Avenue, 
New  York  City,  announce  that  they  Will 
dissolve  partnership  on  May  1,  1915- 
Mr.  Woodwell  will  locate  his  offices  at 
8  West  40th  Street,  where  he  will  con- 
tinue the  general  practise  of  consulting 
engineer,  and  Mr.  Marks  will  retain  his 
offices  at  103  Park  Avenue  and  will 
specialize  as  heretofore  in  illuminating 
engineering. 

Dr.  Henry  Phelps  Gage  and  Prof. 
Simon  Henry  Gage  are  the  authors  of 
a  book  entitled  "Optic  Projection"  pub- 
lished recently  by  the  Comstock  Publish- 
ing Co. 

Mr.  Douglass  Burnett  was  elected 
chairman  of  the  Commercial  Section  of 
the  N.  E.  L.  A.  at  a  meeting  held  in 
Chicago,  February  13. 

Mr.  Wilbur  B.  Foshay,  formerly  with 
the  Northwestern  Electric  Co.,  is  now 
president  of  the  Washington  Public 
Service  Co.  of  Portland,  Ore. 


TRANSACTIONS    I.    E.    S.—  PART   II 


Mr.  H.  Foster  Boggis  is  secretary  and 
treasurer  of  the  Boggis,  Dietz  Electric 
Co.  in  Milwaukee,  Wis. 


Mr.  E.  B.  Rowe,  who  in  the  last  years 
has  held  successively  the  positions  of 
resident  engineer,  assistant  chief  engi- 
neer and  chief  illuminating  engineer  of 
the  Holophane  Works,  severed  his  con- 
nections with  that  organization  March  I. 
Mr.  Rowe  is  now  secretary  and  engineer 
of  the  Enterprise  Electric  Construction 
&  Fixture  Co.,  6509  Euclid  Avenue, 
Cleveland,  Ohio. 


Back  Numbers  of  the  Transactions. 

The  Illuminating  Engineering  Society 
is  desirous  of  obtaining  copies  of  the- 
following  issues  of  the  Transactions  : 

1906  (Volume  I)  : 
Nos.  1,  2,  and  3. 

1907  (Volume  II)  : 
Nos.  1  and  2. 

1914  (Volume  IX)  : 
No.  7- 

Members  or  others  having  copies  of 
these  numbers  which  they  wish  to  dis- 
pose of  should  communicate  with  the 
general  office  of  the  Society,  29  West 
39th  Street,  New  York,  N.  Y. 

/ 


TRANSACTIONS 


OF  THE 


Illuminating 
Engineering  Society 

NO.  3,  1915 
PART  II 

Miscellaneous  Notes 


TRANSACTIONS    I.    E.    S. — PART    II 


Council  Notes. 

At  a  meeting  of  the  Council  held 
March  n,  twenty-seven  applicants  were 
elected  members  of  the  society.  Their 
names  appear  elsewhere  in  this  issue  of 
the  Transactions. 

It  was  resolved  that  final  action  in 
dropping  delinquents  who  owe  for  1913 
and  1914  dues  be  deferred  until  the  June 
meeting. 

Reports  on  section  activities  were 
received  from  the  following  vice-presi- 
dents :  Mr.  Ward  Harrison  for  Pitts- 
burgh ;  Prof!  George  A.  Hoadley  for 
Philadelphia;  G.  H.  Stickney  for  New 
York;  and  F.  A.  Vaughn  for  Chicago. 

It  was  voted  that  the  Council  accept 
the  proposal  of  the  Philadelphia  Section 
to  affiliate  with  the  Engineers'  Society 
of  Philadelphia  for  the  period  of  one 
year,  with  the  understanding  that  the 
cost  to  the  society  will  not  exceed  the 
sum  of  $350.00. 

Progress  reports  were  received  from 
the  following  committees :  Sustaining 
Membership.  Popular  Lectures,  School 
Lighting,  Remodeling  the  Lighting  of 
the  General  Offices,  Exhibition  Booth 
(Gas),  Exhibition  Booth  (Electric), 
Membership,  Constitutional  Revision, 
Lighting  Legislation. 

The  following  committee  appoint- 
ments were  confirmed : 

Mr.  Douglass  Burnett  on  the  National 
Membership  Committee. 

Mr.  Clarence  L.  Law,  chairman  of 
the  Committee  on  Remodeling  the  Light- 
ing of  the  General  Offices. 

Mr.  E.  S.  Marlow,  chairman  of  the 
1915  Convention  Committee. 

The  work  of  the  19 14  Convention 
Committee  being  completed,  it  was  voted 
that  the  committee  be  discharged  with 


a  hearty  vote  of  thanks  from  the  Coun- 
cil and  the  Illuminating  Engineering 
Society  for  services  rendered. 

Those  present  at  the  meeting  were : 
A.  S.  McAllister,  president;  H.  Calvert, 
Ward  Harrison,  S.  G.  Hibben,  George 
A.  Hoadley,  C.  A.  Littlefield,  general 
secretary ;  L.  B.  Marks,  treasurer ; 
Preston  S.  Millar,  Alten  S.  Miller, 
J.  Arnold  Norcross,  G.  H.  Stickney. 
Upon  invitation,  Mr.  A.  Hertz,  chair- 
man of  the  Finance  Committee. 

/ 

A  meeting  of  the  Council  was  held 
April  8  in  the  general  offices  of  the 
Society,  29  West  39th  Street,  New  York, 
N.  Y.  Those  present  were :  A.  S. 
McAllister,  president;  E.  M.  Alger, 
C.  O.  Bond.  H.  Calvert,  J.  D.  Israel, 
C.  A.  Littlefield,  general  secretary ; 
L.  B.  Marks,  treasurer;  Preston  S. 
Millar.  Alten  S.  Miller,  and  J.  Arnold 
Norcross. 

Mr.  Preston  S.  Millar,  chairman  of 
the  Sustaining  Membership  Committee, 
announced  that  the  sustaining  member- 
ship dues  of  the  Edison  Lamp  Works 
of  the  General  Electric  Co..  Harrison, 
N.  J.,  had  been  raised  upon  request  of 
the  member. 

A  written  report  on  the  Philadelphia 
Section  activities  by  Prof.  George  A. 
Hoadley,  vice-president,  was  read  by 
Mr.  H.  Calvert. 

A  written  report  was  received  from 
the  Committee  on  Membership.  The 
report  showed  that  since  October  1,  1914, 
the  additions  to  the  membership  totaled 
117;  the  defections  in  the  membership 
during  the  same  period  totaled  97,  leav- 
ing a  net  gain  of  20.  The  total  indi- 
vidual membership  as  of  April  8  was 
1.492. 


TRANSACTIONS    I.  E.  S. — PART    II 


A  written  report  was  received  from 
the  chairman  of  the  Committee  on 
Remodeling  the  Lighting  of  the  General 
Offices. 

The  committee  was  discharged  with 
thanks. 

A  written  report  containing  a  list  of 
proposed  amendments  to  the  Constitu- 
tion was  received  from  the  Committee 
on  Constitutional  Revision.  The  report 
was  also  accompanied  by  a  communica- 
tion to  the  membership  of  the  society 
which  the  committee  recommended  be 
sent  out  with  the  proposed  amendments 
in  advance  of  the  election. 

The  proposed  amendments  having 
been  received  and  considered  favorably 
by  the  Council,  it  was  resolved  that  the 
general  secretary  be  instructed  to  send 
out  the  aforementioned  communication 
and  proposals  previous  to  the  forthcom- 
ing annual  election. 

The  Committee  on  Glare  from  Reflect- 
ing Surfaces  submitted  two  reports — 
the  second  and  third  of  a  series  to  be 
submitted  by  the  committee — on  the  sub- 
ject of  "The  Optical  Properties  of 
Diffusing  Media."  One  gave  a  classifi- 
cation of  diffusion,  nomenclature  and 
the  physical  theory  of  diffusion;  the 
other  dealt  with  instruments  and  meth- 
ods for  measuring  diffusion  and  the 
theory  of  diffusion  photometry. 

It  was  resolved  that  the  reports  of 
this  committee  be  put  through  the  usual 
channel  of  publication,  as  they  become 
available,  and  published  in  the  Trans- 
actions upon  acceptance  by  the  Com- 
mittee on  Papers. 

Written  reports  were  also  received 
from  the  Committees  on  Editing  and 
Publication,  Reciprocal  Relations  with 
other    Societies,    and    Section    Develop- 


ment. Upon  consideration  of  a  recom- 
mendation contained  in  the  report  of  the 
Committee  on  Editing  and  Publication — 
that  all  Transactions  cuts  which  are 
more  than  three  years  old  be  sold  as 
junk — it  was  ordered  that  all  line  cuts 
which  have  been  used  in  the  Transac- 
tions prior  to  the  first  of  January  of 
this  year  be  destroyed,  but  all  half-tones 
be  retained. 

The  Committee  on  Lighting  Legisla- 
tion submitted  a  report  stating  that  it 
had  considered  (i)  a  report  containing 
material  for  formulating  a  code  on  fac- 
tory lighting,  which  had  been  received 
from  the  Committee  on  Factory  Light- 
ing; (2)  a  report  submitted  by  the  Com- 
mittee on  School  Lighting  containing 
material  upon  which  it  is  proposed  to 
base  a  code  on  school  lighting;  and 
returned  both  reports  to  the  respective 
committees  with  suggestions  for  revi- 
sion. 

The  appointment  of  Mr.  M.  Luckiesh 
to  the  Committee  on  Lighting  Legisla- 
tion was  confirmed. 

It  was  announced  that  the  1915  Con- 
vention of  the  Society  would  be  held  at 
the  New  Willard  Hotel,  Washington, 
D.  C,  September  20-23  inclusive. 

Communications  were  received  from 
Mr.  F.  A.  Vaughn,  delegate  of  the 
I.  E.  S.  to  the  Eleventh  Annual  Con- 
vention of  the  Illinois  Gas  Association ; 
W.  A.  Ferguson  of  the  Commonwealth 
Edison  Company,  in  regard  to  holding 
Council  meetings  outside  the  city  of 
New  York ;  and  E.  C.  Jones,  president 
of  the  American  Gas  Institute,  regard- 
ing the  convention  of  his  organization 
in  San  Francisco. 

It  was  voted  that  Mr.  C.  O.  Bond  be 
asked  to  make  recommendations  to  the 
president  regarding  the  appointment  of 


TRANSACTIONS    I.    E.    S. — PART    II 


two  members  of  the  I.  E.  S.  to  arrange 
for  the  presentation  of  two  papers — to 
be  credited  to  the  I.  E.  S. — to  be  deliv- 
ered at  the  San  Francisco  Convention 
of  the  American  Gas  Institute ;  and  that 
the  president  be  empowered  to  appoint 
such  members. 

It  was  suggested  that  a  future  meeting 
of  the  Council  be  held  in  Philadelphia 
or  a  city  other  than  New  York. 


Section  Activities. 

Chicago  Section. 
Meetings. 

March  25,  1915.  Auditorium,  Western 
Society  of  Engineers,  Monadnock  Block. 
Paper :  "Color  in  Lighting,"  by  M. 
Luckiesh.    Attendance  63. 

The  tentative  program  of  papers  for 
the  Chicago  Section  for  the  season  1914- 
1915  is  as  follows  : 

April — Lighting  of  Small  Interiors  : 
Homes ;  Small  Offices ;  Show  Windows. 
May — Lighting  of  Large  Interiors : 
Churches  ;  Halls ;  Large  Offices. 

June — Lighting  of  Open  Air  Spaces : 
Streets;  Building  Exteriors;   Signs. 

New  England  Section. 
Meetings. 
March  26,  1915,  Afternoon  and  Even- 
ing. Engineers'  Club,  2  Commonwealth 
Ave.,  Boston,  Mass.  Papers  presented 
in  the  afternoon  :  ( 1 )  "Daylight  Glass," 
by  Dr.  H.  P.  Gage;  (2)  "Artificial  Day- 
light," by  R.  B.  Hussey;  (3)  "Semi- 
Indirect  Lighting  by  Gas,"  by  R.  F. 
Pierce.  Papers  presented  in  the  even- 
ing: (1)  "Determining  Factors  in  Arti- 
ficial Illumination  Problems  Primarily 
as  Related  to  Architecture  and  Decora- 
tion," by  D.  Crownfield;  (2)  "Safe- 
guarding the  Eyesight  of  School  Chil- 
dren," by  M.  Luckiesh. 


New  York  Section. 

Meetings. 

March  II,  1915.  Engineering  Societies 
Building.  Paper :  "A  Practical  Study 
of  Car  Lighting  Problems,"  by  Messrs. 
W.  G.  Gove  and  L.  C.  Porter.  Mr.  P.  S. 
Bailey  gave  a  demonstration  of  four 
different  sizes  of  headlight  lamps  for 
interurban  and  suburban  cars.  Mr. 
G.  H.  Stickney  demonstrated  various 
systems  of  interior  car  lighting  by  means 
of  a  booth  erected  for  this  purpose. 
Mr.  W.  P.  Horn  exhibited  /  new  car 
lighting  reflector  which  has  been  sug- 
gested for  railway  cars.    Attendance  80. 

April  19,  1915.  Auditorium  of  the 
Consolidated  Gas  Company's  Building, 
130  East  15th  St.  Joint  meeting  with 
the  National  Electric  Light  Association 
and  the  National  Commercial  Gas  Asso- 
ciation. Address  by  President  Holton 
H.  Scott,  of  the  N.  E.  L.  A.  Papers: 
(1)  "The  Value  of  the  Illuminating 
Engineering  Society  to  Commercial 
Men."  by  Mr.  Norman  Macbeth ;  (2) 
"Illuminating  Engineering  as  Applied  to 
the  Business  of  the  Gas  Company,"  by 
Mr.  R.  F.  Pierce. 

May — To  be  announced  later. 


Philadelphia  Section. 

Meetings. 

March  19.  1915.  Joint  meeting  with 
Franklin  Institute.  Papers:  (1)  "Photo- 
sculpturing,"  by  Prof.  J.  Hammond 
Smith,  illustrated;  (2)  "On  the  Choice 
of  a  Group  of  Observers  for  Hetero- 
chromatic  Measurements" ;  (3)  "Addi- 
tional Experiments  on  Colored  Absorb- 
ing Solutions  for  Use  in  Heterochro- 
matic  Photometry" ;  and  (4)  "A  Method 
of  Correcting  Abnormal  Color  Vision 
and  Its  Application  to  Flicker  Photom- 


TRANSACTIONS    I.    E.    S. — PART   II 


etry,"  by  Dr.  Herbert  E.  Ives  and  Mr. 
E.  F.  Kingsbury.    Attendance  50. 

April  16,  1915.  Drexel  Institute,  32nd 
and  Chestnut  Sts.  Papers:  (1)  "The 
Problems  of  Lighting  Design,"  by  Prof. 
Arthur  J.  Rowland;  (2)  "Safeguarding 
the  Eyesight  of  School  Children,"  by 
M.  Luckiesh. 

The  tentative  program  of  papers  for 
the  Philadelphia  Section  for  the  season 
1915  is  as  follows  : 

May  21 — "Store  Lighting,"  by  W.  R. 
Moulton.  This  meeting  will  be  held  in 
Baltimore,  Md.  The  place  will  be 
announced  later. 

Pittsburgh  Section. 
Meetings. 
March  9,  1915.  Joint  meeting  with  the 
local  section  of  the  American  Institute 
of  Electrical  Engineers.  Papers:  (1) 
"The  Manufacture  of  New  Types  of 
Mazda  Lamps,"  by  Mr.  R.  E.  Myers ; 
(2)  "The  Use  of  Lenses  in  Signal 
Work,"  by  H.  S.  Hower.  Interesting 
exhibits  illustrated  both  papers. 


New  Members. 

The  following  twenty-seven  applicants 

were  elected  members  of  the  society  at 

a  meeting  of  the  Council  held  March  11, 

1915: 

Arenberg,  Albert  L. 

Sales  Engineer,  Central  Electric 
Co.,  320  So.  Fifth  St.,  Chicago,  111. 

Bell,  W.  B. 

Public  Service  Electric  Co.,  188 
Ellison  St.,  Paterson,  N.  J. 

Bull,  John  H. 

Supervising  Engineer,  Ballinger  & 
Perrot,  Marbridge  Building,  New 
York,  N.  Y. 

Cox,  W.  A. 

Public  Service  Electric  Co.,  Newark, 
N.J. 


Duvall,  Benjamin  A. 

Sales  Dept.,  The  Consolidated  Gas 
Electric  Light  &  Power  Co.,  100  W. 
Lexington  St.,  Baltimore,  Md. 

French,  C.  H. 

Public  Service  Electric  Co.,  759 
Broad  St.,  Newark,  N.  J. 

Gorge,  S.  V. 

Electrical  Contractor,  841 1  Eigh- 
teenth Ave.,  Brooklyn,  N.  Y. 

Harrison,  Benjamin 

Electrical  Contractor,  65 11  Eigh- 
teenth Ave.,  Brooklyn,  N.  Y. 

Jones,  W.  L. 

Manager,  Fixture  Dept.,  Electric 
Construction  &  Machinery  Co., 
Electric  Bldg.,  Rock  Island,  111. 

Mayhew,  Zenas  D. 

District  Clerk,  Edison  Electric  Il- 
luminating Co.  of  Brooklyn,  360 
Pearl  St.,  Brooklyn,  N.  Y. 

Owen,  Charles  D. 

New  Business  Assistant  to  the 
Division  Agent,  Public  Service  Elec- 
tric Co.,  118  Main  St.,  Hackensack, 
N.J. 

Potter,  N. 

Public  Service  Gas  Co.,  188  Ellison 
St.,  Paterson,  N.  J. 

Perkins,  M. 

Public  Service  Gas  Co.,  418  Federal 
St.,  Camden,  N.  J. 

Ramsey,  Harold  E. 

Assistant  Electrical  Engineer,  Le- 
high Coal  &  Navigation  Co.,  Elec- 
trical Dept.,  Lansford,  Pa. 

Schwartz,  Frederick 

Store  Manager,  Shapiro  &  Aronson, 
20  Warren  St.,  New  York,  N.  Y. 

Schwartz,  H.  M. 

Propr.  Robt.  Findlay  M'f'g.  Co.,  349 
Adams  St.,  Brooklyn,  N.  Y. 

Shearer,  E.  P. 

Public  Service  Gas  Co.,  271  N. 
Broad  St.,  Elizabeth,  N.  J. 


TRANSACTIONS   I.    E.    S.  —  PART   II 


Smith,  A.  A. 

Public  Service  Electric  Co.,  Newark, 

N.J. 
Smith,  G.  E. 

Public  Service  Electric  Co.,  Newark, 

N.J. 
Stieren,  Edward 

Ophthalmologist,  WestinghouseBldg., 

Pittsburgh,  Pa. 
Taxzer,  E.  Dean 

Assistant  Professor  Electrical  En- 
gineering,   Lafayette    College,   Eas- 

ton,  Pa. 
Thompson,  R.  B. 

Sales     Dept.      (Lighting)      Central 

Hudson    Gas    &    Electric    Co.,    129 

Broadway,  Newburgh,  N.  Y. 
Tingley,  Louisa  Paine 

Physician       (Ophthalmologist),       9 

Massachusetts  Ave.,  Boston,  Mass. 
Van  Gieson,  C.  J. 

Public  Service  Electric  Co.,  Newark, 

N.J. 
Walker,  J.  H. 

Assistant   Engineer,    C.   L.    Reeder, 

921  Equitable  Bldg.,  Baltimore,  Md. 
Xylander,  P. 

Public   Service    Gas    Co.,    118   Main 

St.,  Hackensack,  N.  J. 
Young,  R.  R. 

Public     Service    Electric    Co.,     759 

Broad  St.,  Newark,  N.  J. 

The  following  twenty  applicants  were 
elected  members  of  the  society  at  a 
Council  meeting  held  April  8 : 

Allen,  Chile  C. 

Superintendent,  Geo.  S.  Johnston 
Co.,  5  S.  Wabash  Ave.,  Chicago,  111. 

Ambler,  Thomas  M. 

Manager,  Commercial  Department, 
Brooklyn  Union  Gas  Co.,  176  Rem- 
sen  St.,  Brooklyn,  N.  Y. 

Brauns,  H.  E. 

District  Sales  Agent,  Milwaukee 
Electric  Railway  &  Light  Co.,  429 
Mitchell  St.,  Milwaukee,  Wis. 


Palmer,  Briggs  S. 

Optometrist,  John  W.  Sanborn  Co., 

149  Tremont  St.,  Boston,  Mass. 
Bryant,  Alice  G.  (M.  D.) 

502  Beacon  St.,  Boston,  Mass. 
Callender,  D.  E. 

General  Manager,  Wisconsin  Gas  & 

Electric    Co.,    305    6th    St.,    Racine, 

Wis. 
English,  Frank  F.,  2nd. 

Ilhiminating   Engineer,    51    E.   42nd 

Si.,  New  York,  N.  Y. 

Flynn,  M.  F. 

District  Sales  Agent,  Milwaukee 
Electric  Railway  &  Light  Co.,  Public 
Service  Bldg.,  Milwaukee,  Wis. 

Foote,  Frank  H. 

Manager,  Specialty  Department, 
Pettingell-Andrews  Co.,  511  Atlantic 
Ave.,  Boston,  Mass. 

Grant,  Albert  Weston,  Jr. 

Photometrical  Dept.,  United  Gas 
Improvement  Co.,  Philadelphia,  Pa. 

Harris,  Arthur  C. 

District  Sales  Agent,  Milwaukee 
Electric  Railway  &  Light  Co., 
Racine,  Wis. 

Jamison,  Chas.  M. 

Manager,  Merchandise  Sales  Dept., 
Milwaukee  Electric  Railway  &  Light 
Co.,  Public  Service  Bldg.,  Milwau- 
kee, Wis. 

Johnson,  N.  E. 

Vice-President,  The  Linden  Co., 
1216  Michigan  Ave.,  Chicago,  111. 

Kruse,  O.  J. 

District  Sales  Agent,  Milwaukee 
Electric  Railway  &  Light  Co.,  Public 
Service  Bldg.,  Milwaukee,  Wis. 

Monger,  H.  G. 

Chief  Clerk.  Sales  Dept.,  Milwaukee 
Electric  Railway  &  Light  Co.,  Public 
Service  Bldg.,  Milwaukee,  Wis. 


TRANSACTIONS    I.    E.    S.  —  PART    II 


Montgomery,  T.  M. 

Manager,  Lamp  Dept.,  Elliott-Lewis 
Electrical  Co.,  Inc.,  138-40  N.  10th 
St.,  Philadelphia,  Pa. 

Pevear,  Munroe  Rhodes 

Architect  and  Colored  Light  Special- 
ist, Pevear  Color  Specialty  Co.  and 
Foss  &  Pevear,  Architects,  71 
Brimmer  St.,  Boston,  Mass. 

PvEUTELER,   A.   C. 

Manager,  Watertown  Gas  &  Electric 
Co.,  205  Main  St.,  Watertown,  Wis. 

Van  Derzee,  G.  W. 

Assistant  to  Vice-President,  Mil- 
waukee Electric  Railway  &  Light 
Co.,  Public  Service  Bldg.,  Milwau- 
kee, Wis. 

Wall,  William  L. 

Secretary  and  Treasurer,  Wall  & 
Ocles,  Inc.,  1716  Chestnut  St.,  Phila- 
delphia, Pa. 


Sustaining  Membership. 

The  American  Gas  &  Electric  Co.  of 
New  York,  the  Brooklyn  Union  Gas  Co. 
and  the  Edison  Illuminating  Co.  of 
Detroit  were  elected  sustaining  members 
of  the  society  at  a  Council  meeting  held 
April  8. 

The  following  companies  were  elected 
sustaining  members  of  the  society 
March  1 1 : 

Edison  Lamp  Works  of  General  Elec- 
tric Company,  Harrison,  N.  J. 

Schenectady  Illuminating  Company, 
Schenectady,  N.  Y. 


New  Books. 

Modern    Illumixants    and    Illumi- 
nating   Engineering — by    Leon    Gaster 


and  J.  S.  Dow ;  458  pp.,  price  $5.00,  the 
Macmillan  Co.,  New  York.  Chapters 
on :  history  and  development  of  meth- 
ods of  illumination;  gas  lighting;  elec- 
tric lighting;  oil,  petrol-air  gas  and 
acetylene  lighting;  illumination  and  the 
eye;  color  and  the  eye;  measurement 
df  light  and  illumination;  globes,  shades 
and  reflectors,  and  calculations  of  illumi- 
nation ;  problems  in  interior  illumina- 
tion; outdoor  lighting.  Bibliography 
appended. 


Personals. 


Mr.  Harvey  B.  Wheeler,  formerly 
with  the  National  X-Ray  Reflector  Co., 
Chicago,  111.,  is  now  chief  engineer  of 
the  Pettingell-Andrews  Co.,  Boston, 
Mass. 

Prof.  Alexander  Silverman,  director 
of  the  department  of  chemistry  of 
University  of  Pittsburgh  has  recently 
given  before  several  chemical  societies 
a  lecture  constituting  a  survey  of  the 
chemistry  and  technology  of  glass  mak- 
ing. Numerous  specimens  of  glass  were 
exhibited  at  each  lecture. 


Obituary. 


George  Cutter,  vice-president  of  the 
George  Cutter  Co.,  South  Bend,  Ind., 
died  of  heart  failure  on  April  6,  1915, 
in  Los  Angeles,  Cal.  He  was  born  near 
Boston  in  1853.  In  1889  he  started  in 
business  for  himself  in  Chicago  in  the 
manufacture  of  electrical  appliances.  In 
1898  he  organized  the  George  Cutter  Co., 
manufacturers  of  specialties  for  outdoor 
electric  lighting. 


TRANSACTIONS 

OF  THE 

Illuminating 
Engineering  Society 

NO.  4,  1915 
PART  II 

Miscellaneous  Notes 


TRANSACTIONS   I.    E.    S. — PART   II 


Council  Notes. 

A  meeting  of  the  Council  was  held 
May  13  in  the  general  offices  of  the 
society,  29  West  39th  Street,  New  York, 
N.  Y.  Those  present  were :  A.  S. 
McAllister,  president;  C.  O.  Bond,  H. 
Calvert,  George  A.  Hoadley,  C.  A. 
Littlefield,  general  secretary;  L.  B. 
Marks,  treasurer;  Alten  S.  Miller, 
Preston  S.  Millar,  W.  Cullen  Morris, 
J.  Arnold  Norcross,  and  Geo.  H.  Stick- 
ney;  upon  invitation,  George  S.  Bar- 
rows, C.  E.  Clewell,  A.  Hertz,  and 
F.  K.  Richtmyer. 

Reports  on  section  activities  were  re- 
ceived from  the  following  vice-presi- 
dents :  George  A.  Hoadley,  Philadel- 
phia ;  Ward  Harrison,  Pittsburgh ;  G.  H. 
Stickney,  New  York ;  and  F.  A.  Vaughn, 
Chicago. 

Upon  recommendation  of  the  Finance 
Committee,  vouchers  No.  2088  to  No. 
2095  and  No.  2097  to  No.  2129  inclusive, 
aggregating  $921.81,  were  authorized 
paid. 

After  the  reading  of  a  written  report 
by  the  chairman  of  the  Committee  on 
Factory  Lighting,  it  was  resolved  that 
it  is  the  sense  of  the  Council  that  (1) 
the  Committee  on  Popular  Lectures 
should  with  due  speed  complete  its  lec- 
tures in  order  to  have  them  ready  for 
service;  (2)  that  when  they  are  com- 
pleted, they  shall  be  presented  for 
action  by  the  necessary  committees,  and 
for  approval  by  the  Council;  (3)  that 
immediately  upon  approval  of  the  Coun- 
cil they  shall  be  deemed  ready  for  ser- 
vice upon  demand ;  and  that  (4)  they 
shall  be  printed  in  the  Transactions 
after  approval  by  the  Council  and  the 
usual  committees. 

Mr.  J.  Arnold  Norcross,  representa- 
tive of  the  I.  E.  S.  on  the  International 
Gas    Congress,    asked    that    the    society 


cooperate  in  advertising  the  congress, 
which  is  to  be  held  in  San  Francisco 
next  September.  It  was  voted  that  a 
notice  concerning  the  congress  be 
published  in  the  next  issue  of  the 
Transactions. 

Mr.  C.  O.  Bond  recommended  the 
appointment  of  Messrs.  G.  S.  Barrows 
and  G.  E.  Hulse  to  present  at  the  San 
Francisco  convention  of  the  American 
Gas  Institute  two  papers  which  shall  be 
credited  to  the  I.  E.  S. 

An   oral   report   was   made   by    Prof. 

F.  K.  Richtmyer,  chairman  of  the  Com- 
mittee on  Education.  One  member  of 
the  committee  is  to  present  a  paper 
before  the  coming  convention  of  the 
Society  for  the  Promotion  of  Engineer- 
ing Education. 

A  written  report  was  received  from 
Mr.  Wra.  Hand  Browne,  Jr.,  delegate 
of  the  I.  E.  S.  to  the  presidential  inau- 
gural ceremonies  of  the  University  of 
North  Carolina.  It  was  voted  that  the 
report  be  acknowledged  and  a  vote  of 
thanks  of  the  Council  be  extended  to 
Mr.  Browne. 

Informal  reports  were  made  by   Mr. 

G.  H.  Stickney,  chairman  of  the  Com- 
mittee on  Papers,  and  Mr.  Preston  S. 
Millar,  chairman  of  the  Committee  on 
Sustaining  Membership. 

Communications  were  received  from 
Messrs.  M.  M.  Marks,  president  of  the 
Borough  of  Manhattan ;  S.  G.  Hibben, 
secretary  of  the  Pittsburgh  Section,  and 
C.  L.  Law. 

The  following  committee  appoint- 
ments were  confirmed : 

Committee  on  Factory  Lighting:  D. 
M.  Petty. 

Committee  of  Election  Tellers :  L.  J. 
Lewinson,  chairman ;  H.  V.  Allen,  Edgar 
H.  Bostock,  W.  A.  D.  Evans,  and  A.  L. 
Powell. 


TRANSACTIONS    I.  E.  S. — PART   II 


Section  Activities. 

Chicago  Section 
Meetings 

April  22,  1915.  Auditorium,  Western 
Society  of  Engineers,  Monadnock  Build- 
ing. Paper :  "Knowns  and  Unknowns 
in  the  Lighting  of  Small  Interiors,"  by 
Mr.  James  R.  Cravath.  The  paper 
appears  elsewhere  in  this  issue  of  the 
Transactions.    Attendance  51. 

May  21,  1915.  Auditorium,  Western 
Society  of  Engineers,  Monadnock  Build- 
ing. Paper :  "Principles  of  Scientific 
Street  Lighting,"  by  Mr.  A.  J.  Sweet. 

The  tentative  program  of  papers  for 
the  June  meeting  of  the  Chicago  Sec- 
tion is  as  follows : 

June — "Lighting  of  Open  Air  Spaces : 
Streets,  Building  Exteriors,  Signs." 

New  York  Section 
Meetings 

May  13,  1915.  Engineering  Societies 
Building.  Papers:  (1)  "Illuminating 
Engineering  as  a  Branch  of  Technical 
Instruction,"  by  C.  E.  Clewell;  (2) 
"Sheet  Glass — Its  Manufacture  and  Use 
for  Illuminating  Purposes,"  by  E.  H. 
Bostock.    Attendance  85. 

June — To  be  announced  later. 

Philadelphia  Section 
Meetings 

April  24,  1915.  Joint  meeting  with 
the  American  Electro-chemical  Society 
at  the  University  of  Pennsylvania. 

May  21,  1915.  Baltimore.  Papers : 
(1)  "Store  Lighting,"  by  Mr.  W.  R. 
Moulton;  (2)  "A  Proposal  Relative  to 
Definitions,  Standards  and  Photometric 
Methods,"  by  Dr.  H.  E.  Ives. 

Pittsburgh  Section 
Meetings 
May   7,    1915.     The   Hofbrau,   Cleve- 


land, Ohio.  Papers:  (1)  "Gas  Street 
Lighting  Development,"  by  Mr.  F.  R. 
Hutchinson;  (2)  "Street  Lighting  with 
the  Modern  Arc  Lamp,"  by  Mr.  W.  P. 
Hurley;  (3)  "Recent  Developments  in 
Incandescent  Street  Lighting,"  by  Mr. 
Ward  Harrison.     Attendance  55. 


New  Members. 

The   following  three   applicants   were 
elected    members    of    the    society    at    a 
meeting   of   the   Council   held   May    13, 
1915 : 
Hudson,  Ralph  Gorton 

Instructor  of  Electrical  Engineering, 
Massachusetts  Institute  of  Technol- 
ogy, Boston,  Mass. 

Jelliefe,  C.  N. 

Vice-president  and  Treasurer,  Amer- 
ican Light  &  Traction  Co.,  40  Wall 
St.,  New  York,  N.  Y. 

Turner,  Hunter  Heiner 

Ophthalmologist,  517  Jenkins  Arcade 
Bldg.,  Pittsburgh,  Pa. 


Personals. 


Mr.  J.  C.  Schmidtbauer  has  been 
elected  president  of  the  Milwaukee  Elec- 
trical League. 

Mr.  C.  W.  Bender  has  been  appointed 
general  manager  of  the  Nela  Specialties 
Division,  recently  organized  to  handle 
specialties  manufactured  by  the  National 
Lamp  Works  of  the  General  Electric 
Company.  He  will  also  continue  his 
present  work  as  manager  of  the  com- 
mercial department. 


Obituary. 


Mr.  George  Maurice,  manager  of  the 
heating  and  light  department  of  the 
General  Electric  Company,  Ltd.,  of 
London,  England,  and  one  of  the  direc- 


TRANSACTIONS   I.    E.    S. — PART   II 


tors  of  that  company,  was  one  of  the 
passengers  reported  lost  in  the  sinking 
of  the  steamship  Lusitania  on  May  7, 
1915.  Mr.  Maurice  had  been  in  this 
country  for  several  weeks  on  one  of 
his  numerous  business  trips.  He  was 
widely  known  in  the  electrical  industry, 
both  in  this  country  and  abroad. 


Joint  Session  A.  I.  E.  E.  and  I.  E.  S. 

The  American  Institute  of  Electrical 
Engineers  and  the  I.  E.  S.  will  hold  a 
joint  session  on  Wednesday  evening, 
June  30,  1915,  at  Deer  Park,  Md.,  in 
conjunction  with  the  32nd  annual  con- 
vention of  the  institute.  Two  papers 
are  scheduled  for  this  session :  "Sys- 
tems of  Street  Illumination,"  by  Dr. 
C.  P.  Steinmetz,  and  "The  Effective 
Illumination  of  Streets,"  by  Mr.  Preston 
S.  Millar.  Copies  of  the  latter  paper 
may  be  had  free  about  June  15  upon 
application  to  the  general  office  of  the 
I.  E.  S.,  29  West  39th  Street,  New 
York,  N.  Y. 


Results  of  1915  I.E. S.  Election. 

The  Committee  of  Tellers  met  May 
27,  1915,  in  the  general  office  of  the 
society,  and  counted  the  votes  of  the 
1915  annual  election.  The  results 
reported  by  the  committee  showed  that 
the  following  officers  of  the  society  and 
its  several  sections  were  elected  for 
various  terms  beginning  October  1,  1915  : 

President,  Dr.  C.  P.  Steinmetz ;  gen- 
eral secretary,  Alten  S.  Miller ;  treas- 
urer, L.  B.  Marks ;  vice-presidents, 
Clarence  L.  Law  and  J.  L.  Minick ; 
directors,  W.  A.  Durgin,  M.  Luckiesh, 
and  J.  Arnold  Norcross. 

Chicago  Section — Chairman,  E.  W. 
Lloyd ;  secretary,  O.  L.  Johnson ;  man- 
agers, A.  O.  Dicker,  H.  M.  Frantz,  C.  A. 


Luther,  A.  H.  Meyer,  and  F.  A.  Rogers. 

New  England  Section — Chairman, 
Louis  Bell;  secretary,  S.  C.  Rogers; 
managers,  J.  W.  Cowles,  W.  B.  Lancas- 
ter, George  P.  Smith,  Jr.,  H.  F.  Wallace, 
and  R.  C.  Ware. 

New  York  Section — Chairman,  D. 
McFarlan  Moore;  secretary,  Norman  D. 
Macdonald;  managers,  Thomas  M. 
Ambler,  L.  H.  Graves,  W.  F.  Little, 
E.  R.  Treverton,  and  Herbert  S. 
Whiting. 

Philadelphia  Section — Chairman,  G.  S. 
Crampton ;  secretary,  L.  B.  Eichengreen ; 
managers,  George  S.  Barrows,  Douglass 
Burnett,  C.  E.  Clewell,  R.  B.  Ely,  and 
C.  E.  Ferree. 

Pittsburgh  Section — Chairman,  Lewis 
J.  Kiefer;  secretary,  R.  H.  Skinner; 
managers,  Henry  Harris,  H.  S.  Hower, 
Harold  Kirschberg,  H.  H.  Magdsick, 
and  G.  W.  Roosa. 

The  proposals  to  amend  the  constitu- 
tion of  the  society  were  also  adopted  by 
a  vote  of  more  than  five  to  one.  The 
principal  amendments  include  provisions 
which  create  a  grade  of  membership  to 
be  known  as  members.  The  require- 
ments for  admission  to  this  grade,  as  at 
present  set  forth,  are  somewhat  higher 
than  those  of  the  other  grade  of  indi- 
vidual members  known  as  associate 
members.  The  annual  dues  of  members 
will  be  $10.00  and  of  associate  members 
$5.00. 

DR.  CHARLES  P.  STEINMETZ 
Dr.  Charles  P.  Steinmetz,  president- 
elect, was  born  April  9,  1865,  at  Breslau, 
Germany.  He  was  educated  at  the 
gymnasium  (high  school)  and  then  at 
the  University  of  Breslau,  where  he 
studied  mathematics  and  astronomy, 
then  physics  and  chemistry,  and  finally 
for  a  short  time  medicine  and  national 
economy.     Involved  in  the  social  demo- 


TRANSACTIONS   I.    E.    S. — PART   II 


cratic  agitation  against  the  government, 
he  escaped  to  Switzerland  in  1888,  and 
there  studied  mechanical  engineering  at 
the  Polytechnische  Zurich. 

In  1889  he  immigrated  to  America, 
and  found  a  position  with  the  Oster- 
held  &  Eichemeyer  Manufacturing  Com- 
pany, first  as  draftsman,  then  as  elec- 
trical engineer  and  designer,  and  finally 
on  research  work  in  charge  of  the  Eiche- 
meyer laboratory. 

With  the  absorption  of  the  Eiche- 
meyer interests  by  the  General  Electric 
Company,  Dr.  Steinmetz  joined  the 
latter,  and  was  attached  to  Mr.  H.  F. 
Parshall's  calculating  department  in 
Lynn,  Mass.  With  the  transfer  of  the 
company's  headquarters  to  Schenectady 
in  the  spring  of  1894,  Dr.  Steinmetz 
organized  and  took  charge  of  the  calcu- 
lation and  design  of  the  company's 
apparatus,  and  of  the  research  and 
development  work. 

For  a  number  of  years  Dr.  Steinmetz 
was  professor  of  electrical  engineering 
at  Union  University,  and  at  the  present 
time  is  professor  of  electro-physics  at 
that  university,  at  the  same  time  retain- 
ing his  connection  with  the  General 
Electric  Company  as  chief  consulting 
engineer.  About  the  year  1910  he 
entered  into  closer  relation  with  this 
company  by  organizing  a  consulting 
engineering  department  under  his 
charge. 

Among  the  more  important  publica- 
tions and  articles  of  which  he  is  the 
author  are  a  series  of  papers  on  each 
of  the  following  subjects:  polydimen- 
tional  involutory  correspondence ;  mag- 
netic circuit  and  the  law  of  hysteresis ; 
dielectric  and  electrostatic  phenomena ; 
"Design  and  Performance  of  Electrical 
Apparatus,"  as  transformers,  induction 
machines,  synchronous  machines,  com- 
mutating    machines,    etc. ;    "High    Fre- 


quency Oscillations  and  Surges  in  Elec- 
tric Circuits";  "Radiation,  Light  and 
Illumination" ;  "Mechanical  Thermo- 
dynamics and  Steam  Turbines."  Most 
of  his  papers  on  electrical  subjects  are 
published  in  the  Transactions  of  the 
American  Institute  of  Electrical  Engi- 
neers. 

The  following  books  have  been  pub- 
lished by  Dr.  Steinmetz :  A  popular 
work  on  "Astronomy  and  Meteorology," 
in  the  German  language,  1st  edition 
1889;  "Theory  and  Calculation  of  Alter- 
nating Current  Phenomena,"  1st  edition 
1897,  4th  edition  1908;  "Theoretical  Ele- 
ments of  Electrical  Engineering,"  1st 
edition  1001,  3rd  edition  1909;  "General 
Lectures  on  Electrical  Engineering,"  1st 
edition  1908,  4th  edition  1910;  "Theory 
and  Calculation  of  Transient  Electric 
Phenomena  and  Oscillations,"  1909; 
"Radiation,  Light  and  Illumination," 
1909;  "Electrical  Engineering  Mathe- 
matics," 1st  edition  1910,  2nd  edition 
1914;  "Electric  Discharges,  Waves  and 
Impulses,"  191 1. 

In  1902  Dr.  Steinmetz  received  the 
honorary  A.  M.  degree  from  Harvard 
University,  and  in  1903  the  honorary 
Ph.  D.  degree  from  Union  University. 

Dr.  Steinmetz  is  president  of  the 
National  Association  of  Corporation 
Schools ;  vice-president  of  International 
Association  of  Municipal  Electricians ; 
honorary  president  of  International 
Electrical  Congress ;  past  president  of 
the  American  Institute  of  Electrical  En- 
gineers; honorary  member  of  the 
National  Electric  Light  Association; 
fellow  of  the  American  Association  for 
the  Advancement  of  Science ;  member 
of  the  (British)  Institution  of  Electrical 
Engineers;  members  of  the  American 
Mathematical  Society,  the  Quaternion 
Society,  the  Society  of  Mechanical  Engi- 
neers,   Electrochemical    Society,    Illumi- 


TRANSACTIONS    I.    E.    S.— PART   II 


nating  Engineering  Society,  Physical 
Society,  and  a  number  of  other  organi- 
zations. 

ALTEN  S.  MILLER 

Mr.  Alten  S.  Miller,  general  secretary- 
elect,  was  born  in  Richmond,  Va.,  in 
1868  and  graduated  from  Stevens  Insti- 
tute of  Technology  in  1888  with  the 
degree  of  mechanical  engineer. 

After  leaving  college  he  went  with 
the  United  Gas  Improvement  Company 
of  Philadelphia,  and  the  same  year  was 
sent  by  that  company  to  Omaha  to  take 
charge  of  its  gas  works  in  that  city.  In 
1892  he  was  sent  to  Chicago  as  western 
sales  agent  of  the  United  Gas  Improve- 
ment Company  and  spent  two  years  in 
that  position. 

In  1894  Mr.  Miller  went  to  New  York, 
as  engineer  of  the  East  River  Gas  Com- 
pany of  Long  Island  City.  This  com- 
pany was  then  running  a  tunnel  under 
the  East  River  and  building  a  plant  to 
make  gas  in  Long  Island  City,  which 
was  to  be  sold  in  New  York.  This 
company  was  later  consolidated  with 
one  of  the  New  York  companies,  form- 
ing the  New  Amsterdam  Gas  Company, 
and  Mr.  Miller  was  made  the  engineer 
of  the  latter.  While  holding  that  posi- 
tion he  was  made  constructing  engineer 
of  the  Consolidated  Gas  Company  of 
New  York  in  1900. 

In  1902  he  became  manager  of  the 
Consolidated  Gas  Company  of  Balti- 
more, Md.,  and  in  1905  was  made  vice- 
president  and  general  manager  of  the 
Consolidated  Gas,  Electric  Light  and 
Power  Company  of  that  city,  which  fur- 
nished all  the  gas  and  substantially  all 
the  electricity  to  the  city  and  vicinity. 
While  in  Baltimore  he  built  a  new  elec- 
tric generating  plant  to  replace  the  non- 
condensing  generating  plants,  and  also 
a  new  gas  plant  to  replace  three  other 


manufacturing  stations  that  had  become 
obsolete. 

In  1909  he  went  to  St.  Louis  as  presi- 
dent of  the  Union  Electric  Light  and 
Power  Company  of  that  city.  Here 
much  was  accomplished  in  reducing 
operating  expenses  and  in  gaining  for 
the  company  the  confidence  and  good 
will  of  the  public.  Much  time  was  also 
spent  in  valuing  the  property  and  in  the 
other  details  of  a  rate  case  before  the 
Public  Service  Commission. 

In  191 1  he  joined  Dr.  Alexander 
C.  Humphreys  in  the  company  of 
Humphreys  &  Miller,  Inc.,  of  New 
York,  N.  Y.  Since  then  he  has  confined 
his  work  to  consulting  engineering.  He 
has  made  a  special  study  of  valuations 
and  rate  cases  in  connection  with  public 
service  properties. 

Besides  being  a  member  of  the  Illumi- 
nating Engineering  Society,  Mr.  Miller 
is  a  fellow  of  the  American  Institute  of 
Electrical  Engineers  and  a  member  of 
the  National  Electric  Light  Association, 
American  Gas  Institute,  American 
Society  of  Mechanical  Engineers,  Natu- 
ral Gas  Association,  and  the  Society  of 
Gas  Lighting. 


Special  Transfer  to  Grade  of  Member. 

The  Council  at  its  meeting  held  June 
10,  1915,  approved  a  special  form  of 
application  to  be  used  by  Associate 
Members  in  applying  for  transfer  to  the 
grade  of  Member.  A  copy  of  the  form 
appears  on  a  following  page.  Associate 
members  desiring  to  apply  for  transfer 
may  fill  in  this  form  and  send  it  to  the 
general  offices  of  the  Society,  29  West 
39th  Street,  New  York,  N.  Y 

Under  the  amendments  to  the  Con- 
stitution which  were  adopted  at  the 
recent  annual  election,  all  members  of 
the  Society  passed  automatically  into  a 


TRANSACTIONS   I.    E.    S. — PART    II 


new  grade  of  associate  member,  except 
all  general  officers  of  the  Society  and 
members  of  the  general  Board  of  Ex- 
aminers. 

The  dues  of  members  shall  be  $10.00, 
and    the    dues    of    associate    members 


$5.00.  All  associate  members  trans- 
ferred to  the  grade  of  member  between 
June  10  and  October  1,  1915  shall  not  be 
required  to  pay  any  additional  dues  or 
fees  for  the  fiscal  year  ending  Septem- 
ber 30,  1915. 


TRANSACTIONS 

OF  THE 

Illuminating 
Engineering  Society 

NO.  5,  1915 
PART  II 

Miscellaneous  Notes 


TRANSACTIONS   I.    E.    S. — PART   II 


Council  Notes. 

A  meeting  of  the  Council  was  held 
June  10,  1915,  in  the  general  offices  of 
the  society,  29  West  39th  Street,  New 
York,  N.  Y.  Those  present  were  :  A.  S. 
McAllister,  president;  E.  M.  Alger, 
C.  O.  Bond,  H.  Calvert,  L.  B.  Marks, 
treasurer;  Alten  S.  Miller,  and  G.  H. 
Stickney. 

It  was  resolved  that  the  names  of  all 
those  members  owing  dues  for  periods 
prior  to  October  1,  1914,  be  dropped 
from  the  roll  forthwith. 

It  was  resolved  that  all  members 
(foreign  members  excepted  as  noted 
below)  owing  for  current  dues  be  noti- 
fied that  their  names  will  be  dropped 
from  our  roll,  in  accordance  with  the 
provisions  of  the  Constitution  and  By- 
laws, July  1  if  their  dues  are  not  paid 
in  the  meantime. 

It  was  further  resolved  that  the  names 
of  delinquent  members  whose  current 
dues  are  unpaid  on  July  1  be  dropped 
as  of  that  date.  Foreign  members  shall 
be  allowed  an  additional  60  days'  time ; 
their  names  to  be  dropped  September  1 
unless  their  dues  are  received  by  that 
date. 

A  report  on  New  York  Section  activi- 
ties was  received  from  Mr.  G.  H. 
Stickney. 

A  report  was  received  from  the  Com- 
mittee of  Tellers  giving  the  results  of 
the  annual  election  which  was  held  in 
May.  (The  results  were  published, 
in  accordance  with  a  Co'uncil  order,  in 
the  No.  4  issue  of  the  Transactions.) 

The  Committee  on  Constitutional  Re- 
vision submitted  (1)  a  temporary  trans- 
fer application  blank  to  be  used  by 
associate  members  in  applying  for  trans- 
fer to  the  grade  of  member  up  to  Jan- 
uary 1,  1916;  (2)  a  new  application  form 
to  be  used  by  all  applicants  in  applying 


for  either  the  grade  of  associate  member 
or  member. 

The  Council  directed  that  the  former 
application  be  published  in  the  No.  4 
issue  of  the  Transactions  and  that  a 
separate  blank  be  sent  to  each  member 
of  the  society  at  the  time  of  sending  one 
of  the  several  1915  convention  announce- 
ments. 

After  making  a  few  changes  in  the 
wording  of  the  membership  application 
form  submitted  by  the  committee,  it 
was  ordered  that  this  form  be  printed 
as  the  one  prescribed  by  the  Council, 
in  accordance  with  the  constitutional 
requirements. 

It  was  resolved  that  all  associate 
members  transferred  to  the  grade  of 
member  before  October  1,  1915,  shall 
not  be  required  to  pay  any  additional 
dues  for  the  fiscal  year  ending  Septem- 
ber 30,  1915. 

A  progress  report  was  received  from 
the  Membership  Committee. 

In  accordance  with  a  recommenda- 
tion of  the  committee,  the  Council 
authorized,  subject  to  the  approval  of 
the  Finance  Committee,  an  appropriation 
of  $50.00  for  another  edition  of  the 
pamphlet  on  the  work  and  objects  of 
the  society. 

In  accordance  with  a  recommenda- 
tion of  the  Finance  Committee  payment 
of  vouchers  No.  2096,  and  No.  2130  to 
No.  2166  aggregating  $1,109.58  was 
authorized.  The  Finance  Committee 
submitted  a  report  showing  that  the 
total  receipts  from  all  sources  during 
the  first  eight  months  amounted  to 
$10,367.28,  while  the  total  cash  disburse- 
ments amounted  to  $9,620.97. 

In  a  report  on  the  program  of  papers 
for  the  forthcoming  convention  of  the 
society  in  Washington,  the  Committee 
on  Papers  stated  that  it  had  an  unusually 
large  number  of  excellent  papers  under 


TRANSACTIONS   I.  E.  S. — PART    II 


consideration.  The  number  of  papers 
of  a  commercial  character  scheduled  for 
this  year's  program  will  in  all  probability 
necessitate  separate  sessions  for  them 
on  two  of  the  four  days  of  the  con- 
vention. 

The  Committee  on  Lighting  Legisla- 
tion reported  that  it  expected  to  submit 
during  the  summer  a  final  proof  of  a 
code  on  factory  lighting.  Copies  of  the 
code  are  to  be  available  for  distribution 
at  the  convention. 

A  progress  report  was  received  from 
the  Committee  on  Popular  Lectures  and 
accepted  with  thanks. 


Section  Activities. 

Chicago  Section 
June  22,  19 15.  Auditorium,  Western 
Society  of  Engineers,  Monadnock  Build- 
ing. Prof.  Edw.  L.  Nichols  of  Cornell 
University  gave  a  most  interesting  his- 
torical talk  on  the  subject  of  "Artificial 
Lighting  in  1900  and  1915,"  which  was 
a  resume  of  the  progress  made  in 
illumination  up  to  1915.  An  interesting 
and  lively  discussion  followed  the  pres- 
entation of  the  paper.  Mr.  W.  A. 
Durgin  then  announced  the  incoming 
officers  for  the  next  year  and  adjourned 
the  meeting.  An  enjoyable  dinner  was 
held  previous  to  the  meeting  at  the 
Grand  Pacific  Hotel. 

New  York  Section 
June  14,  1915.  Brevoort  Hotel,  5th 
Avenue  and  8th  Street,  New  York  City. 
Short  talks  on  "What  the  Other  Fellow 
Knows  about  Lighting  Requirements" 
were  given  by  Messrs.  Charles  W. 
Leavitt,  landscape  architect ;  Robert  I. 
Aitken,  sculptor ;  Harry  Rowe  Shelly, 
musician ;  E.  J.  Simmons,  mural  painter, 
and  Horace  Moran,  architect.  Forty- 
eight  members  and  guests  were  present. 


Pittsburgh  Section 
The  final  meeting  of  the  year,  held 
June  11,  1915,  included  an  inspection 
trip  to  several  factories  of  the  United 
States  Glass  Company  and  a  dinner. 
The  members  and  guests  met  at  the 
offices  of  the  glass  company  at  8.00  p.  m. 
and  an  exceptionally  interesting  trip  was 
made  through  departments  where  the 
pressing  and  blowing  of  glass  was  being 
carried  on.  At  10  o'clock  a  special  car 
transferred  the  party  to  the  Fort  Pitt 
Hotel,  Dutch  room,  and  there  followed 
a  dinner  with  several  unique  features. 
Souvenir  drinking  tumblers,  etched  with 
the  society  monogram  and  an  appro- 
priate legend,  were  given  to  those  pres- 
ent. Addresses  were  made  by  members 
of  the  retiring  and  incoming  boards  of 
managers. 


Personals. 


Mr.  L.  B.  Eichengreen  has  resigned 
as  secretary  of  the  Philadelphia  Section. 
Mr.  R.  B.  Ely  has  been  appointed  to 
succeed  Mr.  Eichengreen. 

Mr.  E.  W.  Lloyd  of  the  Chicago  Edi- 
son Company  has  been  elected  president 
of  the  National  Electric  Light  Associa- 
tion for  the  coming  year. 

Mr.  Frederick  Schwartz,  for  the  past 
sixteen  years  with  Shapiro  &  Aronson, 
and  until  recently  their  store  manager, 
has  resigned  to  become  treasurer  and 
member  of  the  recently  incorporated 
concern  of  Robert  Findlay  Manufac- 
turing Co.,  designers  and  manufacturers 
of  lighting  fixtures.  Mr.  Schwartz  will 
be  in  immediate  charge  of  the  New 
York  City  salesrooms. 

Prof.  D.  W.  Blakeslee  has  resigned 
his  position  as  assistant  professor  of 
electrical  engineering  in  the  University 
of  Arkansas  and  is  now  in  the  engineer- 


TRANSACTIONS    I.    E.    S.  —  PART    II 


ing   department    of    the    Carnegie    Steel 
Company,  Farrell,  Pa. 

Mr.  S.  E.  Shaff,  formerly  connected 
with  the  University  at  Iowa  City,  is  now 
with  the  Electric  Machinery  Company, 
Minneapolis,  Minn. 


Obituary. 


Mr.  James  P.  Maila,  chief  electrician 
for  Armour  &  Company.  Chicago,  died 
on  May  29,  as  the  result  of  an  operation 
for  appendicitis.  He  had  been  with 
Armour  &  Company  for  29  years  and 
since  1894  had  been  chief  electrician. 
He  had  charge  of  the  electrical  work 
in  all  of  the  company's  plants.  He  was 
a  member  of  the  Jovian  Order,  of  the 
Illuminating  Engineering  Society,  and 
of  the  Electric  Club  of  Chicago. 


New  Members. 

The   following  seven   applicants   were 

elected    members    of    the    society    at    a 

meeting   of   the   Council   held   June    10, 

1915: 

Houghton,  C.  P. 

Second  Vice-president,  Los  Angeles 
Gas  &  Electric  Corporation,  645  S. 
Hill.  St.,  Los  Angeles,  Cal. 

Humphry,  George  William 

Illuminating  Engineer,  Armstrong, 
Whitworth,  Ltd.,  4  Cottenham  St., 
Newcastle-on-Tyne,   England. 

Jellett,  Stewart  A. 

Consulting  Engineer,  1718  Real  Es- 
tate Trust  Bldg.,    Philadelphia,    Pa. 

Kirk,  James  J. 

Illuminating  Engineer,  Common- 
wealth Edison  Co.,  72  W.  Adams 
St.,  Chicago,  111. 

Swayne,  H.  B. 

General  Contract  Agent,  Penn  Cen- 
tral Light  &  Power  Co.,  1414  Elev- 
enth Ave.,  Altoona,  Pa. 


Van  Winkle,  Frank  D. 

Treasurer,  The  Post  Glover  Elec- 
tric Co.,  314  W.  Fourth  St.,  Cincin- 
nati, Ohio. 

Wilson,  Frank  S. 

Electrical  Engineer,  8  Irvington  St., 
Boston,  Mass. 


Sustaining  Members. 

The  Portland  (Me.)  Gas  Light  Com- 
pany and  the  Providence  (R.  I.)  Gas 
Company  were  elected  sustaining  mem- 
bers at  a  meeting  of  the  Council  held 
June  10,  1915. 


Program  of  1915  Convention. 

Following  is  a  draft  of  the  prelimi- 
nary program  of  the  ninth  annual  con- 
vention of  the  Illuminating  Engineering 
Society  which  is  to  be  held  at  the  New 
Willard  Hotel,  Washington,  D.  C,  Sep- 
tember 20-23  inclusive.  The  papers, 
which  promise  to  be  of  an  unusually 
high  standard,  are  to  be  distributed  over 
ten  sessions.  One  of  the  sessions  will 
be  devoted  especially  to  the  subject  of 
street  lighting ;  commercial,  general,  and 
laboratory  papers  will  each  be  given 
three  sessions.  Inspection  trips,  a  recep- 
tion, and  a  banquet  are  among  the  enter- 
tainment features. 

PROGRAM. 
Sept.   20 — (Morning). 
Formal  opening  of  convention. 
Address    of    Welcome;    President's    ad- 
dress, etc. 
Reports  of  Committees  on  Lighting  Leg- 
islation,   Nomenclature    and    Stand- 
ards, and  Progress. 

Sept.  20 — (Afternoon). 
General  Session. 
Tests    and    Experiments    in    Connection 
with  the  New  Commonwealth  Edi- 


TRANSACTIONS    I.    E.    S. — PART    II 


son  Company  Building,  by   Messrs. 

W.  A.  Durgin  and  J.  B.  Jackson. 
Ship  Lighting,  by  H.  A.  Hornor. 
Illumination    Efficiency   as    Obtained    in 

an    Experimental    Room,    by    Ward 

Harrison. 

Sept.  20 — (Evening). 
Reception. 

Sept.  21 — (Morning). 

General  Session. 

Photometry  with   Portable  Instruments, 

by  W.  F.  Little. 
New  Test   Plate   for  Illumination   Pho- 
tometers, by  C.  H.  Sharp. 
Incandescent    Lamp    Testing    and    Pho- 
tometry, by  G.  W.  Middlekauff. 
Street  Lighting,  by  F.  A.  Vaughn. 

Sept.  21 — (Afternoon). 
Entertainment,  trips. 

Sept.  21 — (Evening). 
Street  Lighting  Session. 

Gas  Street  Lighting.  (Author  not  yet 
announced.) 

Arc  Lamps  for  Street  Illumination,  by 
H.  E.  Clifford. 

New  Types  of  Incandescent  Lamps  and 
Their  Relation  to  the  Street  Light- 
ing Problems,  by  W.  H.  Rolinson. 

Ornamental  Street  Lighting,  by  T.  I. 
Jones. 

Sept.  22 — (Morning). 
Commercial  Session. 

How  to  Attack  a  Lighting  Problem,  by 
W.  R.  Moulton. 

How  can  a  Combination  Gas  and  Elec- 
tric Company  Render  the  Best  Ser- 
vices to  Customers  ?  by  Messrs.  S.  B. 
Burrows  and  N.  H.  Potter. 

Small  Incandescent  Lamps  and  Special 
Illumination  Problems,  by  R.  P. 
Burrows. 

Lighting  of  Office  Buildings,  by  A.  O. 
Dicker. 


Laboratory  Session. 

Crova's  Method  of  Colored  Light  Pho- 
tometry Applied  to  Modern  Incan- 
descent Illuminants,  by  Messrs.  H. 
E.  Ives  and  E.  F.  Kingsbury. 

Differences  in  Threshold  and  Acuity 
Variations,  by  P.  W.  Cobb. 

Visual  Efficiency,  by  Messrs.  Richtmyer 
and  Howes. 

Yellow  Screens,  by  M.  Luckiesh. 

Sept.  22 — (Afternoon). 
Commercial  Session. 

The  Flame  Pilot  Ignition  of  Incandes- 
cent Gas  Lamps,  by  C.  W.  Jordan. 

Practical  Illumination  as  Exemplified  by 
Some  Recent  Installations  of  Incan- 
descent Gas  Lamps,  by  R.  F.  Pierce. 

Mercury  Arc  Lamps  for  Industrial 
Lighting,  by  W.   A  D.  Evans. 

Relation  between  Proper  Illumination 
and  Accident  Prevention,  by  R.  E. 
Simpson. 

Laboratory  Session. 
Retinal  Sensibilities  in  Relation  to  Illu- 
minating    Engineering,     by     P.     G. 
Xutting. 

The  Effect  of  Distribution  of  Light  on 
Muscular  Control,  by  H.  M.  John- 
son. 

Effect  of  Various  Wave-lengths  of 
Radiation  on  Eye  Cataract,  by  W.  E. 
Berge. 

Sept.  23 — (Morning). 
Commercial  Session. 

Artificial  Illumination  of  Interiors,  by 
David  Crownfield. 

Lighting  of  State,  War  and  Navy  Build- 
ings, by  W.  E.  Chapman. 

Lighting  of  Gymnasiums  and  Armories 
with  Incandescent  Lamps,  by  Messrs. 
A.  L.  Powell  and  A.  B.  Oday. 


TRANSACTIONS   I.    E.    S.—  PART   II 


Laboratory  Session. 

The  Effect  of  Surrounding  Gas  on  an 
Incandescent  Filament,  by  C.  F. 
Lorenz. 

The  Parabolic  Mirror,  by  F.  A.  Ben- 
ford,  Jr. 

A  paper  (subject  to  be  announced  later) 
by  C.  E.  Ferree. 

Sept.  23 — (Afternoon). 
General  Session. 

Artificial  Illumination  in  Practical  Pho- 
tography, by  C.  E.  K.  Mees. 

Photographic  and  Visual  Illumination 
Efficiencies,  by  L.  A.  Jones. 

Production  and  Application  of  Ultra- 
Violet  Light,  by  M.  Von  Reckling- 
hausen. 

A  Flux  Method  of  Obtaining  Average 
Illumination,  by  Messrs.  T.  A.  Ben- 
ford  and  H.  E.  Mahan. 
Information  regarding  the  convention 

may  be  had  upon  application  to  the  gen- 
eral office  of  the  society,  29  West  39th 

Street,  New  York. 


International  Gas  Congress. 

The   International   Gas   Congress   will 


be  held  in  San  Francisco  during  the 
week  of  September  27  to  October  3. 
Details  regarding  special  trains  for  dele- 
gates, hotel  accommodations,  papers, 
etc.,  may  be  had  upon  application  to 
Mr.  George  G.  Ramsdell,  29  West  39th 
Street,  New  York,  N.  Y.  The  fee  of 
the  congress  is  $5.00,  which  entitles  the 
member  to  a  copy  of  the  published 
proceedings. 

Among  the  features  of  particular 
interest  to  gas  men  at  the  Panama- 
Pacific  Exposition  are  the  special  instal- 
lations of  gas  lighting,  and  the  gas 
exhibit.  There  are  several  miles  of 
high  pressure  gas  lighting.  The  "Joy 
Zone"  of  the  exposition  is  illuminated 
by  gas  lamps  concealed  in  ornamental 
lanterns.  In  the  Court  of  Abundance 
there  are  gas  fountains  with  serpents 
hissing  streams  of  lighted  gas.  The 
effect  is  both  unique  and  charming. 
The  gas  exhibit  in  the  Palace  of  Manu- 
factures covers  a  floor  space  of  10,000 
square  feet  and  includes  a  variety  of 
interesting  displays  having  to  do  with 
the  manufacture,  distribution  and  use 
of  gas. 


TRANSACTIONS 


OF  THE 


Illuminating 
Engineering  Society 

NO.  6,  1915 
PART  II 

Miscellaneous  Notes 


TRANSACTIONS   I.    E.    S. — PART   II 


Washingto*  C« 


itioa  Papers. 


Below  is  a  condensed  outline  of  the 
papers  and  reports  to  be  presented  at 
the  ninth  annual  convention  of  the 
Illuminating  Engineering  Society,  to  be 
held  at  the  New  Willard  Hotel,  Wash- 
ington, D.  C,  September  20-23,  1915. 
The  summarized  statements  indicate  that 
the  papers  are  replete  with  new  and 
valuable  information  on  practically  every 
phase  of  lighting.  Many  of  the  papers 
cover  extensive  special  investigations 
conducted  by  authorities  of  high  stand- 
ing. For  the  commercial  man  or  the 
solicitor  who  is  interested  chiefly  in  sell- 
ing more  and  better  lighting  service 
there  are  a  number  of  especially  inter- 
esting contributions.  Advance  copies  of 
practically  all  the  papers  and  reports 
will  be  available  for  distribution  by 
September  18  at  the  general  office  of 
the  society,  29  West  39th  Street,  New 
York,  N.  Y. 

Papers  and  Reports. 

1 — Report  of  Committee  on  Nomencla- 
ture and  Standards. 
An  annual  report  containing  new 
terminology,   definitions,   symbols, 
etc. 
2 — Report  of  the  Committee  on  Light- 
ing Legislation. 
A  comprehensive  statement  of  the 
status  on  lighting  legislation;  in- 
cludes  a  code  on  lighting   which 
was  drafted  by  the  committee. 
3 — Report   of   the   Committee    on    Re- 
search. 
Includes   results   of   an   extended 
investigation  of  the  various  meth- 
ods   of    heterochromatic    photom- 
etry. 
4 — Report  of  the  Committee  on  Prog- 
ress. 
Reviews  the   features  of   fighting 


progress  during  the  last  year.  For 
the  most  part  the  report,  which  is 
rather  a  long  one,  is  a  summary 
of  published  matter ;  but  it  also 
contains  much  valuable  informa- 
tion not  heretofore  on  general 
record. 

5 — Lighting  of  Ships,  by  H.  A.  Hornor. 
The  requirements  of  ship  and 
marine  lighting  are  set  forth ; 
methods  of  wiring  and  details  of 
fixtures  are  discussed. 

6 — Lighting  of  a  Passenger  Steamer, 
by  H.  F.  Spaulding. 
Sketches  past  and  present  prac- 
tise in  marine  lighting.  Lighting 
requirements  of  a  passenger  boat 
are  discussed  and  compared  with 
similar  installations  ashore.  De- 
scribes the  lighting  system  on  the 
S.  S.  Noronic,  a  lake  passenger 
boat,  and  includes  illumination 
test  data. 

7 — Life  Testing  of  Incandescent  Lamps 
at  the  Bureau  of   Standards, 
by  G.  W.  Middlekauff,  J.  F. 
Skogland,  and  B.  Mulligan. 
Outlines    the    methods    of    tests 
and   inspections    followed   by   the 
United   States   Bureau  of   Stand- 
ards, and  includes  a  description  of 
laboratory  equipment. 

8 — Use  of  Portable  Photometers,  by 
W.  F.  Little. 
Outlines  desirable  procedure  in 
the  conduct  of  photometric  tests 
with  portable  apparatus.  Dis- 
cusses the  planning  of  a  survey, 
and  precautions  which  should  be 
taken;  a  method  of  testing  can- 
dlepower,  illumination  intensity 
and  brightness ;  maintenance  of 
photometric  apparatus ;  photo- 
metric errors  and  means  of  avoid- 
ing them. 


TRANSACTIONS   I.  E.  S. — PART   II 


9— Compensating  Illuminating  Test- 
Plates,  by  C.  H.  Sharp. 
A  discussion  of  the  various  errors 
inherent  in  illumination  test-plates 
in  use  and  a  description  of  a  new 
form  of  construction  which  has 
been  devised  to  eliminate  those 
errors. 

io— Illumination  Efficiencies  as  Deter- 
mined in  an  Experimental 
Room,  by  Ward  Harrison  and 
Earl  A.  Anderson. 
A  report  on  a  series  of  illumina- 
tion tests  performed  in  a  portable 
room  designed  for  the  purpose. 
The  room  dimensions  and  the 
arrangement  of  the  outlets  were 
varied  to  approximate  the  diverse 
conditions  encountered  in  prac- 
tise. Wall,  ceiling  and  floor  com 
binations  of  white,  black  and  inter- 
mediate colors  were  tested  with 
units  of  three  general  types  of 
light  distribution. 

ii— Semi-direct   Office    Lighting   of    the 
Chicago  Edison   Building,   by 
W.    A.    Durgin     and     J.    B. 
Jackson. 
Gives   a   description   of   a   typical 
office  and  comparative  tests  on  five 
lighting  systems,  showing  the  rela- 
tive  eye   fatigue,   glare,   shadows, 
etc.    Data  are  given  on  the  illumi- 
nating   effectiveness,    appearance, 
dust  factor,  etc.,  for  the  complete 
installation. 

12— Street  Lighting  with  Gas  Lamps,  by 
Geo.  S.  Barrows. 
A    discussion    of    modern    street 
lighting  with  gas. 

13— Arc  Lamps  for  Street  Illumination, 
by  H.  E.  Clifford. 
Outlines  recent  developments  and 
characteristics    of    arc    lamps    de- 
signed for  street  illumination. 


14 — New  Types  of  Incandescent  Lamps 
and  Their  Relation  to  Street 
Lighting  Problems,  by  W.  H. 
Rolinson. 
A  brief  historical  review  and  con- 
sideration    of     the     fundamental 
requisites  of  street  lighting;  vari- 
ous systems  are  classified  accord- 
ing  to    unit    and    location.      The 
choice   of   illuminants,   means    of 
regulation  and  general  equipment 
are  also  discussed.     Special  atten- 
tion is  given  to  the  recent  develop- 
ments    in     electric     incandescent 
lamps  for  street  lighting. 

15 — Application  of  Principles  of  Scien- 
tific Street  Lighting,  by  F.  A. 
Vaughn. 
A  comprehensive  statement  of  the 
requirements  of  street  lighting 
based  upon  a  special  investigation 
conducted  in  Milwaukee,  Wis. 

16 — How   Can  a  Combination   Gas  and 
Electric  Company  Render  the 
Best  Service  to  the  Customer? 
by  A.  B.  Spaulding  and  H.  N. 
Potter. 
Deals  with  the  question  of  proper 
service  to  the  customer;  the  edu- 
cation of   salesmen  and  the  cus- 
tomer;  the   relation   between   the 
salesman  and  the   customer ;   and 
the  question  whether  the  sale  of 
gas      and      electric      illumination 
should  be  handled  on  a  competi- 
tive basis  or  by  combination  men. 

17 — The  Selection  of  a  Standard  Unit 
for  Lighting,  by  W.  H.  Moul- 
ton. 
Discusses  the  problem  of  selecting 
a  new  style  of  standard  fixture 
for  commercial  work.  Features 
of  various  lighting  units  are  out- 
lined. 


TRANSACTIONS   I.    E.    S.      PART   II 


18 — Small      Incandescent      Lamps      and 
Special  Illumination  Problems, 
by  R.  P.  Burrows. 
Deals   with   improvements   in    the 
manufacture    of    small    incandes- 
cent lamps  for  novelties  and  the 
industrial  and   medical   fields.     A 
number  of  the  present  applications 
of  these  lamps  are  mentioned. 
19 — Illumination  and  One  Year's   Acci- 
dents, by  R.  E.  Simpson. 
Gives   results   of   a  study  of   one 
year's  industrial  accident  records, 
the  purpose  of  which  was  to  deter- 
mine   the    effect    of    the    lighting 
conditions    on    the    causation    of 
accidents.      Typical   accidents    are 
mentioned  to   show   how   lighting 
conditions   have   been    responsible 
for  injuries  to  workmen. 
20 — The  Application  of  Crova's  Method 
of  Colored  Light  Photometry 
to  Modern  Incandescent  Illu- 
minants,    by   H.    E.    Ives   and 
R.  F.  Kingsbury. 
Discussion  of  the  advantages  and 
.  requirements    of    Crova's    method 
for   overcoming   color   differences 
in  heterochromatic  photometry. 
21 — The     Relative      Photographic     and 
Visual    Efficiencies    of    Light 
Sources,  by  L.  A.  Jones,  M.  B. 
Hodgsen   and   Kenneth    Russ. 
Sets    forth    the    relation    between 
the   visual   and   photographic   effi- 
ciencies      of       various       lighting 
sources.     Methods   for  the  deter- 
mination   of    these    relations    are 
outlined.    A  large  amount  of  data 
is  included  to  show  the  relations 
between  several  sources  and  three 
types  of  photographic  plates. 
22— A  Method  for  Studying  the  Behav- 
ior of  the  Eye  Under  Differ- 
ent   Conditions    of    Illumina- 
tion, by  F.  K.  Richtmyer  and 
H.  L.  Howes. 


Describes    a   method    of    studying 
visual  efficiency  which  gives  indi- 
cations of  being  well  adapted  to 
quantitative  measurements  of  the 
manner  in  which  different  condi- 
tions   of    illumination    affect    the 
working  eye.     Several  curves  are 
included  to  show  the  resemblances 
and    differences    in    the    rates    of 
reading  various  matter  by  several 
observers.    Other  curves  show  the 
effects  produced  by  placing  frosted 
and  unfrosted  lamps  in  the  field 
of  vision. 
23 — The  Flame  Pilot  Ignition  of  Incan- 
descent Gas  Lamps,  by  C.  W. 
Jordan. 
Features,     advantages,     and     the 
application  of  various  methods  and 
systems  of  pilot  ignition  are  dis- 
cussed. 
24 — Practical    Illumination   as   Exempli- 
fied by  Some  Recent  Installa- 
tions    of     Incandescent     Gas 
Lamps,  by  R.  F.  Pierce. 
A    report   on   the   various    recent 
installations  of  gas  lamps. 
25 — Mercury-vapor    Lamps    for    Indus- 
trial  Lighting,   by   W.   A.   D. 
Evans. 
Outlines  the  lighting  requirements 
of  various  industries,  special  ref- 
erence being  made  to  the  applica- 
tion of  the  mercury-vapor  lamp. 
26 — The  Retinal  Sensibilities  Related  to 
Illuminating    Engineering,    by 
P.  G.  Nutting. 
Points  out  the  retinal  sensibilities 
of  importance  in  illuminating  en- 
gineering,   such    as    sensibility   to 
brightness    and   brightness   differ- 
ences   and    to    color    and    color 
differences.       The     inter-relations 
of  these  sensibilities  are  outlined 
and  methods  given  for  their  quan- 
titative   determination.     The   best 
data  on  each  sensibility,  including 


TRANSACTIONS   I.    E.    S. — PART   II 


much  that  is  new,  are  summarized 
in  each  case. 
27 — Vision  and  Brightness  of  Surround- 
ings, by  P.  W.  Cobb. 
Outlines  the  results  of  an  investi- 
gation of  visual  acuity  and  differ- 
ence-threshold.      Describes     new 
apparatus  and  methods  used. 
28 — A  Flux  Method  of  Obtaining  Aver- 
age Illumination. 
Describes  a  method  of  obtaining 
the   average    illumination    from   a 
lighting   installation   on   the   basis 
of    the    total    flux    generated    by 
the     light     sources.       The     lower 
hemisphere  surrounding  the  light- 
ing unit   is    divided   in   three   300 
zones,  and  the  lighting  unit  classi- 
fied  according   to   the   percentage 
of  flux  delivered  in  these  zones. 
Having     determined     the     proper 
classification  for  any  lighting  unit 
by  means  of  one  or  more  of  the 
graphic     charts     shown,     one     is 
enabled  to  calculate  the  flux  inci- 
dent  on  the   floor  area   for  each 
unit  and  by  adding  these  together 
determine  the  flux  over  the  entire 
floor  space. 
29 — Artificial   Illumination  of   Architec- 
tural     Interiors,      by      David 
Crownfield. 
Deals    with   the    lighting   require- 
ments of  large  interiors  of  differ- 
ent architectural  styles  and  classes. 
30 — Artificial  Lighting  of  Typical  Offices 
in  the  State,  War,  and  Navy 
Department   Building,   by   W. 
E.  Chapman. 
Gives   a   brief   description   of   the 
lighting    conditions    in    a    typical 
office  of  this  building,  which  was 
erected     in     1886.       The     present 
lighting   requirements,   and   a   de- 
scription of  the  latest  remodelled 
installation     employing     tungsten 
lamps  are  given. 


31 — Lighting  in  Downtown  Office  Build- 
ings, by  A.  O.  Dicker  and  J.  J. 
Kirk. 
Contains  a  description  of  typical 
downtown   office  buildings   in  the 
city  of  Chicago,  representative  of 
periods    thirty,    twenty,    fourteen 
and  six  years  ago.     The  lighting 
in    these    buildings    is    contrasted 
with  an  installation  in  a  recently 
completed    building    in    the    same 
district. 
32 — Present  Practise  in  the  Lighting  of 
Armories     and     Gymnasiums 
with        Tungsten        Filament 
Lamps,  by  A.   L.  Powell  and 
A.  B.  Oday. 
Gives     descriptions     and     tabular 
tabular   data   on   the   lighting   re- 
quirements of  numerous  armories 
and  gymnasiums. 
33 — Ultra-violet  Light  and  the  Eye,  by 
W.  R.  Burge. 
An     investigation     to     determine 
which  wave-lengths  in  the  ultra- 
violet region  of  the  spectrum  are 
harmful  to  living  tissue,  and  the 
mode    of    action    of    these    wave- 
lengths in  producing  injury. 
34 — Production      and      Application      of 
Ultra-violet  Rays,  by  M.  von 
Recklinghausen. 
A  brief  description  of  the  differ- 
ent   sources    of    ultra-violet    rays. 
Includes    a    short    description    of 
the  salient  features  of  the  system 
of  sterilization  of  water  by  ultra- 
violet  rays,    and    several   pictures 
of  recent  plants. 
35 — The    Parabolic    Mirror,    by    F.    A. 
Benford. 
Directs  attention  to  the  increasing 
importance  of  parabolic  reflectors 
for    the    projection    of    light    for 
military  and  naval  service,  trans- 
portation, flood  lighting  and  spec- 
tacular illumination.  For  the  most 


TRANSACTIONS    I.    E.    S.  —  PART   II 


part  a  mathematical  treatment  of 
the     reflector     used     with     point, 
spherical  and  disk  sources.     Prob- 
ably the  most  complete  treatment 
of  the  theory  of  the  reflector  that 
has  thus  far  been  presented. 
36 — Some  Experiments  on  the  Eye  with 
Inverted  Reflectors  of  Differ- 
ent Densities,  by  C.  E.  Ferree 
and  G.  Rand. 
The  fourth  of  a  series  of  papers 
in  which  the  effect  of  the  various 
conditions  of  lighting  on  the  eye 
is  investigated.    Gradation  of  sur- 
face brightness  is  made  the  chief 
variable.       Semi-direct     reflectors 
of    six    degrees    of    density    are 
employed     and    a    correlation     is 
made     between     the     illuminating 
effects  obtained  and  the  tendency 
to  cause  loss   of  visual  efficiency 
and  to  produce  ocular  discomfort. 
2,7 — The  Effect  of  Variation  of  Atmos- 
pheric Pressure  on  the   Can- 
dlepower  of  Flames,  by  E.  B. 
Rosa.    E.    C.    Crittenden    and 
A.  H.  Taylor. 
A    summary    of    an    investigation 
conducted    at    the    United    States 
Bureau  of  Standards. 
38 — Yellow  Light,  by  M.  Luckiesh. 

Knowns  and  unknowns  and  the 
various  opinions  regarding  yellow 
light  are  briefly  discussed  with 
respect  to  visual  acuity,  glare, 
fatigue,  penetrating  power,  and 
esthetic  value.  Outlines  the  pro- 
cedure involved  in  altering  the 
light  from  tungsten  lamps  to 
match  a  light  from  the  kerosene 
flame  or  the  old  carbon  incan- 
descent lamp. 
39 — Artificial  Illuminants  for  Use  in 
Practical  Photography,  by 
C.  E.  K.  Mees. 
Illuminants  differ  in  efficiency, 
quality,  size  of  source,  consistency 


and  flicker.  Tables  are  given 
showing  a  classification  of  illumi- 
nants according  to  these  charac- 
teristics when  they  are  to  be  used 
with  each  of  three  classes  of  sen- 
sitive photographic  materials : 
those  sensitized  to  the  whole 
spectrum,  those  with  their  sensi- 
tiveness in  the  blue  violet,  and 
those  sensitive  only  to  the  ultra- 
violet. Another  table  shows  a 
classification  of  various  available 
artificial  light  sources  according 
to  the  photographic  operations 
for  which  they  are  suitable. 


Personals. 


Prof.  W.  S.  Franklin  has  resigned  as 
professor  of  physics  at  the  Lehigh  Uni- 
versity, Bethlehem,  Pa.,  with  which  he 
had  been  associated  since  1897.  He  is 
now  planning  an  extensive  lecture  tour 
of  American  universities  and  engineer- 
ing schools. 

Alfred  O.  Dicker,  who  for  the  greater 
part  of  the  last  six  years  has  been  con- 
nected with  the  illuminating  engineering 
division  of  the  contract  department  of 
the  Commonwealth  Edison  Company, 
Chicago,  has  organized  with  two  asso- 
ciates the  Electrical  Sales  Engineers, 
Inc.,  with  offices  at  19  South  Fifth  Ave- 
nue, Chicago. 

Robert  S.  Orr,  who  is  general  mana- 
ger of  the  Duquesne  Light  Company, 
Pittsburgh,  Pa.,  was  elected  fourth  vice- 
president  of  the  National  Electric  Light 
Association  at  its  convention  at  San 
Francisco  in  June. 

Mr.  Walter  Neumuller.  who  for  the 
past  five  years  has  been  assistant  secre- 
tary of  the  Association  of  Edison  Illu- 
minating Companies,  has  been  appointed 
special  representative  of  the  New  York 
Edison  Company.    He  is  also  a  director, 


TRANSACTIONS   I.    E.    S. — PART   II 


treasurer  and  assistant  secretary  of  the 
Electrical  Show  Company,  director  and 
treasurer  of  the  New  York  Electric 
Vehicle  Association,  and  director  and 
member  of  the  executive  committee  of 
the  Electrical  Refrigerating  Company. 

Mr.  Joseph  D.  Israel,  district  manager 
for  the  Philadelphia  Electric  Company, 
was  elected  recently  to  serve  as  chair- 
man of  next  year's  convention  of  the 
sales  managers  of  Edison  illuminating 
companies. 

Dr.  A.  S.  McAllister,  president  of  the 
Illuminating  Engineering  Society,  re- 
signed the  editorship  of  the  Electrical 
World,  August  I,  1915. 


New  Book*. 

Standard  Handbook  for  Electrical 
Engineers,  compiled  by  Frank  F.  Fowle 
and  a  staff  of  specialists;  1984  pp.,  $5.00; 
McGraw-Hill  Book  Company,  Inc.,  239 
West  39th  Street,  New  York,  N.  Y. 
Contains  chapters  on  the  following  top- 
ics :  illumination ;  units,  conversion  fac- 
tors and  tables ;  electric  and  magnetic 
circuits ;  measurements  and  measuring 
apparatus ;  properties  of  materials ; 
magnets,  induction  coils,  condensers 
and  resistors ;  transformers  and  recti- 
fiers ;  alternating-current  generators  and 
motors ;  direct-current  generators  and 
motors ;  converters  and  double-current 
generators ;  power  plants ;  power  trans- 


mission; distribution  systems;  interior 
wiring;  industrial  motor  applications; 
electric  railways ;  electric  commercial 
vehicles  ;  electric  ship  propulsion ;  elec- 
trochemistry;  batteries;  telephony,  teleg- 
raphy and  radiotelegraphy ;  miscella- 
neous applications  of  electricity;  me- 
chanical section;  standardization  rules 
of  the  American  Institute  of  Electrical 
Engineers ;  general  engineering  econo- 
mics and  central  station  economics. 

The  chapter  on  Illumination  deals 
with  production  of  light,  incandescent 
lamps,  carbon  filament,  metallized  carbon 
filament,  tantalum,  tungsten,  gas-filled 
type ;  arc  lamp  characteristics,  carbon- 
electrode,  flame  arc,  metallic  electrode, 
tube  lamps,  lighting  accessories,  reflec- 
tors, indirect  and  semi-indirect  lighting; 
illumination  calculations,  flux,  candle- 
power,  intensity,  brightness,  efficiency ; 
applied  illumination,  fundamentals  of 
vision,  characteristics  of  illumination, 
physiological  and  psychological  effects, 
methods,  design,  costs ;  photometry, 
fundamentals,  standards,  apparatus, 
spectrophotometers,  colorimeters,  and 
testing. 


Section  Notes. 

The  programs  of  meetings  and  papers 
of  the  several  sections  of  the  society 
for  the  coming  season  will  be  announced 
in  the  next  issue  of  the  Transactions. 


TRANSACTIONS 

OF  THE 

Illuminating 
Engineering  Society 

NO.  7,  1915 
PART  II 

Miscellaneous  Notes 


TRANSACTIONS   I.    E.    S. — PART   II 


Section  Notes. 

New  York  Section 
Meetings 

October  14,  1915.  Engineering  So- 
cieties Building.  Papers:  (1)  "Illumi- 
nation in  the  Navy,"  by  Lieut.  C.  S. 
McDowell  of  the  Brooklyn  Navy  Yard; 
(2)  "Illumination  in  the  Army,"  by 
Capt.  Edward  D.  Ardery,  Corps  of  Engi- 
neers, U.  S.  Army.     Attendance  85. 

The  following  tentative  program  for 
the  rest  of  the  year  has  been  announced : 

November — A  joint  meeting  with 
the  American  Electro-chemical  Society. 
Papers  on  luminous  gases  by  Messrs. 
D.  McFarlan  Moore  and  Walter  V. 
Cady. 

December — A  paper  on  stage  lighting. 

January — A  paper  on  lighting  trans- 
mission and  optical  instruments  by  Dr. 
F.  L.  G.  Kollmorgen;  and  a  paper  on 
projector  lamps. 

February — Joint  meeting  with  the 
American  Society  of  Mechanical  Engi- 
neers. Mr.  C.  E.  Clewell  will  present  a 
paper  on  the  factory  lighting  code  of 
the  Illuminating  Engineering  Society. 

March — A  lecture  on  illuminating 
engineering  by  Dr.  Charles  P.  Steinmetz. 

April — Papers  on  gas  subjects. 

May — Papers  on  street  lighting. 

June — Fine  arts  meeting. 

Philadelphia  Section 
The  following  program  of  the  Phila- 
delphia Section  has  been  announced : 

October  15 — "Opportunities  in  the 
Lighting  Field,"  by  Norman  Macbeth, 
Editor,  Lighting  Journal. 

November  8 — Joint  meeting  with 
Philadelphia  Section  of  American  Insti- 
tute of  Electrical  Engineers.  "New 
Code  of  Lighting  for  Factories,  Mills 
and  Other  Work  Places,"  by  Prof.  C.  E. 
Clewell,  Department  of  Electrical  Engi- 
neering, University  of  Pennsylvania. 


November  19 — "Coal  Mine  Illumina- 
tion and  Its  Relation  to  Accident  Pre- 
vention and  Miners'  Nystagmus,"  by 
R.  E.  Simpson,  Engineer,  The  Travelers' 
Insurance  Company. 

December  17 — Joint  meeting  with 
Engineers'  Club.  "Illuminating  Engi- 
neering," by  Charles  P.  Steinmetz,  A.  M., 
Ph.  D.,  President,  Illuminating  Engineer- 
ing Society;  Chief  Consulting  Engineer, 
General  Electric  Company. 

January  21 — "Illumination  Problems  at 
the  Panama-Pacific  Exposition,"  by 
W.  D'A.  Ryan,  Illuminating  Engineer, 
General  Electric  Company. 

February  18 — ."Tests  of  Street  Illumi- 
nation," by  Preston  S.  Millar,  Past- 
president,  Illuminating  Engineering 
Society ;  General  Manager,  Electrical 
Testing  Laboratories. 

March  13 — Joint  meeting  with  Phila- 
delphia Section,  American  Institute  of 
Electrical  Engineers.  "Engineering 
Training  as  a  Business  Asset,"  by 
Charles  F.  Scott,  Sc.  D..  Past-president, 
American  Institute  of  Electrical  Engi- 
neers ;  Professor  of  Electrical  Engineer- 
ing, Sheffield  Scientific  School  of  Yale 
University. 

March  17 — "Lighting  Legislation,"  by 
L.  B.  Marks,  Past-president,  Illuminat- 
ing Engineering  Society;  Consulting 
Engineer. 

April  21 — "Type  C  Lamps  in  Street 
Lighting,"  by  T.  J.  Pace,  Commercial 
Engineer,  Westinghouse  Electric  & 
Manufacturing  Company. 

May  19 — "Educational  Aspects  of 
Illumination,"  by  Prof.  F.  K.  Richt- 
myer,  Chairman,  Committee  on  Educa- 
tion, Illuminating  Engineering  Society. 

June  16 — "Artificial  Lighting  for  a 
Hundred  Years,"  by  William  J.  Serrill, 
Engineer  of  Distribution,  United  Gas 
Improvement  Company. 


TRANSACTIONS   I.  E.  S. — PART   II 


Annual  Convention. 

The  ninth   annual  convention   of  the 
Illuminating    Engineering    Society    was 
held  at  the  New  Willard  Hotel  hi  Wash- 
ington, D.  C,  September  20-23  inclusive. 
There    were   twelve    sessions,    three    of 
which  were  devoted  to  technical  or  labo- 
ratory   subjects,    three    to    commercial 
papers,  one  to  street  lighting,   and  the 
remaining  four  to  general  topics.     All 
sessions  were  well  attended  and  brought 
out  a  large  amount  of  lively  discussion. 
Among  the  entertainment  features  were 
a  reception  by  Washington  members  and 
guests   at   the   New   Willard   Hotel   on 
Monday  evening,  September  20 ;  a  recep- 
tion at  the  White  House  by  President 
Woodrow  Wilson  at  noon  Tuesday;  a 
drill  by  the   United   States   Cavalry   at 
Fort   Myer,   Va. ;    automobile  trips   for 
the  ladies;  and  the  annual  banquet.     A 
"get  together"  luncheon  and  discussion 
of  society  affairs  was  held  on  Thursday. 
The  total  registration  was  350,  includ- 
ing members  and  their  guests.    Without 
question  the  convention  was  a  success 
and  a  fitting  climax  for  the  year's  activi- 
ties of  the  society. 


New  Members. 

The  following  five  applicants  were 
elected  associate  members  at  a  Council 
Executive  Committee  meeting  held 
August  5 : 

Howe,  Ralph  Sawyer 

Illuminating  Engineer,  Mitchell 
Vance  Company,  24th  Street  and 
Broadway,  New  York,  N.  Y. 

KOCHERSPERGER,  JEROME 

Assistant  Sales  Engineer  and 
Draughtsman,  Central  Electric  Com- 
pany, 320  South  Fifth  Avenue, 
Chicago,  111. 


Myer,  Albert 

Optometrist,  244  Broadway,  Albert 
Lea,  Minn. 

Walker,  Edmund  Ernest 

Sales  Engineer,  Light  and  Power 
Department,  British  Columbia  Elec- 
tric Railway  Company,  Ltd.,  Canal 
Street,  Vancouver,  B.  C. 

Willey,  Llewellyn  M. 

District  Manager,  Diehly  Manufac- 
turing Company,  1017  West  Jackson 
Boulevard,  Chicago,  111. 

At  a  meeting  of  our  Council  Executive 
Committee  held  August  18,  the  follow- 
ing   applicants    were    elected    associate 
members : 
Bolton,  Frank  C. 

Professor  of  Electrical  Engineering, 
Agricultural    and    Mechanical    Col- 
lege of  Texas,  College  Station,  Tex. 
Cressman,  Russell  B. 

Sales  Department,  Gleason  Tiebout 
Glass  Company,  71  West  23rd  Street, 
New  York,  N.  Y. 
Taylor,  A.  Hadlay 

Assistant      Physicist,      Bureau      of 
Standards,  Washington,  D.  C. 

The  following  fifteen  applicants  were 
elected  associate  members  at  a  meeting 
of    the    Council    Executive    Committee 
held  September  23 : 
Anderson,  Earl  A. 

National     Lamp     Works,     General 
Electric  Company,  Nela  Park,  Cleve- 
land, Ohio. 
Burrows,  Robert  P. 

Electrical  Engineer,  National  Lamp 
Works    of    General    Electric    Com- 
pany, Nela  Park,  Cleveland,  Ohio. 
Chapman,  F.  W. 

Director,  Technological  Department, 
Newberry  College,  Newberry,  S.  C. 


TRANSACTIONS   I.    E.    S.       PART   II 


Coe,  Gilbert  A. 

Lighting  Service  Department,  Phila- 
delphia Electric  Company,  iooo 
Chestnut  Street,  Philadelphia,  Pa. 

Dorting,  E.  E. 

Lighting  Engineer,  Interborough 
Rapid  Transit  Company,  600  West 
59th  Street,  New  York,  N.  Y. 

Fuller,  William  J. 

Illuminating  Expert,  Consumers'  Gas 
Company,  19  Toronto  Street, 
Toronto,  Canada. 

Hellmann,  C.  B. 

Salesman,  Luminous  Unit  Company, 
2615  Washington  Avenue,  St.  Louis, 
Mo. 

Howard-Soler,  Antonio 

L.  K.  Comstock  &  Company,  30 
Church  Street,  New  York,  N.  Y. 

Little,  Arlington  P. 

Assistant  Physicist,  Bureau  of 
Standards,  Pierce  Mill  Road,  Wash- 
ington, D.  C. 

Lord,  Albert  C. 

Purchasing  Agent,  Northern  Union 
Gas  Company,  1815  Webster  Ave- 
nue, New  York,  N.  Y. 

Palmer,  H.  C. 

Engineer,  Buffalo  Gas  Company,  186 
Main  Street,  Buffalo,  N.  Y. 

SCHLADT,   G.  J. 

Laboratory  Assistant  in  Photometry, 
Bureau  of  Standards,  Washington, 
D.  C. 

Smith,  Esmond  M. 

Beardslee  Chandler  &  Manufactur- 
ing Company,  216  South  Jefferson 
Street,  Chicago,  111. 

Sullivan,  A.  H. 

Manager  and  Electrical  Engineer, 
Columbia  Electric  &  Engineering 
Company,  144  North  14th  Street, 
Lincoln,  Neb. 

Wilhoite,  L.  J. 

Contract  Agent,  Chattanooga  Rail- 
way &  Light  Company,  710  Market 
Street,  Chattanooga,  Tenn. 


New  Sustaining  Members. 

The  following  companies  were  elected 
sustaining  members  at  a  Council  Execu- 
tive Committee  meeting  held  August  5, 
1915: 
Utah  Gas  &  Coke  Company 

Salt  Lake  City,  Utah. 
St.  Louis  Brass  Manufacturing  Com- 
pany 
St.  Louis,  Mo. 


Transfers. 


The  following  applicants  have  been 
transferred  from  the  grade  of  associate 
member  to  the  grade  of  member : 

August  18,  1915. 

Abbott,  Arthur  L. 

Manager,  Electric  Construction 
Company,  174  East  6th  Street,  St. 
Paul,  Minn. 

Auty,  K.  A. 

Chief  Illuminating  Engineer,  British 
Columbia  Electric  Railway  Com- 
pany, Ltd.,  1 193  Bender  Street, 
West,  Vancouver,  B.  C. 

Blakeslee,  Dorap  Wilmot 

Engineering  Department,  Carnegie 
Steel  Company,  Farrell,  Pa. 

Bond,  Charles  O. 

Manager,  Physical  Laboratory, 
United  Gas  Improvement  Company, 
3101  Passyunk  Avenue,  Philadelphia, 
Pa. 

Clewell,  C.  E. 

Assistant  Professor  of  Electrical 
Engineering,  University  of  Pennsyl- 
vania, Philadelphia,  Pa. 

Crownpield,  David 

Chief  Designer  and  Illuminating 
Engineer,  Pettingell-Andrews  Com- 
pany, 160  Pearl  Street,  Boston, 
Mass. 


TRANSACTIONS    I.    E.    S. — PART    II 


Dates,  Henry  B. 

Professor  of  Electrical  Engineering. 
Case  School  of  Applied  Science, 
Euclid  Avenue,  Cleveland,  Ohio. 

Durgin,  Wm.  A. 

Testing  Engineer,  Commonwealth 
Edison  Company,  28  North  Market 
Street,  Chicago,  111. 

Evans,  William  A.  D. 

Commercial  Engineer.  Cooper- 
Hewitt  Electric  Co..  730  Grand 
Street,  Hoboken.  X.  J. 

Foster,  Spottswood  C. 

Superintendent  and  Electrical  Engi- 
neer. Rappahannock  Electric  Light 
&  Power  Company,  Charles  and 
Amelia  Streets,  Fredericksburg,  Va. 

Floy,  Henry 

Consulting  Engineer.  165  Broadway. 
New  York,  N.  Y. 

Grondahl,  Lars  O. 

Assistant  Professor  of  Physics, 
Carnegie  Institute  of  Technology. 
Pittsburgh,  Pa. 

Gradle,  Harry  S. 

Ophthalmologist,  32  North  State 
Street,  Chicago,  111. 

Jackson,  J.  B. 

Engineer  of  Lighting  Service,  Com- 
monwealth Edison  Company,  72 
West  Adams  Street,  Chicago,  111. 

Johnson,  Otis  L. 

Illuminating  Engineer,  Benjamin 
Electric  Manufacturing  Company, 
120  South  Sangamon  Street,  Chi- 
cago, 111. 

Kirschberg,  Harold 

Consulting  Illuminating  Engineer, 
650  Century  Building,  Pittsburgh. 
Pa. 

Kellogg,  Raymond  Clinton 

Assistant  to  Superintendent  of 
Street  Department  (District  No.  2), 
Brooklyn  Union  Gas  Company,  176 
Remsen  Street,  Brooklyn,  N.  Y. 


Lacombe,  Charles  F. 

Consulting  Engineer,  30  Broad 
Street,  New  York,  N.  Y. 

Lansingh,  Van  Rensselaer 

President,  The  By-Lo  Stores  Com- 
pany, 54  West  Lake  Street,  Chicago, 
111. 

Lloyd,  E.  W. 

General  Contract  Agent,  Common- 
wealth Edison  Company,  72  West 
Adams  Street.  Chicago,  111. 

Luckiesh,  M. 

Physicist,  Nela  Research  Labora- 
tory, National  Lamp  Works  of  Gen- 
eral Electric  Company.  Nela  Park. 
Cleveland,  Ohio. 

Masson,  Chas.  M. 

Illuminating  Engineer,  Southern 
California  Edison  Company,  120 
East  4th  Street,  Los  Angeles,  Cal. 

Moon,  T.  Elmer. 

Consulting  Engineer  in  Illumination, 
1626  Real  Estate  Trust  Building, 
Philadelphia,  Pa. 

Moulton,  Walter  R. 

Illuminating  Engineer,  Consolidated 
Gas,  Electric  Light  &  Power  Com- 
pany, 325  North  Charles  Street.  Bal- 
timore. Md. 

Nichols,  George  B. 

Chief  Engineer,  Department  of  Ar- 
chitecture, New  York  State  Capitol, 
Albany,  N.  Y. 

Nutting,  P.  G. 

Optical  Engineer,  Head  of  Physics, 
Research  Laboratory,  Eastman 
Kodak  Company,  Rochester,  N.  Y. 

Ohmans.  John  L. 

Electrician  in  Charge  of  Car  Light- 
ing, Chicago  &  Western  Indiana 
Railroad  Company,  448  West  51st 
Street,  Chicago,  111. 

Reeder,  Charles  L. 

Consulting  Engineer,  Park  Avenue 
Building,  Park  Avenue  and  Sara- 
toga Street,  Baltimore,  Md. 


TRANSACTIONS    I.    E.    S.  — PART    II 


Rolph,  T.  W. 

Illuminating  Engineer.  Ivanhoe 
Metal  Works  of  General  Electric 
Company,  East  Cleveland,  Ohio. 

Rowe,  E.  B. 

Illuminating  Engineer  and  Secre- 
tary, Enterprise  Electric  Construc- 
tion &  Fixture  Company,  6509 
Euclid  Avenue,  Cleveland,  Ohio. 

Schmidt,  Albert  R. 

A.  R.  Schmidt  Electric  Company. 
262  East  Water  Street.  Milwaukee. 
Wis. 

Scheible,  Albert 

Patent  Attorney  and  Research  Engi- 
neer, 79  West  Monroe  Street,  Chi- 
cago, 111. 

Sharp,  Clayton  H. 

Technical  Director,  Electrical  Test- 
ing Laboratories,  Inc.,  80th  Street 
and  East  End  Avenue,  New  York, 
N.  Y. 

Spencer,  W.  H. 

Engineer  and  Assistant  Manager, 
I.  P.  Frink,  239  Tenth  Avenue,  New 
York,  N.  Y. 

Thomas,  Stephen  A. 

Chief,  Electrical  Division,  Building 
Bureau,  Department  of  Education, 
500  Park  Avenue,  New  York,  N.  Y. 

Wynne,  V.  C. 

Consulting  Engineer,  90  State  Street. 
Albany.  N.  Y. 

September  23,  1915. 

Adam,  John  N. 

New  Business  Department,  Public 
Service  Electric  Company.  271 
North  Broad  Street,  Elizabeth. 
N.J. 

Allen.  Harry  V. 

Department  of  Water  Supply,  City 
of  New  York,  2324  Municipal  Build- 
ing. New  York,  N.  ^  . 

Auerbacher,  Louis  J. 

Representative.  Beck  Searchlights. 
120  Liberty  Street.  New  York.  N.  Y. 


Barrows,  George  S. 

Engineering  Department,  United  Gas 
Improvement  Company,  Broad  and 
Arch  Streets,  Philadelphia,  Pa. 

Bartlett,  P.  H. 

The  Philadelphia  Electric  Company, 
1000  Chestnut  Street,  Philadelphia, 
Pa. 

Benford,  Frank  A..  Jr. 

Illuminating  Engineering  Labora- 
tory, General  Electric  Company, 
Dock  Street.  Schenectady,  N.  Y. 

Bernhard,  Frank  H. 

Associate  Editor,  Electrical  Review 
and  Western  Electrician,  608  South 
Dearborn  Street,  Chicago.  111. 

Betts,  Philander 

Chief  Engineer,  Board  of  Public 
Utility  Commissioners,  790  Broad 
Street,  Newark.  N.  J. 

Bolton,  Frank  C. 

Professor  of  Electrical  Engineering. 
Agricultural  and  Mechanical  College 
of  Texas.  College  Station,  Tex. 

Bowen,  Dudley  A. 

Westinghouse  Electric  &  Manufac- 
turing Company,  165  Broadway. 
New  York,  N.  Y. 

Bronis,  James 

Appraiser  of  Unlisted  Securities  and 
Expert  Accountant  for  Marvyn 
Scudder  and  The  Investors'  Agency. 
Inc.,  55  Wall  Street,  New  York. 
N.  Y. 

Brooks,  Harold  Arthur 

Electrical  Engineer,  Potomac  Elec- 
tric Power  Company.  231  14th  Street, 
N.  W.,  Washington,  D.  C. 

Broom,  Benj.  A. 

Consulting  Mechanical  Engineer,  500 
United  Bank  Building,  Sioux  City, 
la. 

Bryant,  J.  M. 

Professor  of  Electrical  Engineering. 
University  of  Texas.  Austin,  Tex. 


TRANSACTIONS    I.     E.    S. — PART    II 


Burrows,  Stephen  B. 

General  Lighting  Representative. 
Public  Service  Electric  Company. 
759  Broad  Street,  Newark,  X.  J. 

Cline,  W.  B. 

President  and  General  Manager,  Los 
Angeles  Gas  &  Electric  Corporation, 
645  South  Hill  Street,  Los  Angeles. 
Cal. 

Cramptox,  George  S. 

Ophthalmologist,  1700  Walnut  Street. 
Philadelphia,  Pa. 

Cravath,  James  R. 

Consulting  Electrical  and  Illumin- 
ating Engineer,  140  South  Dearborn 
Street,  Chicago.  111. 

Crosby.  Halsey  E. 

Chief  Electrician.  Columbia  Univer- 
sity, 116th  Street  and  Amsterdam 
Avenue,  New  York.  N.  Y. 

Dickersox,  A.  F. 

Illuminating  Engineer,  General  Elec- 
tric Company,  Panama-Pacific  Inter- 
national Exposition.  Service  Build- 
ing. San  Francisco,  Cal. 

Dunning,  Herbert  S. 

Westinghouse  Lamp  Company. 
Bloomfield.  X.  T. 

Edie,  Wm.  W. 

Illuminating  Engineer,  West  Perm 
Electric  Company,  West  Main 
Street,  Connellsville,  Pa. 

Edwards,  Evan  J. 

Associate  Engineer.  Xational  Lamp 
Works  of  General  Electric  Com- 
pany. Xela  Park.  Cleveland,  Ohio. 

Fuller,  W.  W. 

Chief  Engineer  and  Manager. 
Charleston-Isle  of  Palms  Traction 
Company,  Charleston  Hotel  Build- 
ing, Charleston.  S.  C. 

Gast,  Fred  W. 

Mechanical  -  Electrical  Engineer. 
United  States  Treasury  Department, 
Washington,  D.  C. 


Gross,  J.  Harry 

Park  Engineer,  Board  of  Park  Com- 
missioners, Druid  Hill  Park,  Balti- 
more, Md. 

Hare,  Johx  R. 

United  Gas  Improvement  Company, 
134  West  13th  Street.  Philadelphia, 
Pa. 

Harries.  George  Herbert 

H.  M.  Byllesby  &  Company,  Union 
Pacific  Building,  Omaha.  Neb. 

Hatzel,  John  C. 

Hatzel  &  Buehler,  373  4th  Avenue, 
Xew  York,  X.  Y. 

Heilmax.  Doxald  B. 

Mechanical  and  Electrical  Engineer, 
and  Inspector,  Philadelphia  &  Read- 
ing Railway  Company,  Reading,  Pa. 

Hexxixgf.r,  John  G.,  Jr. 

Salesman  and  Illuminating  Engineer, 
Fostoria  Incandescent  Lamp  Divi- 
sion, General  Electric  Company. 
Fostoria,  Ohio. 

Herixg,  Carl 

929  Chestnut  Street.  Philadelphia. 
Pa. 

Herrick,  Charles  Hubbard 

Xational  Meter  Company  of  New 
York,  159  Franklin  Street,  Boston, 
Mass. 

Hkrzog,  Johx  S. 

Newark  Reflector  Division,  National 
Lamp  Works  of  General  Electric 
Company.  Newark.  Ohio. 

Hibbex,  S.  G. 

Illuminating  Engineer.  Macbeth- 
Evans  Glass  Companv.  Pittsburgh. 
Pa. 

Hicks,  Leslie  R. 

Engineering  Department,  C.  H. 
Tenney  &  Company,  201  Devonshire 
Street,  Boston,  Mass. 

HrrzKER,  Albert  J. 

Assistant  Manager,  Federal  Minia- 
ture Lamp  Division,  General  Elec- 
tric Company,  501  South  Jefferson 
Street,  Chicago.  111. 


8 


TRANSACTIONS    I.    E.    S. — PART    II 


Houghton,  C.  P. 

Second  Vice-President.  Los  Angeles 
Gas  &  Electric  Corporation,  645 
South  Hill  Street,  Los  Angeles,  Cal. 

Humphry,  George  William 

Sir  W.  G.  Armstrong-Whitworth, 
Ltd.,  10  Sarah  Street,  Shielsfield, 
Newcastle-on-Tyne,  England. 

Hyde,  E.  N. 

Illuminating  Department,  Northern 
Electric  Company,  Ltd.,  Post  Office 
Drawer  2040,  Montreal,  Can. 

Hyde,  E.  P. 

Director,  Nela  Research  Laboratory, 
National  Lamp  Works  of  General 
Electric  Company,  Nela  Park,  Cleve- 
land, Ohio. 

Jackson,  Dugald  C. 

Professor  of  Electrical  Engineering, 
Massachusetts  Institute  of  Tech- 
nology, 248  Boylston  Street.  Boston, 
Mass. 

Johnson,  Lester  Gurney 

Commercial  Engineer,  General  Elec- 
tric Company,  Schenectady,  N.  Y. 

Jones,  Loyd  A. 

Eastman  Kodak  Company,  Roches- 
ter, N.  Y. 

Jordan,  Horace  W. 

39  Boylston  Street,  Boston,  Mass. 

Kruger,  John  L. 

137  Grand  Avenue,  Brooklyn,  N.  Y. 

Law,  Clarence  L. 

Manager,  Bureau  of  Illuminating 
Engineering,  New  York  Edison 
Company,  130  East  15th  Street,  New- 
York,  N.  Y. 

Le  Page,  Clifford  B. 

Assistant  Professor  of  Physics, 
Stevens  Institute  of  Technology, 
Hoboken,  N.  J. 

Luther,  Chas.  A. 

Illuminating  Engineer,  Peoples  Gas 
Light  &  Coke  Company,  122  North 
Michigan  Boulevard,  Chicago,  111. 


Magdsick.  H.  H. 

Engineering  Department,  National 
Lamp  Works  of  General  Electric 
Company,  Nela  Park,  Cleveland, 
Ohio. 

MlDDLEKAUFF,    GEORGE   W. 

Associate  Physicist,  Bureau  of 
Standards,  Washington,  D.  C. 

Millar,  Preston  S. 

Manager,  Electrical  Testing  Labora- 
tories, Inc.,  80th  Street  and  East 
End  Avenue,  New  York,  N.  Y. 

Morgan,  John  Eyre 

Superintendent  Gas  Plant,  Paw- 
tucket  Gas  Company,  231  Main 
Street,  Pawtucket,  R.  I. 

Morgan,  L.  G.  D. 

Supervising  Engineer,  National 
X-Ray  Reflector  Company,  217 
Stephenson  Building,  Milwaukee, 
Wis. 

Mott.  William  Roy 

Chemical  Engineer,  Research  Labo- 
ratory, National  Carbon  Company, 
Corner  117th  and  Madison  Streets, 
Lakewood,  Ohio. 

Myer,  Albert 

Secretary,  American  Optical  Asso- 
ciation, 244-246  Broadway,  Albert 
Lea,  Minn. 

Neumuller,  Walter 

Special  Representative,  New  York 
Edison  Company,  130  East  15th 
Street,  New  York,  N.  Y. 

Nodell,  W.  L. 

Sub-branch  Manager,  Westinghouse 
Lamp  Company,  121  East  Baltimore 
Street,  Baltimore,  Md. 

Norton,  Guy  Payne 

Sterling  Bronze  Company,  16  West 
40th  Street,  New  York,  N.  Y. 

Owens,  Thurston 

42  Pine  Street,  New  York,  N.  Y. 


TRANSACTIONS    I.    E.    S.—  PART    II 


Patterson,  Robert  B. 

Superintendent,  Street  Lighting  De- 
partment, Potomac  Electric  Power 
Company,  231  14th  Street,  N'.  W., 
Washington,  D.  C. 

Pope,  A.  A. 

Assistant  General  Commercial  Man- 
ager, New  York  Edison  Company, 
130  East  15th  Street,  New  York, 
N.  Y. 

Radcuff,  John  R.,  Jr. 

Sales  Manager  (Electric),  Yonkers 
Electric  Light  &  Power  Company, 
9  Manor  House  Square,  Yonkers, 
N.  Y. 

RlDINGER,   CHAS.  W. 

President,     Iron    City    Engineering 
Company,    711    Grant    Street,    Pitts- 
burgh, Pa. 
Rieha,  Edward  L. 

Gas  Engineer  and  Contractor,  213 
Courtland  Street,  Baltimore,  Md. 

Rochester,  Thomas  W. 

Bureau  Contract  Supervision,  Board 
of  Estimate  and  Apportionment, 
Municipal  Building,  New  York, 
N.Y. 

Sawin,  George  A. 

Illuminating  Engineer,  Public  Ser- 
vice Electric  Company,  759  Broad 
Street,  Newark,  N.  J. 

Schumacher,  John  Henry 

Treasurer  and  Manager,  Schu- 
macher, Gray  Company,  Ltd.,  386 
Donald  Street,  Winnipeg,  Manitoba, 
Can. 

Scofield,  Thomas 

Consolidated  Gas  Company,  130  East 
15th  Street,  New  York,  N.  Y. 

Shaad,  George  C. 

Professor  of  Electrical  Engineering, 
University  of  Kansas,  Engineering 
Building,  University  of  Kansas, 
Lawrence,  Kan. 


Shaw,  Carroll  H. 

Electrical  Engineer,  Sheboygan  Rail- 
way &  Electric  Company,  1514  North 
7th  Street,  Sheboygan,  Wis. 

Sheibley,  Frank  D. 

Assistant  Engineer,  Consolidated 
Telegraph  &  Electrical  Subway 
Company,  54  Lafayette  Street,  New 
York,  N.  Y. 

Silverman,  Alexander 

University  of  Pittsburgh,  Pitts- 
burgh, Pa. 

Steadman,  F.  M. 

Photographer,  Concord,  N.  H. 

Stark,  A.  W. 

Engineer's  Assistant,  Consolidated 
Gas  Company  of  New  York,  130 
East  15th  Street,  New  York,  N.  Y. 

Steinharter,  Jos  J. 

Vice-president,  Lamp  Company,  The 
Metalyte  Company,  366  West  15th 
Street,  New  York,  N.  Y. 

Stevick,  C.  H. 

Superintendent  of  Works,  New 
Amsterdam  Gas  Company,  Ravens- 
wood,  Long  Island  City,  N.  Y. 

Stewart,  Samuel  B. 

General  Contracting  Agent,  Phila- 
delphia Company.  435  Sixth  Avenue, 
Pittsburgh,  Pa. 

Swallow,  Joseph  G. 

Superintendent,  Installation  and  In- 
spection Department,  United  Elec- 
tric Light  &  Power  Company,  130 
East  15th  Street,  New  York,  N.  Y. 

Tomlinson,  L.  C. 

Electrical  and  Sales  Engineer, 
National  Electric  Utility  Corpora- 
tion, 355  West  36th  Street,  New 
York,  N.  Y. 

Tyler,  Randolph  E. 

Manager,  Philadelphia  Office,  Shelby 
Lamp  Division  National  Lamp 
Works  of  General  Electric  Com- 
pany, 1941  Market  Street,  Philadel- 
phia, Pa. 


10 


TRANSACTIONS    I.    E.    S. — PART   II 


Ware,  Richard  C. 

Assistant  to  Second  Vice-president. 
Boston  Consolidated  Gas  Company, 
24  West  Street,  Boston,  Mass. 

Whiting,  H.  S. 

J.  Livingston  &  Company.  70  East 
45th  Street,  New  York,  N.  Y. 

Weaver,  W.  D. 

Charlottesville,  Va. 

Williams,  Arthur 

General  Commercial  Manager,  New 
York  Edison  Company,  130  East 
15th  Street,  New  York,  N.  Y. 

Wilson,  Frank  S. 

Electrical  Enginer,  8  Irvington 
Street,  Boston,  Mass. 

Young,  James  Watts 

Consulting  Electrical  Engineer,  58 
Townsend  Street,  Roxbury,  Mass. 

October  14,  1915. 

Boyce,  Ernest  W. 

Electrical  Engineer,  President  New 
York  Electric  Lamp  Company,  Inc.. 
30  Park  Row.  New  York,  N.  Y. 

Boxell,  Harold  V. 

Consulting  Engineer  and  Professor 
of  Electrical  Engineering.  Univer- 
sity of  Oklahoma,  508  Chautauqua 
Avenue,  Norman.  Okla. 

Bull,  John  H. 

Supervising  Engineer.  Ballinger  & 
Perrot,  Marbridge  Building,  34th 
Street  and  Broadway,  New  York, 
N.  Y. 

Cady,  Francis  E. 

Assistant  to  Director,  Nela  Research 
Laboratory,  Nela  Park,  Ohio. 

Carpenter,  Frank 

Illumination  and  Special  Work, 
Welsbach  Gas  Lamp  Company,  392 
Canal  Street,  New  York,  N.  Y. 

Clinch,  Edward  S.,  Jr. 

Electrical  Engineer,  Cates  &  Shep- 
ard,  1516  Sansom  Street,  Philadel- 
phia, Pa. 


Cowles,  Joseph  W. 

Superintendent  of  Installations,  Edi- 
son Electric  Illuminating  Company 
of  Boston,  39  Boylston  Street,  Bos- 
ton, Mass. 

Doane,  L.  C. 

Commercial  Engineer.  Holophane 
Works  of  General  Electric  Com- 
pany, Cleveland,  Ohio. 

Dodson,  Herbert  K. 

Assistant  Superintendent,  New  Busi- 
ness and  Merchandise  Department, 
Consolidated  Gas,  Electric  Light  & 
Power  Company  of  Baltimore,  200 
West  Lexington  Street.  Baltimore, 
Md. 

Doty,  Paul 

President  and  General  Manager,  St. 
Paul  Gas  Light  Company,  159  East 
6th  Street,  St.  Paul,  Minn. 

Dows,  Chester  L. 

Electrical  Engineer,  National  Lamp 
Works  of  General  Electric  Com- 
pany, Nela  Park.  Cleveland,  Ohio. 

Dutton,  L.  R. 

Manager.  Philadelphia  Suburban 
Gas  &  Electric  Company,  Wyncote. 
Pa. 

Gaxz.  Albert  Frederick 

Consulting  Engineer  and  Professor 
of  Electrical  Engineering,  Stevens 
Institute  of  Technology,  Hoboken. 
X.  J. 

Hanscom,  W.  W. 

Consulting  Engineer,  848  Clayton 
Street,  San  Francisco,   Cal. 

Hess,  William  L. 

Oculist,  400  California  Building, 
Denver,  Colo. 

Holdrege.  H.  A. 

General  Manager,  Omaha  Electric 
Light  &  Power  Company,  Omaha, 
Neb. 

Hulse,  Geo.  E. 

Chief  Engineer,  Safety  Car  Heating 
&  Lighting  Company,  2  Rector 
Street,  New  York.  N.  Y. 


TRANSACTIONS    I.    H.    S.  —PART    II 


11 


Jackson,  Dugald  C. 

Professor  of  Electrical  Engineering, 
Massachusetts  Institute  of  Technol- 
ogy, 248  Boylston  Street,  Boston. 
Mass. 

Keech,  George  C. 

District  Sales  Manager,  Cooper- 
Hewitt  Electric  Company,  215  Fisher 
Building,  Chicago,  111. 

Kellogg,  Alfred  S. 

Consulting  Engineer,  53  State  Street, 
Boston,  Mass. 

Kennedy,  Geo.  M. 

Electrical  Engineer,  Lehigh  Coal  & 
Navigation  Company,  no  East 
Ridge  Street,  Lansford,  Pa. 

Kingsbury,  E.  F. 

Research  Assistant,  United  Gas  Im- 
provement Company,  Physical  Lab- 
oratory, 3101  Passyunk  Avenue, 
Philadelphia,  Pa. 

Magalhaes,  George  W. 

Assistant  to  the  President,  New 
York  &  Queens  Electric  Light  & 
Power  Company,  444  Jackson  Ave- 
nue, Long  Island  City,  N.  Y. 

Marsh,  Loren  W. 

New  England  Manager,  American 
Luxfer  Prism  Company,  49  Federal 
Street,   Boston,   Mass. 

Mixer,  Chas.  A. 

Engineer,  Rum  ford  Falls  Light  & 
Water  Company,  49  Congress  Street, 
Rumford,  Me. 

Morton,  F.  N. 

Engineer,  United  Gas  Improvement 
Company,  Broad  &  Arch  Streets, 
Philadelphia,  Pa. 

Nicolai,  G.  O. 

Superintendent,  Light  &  Power  De- 
partment, Terre  Haute  I.  &  E. 
Traction  Company,  820  Wabash 
Avenue,  Terre  Haute,  Ind. 


O'Leary,  J.J. 

President,  Buffalo  Electric  Contract- 
ing Company,  20  Broadway,  Buffalo, 
N.  Y. 

i'l'ASLEE,  W.  Dhu  Aine 

Consulting  Engineer,  also  Lecturer 
in  Electrical  Engineering,  Oregon 
Agricultural  College,  Corvallis,  Ore. 

Porter,  Lawrence  C. 

Illuminating  Engineer,  Edison  Lamp 
Works  of  General  Electric  Com- 
pany, 417  Sussex  Street,  Harrison, 
N.  J. 

Clover,  Geo.  R. 

District  Manager,  Cooper-Hewitt 
Electric  Company,  427  Ford  Build- 
ing, Detroit,  Mich. 

Rose,  S.  L.  E. 

Illuminating  Engineering  Labora- 
tory, General  Electric  Company, 
Schenectady,  N.  Y. 

Ryan,  Walter  D'Arcy 

Director  of  Illuminating  Engineer- 
ing Laboratories,  General  Electric 
Company,  Schenectady.  N.  Y. 

Simpson,  Richard  E. 

Engineer,  Travelers'  Insurance  Com- 
pany, 700  Main  Street,  Hartford, 
Conn. 

Tingley,  Dr.  Louisa  Paine 

Ophthalmologist,  9  Massachusetts 
Avenue,  Boston,  Mass. 

Treverton,  E.  R. 

Lighting  Engineering  Service  Com- 
pany and  Lighting  Journal,  241 
West  37th  Street,  New  York,  N.  Y. 

Wohlauer,  A.  A. 

Consulting  Engineer,  Allied  Engi- 
neering Company,  546  Fifth  Avenue, 
New  York,  N.  Y. 

Murphy,  John 

Electrical  Engineer,  Government  of 
Canada,  Department  Railways  and 
Canals,  Ottawa,  Can. 


TRANSACTIONS 

OF  THE 

Illuminating 
Engineering  Society 

NO.  8,  1915 
PART  II 

Miscellaneous  Notes 


16 


TRANSACTIONS    I.    E.    S. — PART    II 


Council  Notes. 

A  regular  meeting  of  the  Council  was 
held  in  the  general  offices  of  the  society, 
29  West  39th  Street,  New  York,  Octo- 
ber 14,  1915.  Those  present  were: 
Charles  P.  Steinmetz,  president ;  H. 
Calvert,  \Ym.  A.  Durgin,  Clarence  L. 
Law,  M.  Luckiesh,  A.  S.  McAllister, 
L.  B.  Marks,  treasurer ;  J.  Arnold  Nor- 
cross,  and  G.  H.  Stickney. 

The  minutes  of  the  June  10  meeting 
were  adopted  as  printed. 

The  Council  Executive  Committee 
presented  the  following  report  giving  a 
summary  of  its  activities  on  behalf  of 
the  Council  during  the  summer  months : 
Since  the  last  meeting  of  the  Council  in  June, 
the  Council  Executive  Committee  has: 

(1)  Held  three  meetings,  August  5,  August 
18  and  September  23,  1915. 

(2)  Authorized  the  payment  of  vouchers 
Nos.  2136-2138,  2167-2256  inclusive  aggregating 
$2,461.82. 

(3)  Elected  23  associate  members  and  2  sus- 
taining members. 

(4)  Accepted  the  resignations  of  34  associate 
members. 

(5)  Transferred  123  associate  members  to 
the  grade  of  member. 

The  report  was  adopted. 

Six  applicants  were  elected  associate 
members. 

Twenty-one  associate  members  were 
transferred  to  the  grade  of  member. 

Upon  recommendation  of  the  Finance 
Committee,  payment  of  vouchers  No. 
2257  to  No.  2278  inclusive  aggregating 
$1,250.28  was  authorized. 

Reports  were  given  by  Mr.  G.  H. 
Stickney,  former  vice-president  of  the 
New  York  Section;  Mr.  H.  Calvert  for 
Geo.  A.  Hoadley,  vice-president  of  the 
Philadelphia  Section,  and  Mr.  L.  B. 
Marks,  chairman  of  the  Committee  on 
Lighting  Legislation. 

The  following  committee  appoint- 
ments were  confirmed : 


Finance:  H.  Calvert,  chairman;  J.  A. 
Norcross,  P.  S.  Young. 

Papers:  G  H.  Stickney,  chairman ; 
A.  S.  McAllister,  YV.  F.  Little,  G.  W. 
Roosa,  L.  B.  Marks,  and  the  chairmen 
of  section  Papers  Committees. 

Editing  and  Publication:  C.  H. 
Sharp,  chairman ;  Norman  Macbeth, 
M.  G.  Lloyd. 

Membership:  Douglass  Burnett,  chair- 
man; A.  L  Abbott,  J.  J.  Burns,  W.  R. 
Collier,  S.  L.  E.  Rose,  A.  M.  Wilson, 
R  E.  Simpson,  T.  M.  Ambler,  J.  C. 
McLaughlin,  and  the  chairmen  of  the 
section  Membership  Committees. 

Sustaining  Membership:  W.  M.  Skiff, 
chairman;   S.  G.  Hibben,  E.  W.  Lloyd, 

E.  B.   McLean,    S.    L.   E.    Rose,    E.    B. 
Rowe. 

Popular  Lectures:  E.  J.  Edwards, 
chairman;  A.  J.  Rowland,  vice-chair- 
man. 

a — Sub-committee     on     Residence 
Lighting:    E.  J.  Edwards,  chairman, 
b — Sub-committee     on    Industrial 
Lighting:     W.  A.  D.  Evans,  chair- 
man; R.  ff.  Pierce. 

c — Sub-committee   on  Elementary 
Lecture:    W.  S.  Franklin,  chairman. 
d — Sub-committee  on  Store  Light- 
ing:    A.  L.  Powell,  chairman. 

e — Sub-committee  on  Office  Light- 
ing: C.  E.  Clewell,  chairman. 
Lighting  Legislation:  L.  B.  Marks, 
chairman;  O.  H.  Basquin,  C.  E.  Clewell, 
Oscar  H.  Fogg,  Clarence  L.  Law,  M. 
Luckiesh,  F.  J.  Miller,  G.  H.  Stickney, 
L.  H.  Tanzer,  W.  H.  Tolman,  C.  6. 
Bond,  and  F.  A.  Vaughn. 

Glare:  P.  G.  Nutting,  chairman; 
Nelson  M.  Black,  J.  R.  Cravath,  F.  H. 
Gilpin,   M.    Luckiesh,   F.   K.    Richtmyer, 

F.  A.  Vaughn. 

Progress:  F.  E.  Cady,  chairman; 
Walter  B.  Lancaster,  T.  J.  Litle,  Jr., 
L.  B.  Marks,  F.  N.  Morton,  T.  W. 
Rolph. 


TRANSACTIONS   I.  E.  S. — PART   II 


Section  Development:  General  Sec- 
retary,  chairman ;    section   secretaries. 

Council  Executive  Committee:  Chas. 
P.  Steinmetz,  chairman;  L.  B.  Marks, 
H.  Calvert. 

Reciprocal  Relations:  W.  J.  Serrill, 
chairman;  F.  Park  Lewis,  F.  E.  Wallis, 
chairmen  of  sections,  G.  H.  Stickney, 
C.  H.  Sharp. 

Advertising:  M.  C.  Turpin,  chair- 
man; J.  C.  McQuiston,  Joseph  D.  Israel. 
Nomenclature  and  Standards:  A.  E. 
Kennelly,  chairman;  C.  H.  Sharp,  secre- 
tary; Louis  Bell,  C.  O.  Bond,  S.  E. 
Doane,  W.  A.  Dorey,  E.  P.  Hyde,  C.  O. 
Mailloux,  A.  S.  Miller,  P.  G.  Nutting, 
E.  B.  Rosa,  W.  E.  Saunders. 

Research:  E.  B.  Rosa,  chairman; 
P.  W.  Cobb,  G.  W.  Middlekauff,  P.  G. 
Nutting,  F.  K.  Richtmyer,  C.  H.  Sharp, 
E.  C.  Crittenden,  C.  E.  Ferree,  E.  P. 
Hyde,  E.  F.  Kingsbury,  Preston  S. 
Millar,  W.  E.  Wickenden,  H.  E.  Ives. 

It  was  decided  to  hold  a  semi-annual 
convention  early  in  February  to  cele- 
brate the  ioth  anniversary  of  the  organ- 
ization of  the  society. 

After  a  discussion  of  the  proposal  to 
arrange  for  a  course  of  lectures,  similar 
to  those  presented  at  the  Johns  Hopkins 
University  in  the  fall  of  1910,  to  be 
given  in  the  fall  of  1916  under  the 
auspices  of  the  society,  it  was  moved 
and  carried  that  President  Steinmetz  be 
authorized  to  make  such  preparations 
as  he  deems  desirable  for  the  lecture 
course. 

Thereupon  the  following  committee 
appointments  were  confirmed,  subject  to 
changes : 

a — Committee  on  Ways  and  Means: 
Preston  S.  Millar,  chairman. 

b— Committee  on  Lectures:  L.  B. 
Marks,  chairman. 

The  resignation  of  Mr.  Alten  S. 
Miller,  general  secretary,  was  accepted. 


It  was  moved  and  carried  that  the 
assistant  secretary  write  Mr.  A.  S. 
Miller  that  the  Council  hopes  he  will 
retain  his  seat  as  a  director. 


A  regular  meeting  of  the  Council 
was  held  in  the  offices  of  the  society, 
November  11,  1915-  Those  present 
were:  Charles  P.  Steinmetz,  presi- 
dent; E.  M.  Alger,  H.  Calvert,  G.  A. 
Hoadley,  Clarence  L.  Law,  A.  S. 
McAllister,  J.  L.  Minick,  L.  B.  Marks, 
C.  O.  Bond.  Upon  invitation:  C.  E. 
Clewell,  G.  H.  Stickney. 

The  minutes  of  the  October  meeting 

were  read,  but  adoption  was  postponed 

until  they  shall  have  appeared  in  print. 

Nine  applicants  were  elected  associate 

members  of  the  society. 

Four  applicants  were  elected  sustain- 
ing members. 

Thirty-eight  associate  members  were 
transferred  to  the  grade  of  member. 

Upon  recommendation  of  the  Finance 
Committee,  vouchers  No.  2279  to  No. 
2316  inclusive  aggregating  $1,833.62 
were  authorized  paid  subject  to  the 
approval  of  the  general  secretary. 

A  report  recommending  certain  rules 
of  procedure  with  regard  to  the  publi- 
cation of  papers  and  discussions  was 
received  from  the  Committee  on  Editing 
and  Publication.  Thereupon  the  ques- 
tion of  the  use  of  trade,  firm,  individual 
and  corporate  names  in  the  publications 
of  the  society  was  raised  for  discussion. 
It  was  voted  that  the  Committee  on 
Editing  and  Publication  be  asked  to 
draft  some  definite  policy  on  this  matter 
to  be  submitted  at  an  early  date,  with  the 
aforementioned  rules,  for  the  approval 
of  the  Council.  It  was  understood  that 
the  members  of  the  Council  would  be 
asked  individually  to  communicate  their 
views  on  the  question  to  the  committee. 


TRANSACTIONS   I.    E.    S.      PART   II 


The  following  committee  appoint- 
ments were  confirmed : 

Reciprocal  Relations:  Dr.  E.  M. 
Alger,  chairman. 

School  Lighting:  M.  Luckiesh,  chair- 
man. 

Lighting  Legislation:     C.  E.  Stephens. 

Semi- Annual  Convention:  Arthur 
Williams,  chairman. 

Board  of  Examiners:  A.  S.  McAllis- 
ter, chairman;  W.  Cullen  Morris, 
Bassett  Jones. 

It  was  voted  that  chairmen  of  com- 
mittees who  serve  on  other  committees 
be  listed,  on  the  latter  committees,  as 
co-operating  members. 

The  resignation  of  Mr.  A.  S.  Miller 
as  a  director  was  accepted  with  a  vote 
of  thanks  from  the  Council  for  services 
rendered. 

Mr.  C.  A.  Littlefield  was  appointed 
general  secretary  to  succeed  Mr.  Alten 
S.  Miller,  resigned. 

Mr.  Preston  S.  Millar  was  appointed 
a  director  to  succeed  Mr.  Alten  S. 
Miller,  resigned. 

Mr.  J.  L.  Minick  was  appointed  a 
delegate  of  the  society  to  attend  the 
exercises  of  the  Carnegie  Institute  of 
Technology  in  celebration  of  the  eigh- 
tieth birthday  of  Mr.  Carnegie  and  the 
tenth  anniversary  of  the  founding  of 
the  Institute,  to  be  held  in  Pittsburgh, 
Pa.,  November  23,  24,  1915. 

Reports  on  section  activities  were  re- 
ceived from  Vice-presidents  G.  A. 
Hoadley  and  C.  L.  Law. 

The  question  of  time  and  place  for 
giving  the  lectures  on  illuminating  engi- 
neering was  discussed  informally.  Mr. 
Clewell  said  that  he  thought  the  Uni- 
versity of  Pennsylvania  would  invite  the 
society  to  give  the  lectures  at  the  U. 
of  P. 

It  was  suggested  that  a  design  for  a 
new  membership  certificate  be  drawn  up 


and  submitted  for  the  approval  of  the 
Council. 

It  was  decided  to  make  the  official 
badges  of  the  society  in  the  following 
colors  :  blue  background  for  members ; 
maroon  for  associate  members,  and 
white  for  honorary  members. 

The  question  was  raised  whether  it 
would  be  desirable  to  draft  a  specifica- 
tion or  statement  of  some  kind  for  pho- 
tographs and  lantern  slides  showing 
comparative  illuminated  views  which  are 
used  to  illustrate  papers  given  before 
the  society.  It  was  pointed  out  that 
these  pictures  are  often  misleading 
because  of  the  absence  of  information 
regarding  the  conditions  under  which 
they  are  made.  It  was  voted  to  refer 
this  question  to  the  Committee  on 
Research. 


New  Associate  Members. 

At  the  October  14th  meeting  of  the 
Council,  the  following  six  applicants 
were  elected  to  associate  membership : 

Graff,  Weseey  M.    (Ph.B.,  M.  E.) 
Consulting  Engineer,   Graves  Engi- 
neering Co.,  Inc.,  35  Pine  St.,  New 
York,  N.  Y. 

Newun,  E.  M. 

Agent,  New  York  Edison  Co., 
Irving  Place  and  15th  St.,  New 
York,  N.  Y. 

Newton,  Arthur  Hazeett 

Electrical  Engineer,  Bureau  of  Pub- 
lic Works,  Manila,  P.  I. 

O'Shea,  James  P. 

General  Sales  Agent,  Cooper-Hewitt 
Electric  Co.,  730  Grand  St., 
Hoboken,  N.  J. 

Robnett,  Edwin  H. 

Representative,  Westinghouse  Elec- 
tric &  Manufacturing  Co.,  121  East 
Baltimore   St.,  Baltimore,  Md. 


TRANSACTIONS   I.    E.    S. — PART   II 


SCHERESCHEWSKY,  J.  W. 

Surgeon,  U.  S.  Public  Health  Ser- 
vice, U.  S.  Marine  Hospital,  Pitts- 
burgh, Pa. 


At  the  meeting  of  the  Council  held 
November  n,  the  following  nine  appli- 
cants were  elected  associate  members : 

Brandreth,  Guy  S. 

Lighting  Service  Department,  Phila- 
delphia Electric  Co.,  iooo  Chestnut 
St.,  Philadelphia,  Pa. 

Carder,  Frederick 

Vice-president  and  General  Man- 
ager, Steuben  Glass  Works,  Corn- 
ing, N.  Y. 

Hughes,  David  M. 

Photometric  Testing,  Electrical 
Testing  Laboratories,  8oth  St.  and 
East  End  Ave.,  New  York,  N.  Y. 

Markley,  Ralph  E. 

Lighting  Service  Department,  Phila- 
delphia Electric  Co.,  iooo  Chestnut 
St.,  Philadelphia,  Pa. 

Murray,  Joseph  Bradley 

Acting  Treasurer,  Edison  Electric 
Illuminating  Co.  of  Brooklyn,  360 
Pearl  St.,  Brooklyn,  N.  Y. 

Pearsall,  George  Martin 

Assistant  in  Physics,  Cornell  Uni- 
versity, 415  North  Cayuga  St., 
Ithaca,  N.  Y. 

PlNCKLEY,  W.   F.   T. 

Newcastle  Electric  Supply  Co., 
Hood  St.,  Newcastle-on-Tyne,  Eng- 
land. 

Rein,  Frederick  E. 

Business  Engineer  and  Public 
Accountant,  Frederick  Rein  &  Staff, 
1201  Chestnut  St.,  Philadelphia,  Pa. 

Koehler,  William  F. 

Philadelphia  Electric  Co.,  226  South 
nth  St.,  Philadelphia,  Pa. 


Section  Meetings. 

Chicago  Section 

November  4,  1915,  in  the  Common- 
wealth Edison  Company  Building. 
Paper,  "Semi-indirect  Office  Lighting  in 
the  Edison  Building  of  Chicago"  by 
Messrs.  W.  A.  Durgin  and  J.  B.  Jack- 
son.   Attendance  250. 

The  following  program  of  papers  and 
meetings  has  been  announced : 

December  9 — School  Lighting. 

January  13 — Exterior  Lighting  (Gas 
and  Electric)   of  Buildings. 

February  10 — Practical  Factor}^  Light- 
ing. 

February  28 — Joint  meeting  of  Chi- 
cago sections  of  A.  I.  E.  E.  and  I.  E.  S. 
Paper  on  street  lighting. 

March  23 — Latest  Developments  in 
Incandescent  Lamps. 

April  20 — Latest  Developments  in  Gas 
Lamps. 

May  18 — Relation  of  Illumination  to 
Interior  Architectural  Effects. 

June  15— Modern  Reflectors  and 
Shades  for  Gas  and  Electric  Lighting. 

The  names  of  the  authors  of  these 
papers  will  be  announced  later. 

New  England  Section 
The  first  meeting  of  the  section  this 
year  is  to  be  held  in  February,  1916.    A 
definite     announcement    will    be    made 
later. 

New  York  Section 
November  15,  1915.  Joint  meeting 
with  American  Electrochemical  Society 
in  Engineering  Societies  Building. 
Papers:  (1)  "Unstable  States  in  the 
Arc  and  Glow"  by  Walter  G.  Cady  of 
Wesleyan  University,  Middletown,  Conn. 
(2)  "Gaseous  Conductor  Light"  by  D. 
McFarlan  Moore,  Harrison,  N.  J.  (3) 
"Electric   Arc   in    Complex    Vapors    at 


TRANSACTIONS   I.    E.    S.—  PART   II 


Reduced  Pressures"  by  W.  A.  Darrah, 
Mansfield,  O. 

The  following  meetings  have  been 
announced : 

December  8,  1915 — Papers:  (1)  Prog- 
ress in  Home  Lighting  by  Gas"  by 
Thomas  Scofield;  (2)  "Commercial 
Aspects  of  Gas  Lighting"  by  Charles 
Hodgson. 

January  13,  1916 — Papers:  (1)  "Light 
Transmission  in  Optical  Instruments" 
by  Dr.  F.  L.  G.  Kollmorgen;  (2  "Pro- 
jector Lamps"  by  Mr.  Orange  of  the 
General  Electric  Company. 

March  9,  1916 — Joint  meeting  with 
American  Society  of  Mechanical  Engi- 
neers :  Paper  by  Prof.  C.  E.  Clewell 
of  the  University  of  Pennsylvania  on 
"Application  of  the  New  Factory  Code." 

April  13,  1916 — A  lecture  by  Dr. 
Charles  P.  Steinmetz,  president  of  the 
Illuminating  Engineering  Society,  on 
"Illuminating  Engineering." 

May  11,  1916 — Papers:  "Street  Light- 
ing" by  S.  G.  Rhodes ;  "Office  Lighting" 
by  Bassett  Jones ;  "Stage  Lighting"  by 
David  Belasco. 


Philadelphia  Section 

November  19,  1915,  Engineers'  Club, 
1317  Spruce  Street.  Paper :  "Coal 
Mine  Illumination ;  its  Relation  to  Acci- 
dent Prevention  and  Miners'  Nystac- 
mus"  by  R.  E.  Simpson.    Attendance  33. 

The  program  for  the  rest  of  the  year 
is  as  follows : 

December  17 — Joint  meeting  with 
Engineers'  Club.  "Illuminating  Engi- 
neering," by  Charles  P.  Steinmetz, 
A.  M.,  Ph.  D.,  President,  Illuminating 
Engineering  Society;  Chief  Consulting 
Engineer,   General  Electric  Company. 

January  21 — "Illumination  Problems 
at  the   Panama-Pacific   Exposition,"   by 


W.   D'A.    Ryan,   Illuminating   Engineer, 
General  Electric  Company. 

February  18 — "Tests  of  Street  Illumi- 
nation," by  Preston  S.  Millar,  Past- 
president,  Illuminating  Engineering 
Society;  General  Manager,  Electrical 
Testing  Laboratories. 

March  13 — Joint  meeting  with  Phila- 
delphia Section,  American  Institute  of 
Electrical  Engineers.  "Engineering 
Training  as  a  Business  Assett,"  by 
Charles  F.  Scott,  Sc.  D.,  Past-president, 
American  Institute  of  Electrical  Engi- 
neers; Professor  of  Electrical  Engineer- 
ing, Sheffield  Scientific  School  of  Yale 
University. 

March  17 — "Lighting  Legislation,"  by 
L.  B.  Marks,  Past-president,  Illuminat- 
ing Engineering  Society;  Consulting 
Engineer. 

April  21 — "Type  C  Lamps  in  Street 
Lighting,"  by  T.  J.  Pace,  Commercial 
Engineer,  Westinghouse  Electric  & 
Manufacturing  Company. 

May  19 — "Educational  Aspects  of 
Illumination,"  by  Prof.  F.  K.  Richt- 
myer,  Chairman,  Committee  on  Educa- 
tion,  Illuminating   Engineering   Society. 

June  16— "Artificial  Lighting  for  a 
Hundred  Years,"  by  William  J.  Serrill, 
Engineer  of  Distribution,  United  Gas 
Improvement  Company. 


Pittsburgh  Section 
November  19,  1915.  Educational 
meeting  in  Science  Building,  Carnegie 
Institute  of  Technology.  Papers:  (1) 
"Can  Light  be  Measured?"  by  G.  W. 
Roosa;  (2)  "Instruments  that  are  Used 
in  Measuring  the  Quantity  of  Light"  by 
H.  H.  Magdsick;  (3)  "Instruments  that 
are  Used  in  Measuring  Quality  of 
Light"  by  Dr.  L.  O.  Grondahl. 


TRANSACTIONS    I.    E.    S. — PART   II 


Transfers. 

The    following   twenty-one   applicants 

were    transferred    from    the    grade'    of 

associate  member  to  that  of  member  at 

a  meeting  of  the  Council  held  October 

14,  1915: 

Arenberg,  Albert  L. 

Illuminating  Engineer,  Central  Elec- 
tric Co.,  320  South  5th  Ave.,  Chi- 
cago, 111. 

Brady,  Edward  J. 

Physical  Laboratory,  United  Gas 
Improvement  Co.,  3101  Passyunk 
Ave.,  Philadelphia,  Pa. 

Clark,  Emerson  L. 

Physicist,  National  Carbon  Co., 
Cleveland,  O. 

Eichengreen,  L.  B. 

Gas  Engineer,  Manufacturer  and 
Distributor  of  Gas,  1401  Arch  St., 
Philadelphia,  Pa. 

Gartley,  William  H. 

Vice-president,  Equitable  Illuminat- 
ing Gas  Light  Co.,  1401  Arch  St., 
Philadelphia,  Pa. 

Gilpin,  Francis  H. 

Gas  Engineer,  United  Gas  Improve- 
ment Co.,  3101  Passyunk  Ave., 
Philadelphia,  Pa. 

Ives,  Herbert  E. 

Physicist,  United  Gas  Improvement 
Co.,  3101  Passyunk  Ave.,  Philadel- 
phia, Pa. 

Jordan,  C.  W. 

Assistant,  Physical  Laboratory, 
United  Gas  Improvement  Co.,  3101 
Passyunk  Ave.,  Philadelphia,   Pa. 

Kelly,  J.  B. 

Salesman,  Illuminating  Department, 
Frank  H.  Stewart  Electric  Co.,  37 
North  7th  St.,  Philadelphia,  Pa. 

Kiefer,  Lewis  J. 

Building  Superintendent,  McCreery 
&  Co.,  Sixth  Ave.  and  Wood  St., 
Pittsburgh,  Pa. 


Little,  William  F. 

Engineer  in  Charge  of  Photometry, 
Electrical  Testing  Laboratories,  80th 
St.  and  East  End  Ave.,  New  York, 
N.  Y. 

Macdonald,  Norman  D. 

Assistant  to  Manager,  Electrical 
Testing  Laboratories,  80th  St.  and 
East  End  Ave.,  New  York,  N.  Y. 

Palmer,  H.  C. 

Engineer,  Buffalo  Gas  Co.,  186  Main 
St.,  Buffalo,  N.  Y. 

Pierce,  Robert  ff. 

Manager,  Illuminating  Engineering 
Laboratory,  Welsbach  Co.,  Glouces- 
ter, N.  J. 

Rogers,  Fred.  A. 

Professor  of  Physics  and  Electrical 
Engineering,  Lewis  Institute,  Chi- 
cago, 111. 

Serrill,  William  J. 

Engineer  of  Distribution,  United 
Gas  Improvement  Co.,  1401  Arch 
St.,  Philadelphia,  Pa. 

Sxyder,  Samuel 

Illuminating  Specialist,  New  Busi- 
ness Department,  The  United  Gas 
Improvement  Co.,  134  North  13th 
St.,  Philadelphia,  Pa. 

Spencer,  Paul 

Electrical  Engineer,  United  Gas 
Improvement  Co.,  1401  Arch  St., 
Philadelphia,  Pa. 

Morton,  A.  A. 

Westinghouse  Electric  &  Manufac- 
turing Co.,  Union  Bank  Bldg.,  Pitts- 
burgh, Pa. 

Dicker,  Alfred  Osmond 

Illuminating  Engineer,  Electrical 
Sales  Engineers,  Inc.,  19  South 
Fifth  Ave.,  Chicago,  111. 

Rice,  Harry  C. 

General  Manager,  G.  I.  Lamp  Divi- 
sion, National  Lamp  Works  of 
General  Electric  Co.,  214  Electric 
Bldg.,  Cleveland,  O. 


8 


TRANSACTIONS    I.    E.    S. — PART   II 


The  following  thirty-eight  associate 
members  were  transferred  to  the  grade 
of  member  November  n,  1915 : 

Boyce,  Ernest  W. 

Electrical  Engineer,  President  New 
York  Electric  Lamp  Co.,  Inc.,  38 
Park  Row,  New  York,  N.  Y. 

Boxell,  Harold  V. 

Consulting  Engineer  and  Professor 
of  Electrical  Engineering,  Univer- 
sity of  Oklahoma,  508  Chautauqua 
Ave.,  Norman,  Okla. 

Bull,  John  H. 

Supervising  Engineer,  Ballinger  & 
Perrott,  Marbridge  Bldg.,  34th  St. 
and  Broadway,  New  York,  N.  Y. 

Cady,  Francis  E. 

Assistant  to  director,  Nela  Research 
Laboratory,  Nela  Park,  O. 

Carpenter,  Frank 

Illumination  and  special  work, 
Welsbach  Gas  Lamp  Co.,  392  Canal 
St.,  New  York,  N.  Y. 

Ceinch,  Edward  S.,  Jr. 

Electrical  Engineer,  Gates  &  Shep- 
ard,  1516  Sansom  St.,  Philadelphia, 
Pa. 

Cowees,  Joseph  W. 

Superintendent  of  Installations, 
Edison  Electric  Illuminating  Co.  of 
Boston,  29  Boylston  St.,  Boston, 
Mass. 

Doane,  L.  C. 

Commercial  Engineer,  Holophane 
Works  of  General  Electric  Co., 
Holophane  Works,  Cleveland,  O. 

Dodson,  Herbert  K. 

Assistant  Superintendent,  New 
Business  and  Merchandise  Depart- 
ment, Consolidated  Gas,  Electric 
Light  &  Power  Co.  of  Baltimore, 
200  W.  Lexington  St.,  Baltimore, 
Md. 

Doty,  Paul 

President    and     General     Manager, 


St.    Paul   Gas    Light   Co.,    159   East 

6th  St.,  St.  Paul,  Minn. 
Dows,  Chester  L. 

Electrical  Engineer,  National  Lamp 

Works     of     General     Electric     Co., 

Nela  Park,  Cleveland,  O. 
Dutton,  I.  R. 

Manager,      Philadelphia      Suburban 

Gas  &  Electric  Co.,  Wyncote,  Pa. 
Ganz,  Albert  Frederick 

Consulting  Engineer  and  Professor 

of    Electrical    Engineering,    Stevens 

Institute   of   Technology,   Hoboken, 

N.  J. 
Hanscom,  W.  W. 

Consulting    Engineer,    848    Clayton 

St.,  San  Francisco,  Cal. 

Holdrege,  H.  A. 

General  Manager,  Omaha  Electric 
Light  &  Power  Co.,  Omaha,  Neb. 

Hulse,  Geo.  E. 

Chief  Engineer,  Safety  Car  Heating 
&  Lighting  Co.,  2  Rector  St.,  New 
York,  N.  Y. 

Jackson,  Dugald  C. 

Professor  of  Electrical  Engineer- 
ing, Massachusetts  Institute  of 
Technology,  248  Boylston  St.,  Bos- 
ton, Mass. 

Keech,  George  C. 

District  Sales  Manager,  Cooper- 
Hewitt  Electric  Co.,  215  Fisher 
Bldg.,  Chicago,  111. 

Kellogg,  Alfred  S. 

Consulting  Engineer,  53  State  St., 
Boston,  Mass. 

Kennedy,  Geo.  M. 

Electrical  Engineer,  Lehigh  Coal  & 
Navigation  Co.,  no  E.  Ridge  St., 
Lansford,  Pa. 

Kingsbury,  E.  F. 

Research  Assistant,  United  Gas 
Improvement  Co.,  Physical  Labora- 
tory, 3101  Passyunk  Ave.,  Philadel- 
phia, Pa. 


TRANSACTIONS    I.    E.    S. — PART    II 


Magalhaes,  George  W. 

Assistant  to  the  President,  New 
York  &  Queens  Electric  Light  & 
Power  Co.,  444  Jackson  Ave.,  Long 
Island  City,  N.  Y. 

Marsh,  Loren  W. 

New  England  Manager,  American 
Luxter  Prism  Co.,  49  Federal  St., 
Boston,   Mass. 

Mixer,  Chas.  A. 

Engineer,  Rumford  Falls  Light  & 
Water  Co.,  49  Congress  St.,  Rum- 
ford,  Me. 

Morton,  F.  N. 

Engineer,  United  Gas  Improvement 
Co.,  Broad  and  Arch  Sts.,  Philadel- 
phia, Pa. 

Nicolai,  G.  O. 

Superintendent,  Light  and  Power 
Dept.,  Terre  Haute  I.  &  E.  Traction 
Co.,  80  Wabash  Ave.,  Terre  Haute, 
Ind. 

O'Leary,  J.  J. 

President,  Buffalo  Electric  Con- 
tracting Co.,  20  Broadway,  Buffalo, 
N.  Y. 

Peaslee,  W.  Dhu  Aine 

Consulting  Engineer,  also  Lecturer 
in  Electrical  Engineering,  Oregon 
Agricultural  College,  Corvallis,  Ore. 

Porter,  Lawrence  C. 

Illuminating  Engineer,  Edison  Lamp 
Works  of  General  Electric  Co.,  417 
Sussex  St.,  Harrison,  N.  J. 

Clover,  Geo.  R. 

District  Manager,  Cooper-Hewitt 
Electric  Co.,  427  Ford  Bldg.,  Detroit, 
Mich. 

Rose,  S.  L  E. 

Illuminating  Engineering  Labora- 
tory, General  Electric  Co.,  Schenec- 
tady, N.  Y. 

Ryan,  Walter  DArcy 

Director  of  Illuminating  Engineer- 
ing Laboratories,  General  Electric 
Co.,  Schenectady,  N.  Y. 


Simpson,  Richard  E. 

Engineer,  Travelers  Insurance  Co., 
700  Main  St.,  Hartford,  Conn. 

Tingley,  Dr.  Louisa  Paine 

Ophthalmologist,  9  Massachusetts 
Ave.,  Boston,  Mass. 

Treverton,  E.  R. 

Lighting  Journal,  241  West  37th  St., 
New  York,  N.  Y. 

Wohlauer,  A.  A. 

Consulting  Engineer,  Allied  Engi- 
neering Co.,  546  Fifth  Ave.,  New 
York,  N.  Y. 

Murphy,  John 

Electrical  Engineer,  Government  of 
Canada,  Department  of  Railways 
and  Canals,  Ottawa,  Canada. 


New  Sustaining  Members. 

The  following  companies  were  elected 
sustaining  members  of  the  society  at  a 
meeting  of  the  Council  held  November 
11,  1915: 

Malden  and  Melrose  Gas  Light  Co. 
Clifford    E.     Paige,     representative, 
137  Pleasant  St.,  Maiden,  Mass. 
Suburban  Gas  &  Electric  Co. 

C.   F.   Chisholm,  representative,   150 
Beach  St.,  Revere,  Mass. 
Haverhill  Electric  Co. 

F.  L.  Ball,  representative,  121  Mer- 
rimack St.,  Haverhill,  Mass. 


Personals. 


Mr.  Ray  Palmer,  formerly  commis- 
sioner of  electricity  for  the  City  of 
Chicago,  assumed  the  office  of  vice- 
president  and  general  manager  of  the 
New  York  and  Queens  Electric  Light 
and  Power  Company,  Long  Island  City, 
N.  Y.,  November  i,  1915. 

Mr.  S.  G.  Hibben,  who  has  been  con- 
nected with  the  Macbeth-Evans  Glass 
Company  for  a  number  of  years,  is  now 


10 


TRANSACTIONS    I.    E.    S. — PART    II 


with  the  National  Lighting  Products 
Company,  Jenkins  Arcade,  Pittsburgh, 
Pa. 

Air.  L.  L.  Hopkins,  formerly  with  the 
Macbeth- Evans  Glass  Company,  is  now 
the  Pittsburgh  representative  of  the 
R.  U.  V.  Company,  Inc.,  50  Broad 
Street,  New  York.  His  office  is  in  the 
Magee  Building,  Pittsburgh,  Pa. 


Obituary. 


Mr.  E.  S.  Marlow,  manager  of  the 
commercial  department  of  the  Potomac 
Electric  Power  Company,  Washington, 
D.  C,  died  October  25  after  an  illness 
of    several   months.      Mr.    Marlow   was 


widely  known  in  the  central  station  field 
and  had  been  active  in  the  affairs  of 
the  Illuminating  Engineering  Society 
since  its  inception.  Pie  was  chairman 
of  the  committee  which  had  charge  of 
the  1915  convention  of  the  society  in 
Washington,  D.  C. 


Semi-Annuai  Convention. 

A  special  semi-annual  convention  will 
be  held  in  New  York,  February  10  and 
11,  1916,  to  celebrate  the  tenth  anniver- 
sary of  the  organization  of  the  society. 
A  detailed  announcement  will  be  issued 
later. 


TRANSACTIONS 

OF  THE 

Illuminating 
Engineering  Society 

NO.  9,  1915 
PART  II 

Miscellaneous  Notes 


TRANSACTIONS   I.    E.    S. — PART   II 


Council  Notes. 

Date:     December  9,  1915. 

Place :  General  Offices,  29  West  39th 
Street,  New  York,  N.  Y. 

Present :  Charles  P.  Steinmetz,  presi- 
dent ;  E.  M.  Alger,  C.  O.  Bond,  H.  Cal- 
vert, G.  A.  Hoadley,  Clarence  L.  Law, 
C.  A.  Littlefield,  L.  B.  Marks,  Preston 
S.  Millar,  J.  L.  Minick,  A.  S.  McAllister, 
J.  Arnold  Norcross,  and  S.  C.  Rogers, 
representing  C.  A.  B.  Halvorson. 

The  meeting  was  called  to  order  at 
2.55  p.m.  by  President  Steinmetz. 

The  minutes  of  the  October  and 
November  meetings  were  adopted  as 
printed. 

Six  applicants  were  elected  associate 
members. 

One  applicant  was  elected  a  member 
subject  to  the  approval  of  the  Board  of 
Examiners. 

Two  companies  were  elected  sustain- 
ing members. 

Eleven  associate  members  were  trans- 
ferred to  the  grade  of  member . 

Sixty-three  resignations  were  ac- 
cepted. 

It  was  voted  to  have  the  general  office 
continue  the  occupancy  of  the  present 
quarters  in  the  Engineering  Societies 
Building,  New  York. 

Upon  recommendation  of  the  Finance 
Committee,  payment  of  vouchers  No. 
2317  to  No.  2349  inclusive  aggregating 
$1,085.37  was  authorized. 

An  estimate  of  the  expenses  and  in- 
come for  the  present  fiscal  year  was 
submitted  by  the  Finance  Committee, 
but  no  action  was  taken  on  it. 

Reports  on  section  activities  were 
submitted     by     Vice-presidents     J.     L. 


Minick  (Pittsburgh),  G.  A.  Hoadley 
(Philadelphia),  Clarence  L.  Law  (New 
York).  Mr.  S.  C.  Rogers  reported  on 
the  New  England  Section  activities  for 
Vice-president  C.  A.  B.  Halvorson. 

The  following  committee  appoint- 
ments were  confirmed : 

Committee  on  Lectures:  E.  P.  Hyde, 
chairman;  Louis  Bell,  W.  H.  Gartley, 
L.  B.  Marks,  C.  H.  Sharp,  and  W.  D. 
Weaver. 

Membership  Committee:  W.  A.  Dur- 
gin,  chairman. 

School  Lighting  Committee:  F.  Park 
Lewis,  F.  K.  Richtmyer,  L.  O.  Grondahl, 
N.  M.  Black,  H.  H.  Magdsick,  R.  B. 
Ely. 

Executive  Committee:  Preston  S. 
Millar. 

Semi-annual  Convention  Committee: 
Walter  R  Addicks,  William  H.  Bradley, 
N.  F.  Brady,  A.  W.  Burchard,  Nicholas 
Murray  Butler,  J.  J.  Carty,  Charles  A. 
Coffin,  Geo.  B.  Cortelyou,  Wilbur  C. 
Fisk,  Lewis  B.  Gawtry,  Frank  Hedley, 
W.  Greeley  Hoyt,  A.  C.  Humphreys, 
M.  R  Hutchison,  J.  W.  Lieb,  T.  C. 
Martin,  Wm.  H.  Meadowcroft,  H.  B. 
McLean,  Joseph  B.  Murray,  Thomas  E. 
Murray,  Walter  Newmuller,  L.  A. 
Osborne,  Geo.  F.  Parker,  J.  E.  Phillips, 
Theodore  P.  Shonts,  Frank  W.  Smith, 
B.  W.  Stilwell,  C.  G.  M.  Thomas,  G.  E. 
Tripp,  W.  F.  Wells,  Frederick  Whit- 
ridge,  Timothy  S.  Williams,  William 
Williams,  Clarence  L.  Law,  secretary. 

A  letter  was  received  from  the  pro- 
vost of  the  University  of  Pennsylvania 
inviting  the  society  to  give  its  proposed 
course  of  lectures  on  illuminating  engi- 
neering at  the  U.  of  P.  This  invitation 
was  referred  to  the  Committee  on  Ways 
and  Means. 


TRANSACTIONS   I.  E.  S. — PART   II 


Section  Meetings. 

Chicago  Section 

December  9,  1915,  in  the  Common- 
wealth Edison  Company  Building. 
Paper,  "School  Lighting"  by  M. 
Luckiesh.  Preceding  the  meeting  sup- 
per was  served  at  the  Grand  Pacific 
Hotel. 

The  following  program  of  papers  and 
meetings  have  been  announced: 

January  13— Exterior  Lighting  (Gas 
and  Electric)  of  Buildings. 

February  10 — Practical  Factory  Light- 
ing. 

February  28 — Joint  meeting  of  Chi- 
cago sections  of  A.  I.  E.  E.  and  I.  E.  S. 
Paper  on  street  lighting. 

March  23— Latest  Developments  in 
Incandescent  Lamps. 

April  20 — Latest  Developments  in  Gas 
Lamps. 

May  18 — Relation  of  Illumination  to 
Interior  Architectural  Effects. 

June  15 — Modern  Reflectors  and 
Shades  for  Gas  and  Electric  Lighting. 

The  names  of  the  authors  of  these 
papers  will  be  announced  later. 

New  England  Section 
The  first  meeting  of  the  section  this 
year  is   to  be  held   in   February,   1916. 
A  definite  announcement  will  be  made 
later. 

New  York  Section 
December  8,  1915,  in  Consolidated  Gas 
Company's  auditorium,  130  East  15th 
Street,  New  York,  N.  Y.  Papers,  "Out- 
door Illumination  of  Store  Fronts"  by 
Charles  Hodgson,  and  "Residence  Light- 
ing by  Gas"  by  M.  A.  Combs.  Preced- 
ing the  meeting  an  informal  and  an  a  la 
carte  dinner  was  held  at  Likhow's  Res- 
taurant. 


The  following  meetings  and  papers 
have  been  announced : 

January  13 — A  paper  will  be  presented 
by  Mr.  Kollmorgen  of  the  Eastern 
Optical  Company,  entitled  "Light  Trans- 
mission in  Optical  Instruments"  and 
also  a  paper  by  Mr.  Orange  of  the 
General  Electric  Company,  entitled 
"Projector  Lamps." 

By  motion  of  the  Board,  the  February 
meeting  has  been  canceled  in  favor  of 
the  mid-winter  convention. 

March  14 — Joint  meeting  with  Ameri- 
can Society  of  Mechanical  Engineers. 
A  paper  will  be  presented  by  Prof.  C. 
E.  Clewell  of  the  University  of  Pennsyl- 
vania entitled  "Application  of  the  New 
Factory  Code  Lighting."  Talks  will 
also  be  given  by  Mr.  L.  B.  Marks  and 
a  member  of  the  A.  S.  M.  E. 

April  13 — A  lecture  by  Dr.  Charles  P. 
Steinmetz  on  "Illuminating  Engineer- 
ing." 

May  11 — A  paper  will  be  presented 
by  Mr.  Bassett  Jones,  entitled  "Office 
Lighting." 

June — A  paper  will  be  presented  by 
Mr.  Wm.  Dempsey  of  the  New  York 
Edison  Company,  entitled  "Street  Light- 
ing with  Mazda  C  Lamps." 

It  is  proposed  to  have  the  June  meet- 
ing an  outdoor  meeting  to  include  a 
dinner  and  an  inspection  trip  through 
the  streets  of  New  York. 

Philadelphia  Section 
December  17,  1915,  in  Engineers  Club, 
joint  meeting  with  Engineers  Club  and 
American  Institute  of  Electrical  Engi- 
neers. Dr.  Charles  P.  Steinmetz 
addressed  the  members  on  the  subject 
of   "Illuminating  Engineering." 

The  program  for  the  rest  of  the  year 
is  as  follows : 

January  21 — "Illumination  Problems 
at  the   Panama-Pacific   Exposition,"  by 


TRANSACTIONS   I.    E.    S.       PART   II 


W.  D'A.  Ryan,  Illuminating  Engineer, 
General  Electric  Company. 

February  18 — "Tests  of  Street  Illumi- 
nation," by  Preston  S.  Millar,  Past- 
president,  Illuminating  Engineering 
Society;  General  Manager,  Electrical 
Testing  Laboratories. 

March  13 — Joint  meeting  with  Phila- 
delphia Section,  American  Institute  of 
Electrical  Engineers.  "Engineering 
Training  as  a  Business  Asset,"  by 
Charles  F.  Scott,  Sc.  D.,  Past-president, 
American  Institute  of  Electrical  Engi- 
neers ;  Professor  of  Electrical  Engineer- 
ing, Sheffield  Scientific  School  of  Yale 
University. 

March  17 — "Lighting  Legislation,"  by 
L.  B.  Marks,  Past-president,  Illuminat- 
ing Engineering  Society;  Consulting 
Engineer. 

April  21 — "Type  C  Lamps  in  Street 
Lighting,"  by  T.  J.  Pace,  Commercial 
Engineer,  Westinghouse  Electric  & 
Manufacturing  Company. 

May  19 — "Educational  Aspects  of 
Illumination,"  by  Prof.  F.  K.  Richt- 
myer,  Chairman,  Committee  on  Educa- 
tion, Illuminating  Engineering   Society. 

June  16 — "Artificial  Lighting  for  a 
Hundred  Years,"  by  William  J.  Serrill, 
Engineer  of  Distribution,  United  Gas 
Improvement  Company. 

Pittsburgh  Section 
December  17,  1915,  at  Engineers' 
Society  of  Western  Pennsylvania. 
Paper,  "Design  and  Manufacture  of 
Diffusing  Glass  Reflectors"  by  S.  G. 
Hibben.  An  a  la  carte  dinner  was  held 
at  the  Fort  Pitt  Hotel. 


New  Associate  Members. 

The  following  six  applicants  were 
elected  associate  members  at  a  Coun- 
cil meeting  held  December  9,  1915 : 


Babson,  A.  C. 

Watertown  Manager,  Wisconsin 
Gas  &  Electric  Co.,  205  Main  St., 
Watertown,  Wis. 

Housekeeper,  William  G 

Electrical  Engineer,  Western  Elec- 
tric Co.,  463  West  St.,  New  York, 
N.  Y. 

Marlow,  S.  L. 

Salesman,  Philadelphia  Electric  Co., 
1000  Chestnut  St.,  Philadelphia,  Pa. 

OSHIMA,    HIRO-YOSHI 

Osaka  Electric  Lamp  Co.,  70  Daini, 
Sagisu-cho,  Osaka,  Japan. 

Ruth,  Robert  H. 

Benjamin  Electric  Manufacturing 
Co.,  Pittsburgh,  Pa. 

Spillan,  James  J. 

Laboratory  assistant,  Philadelphia 
Electric  Co.,  226  S.  nth  St.,  Phila- 
delphia, Pa. 


New  Sustaining  Members. 

The  following  companies  were  elected 
sustaining  members  of  the  society  at  a 
Council  meeting  held  December  9,  1915 : 
American  Optical  Co. 

Southbridge,  Mass.     Official  Repre- 
sentative, Howard  T.  Reeve. 
Malden  Electric  Co. 

Maiden,  Mass.     Official  Representa- 
tive, Cyrus  Barnes. 


Transfers. 


Eleven  associate  members  were  trans- 
ferred to  the  grade  of  member  at  a 
meeting  of  the  Council  held  December 
9,  1915: 

BlERMAN,    CHAS.    F. 

Telephone  Engineer,  Wisconsin 
Telephone  Co.,  183  Fifth  Ave.,  Mil- 
waukee, Wis. 


TRANSACTIONS    I.    K.    S. — PART   II 


Bryant,  Alice;  G. 

Physician,  502  Beacon  St.,  Boston, 
Mass. 

Caldwell,  F.  C. 

Professor  of  Electrical  Engineering, 
Ohio  State  University,  Columbus,  O. 

Goldmark,  C.  J. 

Consulting  Engineer,  103  Park  Ave., 
New  York,  N.  Y. 

Macbeth,  Norman 

241  W.  37th  St.,  New  York,  N.  Y. 

Maxwell,  James  T. 

General  Agent,  Philadelphia  Elec- 
tric Co.,  1000  Chestnut  St.,  Phila- 
delphia, Pa. 

McGuire,  Frederick  J. 

Chief  Inspector  investigating  illumi- 
nating and  power  economies,  Dept. 
of  Water  Supply,  Gas  and  Elec- 
tricity, Municipal  Bldg.,  New  York, 
N.  Y. 

Murray,  Joseph  Bradley 

Acting  Treasurer,  Edison  Electric 
Illuminating  Co.  of  Brooklyn,  360 
Pearl  St.,  Brooklyn,  N.  Y. 

Rogers,  S.  C. 

General  Electric  Co.,  West  Lynn, 
Mass. 


Stafford,  Raymond  W. 

New  York  Edison  Co.,  124  E.  15th 
St.,  New  York,  N.  Y. 

Steinmetz,  Charles  P. 

Consulting  Engineer,  General  Elec- 
tric Co.,  Schenectady,  N.  Y. 


New  Books. 

Color  and  Its  Application,  by  M. 
Luckiesh,  Physicist,  Nela  Research  Lab- 
oratory, National  Lamp  Works  of  Gen- 
eral Electric  Company,  Cleveland,  Ohio ; 
360  pp.,  price  $3.00;  published  by  D.  Van 
Nostrand  Company,  25  Park  Place,  New 
York,  N.  Y.  Contents:  light;  the  pro- 
duction of  color ;  color  mixture ;  color 
terminology ;  the  analysis  of  color;  color 
and  vision;  the  effect  of  environment 
on  color;  theories  of  color  vision;  color 
photometry ;  color  photography ;  color  in 
lighting;  color  effects  for  the  stage  and 
displays;  color  phenomena  in  painting; 
color  matching;  the  art  of  mobile  color; 
color  media. 


TF       Illuminating  engineering 

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